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binutils-gdb/gdb/elfread.c
Maciej W. Rozycki 3e29f34a4e MIPS: Keep the ISA bit in compressed code addresses 
1. Background information

The MIPS architecture, as originally designed and implemented in
mid-1980s has a uniform instruction word size that is 4 bytes, naturally
aligned.  As such all MIPS instructions are located at addresses that
have their bits #1 and #0 set to zeroes, and any attempt to execute an
instruction from an address that has any of the two bits set to one
causes an address error exception.  This may for example happen when a
jump-register instruction is executed whose register value used as the
jump target has any of these bits set.

Then in mid 1990s LSI sought a way to improve code density for their
TinyRISC family of MIPS cores and invented an alternatively encoded
instruction set in a joint effort with MIPS Technologies (then a
subsidiary of SGI).  The new instruction set has been named the MIPS16
ASE (Application-Specific Extension) and uses a variable instruction
word size, which is 2 bytes (as the name of the ASE suggests) for most,
but there are a couple of exceptions that take 4 bytes, and then most of
the 2-byte instructions can be treated with a 2-byte extension prefix to
expand the range of the immediate operands used.

As a result instructions are no longer 4-byte aligned, instead they are
aligned to a multiple of 2.  That left the bit #0 still unused for code
references, be it for the standard MIPS (i.e. as originally invented) or
for the MIPS16 instruction set, and based on that observation a clever
trick was invented that on one hand allowed the processor to be
seamlessly switched between the two instruction sets at any time at the
run time while on the other avoided the introduction of any special
control register to do that.

So it is the bit #0 of the instruction address that was chosen as the
selector and named the ISA bit.  Any instruction executed at an even
address is interpreted as a standard MIPS instruction (the address still
has to have its bit #1 clear), any instruction executed at an odd
address is interpreted as a MIPS16 instruction.

To switch between modes ordinary jump instructions are used, such as
used for function calls and returns, specifically the bit #0 of the
source register used in jump-register instructions selects the execution
(ISA) mode for the following piece of code to be interpreted in.
Additionally new jump-immediate instructions were added that flipped the
ISA bit to select the opposite mode upon execution.  They were
considered necessary to avoid the need to make register jumps in all
cases as the original jump-immediate instructions provided no way to
change the bit #0 at all.

This was all important for cases where standard MIPS and MIPS16 code had
to be mixed, either for compatibility with the existing binary code base
or to access resources not reachable from MIPS16 code (the MIPS16
instruction set only provides access to general-purpose registers, and
not for example floating-point unit registers or privileged coprocessor
0 registers) -- pieces of code in the opposite mode can be executed as
ordinary subroutine calls.

A similar approach has been more recently adopted for the MIPS16
replacement instruction set defined as the so called microMIPS ASE.
This is another instruction set encoding introduced to the MIPS
architecture.  Just like the MIPS16 ASE, the microMIPS instruction set
uses a variable-length encoding, where each instruction takes a multiple
of 2 bytes.  The ISA bit has been reused and for microMIPS-capable
processors selects between the standard MIPS and the microMIPS mode
instead.

2. Statement of the problem

To put it shortly, MIPS16 and microMIPS code pointers used by GDB are
different to these observed at the run time.  This results in the same
expressions being evaluated producing different results in GDB and in
the program being debugged.  Obviously it's the results obtained at the
run time that are correct (they define how the program behaves) and
therefore by definition the results obtained in GDB are incorrect.

A bit longer description will record that obviously at the run time the
ISA bit has to be set correctly (refer to background information above
if unsure why so) or the program will not run as expected.  This is
recorded in all the executable file structures used at the run time: the
dynamic symbol table (but not always the static one!), the GOT, and
obviously in all the addresses embedded in code or data of the program
itself, calculated by applying the appropriate relocations at the static
link time.

While a program is being processed by GDB, the ISA bit is stripped off
from any code addresses, presumably to make them the same as the
respective raw memory byte address used by the processor to access the
instruction in the instruction fetch access cycle.  This stripping is
actually performed outside GDB proper, in BFD, specifically
_bfd_mips_elf_symbol_processing (elfxx-mips.c, see the piece of code at
the very bottom of that function, starting with an: "If this is an
odd-valued function symbol, assume it's a MIPS16 or microMIPS one."
comment).

This function is also responsible for symbol table dumps made by
`objdump' too, so you'll never see the ISA bit reported there by that
tool, you need to use `readelf'.

This is however unlike what is ever done at the run time, the ISA bit
once present is never stripped off, for example a cast like this:

(short *) main

will not strip the ISA bit off and if the resulting pointer is intended
to be used to access instructions as data, for example for software
instruction decoding (like for fault recovery or emulation in a signal
handler) or for self-modifying code then the bit still has to be
stripped off by an explicit AND operation.

This is probably best illustrated with a simple real program example.
Let's consider the following simple program:

$ cat foobar.c
int __attribute__ ((mips16)) foo (void)
{
  return 1;
}

int __attribute__ ((mips16)) bar (void)
{
  return 2;
}

int __attribute__ ((nomips16)) foo32 (void)
{
  return 3;
}

int (*foo32p) (void) = foo32;
int (*foop) (void) = foo;
int fooi = (int) foo;

int
main (void)
{
  return foop ();
}
$

This is plain C with no odd tricks, except from the instruction mode
attributes.  They are not necessary to trigger this problem, I just put
them here so that the program can be contained in a single source file
and to make it obvious which function is MIPS16 code and which is not.

Let's try it with Linux, so that everyone can repeat this experiment:

$ mips-linux-gnu-gcc -mips16 -g -O2 -o foobar foobar.c
$

Let's have a look at some interesting symbols:

$ mips-linux-gnu-readelf -s foobar | egrep 'table|foo|bar'
Symbol table '.dynsym' contains 7 entries:
Symbol table '.symtab' contains 95 entries:
    55: 00000000     0 FILE    LOCAL  DEFAULT  ABS foobar.c
    66: 0040068c     4 FUNC    GLOBAL DEFAULT [MIPS16]    12 bar
    68: 00410848     4 OBJECT  GLOBAL DEFAULT   21 foo32p
    70: 00410844     4 OBJECT  GLOBAL DEFAULT   21 foop
    78: 00400684     8 FUNC    GLOBAL DEFAULT   12 foo32
    80: 00400680     4 FUNC    GLOBAL DEFAULT [MIPS16]    12 foo
    88: 00410840     4 OBJECT  GLOBAL DEFAULT   21 fooi
$

Hmm, no sight of the ISA bit, but notice how foo and bar (but not
foo32!) have been marked as MIPS16 functions (ELF symbol structure's
`st_other' field is used for that).

So let's try to run and poke at this program with GDB.  I'll be using a
native system for simplicity (I'll be using ellipses here and there to
remove unrelated clutter):

$ ./foobar
$ echo $?
1
$

So far, so good.

$ gdb ./foobar
[...]
(gdb) break main
Breakpoint 1 at 0x400490: file foobar.c, line 23.
(gdb) run
Starting program: .../foobar

Breakpoint 1, main () at foobar.c:23
23        return foop ();
(gdb)

Yay, it worked!  OK, so let's poke at it:

(gdb) print main
$1 = {int (void)} 0x400490 <main>
(gdb) print foo32
$2 = {int (void)} 0x400684 <foo32>
(gdb) print foo32p
$3 = (int (*)(void)) 0x400684 <foo32>
(gdb) print bar
$4 = {int (void)} 0x40068c <bar>
(gdb) print foo
$5 = {int (void)} 0x400680 <foo>
(gdb) print foop
$6 = (int (*)(void)) 0x400681 <foo>
(gdb)

A-ha!  Here's the difference and finally the ISA bit!

(gdb) print /x fooi
$7 = 0x400681
(gdb) p/x $pc
p/x $pc
$8 = 0x400491
(gdb)

And here as well...

(gdb) advance foo
foo () at foobar.c:4
4       }
(gdb) disassemble
Dump of assembler code for function foo:
   0x00400680 <+0>:     jr      ra
   0x00400682 <+2>:     li      v0,1
End of assembler dump.
(gdb) finish
Run till exit from #0  foo () at foobar.c:4
main () at foobar.c:24
24      }
Value returned is $9 = 1
(gdb) continue
Continuing.
[Inferior 1 (process 14103) exited with code 01]
(gdb)

So let's be a bit inquisitive...

(gdb) run
Starting program: .../foobar

Breakpoint 1, main () at foobar.c:23
23        return foop ();
(gdb)

Actually we do not like to run foo here at all.  Let's run bar instead!

(gdb) set foop = bar
(gdb) print foop
$10 = (int (*)(void)) 0x40068c <bar>
(gdb)

Hmm, no ISA bit.  Is it going to work?

(gdb) advance bar
bar () at foobar.c:9
9       }
(gdb) p/x $pc
$11 = 0x40068c
(gdb) disassemble
Dump of assembler code for function bar:
=> 0x0040068c <+0>:     jr      ra
   0x0040068e <+2>:     li      v0,2
End of assembler dump.
(gdb) finish
Run till exit from #0  bar () at foobar.c:9

Program received signal SIGILL, Illegal instruction.
bar () at foobar.c:9
9       }
(gdb)

Oops!

(gdb) p/x $pc
$12 = 0x40068c
(gdb)

We're still there!

(gdb) continue
Continuing.

Program terminated with signal SIGILL, Illegal instruction.
The program no longer exists.
(gdb)

So let's try something else:

(gdb) run
Starting program: .../foobar

Breakpoint 1, main () at foobar.c:23
23        return foop ();
(gdb) set foop = foo
(gdb) advance foo
foo () at foobar.c:4
4       }
(gdb) disassemble
Dump of assembler code for function foo:
=> 0x00400680 <+0>:     jr      ra
   0x00400682 <+2>:     li      v0,1
End of assembler dump.
(gdb) finish
Run till exit from #0  foo () at foobar.c:4

Program received signal SIGILL, Illegal instruction.
foo () at foobar.c:4
4       }
(gdb) continue
Continuing.

Program terminated with signal SIGILL, Illegal instruction.
The program no longer exists.
(gdb)

The same problem!

(gdb) run
Starting program:
/net/build2-lucid-cs/scratch/macro/mips-linux-fsf-gcc/isa-bit/foobar

Breakpoint 1, main () at foobar.c:23
23        return foop ();
(gdb) set foop = foo32
(gdb) advance foo32
foo32 () at foobar.c:14
14      }
(gdb) disassemble
Dump of assembler code for function foo32:
=> 0x00400684 <+0>:     jr      ra
   0x00400688 <+4>:     li      v0,3
End of assembler dump.
(gdb) finish
Run till exit from #0  foo32 () at foobar.c:14
main () at foobar.c:24
24      }
Value returned is $14 = 3
(gdb) continue
Continuing.
[Inferior 1 (process 14113) exited with code 03]
(gdb)

That did work though, so it's the ISA bit only!

(gdb) quit

Enough!

That's the tip of the iceberg only though.  So let's rebuild the
executable with some dynamic symbols:

$ mips-linux-gnu-gcc -mips16 -Wl,--export-dynamic -g -O2 -o foobar-dyn foobar.c
$ mips-linux-gnu-readelf -s foobar-dyn | egrep 'table|foo|bar'
Symbol table '.dynsym' contains 32 entries:
     6: 004009cd     4 FUNC    GLOBAL DEFAULT   12 bar
     8: 00410b88     4 OBJECT  GLOBAL DEFAULT   21 foo32p
     9: 00410b84     4 OBJECT  GLOBAL DEFAULT   21 foop
    15: 004009c4     8 FUNC    GLOBAL DEFAULT   12 foo32
    17: 004009c1     4 FUNC    GLOBAL DEFAULT   12 foo
    25: 00410b80     4 OBJECT  GLOBAL DEFAULT   21 fooi
Symbol table '.symtab' contains 95 entries:
    55: 00000000     0 FILE    LOCAL  DEFAULT  ABS foobar.c
    69: 004009cd     4 FUNC    GLOBAL DEFAULT   12 bar
    71: 00410b88     4 OBJECT  GLOBAL DEFAULT   21 foo32p
    72: 00410b84     4 OBJECT  GLOBAL DEFAULT   21 foop
    79: 004009c4     8 FUNC    GLOBAL DEFAULT   12 foo32
    81: 004009c1     4 FUNC    GLOBAL DEFAULT   12 foo
    89: 00410b80     4 OBJECT  GLOBAL DEFAULT   21 fooi
$

OK, now the ISA bit is there for a change, but the MIPS16 `st_other'
attribute gone, hmm...  What does `objdump' do then:

$ mips-linux-gnu-objdump -Tt foobar-dyn | egrep 'SYMBOL|foo|bar'
foobar-dyn:     file format elf32-tradbigmips
SYMBOL TABLE:
00000000 l    df *ABS*  00000000              foobar.c
004009cc g     F .text  00000004              0xf0 bar
00410b88 g     O .data  00000004              foo32p
00410b84 g     O .data  00000004              foop
004009c4 g     F .text  00000008              foo32
004009c0 g     F .text  00000004              0xf0 foo
00410b80 g     O .data  00000004              fooi
DYNAMIC SYMBOL TABLE:
004009cc g    DF .text  00000004  Base        0xf0 bar
00410b88 g    DO .data  00000004  Base        foo32p
00410b84 g    DO .data  00000004  Base        foop
004009c4 g    DF .text  00000008  Base        foo32
004009c0 g    DF .text  00000004  Base        0xf0 foo
00410b80 g    DO .data  00000004  Base        fooi
$

Hmm, the attribute (0xf0, printed raw) is back, and the ISA bit gone
again.

Let's have a look at some DWARF-2 records GDB uses (I'll be stripping
off a lot here for brevity) -- debug info:

$ mips-linux-gnu-readelf -wi foobar
Contents of the .debug_info section:
[...]
  Compilation Unit @ offset 0x88:
   Length:        0xbb (32-bit)
   Version:       4
   Abbrev Offset: 62
   Pointer Size:  4
 <0><93>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <94>   DW_AT_producer    : (indirect string, offset: 0x19e): GNU C 4.8.0 20120513 (experimental) -meb -mips16 -march=mips32r2 -mhard-float -mllsc -mplt -mno-synci -mno-shared -mabi=32 -g -O2
    <98>   DW_AT_language    : 1        (ANSI C)
    <99>   DW_AT_name        : (indirect string, offset: 0x190): foobar.c
    <9d>   DW_AT_comp_dir    : (indirect string, offset: 0x225): [...]
    <a1>   DW_AT_ranges      : 0x0
    <a5>   DW_AT_low_pc      : 0x0
    <a9>   DW_AT_stmt_list   : 0x27
 <1><ad>: Abbrev Number: 2 (DW_TAG_subprogram)
    <ae>   DW_AT_external    : 1
    <ae>   DW_AT_name        : foo
    <b2>   DW_AT_decl_file   : 1
    <b3>   DW_AT_decl_line   : 1
    <b4>   DW_AT_prototyped  : 1
    <b4>   DW_AT_type        : <0xc2>
    <b8>   DW_AT_low_pc      : 0x400680
    <bc>   DW_AT_high_pc     : 0x400684
    <c0>   DW_AT_frame_base  : 1 byte block: 9c         (DW_OP_call_frame_cfa)
    <c2>   DW_AT_GNU_all_call_sites: 1
 <1><c2>: Abbrev Number: 3 (DW_TAG_base_type)
    <c3>   DW_AT_byte_size   : 4
    <c4>   DW_AT_encoding    : 5        (signed)
    <c5>   DW_AT_name        : int
 <1><c9>: Abbrev Number: 4 (DW_TAG_subprogram)
    <ca>   DW_AT_external    : 1
    <ca>   DW_AT_name        : (indirect string, offset: 0x18a): foo32
    <ce>   DW_AT_decl_file   : 1
    <cf>   DW_AT_decl_line   : 11
    <d0>   DW_AT_prototyped  : 1
    <d0>   DW_AT_type        : <0xc2>
    <d4>   DW_AT_low_pc      : 0x400684
    <d8>   DW_AT_high_pc     : 0x40068c
    <dc>   DW_AT_frame_base  : 1 byte block: 9c         (DW_OP_call_frame_cfa)
    <de>   DW_AT_GNU_all_call_sites: 1
 <1><de>: Abbrev Number: 2 (DW_TAG_subprogram)
    <df>   DW_AT_external    : 1
    <df>   DW_AT_name        : bar
    <e3>   DW_AT_decl_file   : 1
    <e4>   DW_AT_decl_line   : 6
    <e5>   DW_AT_prototyped  : 1
    <e5>   DW_AT_type        : <0xc2>
    <e9>   DW_AT_low_pc      : 0x40068c
    <ed>   DW_AT_high_pc     : 0x400690
    <f1>   DW_AT_frame_base  : 1 byte block: 9c         (DW_OP_call_frame_cfa)
    <f3>   DW_AT_GNU_all_call_sites: 1
 <1><f3>: Abbrev Number: 5 (DW_TAG_subprogram)
    <f4>   DW_AT_external    : 1
    <f4>   DW_AT_name        : (indirect string, offset: 0x199): main
    <f8>   DW_AT_decl_file   : 1
    <f9>   DW_AT_decl_line   : 21
    <fa>   DW_AT_prototyped  : 1
    <fa>   DW_AT_type        : <0xc2>
    <fe>   DW_AT_low_pc      : 0x400490
    <102>   DW_AT_high_pc     : 0x4004a4
    <106>   DW_AT_frame_base  : 1 byte block: 9c        (DW_OP_call_frame_cfa)
    <108>   DW_AT_GNU_all_tail_call_sites: 1
[...]
$

-- no sign of the ISA bit anywhere -- frame info:

$ mips-linux-gnu-readelf -wf foobar
[...]
Contents of the .debug_frame section:

00000000 0000000c ffffffff CIE
  Version:               1
  Augmentation:          ""
  Code alignment factor: 1
  Data alignment factor: -4
  Return address column: 31

  DW_CFA_def_cfa_register: r29
  DW_CFA_nop

00000010 0000000c 00000000 FDE cie=00000000 pc=00400680..00400684

00000020 0000000c 00000000 FDE cie=00000000 pc=00400684..0040068c

00000030 0000000c 00000000 FDE cie=00000000 pc=0040068c..00400690

00000040 00000018 00000000 FDE cie=00000000 pc=00400490..004004a4
  DW_CFA_advance_loc: 6 to 00400496
  DW_CFA_def_cfa_offset: 32
  DW_CFA_offset: r31 at cfa-4
  DW_CFA_advance_loc: 6 to 0040049c
  DW_CFA_restore: r31
  DW_CFA_def_cfa_offset: 0
  DW_CFA_nop
  DW_CFA_nop
  DW_CFA_nop
[...]
$

-- no sign of the ISA bit anywhere -- range info (GDB doesn't use arange):

$ mips-linux-gnu-readelf -wR foobar
Contents of the .debug_ranges section:

    Offset   Begin    End
    00000000 00400680 00400690
    00000000 00400490 004004a4
    00000000 <End of list>

$

-- no sign of the ISA bit anywhere -- line info:

$ mips-linux-gnu-readelf -wl foobar
Raw dump of debug contents of section .debug_line:
[...]
  Offset:                      0x27
  Length:                      78
  DWARF Version:               2
  Prologue Length:             31
  Minimum Instruction Length:  1
  Initial value of 'is_stmt':  1
  Line Base:                   -5
  Line Range:                  14
  Opcode Base:                 13

 Opcodes:
  Opcode 1 has 0 args
  Opcode 2 has 1 args
  Opcode 3 has 1 args
  Opcode 4 has 1 args
  Opcode 5 has 1 args
  Opcode 6 has 0 args
  Opcode 7 has 0 args
  Opcode 8 has 0 args
  Opcode 9 has 1 args
  Opcode 10 has 0 args
  Opcode 11 has 0 args
  Opcode 12 has 1 args

 The Directory Table is empty.

 The File Name Table:
  Entry Dir     Time    Size    Name
  1     0       0       0       foobar.c

 Line Number Statements:
  Extended opcode 2: set Address to 0x400681
  Special opcode 6: advance Address by 0 to 0x400681 and Line by 1 to 2
  Special opcode 7: advance Address by 0 to 0x400681 and Line by 2 to 4
  Special opcode 55: advance Address by 3 to 0x400684 and Line by 8 to 12
  Special opcode 7: advance Address by 0 to 0x400684 and Line by 2 to 14
  Advance Line by -7 to 7
  Special opcode 131: advance Address by 9 to 0x40068d and Line by 0 to 7
  Special opcode 7: advance Address by 0 to 0x40068d and Line by 2 to 9
  Advance PC by 3 to 0x400690
  Extended opcode 1: End of Sequence

  Extended opcode 2: set Address to 0x400491
  Advance Line by 21 to 22
  Copy
  Special opcode 6: advance Address by 0 to 0x400491 and Line by 1 to 23
  Special opcode 60: advance Address by 4 to 0x400495 and Line by -1 to 22
  Special opcode 34: advance Address by 2 to 0x400497 and Line by 1 to 23
  Special opcode 62: advance Address by 4 to 0x40049b and Line by 1 to 24
  Special opcode 32: advance Address by 2 to 0x40049d and Line by -1 to 23
  Special opcode 6: advance Address by 0 to 0x40049d and Line by 1 to 24
  Advance PC by 7 to 0x4004a4
  Extended opcode 1: End of Sequence
[...]

-- a-ha, the ISA bit is there!  However it's not always right for some
reason, I don't have a small test case to show it, but here's an excerpt
from MIPS16 libc, a prologue of a function:

00019630 <__libc_init_first>:
   19630:       e8a0            jrc     ra
   19632:       6500            nop

00019634 <_init>:
   19634:       f000 6a11       li      v0,17
   19638:       f7d8 0b08       la      v1,15e00 <_DYNAMIC+0x15c54>
   1963c:       f400 3240       sll     v0,16
   19640:       e269            addu    v0,v1
   19642:       659a            move    gp,v0
   19644:       64f6            save    48,ra,s0-s1
   19646:       671c            move    s0,gp
   19648:       d204            sw      v0,16(sp)
   1964a:       f352 984c       lw      v0,-27828(s0)
   1964e:       6724            move    s1,a0

and the corresponding DWARF-2 line info:

 Line Number Statements:
  Extended opcode 2: set Address to 0x19631
  Advance Line by 44 to 45
  Copy
  Special opcode 8: advance Address by 0 to 0x19631 and Line by 3 to 48
  Special opcode 66: advance Address by 4 to 0x19635 and Line by 5 to 53
  Advance PC by constant 17 to 0x19646
  Special opcode 25: advance Address by 1 to 0x19647 and Line by 6 to 59
  Advance Line by -6 to 53
  Special opcode 33: advance Address by 2 to 0x19649 and Line by 0 to 53
  Special opcode 39: advance Address by 2 to 0x1964b and Line by 6 to 59
  Advance Line by -6 to 53
  Special opcode 61: advance Address by 4 to 0x1964f and Line by 0 to 53

-- see that "Advance PC by constant 17" there?  It clears the ISA bit,
however code at 0x19646 is not standard MIPS code at all.  For some
reason the constant is always 17, I've never seen DW_LNS_const_add_pc
used with any other value -- is that a binutils bug or what?

3. Solution:

I think we should retain the value of the ISA bit in code references,
that is effectively treat them as cookies as they indeed are (although
trivially calculated) rather than raw memory byte addresses.

In a perfect world both the static symbol table and the respective
DWARF-2 records should be fixed to include the ISA bit in all the cases.
I think however that this is infeasible.

All the uses of `_bfd_mips_elf_symbol_processing' can not necessarily be
tracked down.  This function is used by `elf_slurp_symbol_table' that in
turn is used by `bfd_canonicalize_symtab' and
`bfd_canonicalize_dynamic_symtab', which are public interfaces.

Similarly DWARF-2 records are used outside GDB, one notable if a bit
questionable is the exception unwinder (libgcc/unwind-dw2.c) -- I have
identified at least bits in `execute_cfa_program' and
`uw_frame_state_for', both around the calls to `_Unwind_IsSignalFrame',
that would need an update as they effectively flip the ISA bit freely;
see also the comment about MASK_RETURN_ADDR in gcc/config/mips/mips.h.
But there may be more places.  Any change in how DWARF-2 records are
produced would require an update there and would cause compatibility
problems with libgcc.a binaries already distributed; given that this is
a static library a complex change involving function renames would
likely be required.

I propose therefore to accept the existing inconsistencies and deal with
them entirely within GDB.  I have figured out that the ISA bit lost in
various places can still be recovered as long as we have symbol
information -- that'll have the `st_other' attribute correctly set to
one of standard MIPS/MIPS16/microMIPS encoding.

Here's the resulting change.  It adds a couple of new `gdbarch' hooks,
one to update symbol information with the ISA bit lost in
`_bfd_mips_elf_symbol_processing', and two other ones to adjust DWARF-2
records as they're processed.  The ISA bit is set in each address
handled according to information retrieved from the symbol table for the
symbol spanning the address if any; limits are adjusted based on the
address they point to related to the respective base address.
Additionally minimal symbol information has to be adjusted accordingly
in its gdbarch hook.

With these changes in place some complications with ISA bit juggling in
the PC that never fully worked can be removed from the MIPS backend.
Conversely, the generic dynamic linker event special breakpoint symbol
handler has to be updated to call the minimal symbol gdbarch hook to
record that the symbol is a MIPS16 or microMIPS address if applicable or
the breakpoint will be set at the wrong address and either fail to work
or cause SIGTRAPs (this is because the symbol is handled early on and
bypasses regular symbol processing).

4. Results obtained

The change fixes the example above -- to repeat only the crucial steps:

(gdb) break main
Breakpoint 1 at 0x400491: file foobar.c, line 23.
(gdb) run
Starting program: .../foobar

Breakpoint 1, main () at foobar.c:23
23        return foop ();
(gdb) print foo
$1 = {int (void)} 0x400681 <foo>
(gdb) set foop = bar
(gdb) advance bar
bar () at foobar.c:9
9       }
(gdb) disassemble
Dump of assembler code for function bar:
=> 0x0040068d <+0>:     jr      ra
   0x0040068f <+2>:     li      v0,2
End of assembler dump.
(gdb) finish
Run till exit from #0  bar () at foobar.c:9
main () at foobar.c:24
24      }
Value returned is $2 = 2
(gdb) continue
Continuing.
[Inferior 1 (process 14128) exited with code 02]
(gdb)

-- excellent!

The change removes about 90 failures per MIPS16 multilib in mips-sde-elf
testing too, results for MIPS16 are now similar to that for standard
MIPS; microMIPS results are a bit worse because of host-I/O problems in
QEMU used instead of MIPSsim for microMIPS testing only:

                === gdb Summary ===

# of expected passes            14299
# of unexpected failures        187
# of expected failures          56
# of known failures             58
# of unresolved testcases       11
# of untested testcases         52
# of unsupported tests          174

MIPS16:

                === gdb Summary ===

# of expected passes            14298
# of unexpected failures        187
# of unexpected successes       2
# of expected failures          54
# of known failures             58
# of unresolved testcases       12
# of untested testcases         52
# of unsupported tests          174

microMIPS:

                === gdb Summary ===

# of expected passes            14149
# of unexpected failures        201
# of unexpected successes       2
# of expected failures          54
# of known failures             58
# of unresolved testcases       7
# of untested testcases         53
# of unsupported tests          175

2014-12-12  Maciej W. Rozycki  <macro@codesourcery.com>
            Maciej W. Rozycki  <macro@mips.com>
            Pedro Alves  <pedro@codesourcery.com>

	gdb/
	* gdbarch.sh (elf_make_msymbol_special): Change type to `F',
	remove `predefault' and `invalid_p' initializers.
	(make_symbol_special): New architecture method.
	(adjust_dwarf2_addr, adjust_dwarf2_line): Likewise.
	(objfile, symbol): New declarations.
	* arch-utils.h (default_elf_make_msymbol_special): Remove
	prototype.
	(default_make_symbol_special): New prototype.
	(default_adjust_dwarf2_addr): Likewise.
	(default_adjust_dwarf2_line): Likewise.
	* mips-tdep.h (mips_unmake_compact_addr): New prototype.
	* arch-utils.c (default_elf_make_msymbol_special): Remove
	function.
	(default_make_symbol_special): New function.
	(default_adjust_dwarf2_addr): Likewise.
	(default_adjust_dwarf2_line): Likewise.
	* dwarf2-frame.c (decode_frame_entry_1): Call
	`gdbarch_adjust_dwarf2_addr'.
	* dwarf2loc.c (dwarf2_find_location_expression): Likewise.
	* dwarf2read.c (create_addrmap_from_index): Likewise.
	(process_psymtab_comp_unit_reader): Likewise.
	(add_partial_symbol): Likewise.
	(add_partial_subprogram): Likewise.
	(process_full_comp_unit): Likewise.
	(read_file_scope): Likewise.
	(read_func_scope): Likewise.  Call `gdbarch_make_symbol_special'.
	(read_lexical_block_scope): Call `gdbarch_adjust_dwarf2_addr'.
	(read_call_site_scope): Likewise.
	(dwarf2_ranges_read): Likewise.
	(dwarf2_record_block_ranges): Likewise.
	(read_attribute_value): Likewise.
	(dwarf_decode_lines_1): Call `gdbarch_adjust_dwarf2_line'.
	(new_symbol_full): Call `gdbarch_adjust_dwarf2_addr'.
	* elfread.c (elf_symtab_read): Don't call
	`gdbarch_elf_make_msymbol_special' if unset.
	* mips-linux-tdep.c (micromips_linux_sigframe_validate): Strip
	the ISA bit from the PC.
	* mips-tdep.c (mips_unmake_compact_addr): New function.
	(mips_elf_make_msymbol_special): Set the ISA bit in the symbol's
	address appropriately.
	(mips_make_symbol_special): New function.
	(mips_pc_is_mips): Set the ISA bit before symbol lookup.
	(mips_pc_is_mips16): Likewise.
	(mips_pc_is_micromips): Likewise.
	(mips_pc_isa): Likewise.
	(mips_adjust_dwarf2_addr): New function.
	(mips_adjust_dwarf2_line): Likewise.
	(mips_read_pc, mips_unwind_pc): Keep the ISA bit.
	(mips_addr_bits_remove): Likewise.
	(mips_skip_trampoline_code): Likewise.
	(mips_write_pc): Don't set the ISA bit.
	(mips_eabi_push_dummy_call): Likewise.
	(mips_o64_push_dummy_call): Likewise.
	(mips_gdbarch_init): Install `mips_make_symbol_special',
	`mips_adjust_dwarf2_addr' and `mips_adjust_dwarf2_line' gdbarch
	handlers.
	* solib.c (gdb_bfd_lookup_symbol_from_symtab): Get
	target-specific symbol address adjustments.
	* gdbarch.h: Regenerate.
	* gdbarch.c: Regenerate.

2014-12-12  Maciej W. Rozycki  <macro@codesourcery.com>

	gdb/testsuite/
	* gdb.base/func-ptrs.c: New file.
	* gdb.base/func-ptrs.exp: New file.
2014-12-12 13:49:06 +00:00

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/* Read ELF (Executable and Linking Format) object files for GDB.
Copyright (C) 1991-2014 Free Software Foundation, Inc.
Written by Fred Fish at Cygnus Support.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#include "defs.h"
#include "bfd.h"
#include "elf-bfd.h"
#include "elf/common.h"
#include "elf/internal.h"
#include "elf/mips.h"
#include "symtab.h"
#include "symfile.h"
#include "objfiles.h"
#include "buildsym.h"
#include "stabsread.h"
#include "gdb-stabs.h"
#include "complaints.h"
#include "demangle.h"
#include "psympriv.h"
#include "filenames.h"
#include "probe.h"
#include "arch-utils.h"
#include "gdbtypes.h"
#include "value.h"
#include "infcall.h"
#include "gdbthread.h"
#include "regcache.h"
#include "bcache.h"
#include "gdb_bfd.h"
#include "build-id.h"
extern void _initialize_elfread (void);
/* Forward declarations. */
static const struct sym_fns elf_sym_fns_gdb_index;
static const struct sym_fns elf_sym_fns_lazy_psyms;
/* The struct elfinfo is available only during ELF symbol table and
psymtab reading. It is destroyed at the completion of psymtab-reading.
It's local to elf_symfile_read. */
struct elfinfo
{
asection *stabsect; /* Section pointer for .stab section */
asection *mdebugsect; /* Section pointer for .mdebug section */
};
/* Per-BFD data for probe info. */
static const struct bfd_data *probe_key = NULL;
static void free_elfinfo (void *);
/* Minimal symbols located at the GOT entries for .plt - that is the real
pointer where the given entry will jump to. It gets updated by the real
function address during lazy ld.so resolving in the inferior. These
minimal symbols are indexed for <tab>-completion. */
#define SYMBOL_GOT_PLT_SUFFIX "@got.plt"
/* Locate the segments in ABFD. */
static struct symfile_segment_data *
elf_symfile_segments (bfd *abfd)
{
Elf_Internal_Phdr *phdrs, **segments;
long phdrs_size;
int num_phdrs, num_segments, num_sections, i;
asection *sect;
struct symfile_segment_data *data;
phdrs_size = bfd_get_elf_phdr_upper_bound (abfd);
if (phdrs_size == -1)
return NULL;
phdrs = alloca (phdrs_size);
num_phdrs = bfd_get_elf_phdrs (abfd, phdrs);
if (num_phdrs == -1)
return NULL;
num_segments = 0;
segments = alloca (sizeof (Elf_Internal_Phdr *) * num_phdrs);
for (i = 0; i < num_phdrs; i++)
if (phdrs[i].p_type == PT_LOAD)
segments[num_segments++] = &phdrs[i];
if (num_segments == 0)
return NULL;
data = XCNEW (struct symfile_segment_data);
data->num_segments = num_segments;
data->segment_bases = XCNEWVEC (CORE_ADDR, num_segments);
data->segment_sizes = XCNEWVEC (CORE_ADDR, num_segments);
for (i = 0; i < num_segments; i++)
{
data->segment_bases[i] = segments[i]->p_vaddr;
data->segment_sizes[i] = segments[i]->p_memsz;
}
num_sections = bfd_count_sections (abfd);
data->segment_info = XCNEWVEC (int, num_sections);
for (i = 0, sect = abfd->sections; sect != NULL; i++, sect = sect->next)
{
int j;
CORE_ADDR vma;
if ((bfd_get_section_flags (abfd, sect) & SEC_ALLOC) == 0)
continue;
vma = bfd_get_section_vma (abfd, sect);
for (j = 0; j < num_segments; j++)
if (segments[j]->p_memsz > 0
&& vma >= segments[j]->p_vaddr
&& (vma - segments[j]->p_vaddr) < segments[j]->p_memsz)
{
data->segment_info[i] = j + 1;
break;
}
/* We should have found a segment for every non-empty section.
If we haven't, we will not relocate this section by any
offsets we apply to the segments. As an exception, do not
warn about SHT_NOBITS sections; in normal ELF execution
environments, SHT_NOBITS means zero-initialized and belongs
in a segment, but in no-OS environments some tools (e.g. ARM
RealView) use SHT_NOBITS for uninitialized data. Since it is
uninitialized, it doesn't need a program header. Such
binaries are not relocatable. */
if (bfd_get_section_size (sect) > 0 && j == num_segments
&& (bfd_get_section_flags (abfd, sect) & SEC_LOAD) != 0)
warning (_("Loadable section \"%s\" outside of ELF segments"),
bfd_section_name (abfd, sect));
}
return data;
}
/* We are called once per section from elf_symfile_read. We
need to examine each section we are passed, check to see
if it is something we are interested in processing, and
if so, stash away some access information for the section.
For now we recognize the dwarf debug information sections and
line number sections from matching their section names. The
ELF definition is no real help here since it has no direct
knowledge of DWARF (by design, so any debugging format can be
used).
We also recognize the ".stab" sections used by the Sun compilers
released with Solaris 2.
FIXME: The section names should not be hardwired strings (what
should they be? I don't think most object file formats have enough
section flags to specify what kind of debug section it is.
-kingdon). */
static void
elf_locate_sections (bfd *ignore_abfd, asection *sectp, void *eip)
{
struct elfinfo *ei;
ei = (struct elfinfo *) eip;
if (strcmp (sectp->name, ".stab") == 0)
{
ei->stabsect = sectp;
}
else if (strcmp (sectp->name, ".mdebug") == 0)
{
ei->mdebugsect = sectp;
}
}
static struct minimal_symbol *
record_minimal_symbol (const char *name, int name_len, int copy_name,
CORE_ADDR address,
enum minimal_symbol_type ms_type,
asection *bfd_section, struct objfile *objfile)
{
struct gdbarch *gdbarch = get_objfile_arch (objfile);
if (ms_type == mst_text || ms_type == mst_file_text
|| ms_type == mst_text_gnu_ifunc)
address = gdbarch_addr_bits_remove (gdbarch, address);
return prim_record_minimal_symbol_full (name, name_len, copy_name, address,
ms_type,
gdb_bfd_section_index (objfile->obfd,
bfd_section),
objfile);
}
/* Read the symbol table of an ELF file.
Given an objfile, a symbol table, and a flag indicating whether the
symbol table contains regular, dynamic, or synthetic symbols, add all
the global function and data symbols to the minimal symbol table.
In stabs-in-ELF, as implemented by Sun, there are some local symbols
defined in the ELF symbol table, which can be used to locate
the beginnings of sections from each ".o" file that was linked to
form the executable objfile. We gather any such info and record it
in data structures hung off the objfile's private data. */
#define ST_REGULAR 0
#define ST_DYNAMIC 1
#define ST_SYNTHETIC 2
static void
elf_symtab_read (struct objfile *objfile, int type,
long number_of_symbols, asymbol **symbol_table,
int copy_names)
{
struct gdbarch *gdbarch = get_objfile_arch (objfile);
asymbol *sym;
long i;
CORE_ADDR symaddr;
CORE_ADDR offset;
enum minimal_symbol_type ms_type;
/* If sectinfo is nonNULL, it contains section info that should end up
filed in the objfile. */
struct stab_section_info *sectinfo = NULL;
/* If filesym is nonzero, it points to a file symbol, but we haven't
seen any section info for it yet. */
asymbol *filesym = 0;
/* Name of filesym. This is either a constant string or is saved on
the objfile's filename cache. */
const char *filesymname = "";
struct dbx_symfile_info *dbx = DBX_SYMFILE_INFO (objfile);
int stripped = (bfd_get_symcount (objfile->obfd) == 0);
int elf_make_msymbol_special_p
= gdbarch_elf_make_msymbol_special_p (gdbarch);
for (i = 0; i < number_of_symbols; i++)
{
sym = symbol_table[i];
if (sym->name == NULL || *sym->name == '\0')
{
/* Skip names that don't exist (shouldn't happen), or names
that are null strings (may happen). */
continue;
}
/* Skip "special" symbols, e.g. ARM mapping symbols. These are
symbols which do not correspond to objects in the symbol table,
but have some other target-specific meaning. */
if (bfd_is_target_special_symbol (objfile->obfd, sym))
{
if (gdbarch_record_special_symbol_p (gdbarch))
gdbarch_record_special_symbol (gdbarch, objfile, sym);
continue;
}
offset = ANOFFSET (objfile->section_offsets,
gdb_bfd_section_index (objfile->obfd, sym->section));
if (type == ST_DYNAMIC
&& sym->section == bfd_und_section_ptr
&& (sym->flags & BSF_FUNCTION))
{
struct minimal_symbol *msym;
bfd *abfd = objfile->obfd;
asection *sect;
/* Symbol is a reference to a function defined in
a shared library.
If its value is non zero then it is usually the address
of the corresponding entry in the procedure linkage table,
plus the desired section offset.
If its value is zero then the dynamic linker has to resolve
the symbol. We are unable to find any meaningful address
for this symbol in the executable file, so we skip it. */
symaddr = sym->value;
if (symaddr == 0)
continue;
/* sym->section is the undefined section. However, we want to
record the section where the PLT stub resides with the
minimal symbol. Search the section table for the one that
covers the stub's address. */
for (sect = abfd->sections; sect != NULL; sect = sect->next)
{
if ((bfd_get_section_flags (abfd, sect) & SEC_ALLOC) == 0)
continue;
if (symaddr >= bfd_get_section_vma (abfd, sect)
&& symaddr < bfd_get_section_vma (abfd, sect)
+ bfd_get_section_size (sect))
break;
}
if (!sect)
continue;
/* On ia64-hpux, we have discovered that the system linker
adds undefined symbols with nonzero addresses that cannot
be right (their address points inside the code of another
function in the .text section). This creates problems
when trying to determine which symbol corresponds to
a given address.
We try to detect those buggy symbols by checking which
section we think they correspond to. Normally, PLT symbols
are stored inside their own section, and the typical name
for that section is ".plt". So, if there is a ".plt"
section, and yet the section name of our symbol does not
start with ".plt", we ignore that symbol. */
if (strncmp (sect->name, ".plt", 4) != 0
&& bfd_get_section_by_name (abfd, ".plt") != NULL)
continue;
msym = record_minimal_symbol
(sym->name, strlen (sym->name), copy_names,
symaddr, mst_solib_trampoline, sect, objfile);
if (msym != NULL)
{
msym->filename = filesymname;
if (elf_make_msymbol_special_p)
gdbarch_elf_make_msymbol_special (gdbarch, sym, msym);
}
continue;
}
/* If it is a nonstripped executable, do not enter dynamic
symbols, as the dynamic symbol table is usually a subset
of the main symbol table. */
if (type == ST_DYNAMIC && !stripped)
continue;
if (sym->flags & BSF_FILE)
{
/* STT_FILE debugging symbol that helps stabs-in-elf debugging.
Chain any old one onto the objfile; remember new sym. */
if (sectinfo != NULL)
{
sectinfo->next = dbx->stab_section_info;
dbx->stab_section_info = sectinfo;
sectinfo = NULL;
}
filesym = sym;
filesymname = bcache (filesym->name, strlen (filesym->name) + 1,
objfile->per_bfd->filename_cache);
}
else if (sym->flags & BSF_SECTION_SYM)
continue;
else if (sym->flags & (BSF_GLOBAL | BSF_LOCAL | BSF_WEAK
| BSF_GNU_UNIQUE))
{
struct minimal_symbol *msym;
/* Select global/local/weak symbols. Note that bfd puts abs
symbols in their own section, so all symbols we are
interested in will have a section. */
/* Bfd symbols are section relative. */
symaddr = sym->value + sym->section->vma;
/* For non-absolute symbols, use the type of the section
they are relative to, to intuit text/data. Bfd provides
no way of figuring this out for absolute symbols. */
if (sym->section == bfd_abs_section_ptr)
{
/* This is a hack to get the minimal symbol type
right for Irix 5, which has absolute addresses
with special section indices for dynamic symbols.
NOTE: uweigand-20071112: Synthetic symbols do not
have an ELF-private part, so do not touch those. */
unsigned int shndx = type == ST_SYNTHETIC ? 0 :
((elf_symbol_type *) sym)->internal_elf_sym.st_shndx;
switch (shndx)
{
case SHN_MIPS_TEXT:
ms_type = mst_text;
break;
case SHN_MIPS_DATA:
ms_type = mst_data;
break;
case SHN_MIPS_ACOMMON:
ms_type = mst_bss;
break;
default:
ms_type = mst_abs;
}
/* If it is an Irix dynamic symbol, skip section name
symbols, relocate all others by section offset. */
if (ms_type != mst_abs)
{
if (sym->name[0] == '.')
continue;
}
}
else if (sym->section->flags & SEC_CODE)
{
if (sym->flags & (BSF_GLOBAL | BSF_WEAK | BSF_GNU_UNIQUE))
{
if (sym->flags & BSF_GNU_INDIRECT_FUNCTION)
ms_type = mst_text_gnu_ifunc;
else
ms_type = mst_text;
}
/* The BSF_SYNTHETIC check is there to omit ppc64 function
descriptors mistaken for static functions starting with 'L'.
*/
else if ((sym->name[0] == '.' && sym->name[1] == 'L'
&& (sym->flags & BSF_SYNTHETIC) == 0)
|| ((sym->flags & BSF_LOCAL)
&& sym->name[0] == '$'
&& sym->name[1] == 'L'))
/* Looks like a compiler-generated label. Skip
it. The assembler should be skipping these (to
keep executables small), but apparently with
gcc on the (deleted) delta m88k SVR4, it loses.
So to have us check too should be harmless (but
I encourage people to fix this in the assembler
instead of adding checks here). */
continue;
else
{
ms_type = mst_file_text;
}
}
else if (sym->section->flags & SEC_ALLOC)
{
if (sym->flags & (BSF_GLOBAL | BSF_WEAK | BSF_GNU_UNIQUE))
{
if (sym->section->flags & SEC_LOAD)
{
ms_type = mst_data;
}
else
{
ms_type = mst_bss;
}
}
else if (sym->flags & BSF_LOCAL)
{
/* Named Local variable in a Data section.
Check its name for stabs-in-elf. */
int special_local_sect;
if (strcmp ("Bbss.bss", sym->name) == 0)
special_local_sect = SECT_OFF_BSS (objfile);
else if (strcmp ("Ddata.data", sym->name) == 0)
special_local_sect = SECT_OFF_DATA (objfile);
else if (strcmp ("Drodata.rodata", sym->name) == 0)
special_local_sect = SECT_OFF_RODATA (objfile);
else
special_local_sect = -1;
if (special_local_sect >= 0)
{
/* Found a special local symbol. Allocate a
sectinfo, if needed, and fill it in. */
if (sectinfo == NULL)
{
int max_index;
size_t size;
max_index = SECT_OFF_BSS (objfile);
if (objfile->sect_index_data > max_index)
max_index = objfile->sect_index_data;
if (objfile->sect_index_rodata > max_index)
max_index = objfile->sect_index_rodata;
/* max_index is the largest index we'll
use into this array, so we must
allocate max_index+1 elements for it.
However, 'struct stab_section_info'
already includes one element, so we
need to allocate max_index aadditional
elements. */
size = (sizeof (struct stab_section_info)
+ (sizeof (CORE_ADDR) * max_index));
sectinfo = (struct stab_section_info *)
xmalloc (size);
memset (sectinfo, 0, size);
sectinfo->num_sections = max_index;
if (filesym == NULL)
{
complaint (&symfile_complaints,
_("elf/stab section information %s "
"without a preceding file symbol"),
sym->name);
}
else
{
sectinfo->filename =
(char *) filesym->name;
}
}
if (sectinfo->sections[special_local_sect] != 0)
complaint (&symfile_complaints,
_("duplicated elf/stab section "
"information for %s"),
sectinfo->filename);
/* BFD symbols are section relative. */
symaddr = sym->value + sym->section->vma;
/* Relocate non-absolute symbols by the
section offset. */
if (sym->section != bfd_abs_section_ptr)
symaddr += offset;
sectinfo->sections[special_local_sect] = symaddr;
/* The special local symbols don't go in the
minimal symbol table, so ignore this one. */
continue;
}
/* Not a special stabs-in-elf symbol, do regular
symbol processing. */
if (sym->section->flags & SEC_LOAD)
{
ms_type = mst_file_data;
}
else
{
ms_type = mst_file_bss;
}
}
else
{
ms_type = mst_unknown;
}
}
else
{
/* FIXME: Solaris2 shared libraries include lots of
odd "absolute" and "undefined" symbols, that play
hob with actions like finding what function the PC
is in. Ignore them if they aren't text, data, or bss. */
/* ms_type = mst_unknown; */
continue; /* Skip this symbol. */
}
msym = record_minimal_symbol
(sym->name, strlen (sym->name), copy_names, symaddr,
ms_type, sym->section, objfile);
if (msym)
{
/* NOTE: uweigand-20071112: A synthetic symbol does not have an
ELF-private part. */
if (type != ST_SYNTHETIC)
{
/* Pass symbol size field in via BFD. FIXME!!! */
elf_symbol_type *elf_sym = (elf_symbol_type *) sym;
SET_MSYMBOL_SIZE (msym, elf_sym->internal_elf_sym.st_size);
}
msym->filename = filesymname;
if (elf_make_msymbol_special_p)
gdbarch_elf_make_msymbol_special (gdbarch, sym, msym);
}
/* If we see a default versioned symbol, install it under
its version-less name. */
if (msym != NULL)
{
const char *atsign = strchr (sym->name, '@');
if (atsign != NULL && atsign[1] == '@' && atsign > sym->name)
{
int len = atsign - sym->name;
record_minimal_symbol (sym->name, len, 1, symaddr,
ms_type, sym->section, objfile);
}
}
/* For @plt symbols, also record a trampoline to the
destination symbol. The @plt symbol will be used in
disassembly, and the trampoline will be used when we are
trying to find the target. */
if (msym && ms_type == mst_text && type == ST_SYNTHETIC)
{
int len = strlen (sym->name);
if (len > 4 && strcmp (sym->name + len - 4, "@plt") == 0)
{
struct minimal_symbol *mtramp;
mtramp = record_minimal_symbol (sym->name, len - 4, 1,
symaddr,
mst_solib_trampoline,
sym->section, objfile);
if (mtramp)
{
SET_MSYMBOL_SIZE (mtramp, MSYMBOL_SIZE (msym));
mtramp->created_by_gdb = 1;
mtramp->filename = filesymname;
if (elf_make_msymbol_special_p)
gdbarch_elf_make_msymbol_special (gdbarch,
sym, mtramp);
}
}
}
}
}
}
/* Build minimal symbols named `function@got.plt' (see SYMBOL_GOT_PLT_SUFFIX)
for later look ups of which function to call when user requests
a STT_GNU_IFUNC function. As the STT_GNU_IFUNC type is found at the target
library defining `function' we cannot yet know while reading OBJFILE which
of the SYMBOL_GOT_PLT_SUFFIX entries will be needed and later
DYN_SYMBOL_TABLE is no longer easily available for OBJFILE. */
static void
elf_rel_plt_read (struct objfile *objfile, asymbol **dyn_symbol_table)
{
bfd *obfd = objfile->obfd;
const struct elf_backend_data *bed = get_elf_backend_data (obfd);
asection *plt, *relplt, *got_plt;
int plt_elf_idx;
bfd_size_type reloc_count, reloc;
char *string_buffer = NULL;
size_t string_buffer_size = 0;
struct cleanup *back_to;
struct gdbarch *gdbarch = get_objfile_arch (objfile);
struct type *ptr_type = builtin_type (gdbarch)->builtin_data_ptr;
size_t ptr_size = TYPE_LENGTH (ptr_type);
if (objfile->separate_debug_objfile_backlink)
return;
plt = bfd_get_section_by_name (obfd, ".plt");
if (plt == NULL)
return;
plt_elf_idx = elf_section_data (plt)->this_idx;
got_plt = bfd_get_section_by_name (obfd, ".got.plt");
if (got_plt == NULL)
{
/* For platforms where there is no separate .got.plt. */
got_plt = bfd_get_section_by_name (obfd, ".got");
if (got_plt == NULL)
return;
}
/* This search algorithm is from _bfd_elf_canonicalize_dynamic_reloc. */
for (relplt = obfd->sections; relplt != NULL; relplt = relplt->next)
if (elf_section_data (relplt)->this_hdr.sh_info == plt_elf_idx
&& (elf_section_data (relplt)->this_hdr.sh_type == SHT_REL
|| elf_section_data (relplt)->this_hdr.sh_type == SHT_RELA))
break;
if (relplt == NULL)
return;
if (! bed->s->slurp_reloc_table (obfd, relplt, dyn_symbol_table, TRUE))
return;
back_to = make_cleanup (free_current_contents, &string_buffer);
reloc_count = relplt->size / elf_section_data (relplt)->this_hdr.sh_entsize;
for (reloc = 0; reloc < reloc_count; reloc++)
{
const char *name;
struct minimal_symbol *msym;
CORE_ADDR address;
const size_t got_suffix_len = strlen (SYMBOL_GOT_PLT_SUFFIX);
size_t name_len;
name = bfd_asymbol_name (*relplt->relocation[reloc].sym_ptr_ptr);
name_len = strlen (name);
address = relplt->relocation[reloc].address;
/* Does the pointer reside in the .got.plt section? */
if (!(bfd_get_section_vma (obfd, got_plt) <= address
&& address < bfd_get_section_vma (obfd, got_plt)
+ bfd_get_section_size (got_plt)))
continue;
/* We cannot check if NAME is a reference to mst_text_gnu_ifunc as in
OBJFILE the symbol is undefined and the objfile having NAME defined
may not yet have been loaded. */
if (string_buffer_size < name_len + got_suffix_len + 1)
{
string_buffer_size = 2 * (name_len + got_suffix_len);
string_buffer = xrealloc (string_buffer, string_buffer_size);
}
memcpy (string_buffer, name, name_len);
memcpy (&string_buffer[name_len], SYMBOL_GOT_PLT_SUFFIX,
got_suffix_len + 1);
msym = record_minimal_symbol (string_buffer, name_len + got_suffix_len,
1, address, mst_slot_got_plt, got_plt,
objfile);
if (msym)
SET_MSYMBOL_SIZE (msym, ptr_size);
}
do_cleanups (back_to);
}
/* The data pointer is htab_t for gnu_ifunc_record_cache_unchecked. */
static const struct objfile_data *elf_objfile_gnu_ifunc_cache_data;
/* Map function names to CORE_ADDR in elf_objfile_gnu_ifunc_cache_data. */
struct elf_gnu_ifunc_cache
{
/* This is always a function entry address, not a function descriptor. */
CORE_ADDR addr;
char name[1];
};
/* htab_hash for elf_objfile_gnu_ifunc_cache_data. */
static hashval_t
elf_gnu_ifunc_cache_hash (const void *a_voidp)
{
const struct elf_gnu_ifunc_cache *a = a_voidp;
return htab_hash_string (a->name);
}
/* htab_eq for elf_objfile_gnu_ifunc_cache_data. */
static int
elf_gnu_ifunc_cache_eq (const void *a_voidp, const void *b_voidp)
{
const struct elf_gnu_ifunc_cache *a = a_voidp;
const struct elf_gnu_ifunc_cache *b = b_voidp;
return strcmp (a->name, b->name) == 0;
}
/* Record the target function address of a STT_GNU_IFUNC function NAME is the
function entry address ADDR. Return 1 if NAME and ADDR are considered as
valid and therefore they were successfully recorded, return 0 otherwise.
Function does not expect a duplicate entry. Use
elf_gnu_ifunc_resolve_by_cache first to check if the entry for NAME already
exists. */
static int
elf_gnu_ifunc_record_cache (const char *name, CORE_ADDR addr)
{
struct bound_minimal_symbol msym;
asection *sect;
struct objfile *objfile;
htab_t htab;
struct elf_gnu_ifunc_cache entry_local, *entry_p;
void **slot;
msym = lookup_minimal_symbol_by_pc (addr);
if (msym.minsym == NULL)
return 0;
if (BMSYMBOL_VALUE_ADDRESS (msym) != addr)
return 0;
/* minimal symbols have always SYMBOL_OBJ_SECTION non-NULL. */
sect = MSYMBOL_OBJ_SECTION (msym.objfile, msym.minsym)->the_bfd_section;
objfile = msym.objfile;
/* If .plt jumps back to .plt the symbol is still deferred for later
resolution and it has no use for GDB. Besides ".text" this symbol can
reside also in ".opd" for ppc64 function descriptor. */
if (strcmp (bfd_get_section_name (objfile->obfd, sect), ".plt") == 0)
return 0;
htab = objfile_data (objfile, elf_objfile_gnu_ifunc_cache_data);
if (htab == NULL)
{
htab = htab_create_alloc_ex (1, elf_gnu_ifunc_cache_hash,
elf_gnu_ifunc_cache_eq,
NULL, &objfile->objfile_obstack,
hashtab_obstack_allocate,
dummy_obstack_deallocate);
set_objfile_data (objfile, elf_objfile_gnu_ifunc_cache_data, htab);
}
entry_local.addr = addr;
obstack_grow (&objfile->objfile_obstack, &entry_local,
offsetof (struct elf_gnu_ifunc_cache, name));
obstack_grow_str0 (&objfile->objfile_obstack, name);
entry_p = obstack_finish (&objfile->objfile_obstack);
slot = htab_find_slot (htab, entry_p, INSERT);
if (*slot != NULL)
{
struct elf_gnu_ifunc_cache *entry_found_p = *slot;
struct gdbarch *gdbarch = get_objfile_arch (objfile);
if (entry_found_p->addr != addr)
{
/* This case indicates buggy inferior program, the resolved address
should never change. */
warning (_("gnu-indirect-function \"%s\" has changed its resolved "
"function_address from %s to %s"),
name, paddress (gdbarch, entry_found_p->addr),
paddress (gdbarch, addr));
}
/* New ENTRY_P is here leaked/duplicate in the OBJFILE obstack. */
}
*slot = entry_p;
return 1;
}
/* Try to find the target resolved function entry address of a STT_GNU_IFUNC
function NAME. If the address is found it is stored to *ADDR_P (if ADDR_P
is not NULL) and the function returns 1. It returns 0 otherwise.
Only the elf_objfile_gnu_ifunc_cache_data hash table is searched by this
function. */
static int
elf_gnu_ifunc_resolve_by_cache (const char *name, CORE_ADDR *addr_p)
{
struct objfile *objfile;
ALL_PSPACE_OBJFILES (current_program_space, objfile)
{
htab_t htab;
struct elf_gnu_ifunc_cache *entry_p;
void **slot;
htab = objfile_data (objfile, elf_objfile_gnu_ifunc_cache_data);
if (htab == NULL)
continue;
entry_p = alloca (sizeof (*entry_p) + strlen (name));
strcpy (entry_p->name, name);
slot = htab_find_slot (htab, entry_p, NO_INSERT);
if (slot == NULL)
continue;
entry_p = *slot;
gdb_assert (entry_p != NULL);
if (addr_p)
*addr_p = entry_p->addr;
return 1;
}
return 0;
}
/* Try to find the target resolved function entry address of a STT_GNU_IFUNC
function NAME. If the address is found it is stored to *ADDR_P (if ADDR_P
is not NULL) and the function returns 1. It returns 0 otherwise.
Only the SYMBOL_GOT_PLT_SUFFIX locations are searched by this function.
elf_gnu_ifunc_resolve_by_cache must have been already called for NAME to
prevent cache entries duplicates. */
static int
elf_gnu_ifunc_resolve_by_got (const char *name, CORE_ADDR *addr_p)
{
char *name_got_plt;
struct objfile *objfile;
const size_t got_suffix_len = strlen (SYMBOL_GOT_PLT_SUFFIX);
name_got_plt = alloca (strlen (name) + got_suffix_len + 1);
sprintf (name_got_plt, "%s" SYMBOL_GOT_PLT_SUFFIX, name);
ALL_PSPACE_OBJFILES (current_program_space, objfile)
{
bfd *obfd = objfile->obfd;
struct gdbarch *gdbarch = get_objfile_arch (objfile);
struct type *ptr_type = builtin_type (gdbarch)->builtin_data_ptr;
size_t ptr_size = TYPE_LENGTH (ptr_type);
CORE_ADDR pointer_address, addr;
asection *plt;
gdb_byte *buf = alloca (ptr_size);
struct bound_minimal_symbol msym;
msym = lookup_minimal_symbol (name_got_plt, NULL, objfile);
if (msym.minsym == NULL)
continue;
if (MSYMBOL_TYPE (msym.minsym) != mst_slot_got_plt)
continue;
pointer_address = BMSYMBOL_VALUE_ADDRESS (msym);
plt = bfd_get_section_by_name (obfd, ".plt");
if (plt == NULL)
continue;
if (MSYMBOL_SIZE (msym.minsym) != ptr_size)
continue;
if (target_read_memory (pointer_address, buf, ptr_size) != 0)
continue;
addr = extract_typed_address (buf, ptr_type);
addr = gdbarch_convert_from_func_ptr_addr (gdbarch, addr,
&current_target);
addr = gdbarch_addr_bits_remove (gdbarch, addr);
if (addr_p)
*addr_p = addr;
if (elf_gnu_ifunc_record_cache (name, addr))
return 1;
}
return 0;
}
/* Try to find the target resolved function entry address of a STT_GNU_IFUNC
function NAME. If the address is found it is stored to *ADDR_P (if ADDR_P
is not NULL) and the function returns 1. It returns 0 otherwise.
Both the elf_objfile_gnu_ifunc_cache_data hash table and
SYMBOL_GOT_PLT_SUFFIX locations are searched by this function. */
static int
elf_gnu_ifunc_resolve_name (const char *name, CORE_ADDR *addr_p)
{
if (elf_gnu_ifunc_resolve_by_cache (name, addr_p))
return 1;
if (elf_gnu_ifunc_resolve_by_got (name, addr_p))
return 1;
return 0;
}
/* Call STT_GNU_IFUNC - a function returning addresss of a real function to
call. PC is theSTT_GNU_IFUNC resolving function entry. The value returned
is the entry point of the resolved STT_GNU_IFUNC target function to call.
*/
static CORE_ADDR
elf_gnu_ifunc_resolve_addr (struct gdbarch *gdbarch, CORE_ADDR pc)
{
const char *name_at_pc;
CORE_ADDR start_at_pc, address;
struct type *func_func_type = builtin_type (gdbarch)->builtin_func_func;
struct value *function, *address_val;
/* Try first any non-intrusive methods without an inferior call. */
if (find_pc_partial_function (pc, &name_at_pc, &start_at_pc, NULL)
&& start_at_pc == pc)
{
if (elf_gnu_ifunc_resolve_name (name_at_pc, &address))
return address;
}
else
name_at_pc = NULL;
function = allocate_value (func_func_type);
set_value_address (function, pc);
/* STT_GNU_IFUNC resolver functions have no parameters. FUNCTION is the
function entry address. ADDRESS may be a function descriptor. */
address_val = call_function_by_hand (function, 0, NULL);
address = value_as_address (address_val);
address = gdbarch_convert_from_func_ptr_addr (gdbarch, address,
&current_target);
address = gdbarch_addr_bits_remove (gdbarch, address);
if (name_at_pc)
elf_gnu_ifunc_record_cache (name_at_pc, address);
return address;
}
/* Handle inferior hit of bp_gnu_ifunc_resolver, see its definition. */
static void
elf_gnu_ifunc_resolver_stop (struct breakpoint *b)
{
struct breakpoint *b_return;
struct frame_info *prev_frame = get_prev_frame (get_current_frame ());
struct frame_id prev_frame_id = get_stack_frame_id (prev_frame);
CORE_ADDR prev_pc = get_frame_pc (prev_frame);
int thread_id = pid_to_thread_id (inferior_ptid);
gdb_assert (b->type == bp_gnu_ifunc_resolver);
for (b_return = b->related_breakpoint; b_return != b;
b_return = b_return->related_breakpoint)
{
gdb_assert (b_return->type == bp_gnu_ifunc_resolver_return);
gdb_assert (b_return->loc != NULL && b_return->loc->next == NULL);
gdb_assert (frame_id_p (b_return->frame_id));
if (b_return->thread == thread_id
&& b_return->loc->requested_address == prev_pc
&& frame_id_eq (b_return->frame_id, prev_frame_id))
break;
}
if (b_return == b)
{
struct symtab_and_line sal;
/* No need to call find_pc_line for symbols resolving as this is only
a helper breakpointer never shown to the user. */
init_sal (&sal);
sal.pspace = current_inferior ()->pspace;
sal.pc = prev_pc;
sal.section = find_pc_overlay (sal.pc);
sal.explicit_pc = 1;
b_return = set_momentary_breakpoint (get_frame_arch (prev_frame), sal,
prev_frame_id,
bp_gnu_ifunc_resolver_return);
/* set_momentary_breakpoint invalidates PREV_FRAME. */
prev_frame = NULL;
/* Add new b_return to the ring list b->related_breakpoint. */
gdb_assert (b_return->related_breakpoint == b_return);
b_return->related_breakpoint = b->related_breakpoint;
b->related_breakpoint = b_return;
}
}
/* Handle inferior hit of bp_gnu_ifunc_resolver_return, see its definition. */
static void
elf_gnu_ifunc_resolver_return_stop (struct breakpoint *b)
{
struct gdbarch *gdbarch = get_frame_arch (get_current_frame ());
struct type *func_func_type = builtin_type (gdbarch)->builtin_func_func;
struct type *value_type = TYPE_TARGET_TYPE (func_func_type);
struct regcache *regcache = get_thread_regcache (inferior_ptid);
struct value *func_func;
struct value *value;
CORE_ADDR resolved_address, resolved_pc;
struct symtab_and_line sal;
struct symtabs_and_lines sals, sals_end;
gdb_assert (b->type == bp_gnu_ifunc_resolver_return);
while (b->related_breakpoint != b)
{
struct breakpoint *b_next = b->related_breakpoint;
switch (b->type)
{
case bp_gnu_ifunc_resolver:
break;
case bp_gnu_ifunc_resolver_return:
delete_breakpoint (b);
break;
default:
internal_error (__FILE__, __LINE__,
_("handle_inferior_event: Invalid "
"gnu-indirect-function breakpoint type %d"),
(int) b->type);
}
b = b_next;
}
gdb_assert (b->type == bp_gnu_ifunc_resolver);
gdb_assert (b->loc->next == NULL);
func_func = allocate_value (func_func_type);
set_value_address (func_func, b->loc->related_address);
value = allocate_value (value_type);
gdbarch_return_value (gdbarch, func_func, value_type, regcache,
value_contents_raw (value), NULL);
resolved_address = value_as_address (value);
resolved_pc = gdbarch_convert_from_func_ptr_addr (gdbarch,
resolved_address,
&current_target);
resolved_pc = gdbarch_addr_bits_remove (gdbarch, resolved_pc);
gdb_assert (current_program_space == b->pspace || b->pspace == NULL);
elf_gnu_ifunc_record_cache (b->addr_string, resolved_pc);
sal = find_pc_line (resolved_pc, 0);
sals.nelts = 1;
sals.sals = &sal;
sals_end.nelts = 0;
b->type = bp_breakpoint;
update_breakpoint_locations (b, sals, sals_end);
}
/* A helper function for elf_symfile_read that reads the minimal
symbols. */
static void
elf_read_minimal_symbols (struct objfile *objfile, int symfile_flags,
const struct elfinfo *ei)
{
bfd *synth_abfd, *abfd = objfile->obfd;
struct cleanup *back_to;
long symcount = 0, dynsymcount = 0, synthcount, storage_needed;
asymbol **symbol_table = NULL, **dyn_symbol_table = NULL;
asymbol *synthsyms;
struct dbx_symfile_info *dbx;
if (symtab_create_debug)
{
fprintf_unfiltered (gdb_stdlog,
"Reading minimal symbols of objfile %s ...\n",
objfile_name (objfile));
}
/* If we already have minsyms, then we can skip some work here.
However, if there were stabs or mdebug sections, we go ahead and
redo all the work anyway, because the psym readers for those
kinds of debuginfo need extra information found here. This can
go away once all types of symbols are in the per-BFD object. */
if (objfile->per_bfd->minsyms_read
&& ei->stabsect == NULL
&& ei->mdebugsect == NULL)
{
if (symtab_create_debug)
fprintf_unfiltered (gdb_stdlog,
"... minimal symbols previously read\n");
return;
}
init_minimal_symbol_collection ();
back_to = make_cleanup_discard_minimal_symbols ();
/* Allocate struct to keep track of the symfile. */
dbx = XCNEW (struct dbx_symfile_info);
set_objfile_data (objfile, dbx_objfile_data_key, dbx);
make_cleanup (free_elfinfo, (void *) objfile);
/* Process the normal ELF symbol table first. This may write some
chain of info into the dbx_symfile_info of the objfile, which can
later be used by elfstab_offset_sections. */
storage_needed = bfd_get_symtab_upper_bound (objfile->obfd);
if (storage_needed < 0)
error (_("Can't read symbols from %s: %s"),
bfd_get_filename (objfile->obfd),
bfd_errmsg (bfd_get_error ()));
if (storage_needed > 0)
{
symbol_table = (asymbol **) xmalloc (storage_needed);
make_cleanup (xfree, symbol_table);
symcount = bfd_canonicalize_symtab (objfile->obfd, symbol_table);
if (symcount < 0)
error (_("Can't read symbols from %s: %s"),
bfd_get_filename (objfile->obfd),
bfd_errmsg (bfd_get_error ()));
elf_symtab_read (objfile, ST_REGULAR, symcount, symbol_table, 0);
}
/* Add the dynamic symbols. */
storage_needed = bfd_get_dynamic_symtab_upper_bound (objfile->obfd);
if (storage_needed > 0)
{
/* Memory gets permanently referenced from ABFD after
bfd_get_synthetic_symtab so it must not get freed before ABFD gets.
It happens only in the case when elf_slurp_reloc_table sees
asection->relocation NULL. Determining which section is asection is
done by _bfd_elf_get_synthetic_symtab which is all a bfd
implementation detail, though. */
dyn_symbol_table = bfd_alloc (abfd, storage_needed);
dynsymcount = bfd_canonicalize_dynamic_symtab (objfile->obfd,
dyn_symbol_table);
if (dynsymcount < 0)
error (_("Can't read symbols from %s: %s"),
bfd_get_filename (objfile->obfd),
bfd_errmsg (bfd_get_error ()));
elf_symtab_read (objfile, ST_DYNAMIC, dynsymcount, dyn_symbol_table, 0);
elf_rel_plt_read (objfile, dyn_symbol_table);
}
/* Contrary to binutils --strip-debug/--only-keep-debug the strip command from
elfutils (eu-strip) moves even the .symtab section into the .debug file.
bfd_get_synthetic_symtab on ppc64 for each function descriptor ELF symbol
'name' creates a new BSF_SYNTHETIC ELF symbol '.name' with its code
address. But with eu-strip files bfd_get_synthetic_symtab would fail to
read the code address from .opd while it reads the .symtab section from
a separate debug info file as the .opd section is SHT_NOBITS there.
With SYNTH_ABFD the .opd section will be read from the original
backlinked binary where it is valid. */
if (objfile->separate_debug_objfile_backlink)
synth_abfd = objfile->separate_debug_objfile_backlink->obfd;
else
synth_abfd = abfd;
/* Add synthetic symbols - for instance, names for any PLT entries. */
synthcount = bfd_get_synthetic_symtab (synth_abfd, symcount, symbol_table,
dynsymcount, dyn_symbol_table,
&synthsyms);
if (synthcount > 0)
{
asymbol **synth_symbol_table;
long i;
make_cleanup (xfree, synthsyms);
synth_symbol_table = xmalloc (sizeof (asymbol *) * synthcount);
for (i = 0; i < synthcount; i++)
synth_symbol_table[i] = synthsyms + i;
make_cleanup (xfree, synth_symbol_table);
elf_symtab_read (objfile, ST_SYNTHETIC, synthcount,
synth_symbol_table, 1);
}
/* Install any minimal symbols that have been collected as the current
minimal symbols for this objfile. The debug readers below this point
should not generate new minimal symbols; if they do it's their
responsibility to install them. "mdebug" appears to be the only one
which will do this. */
install_minimal_symbols (objfile);
do_cleanups (back_to);
if (symtab_create_debug)
fprintf_unfiltered (gdb_stdlog, "Done reading minimal symbols.\n");
}
/* Scan and build partial symbols for a symbol file.
We have been initialized by a call to elf_symfile_init, which
currently does nothing.
SECTION_OFFSETS is a set of offsets to apply to relocate the symbols
in each section. We simplify it down to a single offset for all
symbols. FIXME.
This function only does the minimum work necessary for letting the
user "name" things symbolically; it does not read the entire symtab.
Instead, it reads the external and static symbols and puts them in partial
symbol tables. When more extensive information is requested of a
file, the corresponding partial symbol table is mutated into a full
fledged symbol table by going back and reading the symbols
for real.
We look for sections with specific names, to tell us what debug
format to look for: FIXME!!!
elfstab_build_psymtabs() handles STABS symbols;
mdebug_build_psymtabs() handles ECOFF debugging information.
Note that ELF files have a "minimal" symbol table, which looks a lot
like a COFF symbol table, but has only the minimal information necessary
for linking. We process this also, and use the information to
build gdb's minimal symbol table. This gives us some minimal debugging
capability even for files compiled without -g. */
static void
elf_symfile_read (struct objfile *objfile, int symfile_flags)
{
bfd *abfd = objfile->obfd;
struct elfinfo ei;
memset ((char *) &ei, 0, sizeof (ei));
bfd_map_over_sections (abfd, elf_locate_sections, (void *) & ei);
elf_read_minimal_symbols (objfile, symfile_flags, &ei);
/* ELF debugging information is inserted into the psymtab in the
order of least informative first - most informative last. Since
the psymtab table is searched `most recent insertion first' this
increases the probability that more detailed debug information
for a section is found.
For instance, an object file might contain both .mdebug (XCOFF)
and .debug_info (DWARF2) sections then .mdebug is inserted first
(searched last) and DWARF2 is inserted last (searched first). If
we don't do this then the XCOFF info is found first - for code in
an included file XCOFF info is useless. */
if (ei.mdebugsect)
{
const struct ecoff_debug_swap *swap;
/* .mdebug section, presumably holding ECOFF debugging
information. */
swap = get_elf_backend_data (abfd)->elf_backend_ecoff_debug_swap;
if (swap)
elfmdebug_build_psymtabs (objfile, swap, ei.mdebugsect);
}
if (ei.stabsect)
{
asection *str_sect;
/* Stab sections have an associated string table that looks like
a separate section. */
str_sect = bfd_get_section_by_name (abfd, ".stabstr");
/* FIXME should probably warn about a stab section without a stabstr. */
if (str_sect)
elfstab_build_psymtabs (objfile,
ei.stabsect,
str_sect->filepos,
bfd_section_size (abfd, str_sect));
}
if (dwarf2_has_info (objfile, NULL))
{
/* elf_sym_fns_gdb_index cannot handle simultaneous non-DWARF debug
information present in OBJFILE. If there is such debug info present
never use .gdb_index. */
if (!objfile_has_partial_symbols (objfile)
&& dwarf2_initialize_objfile (objfile))
objfile_set_sym_fns (objfile, &elf_sym_fns_gdb_index);
else
{
/* It is ok to do this even if the stabs reader made some
partial symbols, because OBJF_PSYMTABS_READ has not been
set, and so our lazy reader function will still be called
when needed. */
objfile_set_sym_fns (objfile, &elf_sym_fns_lazy_psyms);
}
}
/* If the file has its own symbol tables it has no separate debug
info. `.dynsym'/`.symtab' go to MSYMBOLS, `.debug_info' goes to
SYMTABS/PSYMTABS. `.gnu_debuglink' may no longer be present with
`.note.gnu.build-id'.
.gnu_debugdata is !objfile_has_partial_symbols because it contains only
.symtab, not .debug_* section. But if we already added .gnu_debugdata as
an objfile via find_separate_debug_file_in_section there was no separate
debug info available. Therefore do not attempt to search for another one,
objfile->separate_debug_objfile->separate_debug_objfile GDB guarantees to
be NULL and we would possibly violate it. */
else if (!objfile_has_partial_symbols (objfile)
&& objfile->separate_debug_objfile == NULL
&& objfile->separate_debug_objfile_backlink == NULL)
{
char *debugfile;
debugfile = find_separate_debug_file_by_buildid (objfile);
if (debugfile == NULL)
debugfile = find_separate_debug_file_by_debuglink (objfile);
if (debugfile)
{
struct cleanup *cleanup = make_cleanup (xfree, debugfile);
bfd *abfd = symfile_bfd_open (debugfile);
make_cleanup_bfd_unref (abfd);
symbol_file_add_separate (abfd, debugfile, symfile_flags, objfile);
do_cleanups (cleanup);
}
}
}
/* Callback to lazily read psymtabs. */
static void
read_psyms (struct objfile *objfile)
{
if (dwarf2_has_info (objfile, NULL))
dwarf2_build_psymtabs (objfile);
}
/* This cleans up the objfile's dbx symfile info, and the chain of
stab_section_info's, that might be dangling from it. */
static void
free_elfinfo (void *objp)
{
struct objfile *objfile = (struct objfile *) objp;
struct dbx_symfile_info *dbxinfo = DBX_SYMFILE_INFO (objfile);
struct stab_section_info *ssi, *nssi;
ssi = dbxinfo->stab_section_info;
while (ssi)
{
nssi = ssi->next;
xfree (ssi);
ssi = nssi;
}
dbxinfo->stab_section_info = 0; /* Just say No mo info about this. */
}
/* Initialize anything that needs initializing when a completely new symbol
file is specified (not just adding some symbols from another file, e.g. a
shared library).
We reinitialize buildsym, since we may be reading stabs from an ELF
file. */
static void
elf_new_init (struct objfile *ignore)
{
stabsread_new_init ();
buildsym_new_init ();
}
/* Perform any local cleanups required when we are done with a particular
objfile. I.E, we are in the process of discarding all symbol information
for an objfile, freeing up all memory held for it, and unlinking the
objfile struct from the global list of known objfiles. */
static void
elf_symfile_finish (struct objfile *objfile)
{
dwarf2_free_objfile (objfile);
}
/* ELF specific initialization routine for reading symbols.
It is passed a pointer to a struct sym_fns which contains, among other
things, the BFD for the file whose symbols are being read, and a slot for
a pointer to "private data" which we can fill with goodies.
For now at least, we have nothing in particular to do, so this function is
just a stub. */
static void
elf_symfile_init (struct objfile *objfile)
{
/* ELF objects may be reordered, so set OBJF_REORDERED. If we
find this causes a significant slowdown in gdb then we could
set it in the debug symbol readers only when necessary. */
objfile->flags |= OBJF_REORDERED;
}
/* When handling an ELF file that contains Sun STABS debug info,
some of the debug info is relative to the particular chunk of the
section that was generated in its individual .o file. E.g.
offsets to static variables are relative to the start of the data
segment *for that module before linking*. This information is
painfully squirreled away in the ELF symbol table as local symbols
with wierd names. Go get 'em when needed. */
void
elfstab_offset_sections (struct objfile *objfile, struct partial_symtab *pst)
{
const char *filename = pst->filename;
struct dbx_symfile_info *dbx = DBX_SYMFILE_INFO (objfile);
struct stab_section_info *maybe = dbx->stab_section_info;
struct stab_section_info *questionable = 0;
int i;
/* The ELF symbol info doesn't include path names, so strip the path
(if any) from the psymtab filename. */
filename = lbasename (filename);
/* FIXME: This linear search could speed up significantly
if it was chained in the right order to match how we search it,
and if we unchained when we found a match. */
for (; maybe; maybe = maybe->next)
{
if (filename[0] == maybe->filename[0]
&& filename_cmp (filename, maybe->filename) == 0)
{
/* We found a match. But there might be several source files
(from different directories) with the same name. */
if (0 == maybe->found)
break;
questionable = maybe; /* Might use it later. */
}
}
if (maybe == 0 && questionable != 0)
{
complaint (&symfile_complaints,
_("elf/stab section information questionable for %s"),
filename);
maybe = questionable;
}
if (maybe)
{
/* Found it! Allocate a new psymtab struct, and fill it in. */
maybe->found++;
pst->section_offsets = (struct section_offsets *)
obstack_alloc (&objfile->objfile_obstack,
SIZEOF_N_SECTION_OFFSETS (objfile->num_sections));
for (i = 0; i < maybe->num_sections; i++)
(pst->section_offsets)->offsets[i] = maybe->sections[i];
return;
}
/* We were unable to find any offsets for this file. Complain. */
if (dbx->stab_section_info) /* If there *is* any info, */
complaint (&symfile_complaints,
_("elf/stab section information missing for %s"), filename);
}
/* Implementation of `sym_get_probes', as documented in symfile.h. */
static VEC (probe_p) *
elf_get_probes (struct objfile *objfile)
{
VEC (probe_p) *probes_per_bfd;
/* Have we parsed this objfile's probes already? */
probes_per_bfd = bfd_data (objfile->obfd, probe_key);
if (!probes_per_bfd)
{
int ix;
const struct probe_ops *probe_ops;
/* Here we try to gather information about all types of probes from the
objfile. */
for (ix = 0; VEC_iterate (probe_ops_cp, all_probe_ops, ix, probe_ops);
ix++)
probe_ops->get_probes (&probes_per_bfd, objfile);
if (probes_per_bfd == NULL)
{
VEC_reserve (probe_p, probes_per_bfd, 1);
gdb_assert (probes_per_bfd != NULL);
}
set_bfd_data (objfile->obfd, probe_key, probes_per_bfd);
}
return probes_per_bfd;
}
/* Helper function used to free the space allocated for storing SystemTap
probe information. */
static void
probe_key_free (bfd *abfd, void *d)
{
int ix;
VEC (probe_p) *probes = d;
struct probe *probe;
for (ix = 0; VEC_iterate (probe_p, probes, ix, probe); ix++)
probe->pops->destroy (probe);
VEC_free (probe_p, probes);
}
/* Implementation `sym_probe_fns', as documented in symfile.h. */
static const struct sym_probe_fns elf_probe_fns =
{
elf_get_probes, /* sym_get_probes */
};
/* Register that we are able to handle ELF object file formats. */
static const struct sym_fns elf_sym_fns =
{
elf_new_init, /* init anything gbl to entire symtab */
elf_symfile_init, /* read initial info, setup for sym_read() */
elf_symfile_read, /* read a symbol file into symtab */
NULL, /* sym_read_psymbols */
elf_symfile_finish, /* finished with file, cleanup */
default_symfile_offsets, /* Translate ext. to int. relocation */
elf_symfile_segments, /* Get segment information from a file. */
NULL,
default_symfile_relocate, /* Relocate a debug section. */
&elf_probe_fns, /* sym_probe_fns */
&psym_functions
};
/* The same as elf_sym_fns, but not registered and lazily reads
psymbols. */
static const struct sym_fns elf_sym_fns_lazy_psyms =
{
elf_new_init, /* init anything gbl to entire symtab */
elf_symfile_init, /* read initial info, setup for sym_read() */
elf_symfile_read, /* read a symbol file into symtab */
read_psyms, /* sym_read_psymbols */
elf_symfile_finish, /* finished with file, cleanup */
default_symfile_offsets, /* Translate ext. to int. relocation */
elf_symfile_segments, /* Get segment information from a file. */
NULL,
default_symfile_relocate, /* Relocate a debug section. */
&elf_probe_fns, /* sym_probe_fns */
&psym_functions
};
/* The same as elf_sym_fns, but not registered and uses the
DWARF-specific GNU index rather than psymtab. */
static const struct sym_fns elf_sym_fns_gdb_index =
{
elf_new_init, /* init anything gbl to entire symab */
elf_symfile_init, /* read initial info, setup for sym_red() */
elf_symfile_read, /* read a symbol file into symtab */
NULL, /* sym_read_psymbols */
elf_symfile_finish, /* finished with file, cleanup */
default_symfile_offsets, /* Translate ext. to int. relocatin */
elf_symfile_segments, /* Get segment information from a file. */
NULL,
default_symfile_relocate, /* Relocate a debug section. */
&elf_probe_fns, /* sym_probe_fns */
&dwarf2_gdb_index_functions
};
/* STT_GNU_IFUNC resolver vector to be installed to gnu_ifunc_fns_p. */
static const struct gnu_ifunc_fns elf_gnu_ifunc_fns =
{
elf_gnu_ifunc_resolve_addr,
elf_gnu_ifunc_resolve_name,
elf_gnu_ifunc_resolver_stop,
elf_gnu_ifunc_resolver_return_stop
};
void
_initialize_elfread (void)
{
probe_key = register_bfd_data_with_cleanup (NULL, probe_key_free);
add_symtab_fns (bfd_target_elf_flavour, &elf_sym_fns);
elf_objfile_gnu_ifunc_cache_data = register_objfile_data ();
gnu_ifunc_fns_p = &elf_gnu_ifunc_fns;
}
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