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binutils-gdb/gdb/rs6000-lynx178-tdep.c
Andrew Burgess 08106042d9 gdb: move the type cast into gdbarch_tdep 
I built GDB for all targets on a x86-64/GNU-Linux system, and
then (accidentally) passed GDB a RISC-V binary, and asked GDB to "run"
the binary on the native target.  I got this error:

  (gdb) show architecture
  The target architecture is set to "auto" (currently "i386").
  (gdb) file /tmp/hello.rv32.exe
  Reading symbols from /tmp/hello.rv32.exe...
  (gdb) show architecture
  The target architecture is set to "auto" (currently "riscv:rv32").
  (gdb) run
  Starting program: /tmp/hello.rv32.exe
  ../../src/gdb/i387-tdep.c:596: internal-error: i387_supply_fxsave: Assertion `tdep->st0_regnum >= I386_ST0_REGNUM' failed.

What's going on here is this; initially the architecture is i386, this
is based on the default architecture, which is set based on the native
target.  After loading the RISC-V executable the architecture of the
current inferior is updated based on the architecture of the
executable.

When we "run", GDB does a fork & exec, with the inferior being
controlled through ptrace.  GDB sees an initial stop from the inferior
as soon as the inferior comes to life.  In response to this stop GDB
ends up calling save_stop_reason (linux-nat.c), which ends up trying
to read register from the inferior, to do this we end up calling
target_ops::fetch_registers, which, for the x86-64 native target,
calls amd64_linux_nat_target::fetch_registers.

After this I eventually end up in i387_supply_fxsave, different x86
based targets will end in different functions to fetch registers, but
it doesn't really matter which function we end up in, the problem is
this line, which is repeated in many places:

  i386_gdbarch_tdep *tdep = (i386_gdbarch_tdep *) gdbarch_tdep (arch);

The problem here is that the ARCH in this line comes from the current
inferior, which, as we discussed above, will be a RISC-V gdbarch, the
tdep field will actually be of type riscv_gdbarch_tdep, not
i386_gdbarch_tdep.  After this cast we are relying on undefined
behaviour, in my case I happen to trigger an assert, but this might
not always be the case.

The thing I tried that exposed this problem was of course, trying to
start an executable of the wrong architecture on a native target.  I
don't think that the correct solution for this problem is to detect,
at the point of cast, that the gdbarch_tdep object is of the wrong
type, but, I did wonder, is there a way that we could protect
ourselves from incorrectly casting the gdbarch_tdep object?

I think that there is something we can do here, and this commit is the
first step in that direction, though no actual check is added by this
commit.

This commit can be split into two parts:

 (1) In gdbarch.h and arch-utils.c.  In these files I have modified
 gdbarch_tdep (the function) so that it now takes a template argument,
 like this:

    template<typename TDepType>
    static inline TDepType *
    gdbarch_tdep (struct gdbarch *gdbarch)
    {
      struct gdbarch_tdep *tdep = gdbarch_tdep_1 (gdbarch);
      return static_cast<TDepType *> (tdep);
    }

  After this change we are no better protected, but the cast is now
  done within the gdbarch_tdep function rather than at the call sites,
  this leads to the second, much larger change in this commit,

  (2) Everywhere gdbarch_tdep is called, we make changes like this:

    -  i386_gdbarch_tdep *tdep = (i386_gdbarch_tdep *) gdbarch_tdep (arch);
    +  i386_gdbarch_tdep *tdep = gdbarch_tdep<i386_gdbarch_tdep> (arch);

There should be no functional change after this commit.

In the next commit I will build on this change to add an assertion in
gdbarch_tdep that checks we are casting to the correct type.
2022-07-21 15:19:42 +01:00

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/* Copyright (C) 2012-2022 Free Software Foundation, Inc.
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 "osabi.h"
#include "regcache.h"
#include "gdbcore.h"
#include "gdbtypes.h"
#include "infcall.h"
#include "ppc-tdep.h"
#include "target-float.h"
#include "value.h"
#include "xcoffread.h"
/* Implement the "push_dummy_call" gdbarch method. */
static CORE_ADDR
rs6000_lynx178_push_dummy_call (struct gdbarch *gdbarch,
struct value *function,
struct regcache *regcache, CORE_ADDR bp_addr,
int nargs, struct value **args, CORE_ADDR sp,
function_call_return_method return_method,
CORE_ADDR struct_addr)
{
ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep> (gdbarch);
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
int ii;
int len = 0;
int argno; /* current argument number */
int argbytes; /* current argument byte */
gdb_byte tmp_buffer[50];
int f_argno = 0; /* current floating point argno */
int wordsize = tdep->wordsize;
struct value *arg = 0;
struct type *type;
ULONGEST saved_sp;
/* The calling convention this function implements assumes the
processor has floating-point registers. We shouldn't be using it
on PPC variants that lack them. */
gdb_assert (ppc_floating_point_unit_p (gdbarch));
/* The first eight words of ther arguments are passed in registers.
Copy them appropriately. */
ii = 0;
/* If the function is returning a `struct', then the first word
(which will be passed in r3) is used for struct return address.
In that case we should advance one word and start from r4
register to copy parameters. */
if (return_method == return_method_struct)
{
regcache_raw_write_unsigned (regcache, tdep->ppc_gp0_regnum + 3,
struct_addr);
ii++;
}
/* Effectively indirect call... gcc does...
return_val example( float, int);
eabi:
float in fp0, int in r3
offset of stack on overflow 8/16
for varargs, must go by type.
power open:
float in r3&r4, int in r5
offset of stack on overflow different
both:
return in r3 or f0. If no float, must study how gcc emulates floats;
pay attention to arg promotion.
User may have to cast\args to handle promotion correctly
since gdb won't know if prototype supplied or not. */
for (argno = 0, argbytes = 0; argno < nargs && ii < 8; ++ii)
{
int reg_size = register_size (gdbarch, ii + 3);
arg = args[argno];
type = check_typedef (value_type (arg));
len = TYPE_LENGTH (type);
if (type->code () == TYPE_CODE_FLT)
{
/* Floating point arguments are passed in fpr's, as well as gpr's.
There are 13 fpr's reserved for passing parameters. At this point
there is no way we would run out of them.
Always store the floating point value using the register's
floating-point format. */
const int fp_regnum = tdep->ppc_fp0_regnum + 1 + f_argno;
gdb_byte reg_val[PPC_MAX_REGISTER_SIZE];
struct type *reg_type = register_type (gdbarch, fp_regnum);
gdb_assert (len <= 8);
target_float_convert (value_contents (arg).data (), type, reg_val,
reg_type);
regcache->cooked_write (fp_regnum, reg_val);
++f_argno;
}
if (len > reg_size)
{
/* Argument takes more than one register. */
while (argbytes < len)
{
gdb_byte word[PPC_MAX_REGISTER_SIZE];
memset (word, 0, reg_size);
memcpy (word,
((char *) value_contents (arg).data ()) + argbytes,
(len - argbytes) > reg_size
? reg_size : len - argbytes);
regcache->cooked_write (tdep->ppc_gp0_regnum + 3 + ii, word);
++ii, argbytes += reg_size;
if (ii >= 8)
goto ran_out_of_registers_for_arguments;
}
argbytes = 0;
--ii;
}
else
{
/* Argument can fit in one register. No problem. */
gdb_byte word[PPC_MAX_REGISTER_SIZE];
memset (word, 0, reg_size);
memcpy (word, value_contents (arg).data (), len);
regcache->cooked_write (tdep->ppc_gp0_regnum + 3 +ii, word);
}
++argno;
}
ran_out_of_registers_for_arguments:
regcache_cooked_read_unsigned (regcache,
gdbarch_sp_regnum (gdbarch),
&saved_sp);
/* Location for 8 parameters are always reserved. */
sp -= wordsize * 8;
/* Another six words for back chain, TOC register, link register, etc. */
sp -= wordsize * 6;
/* Stack pointer must be quadword aligned. */
sp = align_down (sp, 16);
/* If there are more arguments, allocate space for them in
the stack, then push them starting from the ninth one. */
if ((argno < nargs) || argbytes)
{
int space = 0, jj;
if (argbytes)
{
space += align_up (len - argbytes, 4);
jj = argno + 1;
}
else
jj = argno;
for (; jj < nargs; ++jj)
{
struct value *val = args[jj];
space += align_up (TYPE_LENGTH (value_type (val)), 4);
}
/* Add location required for the rest of the parameters. */
space = align_up (space, 16);
sp -= space;
/* This is another instance we need to be concerned about
securing our stack space. If we write anything underneath %sp
(r1), we might conflict with the kernel who thinks he is free
to use this area. So, update %sp first before doing anything
else. */
regcache_raw_write_signed (regcache,
gdbarch_sp_regnum (gdbarch), sp);
/* If the last argument copied into the registers didn't fit there
completely, push the rest of it into stack. */
if (argbytes)
{
write_memory (sp + 24 + (ii * 4),
value_contents (arg).data () + argbytes,
len - argbytes);
++argno;
ii += align_up (len - argbytes, 4) / 4;
}
/* Push the rest of the arguments into stack. */
for (; argno < nargs; ++argno)
{
arg = args[argno];
type = check_typedef (value_type (arg));
len = TYPE_LENGTH (type);
/* Float types should be passed in fpr's, as well as in the
stack. */
if (type->code () == TYPE_CODE_FLT && f_argno < 13)
{
gdb_assert (len <= 8);
regcache->cooked_write (tdep->ppc_fp0_regnum + 1 + f_argno,
value_contents (arg).data ());
++f_argno;
}
write_memory (sp + 24 + (ii * 4), value_contents (arg).data (), len);
ii += align_up (len, 4) / 4;
}
}
/* Set the stack pointer. According to the ABI, the SP is meant to
be set _before_ the corresponding stack space is used. On AIX,
this even applies when the target has been completely stopped!
Not doing this can lead to conflicts with the kernel which thinks
that it still has control over this not-yet-allocated stack
region. */
regcache_raw_write_signed (regcache, gdbarch_sp_regnum (gdbarch), sp);
/* Set back chain properly. */
store_unsigned_integer (tmp_buffer, wordsize, byte_order, saved_sp);
write_memory (sp, tmp_buffer, wordsize);
/* Point the inferior function call's return address at the dummy's
breakpoint. */
regcache_raw_write_signed (regcache, tdep->ppc_lr_regnum, bp_addr);
target_store_registers (regcache, -1);
return sp;
}
/* Implement the "return_value" gdbarch method. */
static enum return_value_convention
rs6000_lynx178_return_value (struct gdbarch *gdbarch, struct value *function,
struct type *valtype, struct regcache *regcache,
gdb_byte *readbuf, const gdb_byte *writebuf)
{
ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep> (gdbarch);
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
/* The calling convention this function implements assumes the
processor has floating-point registers. We shouldn't be using it
on PowerPC variants that lack them. */
gdb_assert (ppc_floating_point_unit_p (gdbarch));
/* AltiVec extension: Functions that declare a vector data type as a
return value place that return value in VR2. */
if (valtype->code () == TYPE_CODE_ARRAY && valtype->is_vector ()
&& TYPE_LENGTH (valtype) == 16)
{
if (readbuf)
regcache->cooked_read (tdep->ppc_vr0_regnum + 2, readbuf);
if (writebuf)
regcache->cooked_write (tdep->ppc_vr0_regnum + 2, writebuf);
return RETURN_VALUE_REGISTER_CONVENTION;
}
/* If the called subprogram returns an aggregate, there exists an
implicit first argument, whose value is the address of a caller-
allocated buffer into which the callee is assumed to store its
return value. All explicit parameters are appropriately
relabeled. */
if (valtype->code () == TYPE_CODE_STRUCT
|| valtype->code () == TYPE_CODE_UNION
|| valtype->code () == TYPE_CODE_ARRAY)
return RETURN_VALUE_STRUCT_CONVENTION;
/* Scalar floating-point values are returned in FPR1 for float or
double, and in FPR1:FPR2 for quadword precision. Fortran
complex*8 and complex*16 are returned in FPR1:FPR2, and
complex*32 is returned in FPR1:FPR4. */
if (valtype->code () == TYPE_CODE_FLT
&& (TYPE_LENGTH (valtype) == 4 || TYPE_LENGTH (valtype) == 8))
{
struct type *regtype = register_type (gdbarch, tdep->ppc_fp0_regnum);
gdb_byte regval[8];
/* FIXME: kettenis/2007-01-01: Add support for quadword
precision and complex. */
if (readbuf)
{
regcache->cooked_read (tdep->ppc_fp0_regnum + 1, regval);
target_float_convert (regval, regtype, readbuf, valtype);
}
if (writebuf)
{
target_float_convert (writebuf, valtype, regval, regtype);
regcache->cooked_write (tdep->ppc_fp0_regnum + 1, regval);
}
return RETURN_VALUE_REGISTER_CONVENTION;
}
/* Values of the types int, long, short, pointer, and char (length
is less than or equal to four bytes), as well as bit values of
lengths less than or equal to 32 bits, must be returned right
justified in GPR3 with signed values sign extended and unsigned
values zero extended, as necessary. */
if (TYPE_LENGTH (valtype) <= tdep->wordsize)
{
if (readbuf)
{
ULONGEST regval;
/* For reading we don't have to worry about sign extension. */
regcache_cooked_read_unsigned (regcache, tdep->ppc_gp0_regnum + 3,
&regval);
store_unsigned_integer (readbuf, TYPE_LENGTH (valtype), byte_order,
regval);
}
if (writebuf)
{
/* For writing, use unpack_long since that should handle any
required sign extension. */
regcache_cooked_write_unsigned (regcache, tdep->ppc_gp0_regnum + 3,
unpack_long (valtype, writebuf));
}
return RETURN_VALUE_REGISTER_CONVENTION;
}
/* Eight-byte non-floating-point scalar values must be returned in
GPR3:GPR4. */
if (TYPE_LENGTH (valtype) == 8)
{
gdb_assert (valtype->code () != TYPE_CODE_FLT);
gdb_assert (tdep->wordsize == 4);
if (readbuf)
{
gdb_byte regval[8];
regcache->cooked_read (tdep->ppc_gp0_regnum + 3, regval);
regcache->cooked_read (tdep->ppc_gp0_regnum + 4, regval + 4);
memcpy (readbuf, regval, 8);
}
if (writebuf)
{
regcache->cooked_write (tdep->ppc_gp0_regnum + 3, writebuf);
regcache->cooked_write (tdep->ppc_gp0_regnum + 4, writebuf + 4);
}
return RETURN_VALUE_REGISTER_CONVENTION;
}
return RETURN_VALUE_STRUCT_CONVENTION;
}
/* PowerPC Lynx178 OSABI sniffer. */
static enum gdb_osabi
rs6000_lynx178_osabi_sniffer (bfd *abfd)
{
if (bfd_get_flavour (abfd) != bfd_target_xcoff_flavour)
return GDB_OSABI_UNKNOWN;
/* The only noticeable difference between Lynx178 XCOFF files and
AIX XCOFF files comes from the fact that there are no shared
libraries on Lynx178. So if the number of import files is
different from zero, it cannot be a Lynx178 binary. */
if (xcoff_get_n_import_files (abfd) != 0)
return GDB_OSABI_UNKNOWN;
return GDB_OSABI_LYNXOS178;
}
/* Callback for powerpc-lynx178 initialization. */
static void
rs6000_lynx178_init_osabi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
set_gdbarch_push_dummy_call (gdbarch, rs6000_lynx178_push_dummy_call);
set_gdbarch_return_value (gdbarch, rs6000_lynx178_return_value);
set_gdbarch_long_double_bit (gdbarch, 8 * TARGET_CHAR_BIT);
}
void _initialize_rs6000_lynx178_tdep ();
void
_initialize_rs6000_lynx178_tdep ()
{
gdbarch_register_osabi_sniffer (bfd_arch_rs6000,
bfd_target_xcoff_flavour,
rs6000_lynx178_osabi_sniffer);
gdbarch_register_osabi (bfd_arch_rs6000, 0, GDB_OSABI_LYNXOS178,
rs6000_lynx178_init_osabi);
}
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