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binutils-gdb/gdb/m68k-linux-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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/* Motorola m68k target-dependent support for GNU/Linux.
Copyright (C) 1996-2022 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 "gdbcore.h"
#include "frame.h"
#include "target.h"
#include "gdbtypes.h"
#include "osabi.h"
#include "regcache.h"
#include "objfiles.h"
#include "symtab.h"
#include "m68k-tdep.h"
#include "trad-frame.h"
#include "frame-unwind.h"
#include "glibc-tdep.h"
#include "solib-svr4.h"
#include "auxv.h"
#include "observable.h"
#include "elf/common.h"
#include "linux-tdep.h"
#include "regset.h"
/* Offsets (in target ints) into jmp_buf. */
#define M68K_LINUX_JB_ELEMENT_SIZE 4
#define M68K_LINUX_JB_PC 7
/* Check whether insn1 and insn2 are parts of a signal trampoline. */
#define IS_SIGTRAMP(insn1, insn2) \
(/* addaw #20,sp; moveq #119,d0; trap #0 */ \
(insn1 == 0xdefc0014 && insn2 == 0x70774e40) \
/* moveq #119,d0; trap #0 */ \
|| insn1 == 0x70774e40)
#define IS_RT_SIGTRAMP(insn1, insn2) \
(/* movel #173,d0; trap #0 */ \
(insn1 == 0x203c0000 && insn2 == 0x00ad4e40) \
/* moveq #82,d0; notb d0; trap #0 */ \
|| (insn1 == 0x70524600 && (insn2 >> 16) == 0x4e40))
/* Return non-zero if THIS_FRAME corresponds to a signal trampoline. For
the sake of m68k_linux_get_sigtramp_info we also distinguish between
non-RT and RT signal trampolines. */
static int
m68k_linux_pc_in_sigtramp (struct frame_info *this_frame)
{
struct gdbarch *gdbarch = get_frame_arch (this_frame);
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
gdb_byte buf[12];
unsigned long insn0, insn1, insn2;
CORE_ADDR pc = get_frame_pc (this_frame);
if (!safe_frame_unwind_memory (this_frame, pc - 4, {buf, sizeof (buf)}))
return 0;
insn1 = extract_unsigned_integer (buf + 4, 4, byte_order);
insn2 = extract_unsigned_integer (buf + 8, 4, byte_order);
if (IS_SIGTRAMP (insn1, insn2))
return 1;
if (IS_RT_SIGTRAMP (insn1, insn2))
return 2;
insn0 = extract_unsigned_integer (buf, 4, byte_order);
if (IS_SIGTRAMP (insn0, insn1))
return 1;
if (IS_RT_SIGTRAMP (insn0, insn1))
return 2;
insn0 = ((insn0 << 16) & 0xffffffff) | (insn1 >> 16);
insn1 = ((insn1 << 16) & 0xffffffff) | (insn2 >> 16);
if (IS_SIGTRAMP (insn0, insn1))
return 1;
if (IS_RT_SIGTRAMP (insn0, insn1))
return 2;
return 0;
}
/* From <asm/sigcontext.h>. */
static int m68k_linux_sigcontext_reg_offset[M68K_NUM_REGS] =
{
2 * 4, /* %d0 */
3 * 4, /* %d1 */
-1, /* %d2 */
-1, /* %d3 */
-1, /* %d4 */
-1, /* %d5 */
-1, /* %d6 */
-1, /* %d7 */
4 * 4, /* %a0 */
5 * 4, /* %a1 */
-1, /* %a2 */
-1, /* %a3 */
-1, /* %a4 */
-1, /* %a5 */
-1, /* %fp */
1 * 4, /* %sp */
6 * 4, /* %sr */
6 * 4 + 2, /* %pc */
8 * 4, /* %fp0 */
11 * 4, /* %fp1 */
-1, /* %fp2 */
-1, /* %fp3 */
-1, /* %fp4 */
-1, /* %fp5 */
-1, /* %fp6 */
-1, /* %fp7 */
14 * 4, /* %fpcr */
15 * 4, /* %fpsr */
16 * 4 /* %fpiaddr */
};
static int m68k_uclinux_sigcontext_reg_offset[M68K_NUM_REGS] =
{
2 * 4, /* %d0 */
3 * 4, /* %d1 */
-1, /* %d2 */
-1, /* %d3 */
-1, /* %d4 */
-1, /* %d5 */
-1, /* %d6 */
-1, /* %d7 */
4 * 4, /* %a0 */
5 * 4, /* %a1 */
-1, /* %a2 */
-1, /* %a3 */
-1, /* %a4 */
6 * 4, /* %a5 */
-1, /* %fp */
1 * 4, /* %sp */
7 * 4, /* %sr */
7 * 4 + 2, /* %pc */
-1, /* %fp0 */
-1, /* %fp1 */
-1, /* %fp2 */
-1, /* %fp3 */
-1, /* %fp4 */
-1, /* %fp5 */
-1, /* %fp6 */
-1, /* %fp7 */
-1, /* %fpcr */
-1, /* %fpsr */
-1 /* %fpiaddr */
};
/* From <asm/ucontext.h>. */
static int m68k_linux_ucontext_reg_offset[M68K_NUM_REGS] =
{
6 * 4, /* %d0 */
7 * 4, /* %d1 */
8 * 4, /* %d2 */
9 * 4, /* %d3 */
10 * 4, /* %d4 */
11 * 4, /* %d5 */
12 * 4, /* %d6 */
13 * 4, /* %d7 */
14 * 4, /* %a0 */
15 * 4, /* %a1 */
16 * 4, /* %a2 */
17 * 4, /* %a3 */
18 * 4, /* %a4 */
19 * 4, /* %a5 */
20 * 4, /* %fp */
21 * 4, /* %sp */
23 * 4, /* %sr */
22 * 4, /* %pc */
27 * 4, /* %fp0 */
30 * 4, /* %fp1 */
33 * 4, /* %fp2 */
36 * 4, /* %fp3 */
39 * 4, /* %fp4 */
42 * 4, /* %fp5 */
45 * 4, /* %fp6 */
48 * 4, /* %fp7 */
24 * 4, /* %fpcr */
25 * 4, /* %fpsr */
26 * 4 /* %fpiaddr */
};
/* Get info about saved registers in sigtramp. */
struct m68k_linux_sigtramp_info
{
/* Address of sigcontext. */
CORE_ADDR sigcontext_addr;
/* Offset of registers in `struct sigcontext'. */
int *sc_reg_offset;
};
/* Nonzero if running on uClinux. */
static int target_is_uclinux;
static void
m68k_linux_inferior_created (inferior *inf)
{
/* Record that we will need to re-evaluate whether we are running on a
uClinux or normal GNU/Linux target (see m68k_linux_get_sigtramp_info). */
target_is_uclinux = -1;
}
static struct m68k_linux_sigtramp_info
m68k_linux_get_sigtramp_info (struct frame_info *this_frame)
{
struct gdbarch *gdbarch = get_frame_arch (this_frame);
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
CORE_ADDR sp;
struct m68k_linux_sigtramp_info info;
/* Determine whether we are running on a uClinux or normal GNU/Linux
target so we can use the correct sigcontext layouts. */
if (target_is_uclinux == -1)
target_is_uclinux = linux_is_uclinux ();
sp = get_frame_register_unsigned (this_frame, M68K_SP_REGNUM);
/* Get sigcontext address, it is the third parameter on the stack. */
info.sigcontext_addr = read_memory_unsigned_integer (sp + 8, 4, byte_order);
if (m68k_linux_pc_in_sigtramp (this_frame) == 2)
info.sc_reg_offset = m68k_linux_ucontext_reg_offset;
else
info.sc_reg_offset = (target_is_uclinux
? m68k_uclinux_sigcontext_reg_offset
: m68k_linux_sigcontext_reg_offset);
return info;
}
/* Signal trampolines. */
static struct trad_frame_cache *
m68k_linux_sigtramp_frame_cache (struct frame_info *this_frame,
void **this_cache)
{
struct frame_id this_id;
struct trad_frame_cache *cache;
struct gdbarch *gdbarch = get_frame_arch (this_frame);
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
struct m68k_linux_sigtramp_info info;
gdb_byte buf[4];
int i;
if (*this_cache)
return (struct trad_frame_cache *) *this_cache;
cache = trad_frame_cache_zalloc (this_frame);
/* FIXME: cagney/2004-05-01: This is is long standing broken code.
The frame ID's code address should be the start-address of the
signal trampoline and not the current PC within that
trampoline. */
get_frame_register (this_frame, M68K_SP_REGNUM, buf);
/* See the end of m68k_push_dummy_call. */
this_id = frame_id_build (extract_unsigned_integer (buf, 4, byte_order)
- 4 + 8, get_frame_pc (this_frame));
trad_frame_set_id (cache, this_id);
info = m68k_linux_get_sigtramp_info (this_frame);
for (i = 0; i < M68K_NUM_REGS; i++)
if (info.sc_reg_offset[i] != -1)
trad_frame_set_reg_addr (cache, i,
info.sigcontext_addr + info.sc_reg_offset[i]);
*this_cache = cache;
return cache;
}
static void
m68k_linux_sigtramp_frame_this_id (struct frame_info *this_frame,
void **this_cache,
struct frame_id *this_id)
{
struct trad_frame_cache *cache =
m68k_linux_sigtramp_frame_cache (this_frame, this_cache);
trad_frame_get_id (cache, this_id);
}
static struct value *
m68k_linux_sigtramp_frame_prev_register (struct frame_info *this_frame,
void **this_cache,
int regnum)
{
/* Make sure we've initialized the cache. */
struct trad_frame_cache *cache =
m68k_linux_sigtramp_frame_cache (this_frame, this_cache);
return trad_frame_get_register (cache, this_frame, regnum);
}
static int
m68k_linux_sigtramp_frame_sniffer (const struct frame_unwind *self,
struct frame_info *this_frame,
void **this_prologue_cache)
{
return m68k_linux_pc_in_sigtramp (this_frame);
}
static const struct frame_unwind m68k_linux_sigtramp_frame_unwind =
{
"m68k linux sigtramp",
SIGTRAMP_FRAME,
default_frame_unwind_stop_reason,
m68k_linux_sigtramp_frame_this_id,
m68k_linux_sigtramp_frame_prev_register,
NULL,
m68k_linux_sigtramp_frame_sniffer
};
/* Register maps for supply/collect regset functions. */
static const struct regcache_map_entry m68k_linux_gregmap[] =
{
{ 7, M68K_D1_REGNUM, 4 }, /* d1 ... d7 */
{ 7, M68K_A0_REGNUM, 4 }, /* a0 ... a6 */
{ 1, M68K_D0_REGNUM, 4 },
{ 1, M68K_SP_REGNUM, 4 },
{ 1, REGCACHE_MAP_SKIP, 4 }, /* orig_d0 (skip) */
{ 1, M68K_PS_REGNUM, 4 },
{ 1, M68K_PC_REGNUM, 4 },
/* Ignore 16-bit fields 'fmtvec' and '__fill'. */
{ 0 }
};
#define M68K_LINUX_GREGS_SIZE (20 * 4)
static const struct regcache_map_entry m68k_linux_fpregmap[] =
{
{ 8, M68K_FP0_REGNUM, 12 }, /* fp0 ... fp7 */
{ 1, M68K_FPC_REGNUM, 4 },
{ 1, M68K_FPS_REGNUM, 4 },
{ 1, M68K_FPI_REGNUM, 4 },
{ 0 }
};
#define M68K_LINUX_FPREGS_SIZE (27 * 4)
/* Register sets. */
static const struct regset m68k_linux_gregset =
{
m68k_linux_gregmap,
regcache_supply_regset, regcache_collect_regset
};
static const struct regset m68k_linux_fpregset =
{
m68k_linux_fpregmap,
regcache_supply_regset, regcache_collect_regset
};
/* Iterate over core file register note sections. */
static void
m68k_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
iterate_over_regset_sections_cb *cb,
void *cb_data,
const struct regcache *regcache)
{
cb (".reg", M68K_LINUX_GREGS_SIZE, M68K_LINUX_GREGS_SIZE, &m68k_linux_gregset,
NULL, cb_data);
cb (".reg2", M68K_LINUX_FPREGS_SIZE, M68K_LINUX_FPREGS_SIZE,
&m68k_linux_fpregset, NULL, cb_data);
}
static void
m68k_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
m68k_gdbarch_tdep *tdep = gdbarch_tdep<m68k_gdbarch_tdep> (gdbarch);
linux_init_abi (info, gdbarch, 0);
tdep->jb_pc = M68K_LINUX_JB_PC;
tdep->jb_elt_size = M68K_LINUX_JB_ELEMENT_SIZE;
/* GNU/Linux uses a calling convention that's similar to SVR4. It
returns integer values in %d0/%d1, pointer values in %a0 and
floating values in %fp0, just like SVR4, but uses %a1 to pass the
address to store a structure value. It also returns small
structures in registers instead of memory. */
m68k_svr4_init_abi (info, gdbarch);
tdep->struct_value_regnum = M68K_A1_REGNUM;
tdep->struct_return = reg_struct_return;
set_gdbarch_decr_pc_after_break (gdbarch, 2);
frame_unwind_append_unwinder (gdbarch, &m68k_linux_sigtramp_frame_unwind);
/* Shared library handling. */
/* GNU/Linux uses SVR4-style shared libraries. */
set_solib_svr4_fetch_link_map_offsets (gdbarch,
linux_ilp32_fetch_link_map_offsets);
/* GNU/Linux uses the dynamic linker included in the GNU C Library. */
set_gdbarch_skip_solib_resolver (gdbarch, glibc_skip_solib_resolver);
set_gdbarch_skip_trampoline_code (gdbarch, find_solib_trampoline_target);
/* Core file support. */
set_gdbarch_iterate_over_regset_sections
(gdbarch, m68k_linux_iterate_over_regset_sections);
/* Enable TLS support. */
set_gdbarch_fetch_tls_load_module_address (gdbarch,
svr4_fetch_objfile_link_map);
}
void _initialize_m68k_linux_tdep ();
void
_initialize_m68k_linux_tdep ()
{
gdbarch_register_osabi (bfd_arch_m68k, 0, GDB_OSABI_LINUX,
m68k_linux_init_abi);
gdb::observers::inferior_created.attach (m68k_linux_inferior_created,
"m68k-linux-tdep");
}
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