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binutils-gdb/gdb/sh-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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/* Target-dependent code for GNU/Linux Super-H.
Copyright (C) 2005-2022 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 "solib-svr4.h"
#include "symtab.h"
#include "trad-frame.h"
#include "tramp-frame.h"
#include "glibc-tdep.h"
#include "sh-tdep.h"
#include "linux-tdep.h"
#include "gdbarch.h"
#define REGSx16(base) \
{(base), 0}, \
{(base) + 1, 4}, \
{(base) + 2, 8}, \
{(base) + 3, 12}, \
{(base) + 4, 16}, \
{(base) + 5, 20}, \
{(base) + 6, 24}, \
{(base) + 7, 28}, \
{(base) + 8, 32}, \
{(base) + 9, 36}, \
{(base) + 10, 40}, \
{(base) + 11, 44}, \
{(base) + 12, 48}, \
{(base) + 13, 52}, \
{(base) + 14, 56}, \
{(base) + 15, 60}
/* Describe the contents of the .reg section of the core file. */
static const struct sh_corefile_regmap gregs_table[] =
{
REGSx16 (R0_REGNUM),
{PC_REGNUM, 64},
{PR_REGNUM, 68},
{SR_REGNUM, 72},
{GBR_REGNUM, 76},
{MACH_REGNUM, 80},
{MACL_REGNUM, 84},
{-1 /* Terminator. */, 0}
};
/* Describe the contents of the .reg2 section of the core file. */
static const struct sh_corefile_regmap fpregs_table[] =
{
REGSx16 (FR0_REGNUM),
/* REGSx16 xfp_regs omitted. */
{FPSCR_REGNUM, 128},
{FPUL_REGNUM, 132},
{-1 /* Terminator. */, 0}
};
/* SH signal handler frame support. */
static void
sh_linux_sigtramp_cache (struct frame_info *this_frame,
struct trad_frame_cache *this_cache,
CORE_ADDR func, int regs_offset)
{
int i;
struct gdbarch *gdbarch = get_frame_arch (this_frame);
CORE_ADDR base = get_frame_register_unsigned (this_frame,
gdbarch_sp_regnum (gdbarch));
CORE_ADDR regs = base + regs_offset;
for (i = 0; i < 18; i++)
trad_frame_set_reg_addr (this_cache, i, regs + i * 4);
trad_frame_set_reg_addr (this_cache, SR_REGNUM, regs + 18 * 4);
trad_frame_set_reg_addr (this_cache, GBR_REGNUM, regs + 19 * 4);
trad_frame_set_reg_addr (this_cache, MACH_REGNUM, regs + 20 * 4);
trad_frame_set_reg_addr (this_cache, MACL_REGNUM, regs + 21 * 4);
/* Restore FP state if we have an FPU. */
if (gdbarch_fp0_regnum (gdbarch) != -1)
{
CORE_ADDR fpregs = regs + 22 * 4;
for (i = FR0_REGNUM; i <= FP_LAST_REGNUM; i++)
trad_frame_set_reg_addr (this_cache, i, fpregs + i * 4);
trad_frame_set_reg_addr (this_cache, FPSCR_REGNUM, fpregs + 32 * 4);
trad_frame_set_reg_addr (this_cache, FPUL_REGNUM, fpregs + 33 * 4);
}
/* Save a frame ID. */
trad_frame_set_id (this_cache, frame_id_build (base, func));
}
/* Implement struct tramp_frame "init" callbacks for signal
trampolines on 32-bit SH. */
static void
sh_linux_sigreturn_init (const struct tramp_frame *self,
struct frame_info *this_frame,
struct trad_frame_cache *this_cache,
CORE_ADDR func)
{
/* SH 32-bit sigframe: sigcontext at start of sigframe,
registers start after a single 'oldmask' word. */
sh_linux_sigtramp_cache (this_frame, this_cache, func, 4);
}
static void
sh_linux_rt_sigreturn_init (const struct tramp_frame *self,
struct frame_info *this_frame,
struct trad_frame_cache *this_cache,
CORE_ADDR func)
{
/* SH 32-bit rt_sigframe: starts with a siginfo (128 bytes), then
we can find sigcontext embedded within a ucontext (offset 20 bytes).
Then registers start after a single 'oldmask' word. */
sh_linux_sigtramp_cache (this_frame, this_cache, func,
128 /* sizeof (struct siginfo) */
+ 20 /* offsetof (struct ucontext, uc_mcontext) */
+ 4 /* oldmask word at start of sigcontext */);
}
/* Instruction patterns. */
#define SH_MOVW 0x9305
#define SH_TRAP 0xc300
#define SH_OR_R0_R0 0x200b
/* SH sigreturn syscall numbers. */
#define SH_NR_SIGRETURN 0x0077
#define SH_NR_RT_SIGRETURN 0x00ad
static struct tramp_frame sh_linux_sigreturn_tramp_frame = {
SIGTRAMP_FRAME,
2,
{
{ SH_MOVW, 0xffff },
{ SH_TRAP, 0xff00 }, /* #imm argument part filtered out. */
{ SH_OR_R0_R0, 0xffff },
{ SH_OR_R0_R0, 0xffff },
{ SH_OR_R0_R0, 0xffff },
{ SH_OR_R0_R0, 0xffff },
{ SH_OR_R0_R0, 0xffff },
{ SH_NR_SIGRETURN, 0xffff },
{ TRAMP_SENTINEL_INSN }
},
sh_linux_sigreturn_init
};
static struct tramp_frame sh_linux_rt_sigreturn_tramp_frame = {
SIGTRAMP_FRAME,
2,
{
{ SH_MOVW, 0xffff },
{ SH_TRAP, 0xff00 }, /* #imm argument part filtered out. */
{ SH_OR_R0_R0, 0xffff },
{ SH_OR_R0_R0, 0xffff },
{ SH_OR_R0_R0, 0xffff },
{ SH_OR_R0_R0, 0xffff },
{ SH_OR_R0_R0, 0xffff },
{ SH_NR_RT_SIGRETURN, 0xffff },
{ TRAMP_SENTINEL_INSN }
},
sh_linux_rt_sigreturn_init
};
static void
sh_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
linux_init_abi (info, gdbarch, 0);
/* GNU/Linux uses SVR4-style shared libraries. */
set_gdbarch_skip_trampoline_code (gdbarch, find_solib_trampoline_target);
set_solib_svr4_fetch_link_map_offsets
(gdbarch, linux_ilp32_fetch_link_map_offsets);
set_gdbarch_skip_solib_resolver (gdbarch, glibc_skip_solib_resolver);
set_gdbarch_fetch_tls_load_module_address (gdbarch,
svr4_fetch_objfile_link_map);
sh_gdbarch_tdep *tdep = gdbarch_tdep<sh_gdbarch_tdep> (gdbarch);
/* Remember regset characteristics. The sizes should match
elf_gregset_t and elf_fpregset_t from Linux. */
tdep->core_gregmap = (struct sh_corefile_regmap *) gregs_table;
tdep->sizeof_gregset = 92;
tdep->core_fpregmap = (struct sh_corefile_regmap *) fpregs_table;
tdep->sizeof_fpregset = 136;
tramp_frame_prepend_unwinder (gdbarch, &sh_linux_sigreturn_tramp_frame);
tramp_frame_prepend_unwinder (gdbarch, &sh_linux_rt_sigreturn_tramp_frame);
}
void _initialize_sh_linux_tdep ();
void
_initialize_sh_linux_tdep ()
{
gdbarch_register_osabi (bfd_arch_sh, 0, GDB_OSABI_LINUX, sh_linux_init_abi);
}
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