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binutils-gdb/gdb/tic6x-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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/* GNU/Linux on TI C6x target support.
Copyright (C) 2011-2022 Free Software Foundation, Inc.
Contributed by Yao Qi <yao@codesourcery.com>
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 "solib.h"
#include "osabi.h"
#include "linux-tdep.h"
#include "tic6x-tdep.h"
#include "trad-frame.h"
#include "tramp-frame.h"
#include "elf-bfd.h"
#include "elf/tic6x.h"
#include "gdbarch.h"
/* The offset from rt_sigframe pointer to SP register. */
#define TIC6X_SP_RT_SIGFRAME 8
/* Size of struct siginfo info. */
#define TIC6X_SIGINFO_SIZE 128
/* Size of type stack_t, which contains three fields of type void*, int, and
size_t respectively. */
#define TIC6X_STACK_T_SIZE (3 * 4)
static const gdb_byte tic6x_bkpt_bnop_be[] = { 0x00, 0x00, 0xa1, 0x22 };
static const gdb_byte tic6x_bkpt_bnop_le[] = { 0x22, 0xa1, 0x00, 0x00 };
/* Return the offset of register REGNUM in struct sigcontext. Return 0 if no
such register in sigcontext. */
static unsigned int
tic6x_register_sigcontext_offset (unsigned int regnum, struct gdbarch *gdbarch)
{
tic6x_gdbarch_tdep *tdep = gdbarch_tdep<tic6x_gdbarch_tdep> (gdbarch);
if (regnum == TIC6X_A4_REGNUM || regnum == TIC6X_A4_REGNUM + 2
|| regnum == TIC6X_A4_REGNUM + 4)
return 4 * (regnum - TIC6X_A4_REGNUM + 2); /* A4, A6, A8 */
else if (regnum == TIC6X_A5_REGNUM || regnum == TIC6X_A5_REGNUM + 2
|| regnum == TIC6X_A5_REGNUM + 4)
return 4 * (regnum - TIC6X_A5_REGNUM + 12); /* A5, A7, A9 */
else if (regnum == TIC6X_B4_REGNUM || regnum == TIC6X_B4_REGNUM + 2
|| regnum == TIC6X_B4_REGNUM + 4)
return 4 * (regnum - TIC6X_B4_REGNUM + 3); /* B4, B6, B8 */
else if (regnum == TIC6X_B5_REGNUM || regnum == TIC6X_B5_REGNUM + 2
|| regnum == TIC6X_B5_REGNUM + 4)
return 4 * (regnum - TIC6X_B5_REGNUM + 19); /* B5, B7, B9 */
else if (regnum < TIC6X_A4_REGNUM)
return 4 * (regnum - 0 + 8); /* A0 - A3 */
else if (regnum >= TIC6X_B0_REGNUM && regnum < TIC6X_B4_REGNUM)
return 4 * (regnum - TIC6X_B0_REGNUM + 15); /* B0 - B3 */
else if (regnum >= 34 && regnum < 34 + 32)
return 4 * (regnum - 34 + 23); /* A16 - A31, B16 - B31 */
else if (regnum == TIC6X_PC_REGNUM)
return 4 * (tdep->has_gp ? 55 : 23);
else if (regnum == TIC6X_SP_REGNUM)
return 4;
return 0;
}
/* Support unwinding frame in signal trampoline. We don't check sigreturn,
since it is not used in kernel. */
static void
tic6x_linux_rt_sigreturn_init (const struct tramp_frame *self,
struct frame_info *this_frame,
struct trad_frame_cache *this_cache,
CORE_ADDR func)
{
struct gdbarch *gdbarch = get_frame_arch (this_frame);
CORE_ADDR sp = get_frame_register_unsigned (this_frame, TIC6X_SP_REGNUM);
/* The base of struct sigcontext is computed by examining the definition of
struct rt_sigframe in linux kernel source arch/c6x/kernel/signal.c. */
CORE_ADDR base = (sp + TIC6X_SP_RT_SIGFRAME
/* Pointer type *pinfo and *puc in struct rt_sigframe. */
+ 4 + 4
+ TIC6X_SIGINFO_SIZE
+ 4 + 4 /* uc_flags and *uc_link in struct ucontext. */
+ TIC6X_STACK_T_SIZE);
tic6x_gdbarch_tdep *tdep = gdbarch_tdep<tic6x_gdbarch_tdep> (gdbarch);
unsigned int reg_offset;
unsigned int i;
for (i = 0; i < 10; i++) /* A0 - A9 */
{
reg_offset = tic6x_register_sigcontext_offset (i, gdbarch);
gdb_assert (reg_offset != 0);
trad_frame_set_reg_addr (this_cache, i, base + reg_offset);
}
for (i = TIC6X_B0_REGNUM; i < TIC6X_B0_REGNUM + 10; i++) /* B0 - B9 */
{
reg_offset = tic6x_register_sigcontext_offset (i, gdbarch);
gdb_assert (reg_offset != 0);
trad_frame_set_reg_addr (this_cache, i, base + reg_offset);
}
if (tdep->has_gp)
for (i = 34; i < 34 + 32; i++) /* A16 - A31, B16 - B31 */
{
reg_offset = tic6x_register_sigcontext_offset (i, gdbarch);
gdb_assert (reg_offset != 0);
trad_frame_set_reg_addr (this_cache, i, base + reg_offset);
}
trad_frame_set_reg_addr (this_cache, TIC6X_PC_REGNUM,
base + tic6x_register_sigcontext_offset (TIC6X_PC_REGNUM,
gdbarch));
trad_frame_set_reg_addr (this_cache, TIC6X_SP_REGNUM,
base + tic6x_register_sigcontext_offset (TIC6X_SP_REGNUM,
gdbarch));
/* Save a frame ID. */
trad_frame_set_id (this_cache, frame_id_build (sp, func));
}
static struct tramp_frame tic6x_linux_rt_sigreturn_tramp_frame =
{
SIGTRAMP_FRAME,
4,
{
{0x000045aa, 0x0fffffff}, /* mvk .S2 139,b0 */
{0x10000000, ULONGEST_MAX}, /* swe */
{TRAMP_SENTINEL_INSN}
},
tic6x_linux_rt_sigreturn_init
};
/* When FRAME is at a syscall instruction, return the PC of the next
instruction to be executed. */
static CORE_ADDR
tic6x_linux_syscall_next_pc (struct frame_info *frame)
{
ULONGEST syscall_number = get_frame_register_unsigned (frame,
TIC6X_B0_REGNUM);
CORE_ADDR pc = get_frame_pc (frame);
if (syscall_number == 139 /* rt_sigreturn */)
return frame_unwind_caller_pc (frame);
return pc + 4;
}
extern struct target_so_ops dsbt_so_ops;
static void
tic6x_uclinux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
tic6x_gdbarch_tdep *tdep = gdbarch_tdep<tic6x_gdbarch_tdep> (gdbarch);
linux_init_abi (info, gdbarch, 0);
/* Shared library handling. */
set_solib_ops (gdbarch, &dsbt_so_ops);
tdep->syscall_next_pc = tic6x_linux_syscall_next_pc;
#ifdef HAVE_ELF
/* In tic6x Linux kernel, breakpoint instructions varies on different archs.
On C64x+ and C67x+, breakpoint instruction is 0x56454314, which is an
illegal opcode. On other arch, breakpoint instruction is 0x0000a122
(BNOP .S2 0,5). */
if (info.abfd)
switch (bfd_elf_get_obj_attr_int (info.abfd, OBJ_ATTR_PROC, Tag_ISA))
{
case C6XABI_Tag_ISA_C64XP:
case C6XABI_Tag_ISA_C67XP:
if (info.byte_order == BFD_ENDIAN_BIG)
tdep->breakpoint = tic6x_bkpt_illegal_opcode_be;
else
tdep->breakpoint = tic6x_bkpt_illegal_opcode_le;
break;
default:
{
if (info.byte_order == BFD_ENDIAN_BIG)
tdep->breakpoint = tic6x_bkpt_bnop_be;
else
tdep->breakpoint = tic6x_bkpt_bnop_le;
}
}
#endif
/* Signal trampoline support. */
tramp_frame_prepend_unwinder (gdbarch,
&tic6x_linux_rt_sigreturn_tramp_frame);
}
void _initialize_tic6x_linux_tdep ();
void
_initialize_tic6x_linux_tdep ()
{
gdbarch_register_osabi (bfd_arch_tic6x, 0, GDB_OSABI_LINUX,
tic6x_uclinux_init_abi);
}
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