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08106042d9
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.
89 lines
2.4 KiB
C
89 lines
2.4 KiB
C
/* Target-dependent code for i386 BSD's.
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Copyright (C) 2001-2022 Free Software Foundation, Inc.
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This file is part of GDB.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#include "defs.h"
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#include "arch-utils.h"
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#include "frame.h"
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#include "gdbcore.h"
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#include "regcache.h"
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#include "osabi.h"
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#include "i386-tdep.h"
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/* Support for signal handlers. */
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/* Assuming THIS_FRAME is for a BSD sigtramp routine, return the
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address of the associated sigcontext structure. */
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static CORE_ADDR
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i386bsd_sigcontext_addr (struct frame_info *this_frame)
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{
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struct gdbarch *gdbarch = get_frame_arch (this_frame);
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enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
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gdb_byte buf[4];
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CORE_ADDR sp;
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get_frame_register (this_frame, I386_ESP_REGNUM, buf);
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sp = extract_unsigned_integer (buf, 4, byte_order);
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return read_memory_unsigned_integer (sp + 8, 4, byte_order);
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}
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/* Support for shared libraries. */
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/* Traditional BSD (4.3 BSD, still used for BSDI and 386BSD). */
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/* From <machine/signal.h>. */
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int i386bsd_sc_reg_offset[] =
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{
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-1, /* %eax */
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-1, /* %ecx */
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-1, /* %edx */
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-1, /* %ebx */
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8 + 0 * 4, /* %esp */
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8 + 1 * 4, /* %ebp */
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-1, /* %esi */
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-1, /* %edi */
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8 + 3 * 4, /* %eip */
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8 + 4 * 4, /* %eflags */
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-1, /* %cs */
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-1, /* %ss */
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-1, /* %ds */
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-1, /* %es */
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-1, /* %fs */
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-1 /* %gs */
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};
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void
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i386bsd_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
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{
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i386_gdbarch_tdep *tdep = gdbarch_tdep<i386_gdbarch_tdep> (gdbarch);
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tdep->jb_pc_offset = 0;
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tdep->sigtramp_start = 0xfdbfdfc0;
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tdep->sigtramp_end = 0xfdbfe000;
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tdep->sigcontext_addr = i386bsd_sigcontext_addr;
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tdep->sc_reg_offset = i386bsd_sc_reg_offset;
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tdep->sc_num_regs = ARRAY_SIZE (i386bsd_sc_reg_offset);
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}
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