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binutils-gdb/gdb/i386-windows-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 Windows (including Cygwin) running on i386's,
for GDB.
Copyright (C) 2003-2022 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 "i386-tdep.h"
#include "windows-tdep.h"
#include "regset.h"
#include "gdbsupport/gdb_obstack.h"
#include "xml-support.h"
#include "gdbcore.h"
#include "inferior.h"
/* Core file support. */
/* This vector maps GDB's idea of a register's number into an address
in the windows exception context vector. */
static int i386_windows_gregset_reg_offset[] =
{
176, /* eax */
172, /* ecx */
168, /* edx */
164, /* ebx */
196, /* esp */
180, /* ebp */
160, /* esi */
156, /* edi */
184, /* eip */
192, /* eflags */
188, /* cs */
200, /* ss */
152, /* ds */
148, /* es */
144, /* fs */
140, /* gs */
56, /* FloatSave.RegisterArea[0 * 10] */
66, /* FloatSave.RegisterArea[1 * 10] */
76, /* FloatSave.RegisterArea[2 * 10] */
86, /* FloatSave.RegisterArea[3 * 10] */
96, /* FloatSave.RegisterArea[4 * 10] */
106, /* FloatSave.RegisterArea[5 * 10] */
116, /* FloatSave.RegisterArea[6 * 10] */
126, /* FloatSave.RegisterArea[7 * 10] */
28, /* FloatSave.ControlWord */
32, /* FloatSave.StatusWord */
36, /* FloatSave.TagWord */
44, /* FloatSave.ErrorSelector */
40, /* FloatSave.ErrorOffset */
52, /* FloatSave.DataSelector */
48, /* FloatSave.DataOffset */
44, /* FloatSave.ErrorSelector */
/* XMM0-7 */
364, /* ExtendedRegisters[10*16] */
380, /* ExtendedRegisters[11*16] */
396, /* ExtendedRegisters[12*16] */
412, /* ExtendedRegisters[13*16] */
428, /* ExtendedRegisters[14*16] */
444, /* ExtendedRegisters[15*16] */
460, /* ExtendedRegisters[16*16] */
476, /* ExtendedRegisters[17*16] */
/* MXCSR */
228 /* ExtendedRegisters[24] */
};
#define I386_WINDOWS_SIZEOF_GREGSET 716
static CORE_ADDR
i386_windows_skip_trampoline_code (struct frame_info *frame, CORE_ADDR pc)
{
return i386_pe_skip_trampoline_code (frame, pc, NULL);
}
static const char *
i386_windows_auto_wide_charset (void)
{
return "UTF-16";
}
/* Implement the "push_dummy_call" gdbarch method. */
static CORE_ADDR
i386_windows_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)
{
/* For non-static member functions of 32bit Windows programs, the thiscall
calling convention is used, so the 'this' pointer is passed in ECX. */
bool thiscall = false;
struct type *type = check_typedef (value_type (function));
if (type->code () == TYPE_CODE_PTR)
type = check_typedef (TYPE_TARGET_TYPE (type));
/* read_subroutine_type sets for non-static member functions the
artificial flag of the first parameter ('this' pointer). */
if (type->code () == TYPE_CODE_METHOD
&& type->num_fields () > 0
&& TYPE_FIELD_ARTIFICIAL (type, 0)
&& type->field (0).type ()->code () == TYPE_CODE_PTR)
thiscall = 1;
return i386_thiscall_push_dummy_call (gdbarch, function, regcache, bp_addr,
nargs, args, sp, return_method,
struct_addr, thiscall);
}
/* Common parts for gdbarch initialization for Windows and Cygwin on i386. */
static void
i386_windows_init_abi_common (struct gdbarch_info info, struct gdbarch *gdbarch)
{
i386_gdbarch_tdep *tdep = gdbarch_tdep<i386_gdbarch_tdep> (gdbarch);
set_gdbarch_skip_trampoline_code (gdbarch, i386_windows_skip_trampoline_code);
set_gdbarch_skip_main_prologue (gdbarch, i386_skip_main_prologue);
tdep->struct_return = reg_struct_return;
tdep->gregset_reg_offset = i386_windows_gregset_reg_offset;
tdep->gregset_num_regs = ARRAY_SIZE (i386_windows_gregset_reg_offset);
tdep->sizeof_gregset = I386_WINDOWS_SIZEOF_GREGSET;
tdep->sizeof_fpregset = 0;
/* Core file support. */
set_gdbarch_core_xfer_shared_libraries
(gdbarch, windows_core_xfer_shared_libraries);
set_gdbarch_core_pid_to_str (gdbarch, windows_core_pid_to_str);
set_gdbarch_auto_wide_charset (gdbarch, i386_windows_auto_wide_charset);
}
/* gdbarch initialization for Windows on i386. */
static void
i386_windows_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
i386_windows_init_abi_common (info, gdbarch);
windows_init_abi (info, gdbarch);
set_gdbarch_push_dummy_call (gdbarch, i386_windows_push_dummy_call);
}
/* gdbarch initialization for Cygwin on i386. */
static void
i386_cygwin_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
i386_windows_init_abi_common (info, gdbarch);
cygwin_init_abi (info, gdbarch);
}
static gdb_osabi
i386_windows_osabi_sniffer (bfd *abfd)
{
const char *target_name = bfd_get_target (abfd);
if (!streq (target_name, "pei-i386"))
return GDB_OSABI_UNKNOWN;
if (is_linked_with_cygwin_dll (abfd))
return GDB_OSABI_CYGWIN;
return GDB_OSABI_WINDOWS;
}
static enum gdb_osabi
i386_cygwin_core_osabi_sniffer (bfd *abfd)
{
const char *target_name = bfd_get_target (abfd);
/* Cygwin uses elf core dumps. Do not claim all ELF executables,
check whether there is a .reg section of proper size. */
if (strcmp (target_name, "elf32-i386") == 0)
{
asection *section = bfd_get_section_by_name (abfd, ".reg");
if (section != nullptr
&& bfd_section_size (section) == I386_WINDOWS_SIZEOF_GREGSET)
return GDB_OSABI_CYGWIN;
}
return GDB_OSABI_UNKNOWN;
}
void _initialize_i386_windows_tdep ();
void
_initialize_i386_windows_tdep ()
{
gdbarch_register_osabi_sniffer (bfd_arch_i386, bfd_target_coff_flavour,
i386_windows_osabi_sniffer);
/* Cygwin uses elf core dumps. */
gdbarch_register_osabi_sniffer (bfd_arch_i386, bfd_target_elf_flavour,
i386_cygwin_core_osabi_sniffer);
gdbarch_register_osabi (bfd_arch_i386, 0, GDB_OSABI_WINDOWS,
i386_windows_init_abi);
gdbarch_register_osabi (bfd_arch_i386, 0, GDB_OSABI_CYGWIN,
i386_cygwin_init_abi);
}
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