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binutils-gdb/gdb/i386-fbsd-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 FreeBSD/i386.
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 "regcache.h"
#include "regset.h"
#include "trad-frame.h"
#include "tramp-frame.h"
#include "i386-fbsd-tdep.h"
#include "gdbsupport/x86-xstate.h"
#include "i386-tdep.h"
#include "i387-tdep.h"
#include "fbsd-tdep.h"
#include "solib-svr4.h"
#include "inferior.h"
/* The general-purpose regset consists of 19 32-bit slots. */
#define I386_FBSD_SIZEOF_GREGSET (19 * 4)
/* The segment base register set consists of 2 32-bit registers. */
#define I386_FBSD_SIZEOF_SEGBASES_REGSET (2 * 4)
/* Register maps. */
static const struct regcache_map_entry i386_fbsd_gregmap[] =
{
{ 1, I386_FS_REGNUM, 4 },
{ 1, I386_ES_REGNUM, 4 },
{ 1, I386_DS_REGNUM, 4 },
{ 1, I386_EDI_REGNUM, 0 },
{ 1, I386_ESI_REGNUM, 0 },
{ 1, I386_EBP_REGNUM, 0 },
{ 1, REGCACHE_MAP_SKIP, 4 }, /* isp */
{ 1, I386_EBX_REGNUM, 0 },
{ 1, I386_EDX_REGNUM, 0 },
{ 1, I386_ECX_REGNUM, 0 },
{ 1, I386_EAX_REGNUM, 0 },
{ 1, REGCACHE_MAP_SKIP, 4 }, /* trapno */
{ 1, REGCACHE_MAP_SKIP, 4 }, /* err */
{ 1, I386_EIP_REGNUM, 0 },
{ 1, I386_CS_REGNUM, 4 },
{ 1, I386_EFLAGS_REGNUM, 0 },
{ 1, I386_ESP_REGNUM, 0 },
{ 1, I386_SS_REGNUM, 4 },
{ 1, I386_GS_REGNUM, 4 },
{ 0 }
};
static const struct regcache_map_entry i386_fbsd_segbases_regmap[] =
{
{ 1, I386_FSBASE_REGNUM, 0 },
{ 1, I386_GSBASE_REGNUM, 0 },
{ 0 }
};
/* This layout including fsbase and gsbase was adopted in FreeBSD
8.0. */
static const struct regcache_map_entry i386_fbsd_mcregmap[] =
{
{ 1, REGCACHE_MAP_SKIP, 4 }, /* mc_onstack */
{ 1, I386_GS_REGNUM, 4 },
{ 1, I386_FS_REGNUM, 4 },
{ 1, I386_ES_REGNUM, 4 },
{ 1, I386_DS_REGNUM, 4 },
{ 1, I386_EDI_REGNUM, 0 },
{ 1, I386_ESI_REGNUM, 0 },
{ 1, I386_EBP_REGNUM, 0 },
{ 1, REGCACHE_MAP_SKIP, 4 }, /* isp */
{ 1, I386_EBX_REGNUM, 0 },
{ 1, I386_EDX_REGNUM, 0 },
{ 1, I386_ECX_REGNUM, 0 },
{ 1, I386_EAX_REGNUM, 0 },
{ 1, REGCACHE_MAP_SKIP, 4 }, /* mc_trapno */
{ 1, REGCACHE_MAP_SKIP, 4 }, /* mc_err */
{ 1, I386_EIP_REGNUM, 0 },
{ 1, I386_CS_REGNUM, 4 },
{ 1, I386_EFLAGS_REGNUM, 0 },
{ 1, I386_ESP_REGNUM, 0 },
{ 1, I386_SS_REGNUM, 4 },
{ 1, REGCACHE_MAP_SKIP, 4 }, /* mc_len */
{ 1, REGCACHE_MAP_SKIP, 4 }, /* mc_fpformat */
{ 1, REGCACHE_MAP_SKIP, 4 }, /* mc_ownedfp */
{ 1, REGCACHE_MAP_SKIP, 4 }, /* mc_flags */
{ 128, REGCACHE_MAP_SKIP, 4 },/* mc_fpstate */
{ 1, I386_FSBASE_REGNUM, 0 },
{ 1, I386_GSBASE_REGNUM, 0 },
{ 0 }
};
/* Register set definitions. */
const struct regset i386_fbsd_gregset =
{
i386_fbsd_gregmap, regcache_supply_regset, regcache_collect_regset
};
const struct regset i386_fbsd_segbases_regset =
{
i386_fbsd_segbases_regmap, regcache_supply_regset, regcache_collect_regset
};
/* Support for signal handlers. */
/* In a signal frame, esp points to a 'struct sigframe' which is
defined as:
struct sigframe {
register_t sf_signum;
register_t sf_siginfo;
register_t sf_ucontext;
register_t sf_addr;
union {
__siginfohandler_t *sf_action;
__sighandler_t *sf_handler;
} sf_ahu;
ucontext_t sf_uc;
...
}
ucontext_t is defined as:
struct __ucontext {
sigset_t uc_sigmask;
mcontext_t uc_mcontext;
...
};
The mcontext_t contains the general purpose register set as well
as the floating point or XSAVE state. */
/* NB: There is a 12 byte padding hole between sf_ahu and sf_uc. */
#define I386_SIGFRAME_UCONTEXT_OFFSET 32
#define I386_UCONTEXT_MCONTEXT_OFFSET 16
#define I386_SIZEOF_MCONTEXT_T 640
/* Implement the "init" method of struct tramp_frame. */
static void
i386_fbsd_sigframe_init (const struct tramp_frame *self,
struct frame_info *this_frame,
struct trad_frame_cache *this_cache,
CORE_ADDR func)
{
CORE_ADDR sp = get_frame_register_unsigned (this_frame, I386_ESP_REGNUM);
CORE_ADDR mcontext_addr
= (sp
+ I386_SIGFRAME_UCONTEXT_OFFSET
+ I386_UCONTEXT_MCONTEXT_OFFSET);
trad_frame_set_reg_regmap (this_cache, i386_fbsd_mcregmap, mcontext_addr,
I386_SIZEOF_MCONTEXT_T);
/* Don't bother with floating point or XSAVE state for now. The
current helper routines for parsing FXSAVE and XSAVE state only
work with regcaches. This could perhaps create a temporary
regcache, collect the register values from mc_fpstate and
mc_xfpustate, and then set register values in the trad_frame. */
trad_frame_set_id (this_cache, frame_id_build (sp, func));
}
static const struct tramp_frame i386_fbsd_sigframe =
{
SIGTRAMP_FRAME,
1,
{
{0x8d, ULONGEST_MAX}, /* lea SIGF_UC(%esp),%eax */
{0x44, ULONGEST_MAX},
{0x24, ULONGEST_MAX},
{0x20, ULONGEST_MAX},
{0x50, ULONGEST_MAX}, /* pushl %eax */
{0xf7, ULONGEST_MAX}, /* testl $PSL_VM,UC_EFLAGS(%eax) */
{0x40, ULONGEST_MAX},
{0x54, ULONGEST_MAX},
{0x00, ULONGEST_MAX},
{0x00, ULONGEST_MAX},
{0x02, ULONGEST_MAX},
{0x00, ULONGEST_MAX},
{0x75, ULONGEST_MAX}, /* jne +3 */
{0x03, ULONGEST_MAX},
{0x8e, ULONGEST_MAX}, /* mov UC_GS(%eax),%gs */
{0x68, ULONGEST_MAX},
{0x14, ULONGEST_MAX},
{0xb8, ULONGEST_MAX}, /* movl $SYS_sigreturn,%eax */
{0xa1, ULONGEST_MAX},
{0x01, ULONGEST_MAX},
{0x00, ULONGEST_MAX},
{0x00, ULONGEST_MAX},
{0x50, ULONGEST_MAX}, /* pushl %eax */
{0xcd, ULONGEST_MAX}, /* int $0x80 */
{0x80, ULONGEST_MAX},
{TRAMP_SENTINEL_INSN, ULONGEST_MAX}
},
i386_fbsd_sigframe_init
};
/* FreeBSD/i386 binaries running under an amd64 kernel use a different
trampoline. This trampoline differs from the i386 kernel trampoline
in that it omits a middle section that conditionally restores
%gs. */
static const struct tramp_frame i386_fbsd64_sigframe =
{
SIGTRAMP_FRAME,
1,
{
{0x8d, ULONGEST_MAX}, /* lea SIGF_UC(%esp),%eax */
{0x44, ULONGEST_MAX},
{0x24, ULONGEST_MAX},
{0x20, ULONGEST_MAX},
{0x50, ULONGEST_MAX}, /* pushl %eax */
{0xb8, ULONGEST_MAX}, /* movl $SYS_sigreturn,%eax */
{0xa1, ULONGEST_MAX},
{0x01, ULONGEST_MAX},
{0x00, ULONGEST_MAX},
{0x00, ULONGEST_MAX},
{0x50, ULONGEST_MAX}, /* pushl %eax */
{0xcd, ULONGEST_MAX}, /* int $0x80 */
{0x80, ULONGEST_MAX},
{TRAMP_SENTINEL_INSN, ULONGEST_MAX}
},
i386_fbsd_sigframe_init
};
/* Get XSAVE extended state xcr0 from core dump. */
uint64_t
i386fbsd_core_read_xcr0 (bfd *abfd)
{
asection *xstate = bfd_get_section_by_name (abfd, ".reg-xstate");
uint64_t xcr0;
if (xstate)
{
size_t size = bfd_section_size (xstate);
/* Check extended state size. */
if (size < X86_XSTATE_AVX_SIZE)
xcr0 = X86_XSTATE_SSE_MASK;
else
{
char contents[8];
if (! bfd_get_section_contents (abfd, xstate, contents,
I386_FBSD_XSAVE_XCR0_OFFSET,
8))
{
warning (_("Couldn't read `xcr0' bytes from "
"`.reg-xstate' section in core file."));
return X86_XSTATE_SSE_MASK;
}
xcr0 = bfd_get_64 (abfd, contents);
}
}
else
xcr0 = X86_XSTATE_SSE_MASK;
return xcr0;
}
/* Implement the core_read_description gdbarch method. */
static const struct target_desc *
i386fbsd_core_read_description (struct gdbarch *gdbarch,
struct target_ops *target,
bfd *abfd)
{
return i386_target_description (i386fbsd_core_read_xcr0 (abfd), true);
}
/* Similar to i386_supply_fpregset, but use XSAVE extended state. */
static void
i386fbsd_supply_xstateregset (const struct regset *regset,
struct regcache *regcache, int regnum,
const void *xstateregs, size_t len)
{
i387_supply_xsave (regcache, regnum, xstateregs);
}
/* Similar to i386_collect_fpregset, but use XSAVE extended state. */
static void
i386fbsd_collect_xstateregset (const struct regset *regset,
const struct regcache *regcache,
int regnum, void *xstateregs, size_t len)
{
i387_collect_xsave (regcache, regnum, xstateregs, 1);
}
/* Register set definitions. */
static const struct regset i386fbsd_xstateregset =
{
NULL,
i386fbsd_supply_xstateregset,
i386fbsd_collect_xstateregset
};
/* Iterate over core file register note sections. */
static void
i386fbsd_iterate_over_regset_sections (struct gdbarch *gdbarch,
iterate_over_regset_sections_cb *cb,
void *cb_data,
const struct regcache *regcache)
{
i386_gdbarch_tdep *tdep = gdbarch_tdep<i386_gdbarch_tdep> (gdbarch);
cb (".reg", I386_FBSD_SIZEOF_GREGSET, I386_FBSD_SIZEOF_GREGSET,
&i386_fbsd_gregset, NULL, cb_data);
cb (".reg2", tdep->sizeof_fpregset, tdep->sizeof_fpregset, &i386_fpregset,
NULL, cb_data);
cb (".reg-x86-segbases", I386_FBSD_SIZEOF_SEGBASES_REGSET,
I386_FBSD_SIZEOF_SEGBASES_REGSET, &i386_fbsd_segbases_regset,
"segment bases", cb_data);
if (tdep->xcr0 & X86_XSTATE_AVX)
cb (".reg-xstate", X86_XSTATE_SIZE (tdep->xcr0),
X86_XSTATE_SIZE (tdep->xcr0), &i386fbsd_xstateregset,
"XSAVE extended state", cb_data);
}
/* Implement the get_thread_local_address gdbarch method. */
static CORE_ADDR
i386fbsd_get_thread_local_address (struct gdbarch *gdbarch, ptid_t ptid,
CORE_ADDR lm_addr, CORE_ADDR offset)
{
struct regcache *regcache;
regcache = get_thread_arch_regcache (current_inferior ()->process_target (),
ptid, gdbarch);
target_fetch_registers (regcache, I386_GSBASE_REGNUM);
ULONGEST gsbase;
if (regcache->cooked_read (I386_GSBASE_REGNUM, &gsbase) != REG_VALID)
error (_("Unable to fetch %%gsbase"));
CORE_ADDR dtv_addr = gsbase + gdbarch_ptr_bit (gdbarch) / 8;
return fbsd_get_thread_local_address (gdbarch, dtv_addr, lm_addr, offset);
}
static void
i386fbsd_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
i386_gdbarch_tdep *tdep = gdbarch_tdep<i386_gdbarch_tdep> (gdbarch);
/* Generic FreeBSD support. */
fbsd_init_abi (info, gdbarch);
/* Obviously FreeBSD is BSD-based. */
i386bsd_init_abi (info, gdbarch);
/* FreeBSD reserves some space for its FPU emulator in
`struct fpreg'. */
tdep->sizeof_fpregset = 176;
/* FreeBSD uses -freg-struct-return by default. */
tdep->struct_return = reg_struct_return;
tramp_frame_prepend_unwinder (gdbarch, &i386_fbsd_sigframe);
tramp_frame_prepend_unwinder (gdbarch, &i386_fbsd64_sigframe);
i386_elf_init_abi (info, gdbarch);
tdep->xsave_xcr0_offset = I386_FBSD_XSAVE_XCR0_OFFSET;
/* Iterate over core file register note sections. */
set_gdbarch_iterate_over_regset_sections
(gdbarch, i386fbsd_iterate_over_regset_sections);
set_gdbarch_core_read_description (gdbarch,
i386fbsd_core_read_description);
/* FreeBSD uses SVR4-style shared libraries. */
set_solib_svr4_fetch_link_map_offsets
(gdbarch, svr4_ilp32_fetch_link_map_offsets);
set_gdbarch_fetch_tls_load_module_address (gdbarch,
svr4_fetch_objfile_link_map);
set_gdbarch_get_thread_local_address (gdbarch,
i386fbsd_get_thread_local_address);
}
void _initialize_i386fbsd_tdep ();
void
_initialize_i386fbsd_tdep ()
{
gdbarch_register_osabi (bfd_arch_i386, 0, GDB_OSABI_FREEBSD,
i386fbsd_init_abi);
}
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