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binutils-gdb/gdb/arm-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/arm.
Copyright (C) 2017-2022 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 "elf/common.h"
#include "target-descriptions.h"
#include "aarch32-tdep.h"
#include "arm-tdep.h"
#include "arm-fbsd-tdep.h"
#include "auxv.h"
#include "fbsd-tdep.h"
#include "gdbcore.h"
#include "inferior.h"
#include "osabi.h"
#include "solib-svr4.h"
#include "trad-frame.h"
#include "tramp-frame.h"
/* Register maps. */
static const struct regcache_map_entry arm_fbsd_gregmap[] =
{
{ 13, ARM_A1_REGNUM, 4 }, /* r0 ... r12 */
{ 1, ARM_SP_REGNUM, 4 },
{ 1, ARM_LR_REGNUM, 4 },
{ 1, ARM_PC_REGNUM, 4 },
{ 1, ARM_PS_REGNUM, 4 },
{ 0 }
};
static const struct regcache_map_entry arm_fbsd_vfpregmap[] =
{
{ 32, ARM_D0_REGNUM, 8 }, /* d0 ... d31 */
{ 1, ARM_FPSCR_REGNUM, 4 },
{ 0 }
};
/* In a signal frame, sp points to a 'struct sigframe' which is
defined as:
struct sigframe {
siginfo_t sf_si;
ucontext_t sf_uc;
mcontext_vfp_t sf_vfp;
};
ucontext_t is defined as:
struct __ucontext {
sigset_t uc_sigmask;
mcontext_t uc_mcontext;
...
};
mcontext_t is defined as:
struct {
unsigned int __gregs[17];
size_t mc_vfp_size;
void *mc_vfp_ptr;
...
};
mcontext_vfp_t is defined as:
struct {
uint64_t mcv_reg[32];
uint32_t mcv_fpscr;
};
If the VFP state is valid, then mc_vfp_ptr will point to sf_vfp in
the sigframe, otherwise it is NULL. There is no non-VFP floating
point register state saved in the signal frame. */
#define ARM_SIGFRAME_UCONTEXT_OFFSET 64
#define ARM_UCONTEXT_MCONTEXT_OFFSET 16
#define ARM_MCONTEXT_VFP_PTR_OFFSET 72
/* Implement the "init" method of struct tramp_frame. */
static void
arm_fbsd_sigframe_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);
enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
CORE_ADDR sp = get_frame_register_unsigned (this_frame, ARM_SP_REGNUM);
CORE_ADDR mcontext_addr = (sp
+ ARM_SIGFRAME_UCONTEXT_OFFSET
+ ARM_UCONTEXT_MCONTEXT_OFFSET);
ULONGEST mcontext_vfp_addr;
trad_frame_set_reg_regmap (this_cache, arm_fbsd_gregmap, mcontext_addr,
regcache_map_entry_size (arm_fbsd_gregmap));
if (safe_read_memory_unsigned_integer (mcontext_addr
+ ARM_MCONTEXT_VFP_PTR_OFFSET, 4,
byte_order,
&mcontext_vfp_addr)
&& mcontext_vfp_addr != 0)
trad_frame_set_reg_regmap (this_cache, arm_fbsd_vfpregmap, mcontext_vfp_addr,
regcache_map_entry_size (arm_fbsd_vfpregmap));
trad_frame_set_id (this_cache, frame_id_build (sp, func));
}
static const struct tramp_frame arm_fbsd_sigframe =
{
SIGTRAMP_FRAME,
4,
{
{0xe1a0000d, ULONGEST_MAX}, /* mov r0, sp */
{0xe2800040, ULONGEST_MAX}, /* add r0, r0, #SIGF_UC */
{0xe59f700c, ULONGEST_MAX}, /* ldr r7, [pc, #12] */
{0xef0001a1, ULONGEST_MAX}, /* swi SYS_sigreturn */
{TRAMP_SENTINEL_INSN, ULONGEST_MAX}
},
arm_fbsd_sigframe_init
};
/* Register set definitions. */
const struct regset arm_fbsd_gregset =
{
arm_fbsd_gregmap,
regcache_supply_regset, regcache_collect_regset
};
const struct regset arm_fbsd_vfpregset =
{
arm_fbsd_vfpregmap,
regcache_supply_regset, regcache_collect_regset
};
/* Implement the "iterate_over_regset_sections" gdbarch method. */
static void
arm_fbsd_iterate_over_regset_sections (struct gdbarch *gdbarch,
iterate_over_regset_sections_cb *cb,
void *cb_data,
const struct regcache *regcache)
{
arm_gdbarch_tdep *tdep = gdbarch_tdep<arm_gdbarch_tdep> (gdbarch);
cb (".reg", ARM_FBSD_SIZEOF_GREGSET, ARM_FBSD_SIZEOF_GREGSET,
&arm_fbsd_gregset, NULL, cb_data);
if (tdep->tls_regnum > 0)
{
const struct regcache_map_entry arm_fbsd_tlsregmap[] =
{
{ 1, tdep->tls_regnum, 4 },
{ 0 }
};
const struct regset arm_fbsd_tlsregset =
{
arm_fbsd_tlsregmap,
regcache_supply_regset, regcache_collect_regset
};
cb (".reg-aarch-tls", ARM_FBSD_SIZEOF_TLSREGSET, ARM_FBSD_SIZEOF_TLSREGSET,
&arm_fbsd_tlsregset, NULL, cb_data);
}
/* While FreeBSD/arm cores do contain a NT_FPREGSET / ".reg2"
register set, it is not populated with register values by the
kernel but just contains all zeroes. */
if (tdep->vfp_register_count > 0)
cb (".reg-arm-vfp", ARM_FBSD_SIZEOF_VFPREGSET, ARM_FBSD_SIZEOF_VFPREGSET,
&arm_fbsd_vfpregset, "VFP floating-point", cb_data);
}
/* Lookup a target description from a target's AT_HWCAP auxiliary
vector. */
const struct target_desc *
arm_fbsd_read_description_auxv (struct target_ops *target, bool tls)
{
CORE_ADDR arm_hwcap = 0;
if (target_auxv_search (target, AT_FREEBSD_HWCAP, &arm_hwcap) != 1)
return arm_read_description (ARM_FP_TYPE_NONE, tls);
if (arm_hwcap & HWCAP_VFP)
{
if (arm_hwcap & HWCAP_NEON)
return aarch32_read_description ();
else if ((arm_hwcap & (HWCAP_VFPv3 | HWCAP_VFPD32))
== (HWCAP_VFPv3 | HWCAP_VFPD32))
return arm_read_description (ARM_FP_TYPE_VFPV3, tls);
else
return arm_read_description (ARM_FP_TYPE_VFPV2, tls);
}
return arm_read_description (ARM_FP_TYPE_NONE, tls);
}
/* Implement the "core_read_description" gdbarch method. */
static const struct target_desc *
arm_fbsd_core_read_description (struct gdbarch *gdbarch,
struct target_ops *target,
bfd *abfd)
{
asection *tls = bfd_get_section_by_name (abfd, ".reg-aarch-tls");
return arm_fbsd_read_description_auxv (target, tls != nullptr);
}
/* Implement the get_thread_local_address gdbarch method. */
static CORE_ADDR
arm_fbsd_get_thread_local_address (struct gdbarch *gdbarch, ptid_t ptid,
CORE_ADDR lm_addr, CORE_ADDR offset)
{
arm_gdbarch_tdep *tdep = gdbarch_tdep<arm_gdbarch_tdep> (gdbarch);
struct regcache *regcache;
regcache = get_thread_arch_regcache (current_inferior ()->process_target (),
ptid, gdbarch);
target_fetch_registers (regcache, tdep->tls_regnum);
ULONGEST tpidruro;
if (regcache->cooked_read (tdep->tls_regnum, &tpidruro) != REG_VALID)
error (_("Unable to fetch %%tpidruro"));
/* %tpidruro points to the TCB whose first member is the dtv
pointer. */
CORE_ADDR dtv_addr = tpidruro;
return fbsd_get_thread_local_address (gdbarch, dtv_addr, lm_addr, offset);
}
/* Implement the 'init_osabi' method of struct gdb_osabi_handler. */
static void
arm_fbsd_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
arm_gdbarch_tdep *tdep = gdbarch_tdep<arm_gdbarch_tdep> (gdbarch);
/* Generic FreeBSD support. */
fbsd_init_abi (info, gdbarch);
if (tdep->fp_model == ARM_FLOAT_AUTO)
tdep->fp_model = ARM_FLOAT_SOFT_VFP;
tramp_frame_prepend_unwinder (gdbarch, &arm_fbsd_sigframe);
set_solib_svr4_fetch_link_map_offsets
(gdbarch, svr4_ilp32_fetch_link_map_offsets);
tdep->jb_pc = 24;
tdep->jb_elt_size = 4;
set_gdbarch_iterate_over_regset_sections
(gdbarch, arm_fbsd_iterate_over_regset_sections);
set_gdbarch_core_read_description (gdbarch, arm_fbsd_core_read_description);
if (tdep->tls_regnum > 0)
{
set_gdbarch_fetch_tls_load_module_address (gdbarch,
svr4_fetch_objfile_link_map);
set_gdbarch_get_thread_local_address (gdbarch,
arm_fbsd_get_thread_local_address);
}
/* Single stepping. */
set_gdbarch_software_single_step (gdbarch, arm_software_single_step);
}
void _initialize_arm_fbsd_tdep ();
void
_initialize_arm_fbsd_tdep ()
{
gdbarch_register_osabi (bfd_arch_arm, 0, GDB_OSABI_FREEBSD,
arm_fbsd_init_abi);
}
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