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binutils-gdb/gdb/arm-netbsd-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 NetBSD/arm.
Copyright (C) 2002-2022 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 "arch/arm.h"
#include "arm-netbsd-tdep.h"
#include "netbsd-tdep.h"
#include "arm-tdep.h"
#include "regset.h"
#include "solib-svr4.h"
/* Description of the longjmp buffer. */
#define ARM_NBSD_JB_PC 24
#define ARM_NBSD_JB_ELEMENT_SIZE ARM_INT_REGISTER_SIZE
/* For compatibility with previous implementations of GDB on arm/NetBSD,
override the default little-endian breakpoint. */
static const gdb_byte arm_nbsd_arm_le_breakpoint[] = {0x11, 0x00, 0x00, 0xe6};
static const gdb_byte arm_nbsd_arm_be_breakpoint[] = {0xe6, 0x00, 0x00, 0x11};
static const gdb_byte arm_nbsd_thumb_le_breakpoint[] = {0xfe, 0xde};
static const gdb_byte arm_nbsd_thumb_be_breakpoint[] = {0xde, 0xfe};
/* This matches struct reg from NetBSD's sys/arch/arm/include/reg.h:
https://github.com/NetBSD/src/blob/7c13e6e6773bb171f4ed3ed53013e9d24b3c1eac/sys/arch/arm/include/reg.h#L39
*/
struct arm_nbsd_reg
{
uint32_t reg[13];
uint32_t sp;
uint32_t lr;
uint32_t pc;
uint32_t cpsr;
};
void
arm_nbsd_supply_gregset (const struct regset *regset, struct regcache *regcache,
int regnum, const void *gregs, size_t len)
{
const arm_nbsd_reg *gregset = static_cast<const arm_nbsd_reg *>(gregs);
gdb_assert (len >= sizeof (arm_nbsd_reg));
/* Integer registers. */
for (int i = ARM_A1_REGNUM; i < ARM_SP_REGNUM; i++)
if (regnum == -1 || regnum == i)
regcache->raw_supply (i, (char *) &gregset->reg[i]);
if (regnum == -1 || regnum == ARM_SP_REGNUM)
regcache->raw_supply (ARM_SP_REGNUM, (char *) &gregset->sp);
if (regnum == -1 || regnum == ARM_LR_REGNUM)
regcache->raw_supply (ARM_LR_REGNUM, (char *) &gregset->lr);
if (regnum == -1 || regnum == ARM_PC_REGNUM)
{
CORE_ADDR r_pc = gdbarch_addr_bits_remove (regcache->arch (), gregset->pc);
regcache->raw_supply (ARM_PC_REGNUM, (char *) &r_pc);
}
if (regnum == -1 || regnum == ARM_PS_REGNUM)
{
if (arm_apcs_32)
regcache->raw_supply (ARM_PS_REGNUM, (char *) &gregset->cpsr);
else
regcache->raw_supply (ARM_PS_REGNUM, (char *) &gregset->pc);
}
}
static const struct regset arm_nbsd_regset = {
nullptr,
arm_nbsd_supply_gregset,
/* We don't need a collect function because we only use this reading registers
(via iterate_over_regset_sections and fetch_regs/fetch_register). */
nullptr,
0
};
static void
arm_nbsd_iterate_over_regset_sections (struct gdbarch *gdbarch,
iterate_over_regset_sections_cb *cb,
void *cb_data,
const struct regcache *regcache)
{
cb (".reg", sizeof (arm_nbsd_reg), sizeof (arm_nbsd_reg), &arm_nbsd_regset,
NULL, cb_data);
/* cbiesinger/2020-02-12 -- as far as I can tell, ARM/NetBSD does
not write any floating point registers into the core file (tested
with NetBSD 9.1_RC1). When it does, this function will need to read them,
and the arm-netbsd gdbarch will need a core_read_description function
to return the right description for them. */
}
static void
arm_netbsd_init_abi_common (struct gdbarch_info info,
struct gdbarch *gdbarch)
{
arm_gdbarch_tdep *tdep = gdbarch_tdep<arm_gdbarch_tdep> (gdbarch);
tdep->lowest_pc = 0x8000;
switch (info.byte_order)
{
case BFD_ENDIAN_LITTLE:
tdep->arm_breakpoint = arm_nbsd_arm_le_breakpoint;
tdep->thumb_breakpoint = arm_nbsd_thumb_le_breakpoint;
tdep->arm_breakpoint_size = sizeof (arm_nbsd_arm_le_breakpoint);
tdep->thumb_breakpoint_size = sizeof (arm_nbsd_thumb_le_breakpoint);
break;
case BFD_ENDIAN_BIG:
tdep->arm_breakpoint = arm_nbsd_arm_be_breakpoint;
tdep->thumb_breakpoint = arm_nbsd_thumb_be_breakpoint;
tdep->arm_breakpoint_size = sizeof (arm_nbsd_arm_be_breakpoint);
tdep->thumb_breakpoint_size = sizeof (arm_nbsd_thumb_be_breakpoint);
break;
default:
internal_error (__FILE__, __LINE__,
_("arm_gdbarch_init: bad byte order for float format"));
}
tdep->jb_pc = ARM_NBSD_JB_PC;
tdep->jb_elt_size = ARM_NBSD_JB_ELEMENT_SIZE;
set_gdbarch_iterate_over_regset_sections
(gdbarch, arm_nbsd_iterate_over_regset_sections);
/* Single stepping. */
set_gdbarch_software_single_step (gdbarch, arm_software_single_step);
}
static void
arm_netbsd_elf_init_abi (struct gdbarch_info info,
struct gdbarch *gdbarch)
{
arm_gdbarch_tdep *tdep = gdbarch_tdep<arm_gdbarch_tdep> (gdbarch);
arm_netbsd_init_abi_common (info, gdbarch);
nbsd_init_abi (info, gdbarch);
if (tdep->fp_model == ARM_FLOAT_AUTO)
tdep->fp_model = ARM_FLOAT_SOFT_VFP;
/* NetBSD ELF uses SVR4-style shared libraries. */
set_solib_svr4_fetch_link_map_offsets
(gdbarch, svr4_ilp32_fetch_link_map_offsets);
}
void _initialize_arm_netbsd_tdep ();
void
_initialize_arm_netbsd_tdep ()
{
gdbarch_register_osabi (bfd_arch_arm, 0, GDB_OSABI_NETBSD,
arm_netbsd_elf_init_abi);
}
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