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binutils-gdb/gdb/alpha-linux-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 GNU/Linux on Alpha.
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 "frame.h"
#include "osabi.h"
#include "solib-svr4.h"
#include "symtab.h"
#include "regset.h"
#include "regcache.h"
#include "linux-tdep.h"
#include "alpha-tdep.h"
#include "gdbarch.h"
/* This enum represents the signals' numbers on the Alpha
architecture. It just contains the signal definitions which are
different from the generic implementation.
It is derived from the file <arch/alpha/include/uapi/asm/signal.h>,
from the Linux kernel tree. */
enum
{
/* SIGABRT is the same as in the generic implementation, but is
defined here because SIGIOT depends on it. */
ALPHA_LINUX_SIGABRT = 6,
ALPHA_LINUX_SIGEMT = 7,
ALPHA_LINUX_SIGBUS = 10,
ALPHA_LINUX_SIGSYS = 12,
ALPHA_LINUX_SIGURG = 16,
ALPHA_LINUX_SIGSTOP = 17,
ALPHA_LINUX_SIGTSTP = 18,
ALPHA_LINUX_SIGCONT = 19,
ALPHA_LINUX_SIGCHLD = 20,
ALPHA_LINUX_SIGIO = 23,
ALPHA_LINUX_SIGINFO = 29,
ALPHA_LINUX_SIGUSR1 = 30,
ALPHA_LINUX_SIGUSR2 = 31,
ALPHA_LINUX_SIGPOLL = ALPHA_LINUX_SIGIO,
ALPHA_LINUX_SIGPWR = ALPHA_LINUX_SIGINFO,
ALPHA_LINUX_SIGIOT = ALPHA_LINUX_SIGABRT,
};
/* Under GNU/Linux, signal handler invocations can be identified by
the designated code sequence that is used to return from a signal
handler. In particular, the return address of a signal handler
points to a sequence that copies $sp to $16, loads $0 with the
appropriate syscall number, and finally enters the kernel.
This is somewhat complicated in that:
(1) the expansion of the "mov" assembler macro has changed over
time, from "bis src,src,dst" to "bis zero,src,dst",
(2) the kernel has changed from using "addq" to "lda" to load the
syscall number,
(3) there is a "normal" sigreturn and an "rt" sigreturn which
has a different stack layout. */
static long
alpha_linux_sigtramp_offset_1 (struct gdbarch *gdbarch, CORE_ADDR pc)
{
switch (alpha_read_insn (gdbarch, pc))
{
case 0x47de0410: /* bis $30,$30,$16 */
case 0x47fe0410: /* bis $31,$30,$16 */
return 0;
case 0x43ecf400: /* addq $31,103,$0 */
case 0x201f0067: /* lda $0,103($31) */
case 0x201f015f: /* lda $0,351($31) */
return 4;
case 0x00000083: /* call_pal callsys */
return 8;
default:
return -1;
}
}
static LONGEST
alpha_linux_sigtramp_offset (struct gdbarch *gdbarch, CORE_ADDR pc)
{
long i, off;
if (pc & 3)
return -1;
/* Guess where we might be in the sequence. */
off = alpha_linux_sigtramp_offset_1 (gdbarch, pc);
if (off < 0)
return -1;
/* Verify that the other two insns of the sequence are as we expect. */
pc -= off;
for (i = 0; i < 12; i += 4)
{
if (i == off)
continue;
if (alpha_linux_sigtramp_offset_1 (gdbarch, pc + i) != i)
return -1;
}
return off;
}
static int
alpha_linux_pc_in_sigtramp (struct gdbarch *gdbarch,
CORE_ADDR pc, const char *func_name)
{
return alpha_linux_sigtramp_offset (gdbarch, pc) >= 0;
}
static CORE_ADDR
alpha_linux_sigcontext_addr (struct frame_info *this_frame)
{
struct gdbarch *gdbarch = get_frame_arch (this_frame);
CORE_ADDR pc;
ULONGEST sp;
long off;
pc = get_frame_pc (this_frame);
sp = get_frame_register_unsigned (this_frame, ALPHA_SP_REGNUM);
off = alpha_linux_sigtramp_offset (gdbarch, pc);
gdb_assert (off >= 0);
/* __NR_rt_sigreturn has a couple of structures on the stack. This is:
struct rt_sigframe {
struct siginfo info;
struct ucontext uc;
};
offsetof (struct rt_sigframe, uc.uc_mcontext); */
if (alpha_read_insn (gdbarch, pc - off + 4) == 0x201f015f)
return sp + 176;
/* __NR_sigreturn has the sigcontext structure at the top of the stack. */
return sp;
}
/* Supply register REGNUM from the buffer specified by GREGS and LEN
in the general-purpose register set REGSET to register cache
REGCACHE. If REGNUM is -1, do this for all registers in REGSET. */
static void
alpha_linux_supply_gregset (const struct regset *regset,
struct regcache *regcache,
int regnum, const void *gregs, size_t len)
{
const gdb_byte *regs = (const gdb_byte *) gregs;
gdb_assert (len >= 32 * 8);
alpha_supply_int_regs (regcache, regnum, regs, regs + 31 * 8,
len >= 33 * 8 ? regs + 32 * 8 : NULL);
}
/* Collect register REGNUM from the register cache REGCACHE and store
it in the buffer specified by GREGS and LEN as described by the
general-purpose register set REGSET. If REGNUM is -1, do this for
all registers in REGSET. */
static void
alpha_linux_collect_gregset (const struct regset *regset,
const struct regcache *regcache,
int regnum, void *gregs, size_t len)
{
gdb_byte *regs = (gdb_byte *) gregs;
gdb_assert (len >= 32 * 8);
alpha_fill_int_regs (regcache, regnum, regs, regs + 31 * 8,
len >= 33 * 8 ? regs + 32 * 8 : NULL);
}
/* Supply register REGNUM from the buffer specified by FPREGS and LEN
in the floating-point register set REGSET to register cache
REGCACHE. If REGNUM is -1, do this for all registers in REGSET. */
static void
alpha_linux_supply_fpregset (const struct regset *regset,
struct regcache *regcache,
int regnum, const void *fpregs, size_t len)
{
const gdb_byte *regs = (const gdb_byte *) fpregs;
gdb_assert (len >= 32 * 8);
alpha_supply_fp_regs (regcache, regnum, regs, regs + 31 * 8);
}
/* Collect register REGNUM from the register cache REGCACHE and store
it in the buffer specified by FPREGS and LEN as described by the
general-purpose register set REGSET. If REGNUM is -1, do this for
all registers in REGSET. */
static void
alpha_linux_collect_fpregset (const struct regset *regset,
const struct regcache *regcache,
int regnum, void *fpregs, size_t len)
{
gdb_byte *regs = (gdb_byte *) fpregs;
gdb_assert (len >= 32 * 8);
alpha_fill_fp_regs (regcache, regnum, regs, regs + 31 * 8);
}
static const struct regset alpha_linux_gregset =
{
NULL,
alpha_linux_supply_gregset, alpha_linux_collect_gregset
};
static const struct regset alpha_linux_fpregset =
{
NULL,
alpha_linux_supply_fpregset, alpha_linux_collect_fpregset
};
/* Iterate over core file register note sections. */
static void
alpha_linux_iterate_over_regset_sections (struct gdbarch *gdbarch,
iterate_over_regset_sections_cb *cb,
void *cb_data,
const struct regcache *regcache)
{
cb (".reg", 32 * 8, 32 * 8, &alpha_linux_gregset, NULL, cb_data);
cb (".reg2", 32 * 8, 32 * 8, &alpha_linux_fpregset, NULL, cb_data);
}
/* Implementation of `gdbarch_gdb_signal_from_target', as defined in
gdbarch.h. */
static enum gdb_signal
alpha_linux_gdb_signal_from_target (struct gdbarch *gdbarch,
int signal)
{
switch (signal)
{
case ALPHA_LINUX_SIGEMT:
return GDB_SIGNAL_EMT;
case ALPHA_LINUX_SIGBUS:
return GDB_SIGNAL_BUS;
case ALPHA_LINUX_SIGSYS:
return GDB_SIGNAL_SYS;
case ALPHA_LINUX_SIGURG:
return GDB_SIGNAL_URG;
case ALPHA_LINUX_SIGSTOP:
return GDB_SIGNAL_STOP;
case ALPHA_LINUX_SIGTSTP:
return GDB_SIGNAL_TSTP;
case ALPHA_LINUX_SIGCONT:
return GDB_SIGNAL_CONT;
case ALPHA_LINUX_SIGCHLD:
return GDB_SIGNAL_CHLD;
/* No way to differentiate between SIGIO and SIGPOLL.
Therefore, we just handle the first one. */
case ALPHA_LINUX_SIGIO:
return GDB_SIGNAL_IO;
/* No way to differentiate between SIGINFO and SIGPWR.
Therefore, we just handle the first one. */
case ALPHA_LINUX_SIGINFO:
return GDB_SIGNAL_INFO;
case ALPHA_LINUX_SIGUSR1:
return GDB_SIGNAL_USR1;
case ALPHA_LINUX_SIGUSR2:
return GDB_SIGNAL_USR2;
}
return linux_gdb_signal_from_target (gdbarch, signal);
}
/* Implementation of `gdbarch_gdb_signal_to_target', as defined in
gdbarch.h. */
static int
alpha_linux_gdb_signal_to_target (struct gdbarch *gdbarch,
enum gdb_signal signal)
{
switch (signal)
{
case GDB_SIGNAL_EMT:
return ALPHA_LINUX_SIGEMT;
case GDB_SIGNAL_BUS:
return ALPHA_LINUX_SIGBUS;
case GDB_SIGNAL_SYS:
return ALPHA_LINUX_SIGSYS;
case GDB_SIGNAL_URG:
return ALPHA_LINUX_SIGURG;
case GDB_SIGNAL_STOP:
return ALPHA_LINUX_SIGSTOP;
case GDB_SIGNAL_TSTP:
return ALPHA_LINUX_SIGTSTP;
case GDB_SIGNAL_CONT:
return ALPHA_LINUX_SIGCONT;
case GDB_SIGNAL_CHLD:
return ALPHA_LINUX_SIGCHLD;
case GDB_SIGNAL_IO:
return ALPHA_LINUX_SIGIO;
case GDB_SIGNAL_INFO:
return ALPHA_LINUX_SIGINFO;
case GDB_SIGNAL_USR1:
return ALPHA_LINUX_SIGUSR1;
case GDB_SIGNAL_USR2:
return ALPHA_LINUX_SIGUSR2;
case GDB_SIGNAL_POLL:
return ALPHA_LINUX_SIGPOLL;
case GDB_SIGNAL_PWR:
return ALPHA_LINUX_SIGPWR;
}
return linux_gdb_signal_to_target (gdbarch, signal);
}
static void
alpha_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
linux_init_abi (info, gdbarch, 0);
/* Hook into the DWARF CFI frame unwinder. */
alpha_dwarf2_init_abi (info, gdbarch);
/* Hook into the MDEBUG frame unwinder. */
alpha_mdebug_init_abi (info, gdbarch);
alpha_gdbarch_tdep *tdep = gdbarch_tdep<alpha_gdbarch_tdep> (gdbarch);
tdep->dynamic_sigtramp_offset = alpha_linux_sigtramp_offset;
tdep->sigcontext_addr = alpha_linux_sigcontext_addr;
tdep->pc_in_sigtramp = alpha_linux_pc_in_sigtramp;
tdep->jb_pc = 2;
tdep->jb_elt_size = 8;
set_gdbarch_skip_trampoline_code (gdbarch, find_solib_trampoline_target);
set_solib_svr4_fetch_link_map_offsets
(gdbarch, linux_lp64_fetch_link_map_offsets);
/* Enable TLS support. */
set_gdbarch_fetch_tls_load_module_address (gdbarch,
svr4_fetch_objfile_link_map);
set_gdbarch_iterate_over_regset_sections
(gdbarch, alpha_linux_iterate_over_regset_sections);
set_gdbarch_gdb_signal_from_target (gdbarch,
alpha_linux_gdb_signal_from_target);
set_gdbarch_gdb_signal_to_target (gdbarch,
alpha_linux_gdb_signal_to_target);
}
void _initialize_alpha_linux_tdep ();
void
_initialize_alpha_linux_tdep ()
{
gdbarch_register_osabi (bfd_arch_alpha, 0, GDB_OSABI_LINUX,
alpha_linux_init_abi);
}
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