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binutils-gdb/gdb/ppc-obsd-nat.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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/* Native-dependent code for OpenBSD/powerpc.
Copyright (C) 2004-2022 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 "gdbcore.h"
#include "inferior.h"
#include "regcache.h"
#include <sys/types.h>
#include <sys/ptrace.h>
#include <sys/signal.h>
#include <machine/frame.h>
#include <machine/pcb.h>
#include <machine/reg.h>
#include "ppc-tdep.h"
#include "ppc-obsd-tdep.h"
#include "inf-ptrace.h"
#include "obsd-nat.h"
#include "bsd-kvm.h"
struct ppc_obsd_nat_target final : public obsd_nat_target
{
void fetch_registers (struct regcache *, int) override;
void store_registers (struct regcache *, int) override;
};
static ppc_obsd_nat_target the_ppc_obsd_nat_target;
/* OpenBSD/powerpc didn't have PT_GETFPREGS/PT_SETFPREGS until release
4.0. On older releases the floating-point registers are handled by
PT_GETREGS/PT_SETREGS, but fpscr wasn't available.. */
#ifdef PT_GETFPREGS
/* Returns true if PT_GETFPREGS fetches this register. */
static int
getfpregs_supplies (struct gdbarch *gdbarch, int regnum)
{
ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep> (gdbarch);
/* FIXME: jimb/2004-05-05: Some PPC variants don't have floating
point registers. Traditionally, GDB's register set has still
listed the floating point registers for such machines, so this
code is harmless. However, the new E500 port actually omits the
floating point registers entirely from the register set --- they
don't even have register numbers assigned to them.
It's not clear to me how best to update this code, so this assert
will alert the first person to encounter the NetBSD/E500
combination to the problem. */
gdb_assert (ppc_floating_point_unit_p (gdbarch));
return ((regnum >= tdep->ppc_fp0_regnum
&& regnum < tdep->ppc_fp0_regnum + ppc_num_fprs)
|| regnum == tdep->ppc_fpscr_regnum);
}
#endif /* PT_GETFPREGS */
/* Fetch register REGNUM from the inferior. If REGNUM is -1, do this
for all registers. */
void
ppc_obsd_nat_target::fetch_registers (struct regcache *regcache, int regnum)
{
struct reg regs;
pid_t pid = regcache->ptid ().pid ();
if (ptrace (PT_GETREGS, pid, (PTRACE_TYPE_ARG3) &regs, 0) == -1)
perror_with_name (_("Couldn't get registers"));
ppc_supply_gregset (&ppcobsd_gregset, regcache, -1,
&regs, sizeof regs);
#ifndef PT_GETFPREGS
ppc_supply_fpregset (&ppcobsd_gregset, regcache, -1,
&regs, sizeof regs);
#endif
#ifdef PT_GETFPREGS
if (regnum == -1
|| getfpregs_supplies (regcache->arch (), regnum))
{
struct fpreg fpregs;
if (ptrace (PT_GETFPREGS, pid, (PTRACE_TYPE_ARG3) &fpregs, 0) == -1)
perror_with_name (_("Couldn't get floating point status"));
ppc_supply_fpregset (&ppcobsd_fpregset, regcache, -1,
&fpregs, sizeof fpregs);
}
#endif
}
/* Store register REGNUM back into the inferior. If REGNUM is -1, do
this for all registers. */
void
ppc_obsd_nat_target::store_registers (struct regcache *regcache, int regnum)
{
struct reg regs;
pid_t pid = regcache->ptid ().pid ();
if (ptrace (PT_GETREGS, pid, (PTRACE_TYPE_ARG3) &regs, 0) == -1)
perror_with_name (_("Couldn't get registers"));
ppc_collect_gregset (&ppcobsd_gregset, regcache,
regnum, &regs, sizeof regs);
#ifndef PT_GETFPREGS
ppc_collect_fpregset (&ppcobsd_gregset, regcache,
regnum, &regs, sizeof regs);
#endif
if (ptrace (PT_SETREGS, pid, (PTRACE_TYPE_ARG3) &regs, 0) == -1)
perror_with_name (_("Couldn't write registers"));
#ifdef PT_GETFPREGS
if (regnum == -1
|| getfpregs_supplies (regcache->arch (), regnum))
{
struct fpreg fpregs;
if (ptrace (PT_GETFPREGS, pid, (PTRACE_TYPE_ARG3) &fpregs, 0) == -1)
perror_with_name (_("Couldn't get floating point status"));
ppc_collect_fpregset (&ppcobsd_fpregset, regcache,
regnum, &fpregs, sizeof fpregs);
if (ptrace (PT_SETFPREGS, pid, (PTRACE_TYPE_ARG3) &fpregs, 0) == -1)
perror_with_name (_("Couldn't write floating point status"));
}
#endif
}
static int
ppcobsd_supply_pcb (struct regcache *regcache, struct pcb *pcb)
{
struct gdbarch *gdbarch = regcache->arch ();
ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep> (gdbarch);
struct switchframe sf;
struct callframe cf;
int i, regnum;
/* The following is true for OpenBSD 3.7:
The pcb contains %r1 (the stack pointer) at the point of the
context switch in cpu_switch(). At that point we have a stack
frame as described by `struct switchframe', and below that a call
frame as described by `struct callframe'. From this information
we reconstruct the register state as it would look when we are in
cpu_switch(). */
/* The stack pointer shouldn't be zero. */
if (pcb->pcb_sp == 0)
return 0;
read_memory (pcb->pcb_sp, (gdb_byte *)&sf, sizeof sf);
regcache->raw_supply (gdbarch_sp_regnum (gdbarch), &sf.sp);
regcache->raw_supply (tdep->ppc_cr_regnum, &sf.cr);
regcache->raw_supply (tdep->ppc_gp0_regnum + 2, &sf.fixreg2);
for (i = 0, regnum = tdep->ppc_gp0_regnum + 13; i < 19; i++, regnum++)
regcache->raw_supply (regnum, &sf.fixreg[i]);
read_memory (sf.sp, (gdb_byte *)&cf, sizeof cf);
regcache->raw_supply (gdbarch_pc_regnum (gdbarch), &cf.lr);
regcache->raw_supply (tdep->ppc_gp0_regnum + 30, &cf.r30);
regcache->raw_supply (tdep->ppc_gp0_regnum + 31, &cf.r31);
return 1;
}
void _initialize_ppcobsd_nat ();
void
_initialize_ppcobsd_nat ()
{
add_inf_child_target (&the_ppc_obsd_nat_target);
/* General-purpose registers. */
ppcobsd_reg_offsets.r0_offset = offsetof (struct reg, gpr);
ppcobsd_reg_offsets.gpr_size = 4;
ppcobsd_reg_offsets.xr_size = 4;
ppcobsd_reg_offsets.pc_offset = offsetof (struct reg, pc);
ppcobsd_reg_offsets.ps_offset = offsetof (struct reg, ps);
ppcobsd_reg_offsets.cr_offset = offsetof (struct reg, cnd);
ppcobsd_reg_offsets.lr_offset = offsetof (struct reg, lr);
ppcobsd_reg_offsets.ctr_offset = offsetof (struct reg, cnt);
ppcobsd_reg_offsets.xer_offset = offsetof (struct reg, xer);
ppcobsd_reg_offsets.mq_offset = offsetof (struct reg, mq);
/* Floating-point registers. */
ppcobsd_reg_offsets.f0_offset = offsetof (struct reg, fpr);
ppcobsd_reg_offsets.fpscr_offset = -1;
#ifdef PT_GETFPREGS
ppcobsd_fpreg_offsets.f0_offset = offsetof (struct fpreg, fpr);
ppcobsd_fpreg_offsets.fpscr_offset = offsetof (struct fpreg, fpscr);
ppcobsd_fpreg_offsets.fpscr_size = 4;
#endif
/* Support debugging kernel virtual memory images. */
bsd_kvm_add_target (ppcobsd_supply_pcb);
}
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