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powerpc: Remove backtrace implementation 

The powerpc optimization to provide a fast stacktrace requires some
ad-hoc code to handle Linux signal frames and the change is fragile
once the kernel decides to slight change its execution sequence [1].

The generic implementation work as-is and it should be future proof
since the kernel provides the expected CFI directives in vDSO shared
page.

Checked on powerpc-linux-gnu, powerpc64le-linux-gnu, and
powerpc64-linux-gnu.

[1] https://sourceware.org/pipermail/libc-alpha/2021-January/122027.html
This commit is contained in:
Adhemerval Zanella 2021-02-12 19:20:27 +03:00
parent 2c6cabb3a4
commit 82fd7314c7
5 changed files with 0 additions and 277 deletions
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133
sysdeps/powerpc/powerpc32/backtrace.c
View File

@ -1,133 +0,0 @@
/* Return backtrace of current program state.
Copyright (C) 1998-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <execinfo.h>
#include <stddef.h>
#include <string.h>
#include <signal.h>
#include <libc-vdso.h>
/* This is the stack layout we see with every stack frame.
Note that every routine is required by the ABI to lay out the stack
like this.
+----------------+ +-----------------+
%r1 -> | %r1 last frame--------> | %r1 last frame--->... --> NULL
| | | |
| (unused) | | return address |
+----------------+ +-----------------+
*/
struct layout
{
struct layout *next;
void *return_address;
};
#define SIGNAL_FRAMESIZE 64
/* Since the signal handler is just like any other function it needs to
save/restore its LR and it will save it into callers stack frame.
Since a signal handler doesn't have a caller, the kernel creates a
dummy frame to make it look like it has a caller. */
struct signal_frame_32 {
char dummy[SIGNAL_FRAMESIZE];
struct sigcontext sctx;
mcontext_t mctx;
/* We don't care about the rest, since IP value is at 'mctx' field. */
};
static inline bool
is_sigtramp_address (void *nip)
{
#ifdef HAVE_SIGTRAMP_RT32
if (nip == GLRO (dl_vdso_sigtramp_32))
return true;
#endif
return false;
}
struct rt_signal_frame_32 {
char dummy[SIGNAL_FRAMESIZE + 16];
siginfo_t info;
ucontext_t uc;
/* We don't care about the rest, since IP value is at 'uc' field. */
};
static inline bool
is_sigtramp_address_rt (void * nip)
{
#ifdef HAVE_SIGTRAMP_32
if (nip == GLRO (dl_vdso_sigtramp_rt32))
return true;
#endif
return false;
}
int
__backtrace (void **array, int size)
{
struct layout *current;
int count;
/* Force gcc to spill LR. */
asm volatile ("" : "=l"(current));
/* Get the address on top-of-stack. */
asm volatile ("lwz %0,0(1)" : "=r"(current));
for ( count = 0;
current != NULL && count < size;
current = current->next, count++)
{
gregset_t *gregset = NULL;
array[count] = current->return_address;
/* Check if the symbol is the signal trampoline and get the interrupted
* symbol address from the trampoline saved area. */
if (is_sigtramp_address (current->return_address))
{
struct signal_frame_32 *sigframe =
(struct signal_frame_32*) current;
gregset = &sigframe->mctx.gregs;
}
else if (is_sigtramp_address_rt (current->return_address))
{
struct rt_signal_frame_32 *sigframe =
(struct rt_signal_frame_32*) current;
gregset = &sigframe->uc.uc_mcontext.uc_regs->gregs;
}
if (gregset)
{
if (count + 1 == size)
break;
array[++count] = (void*)((*gregset)[PT_NIP]);
current = (void*)((*gregset)[PT_R1]);
}
}
/* It's possible the second-last stack frame can't return
(that is, it's __libc_start_main), in which case
the CRT startup code will have set its LR to 'NULL'. */
if (count > 0 && array[count-1] == NULL)
count--;
return count;
}
weak_alias (__backtrace, backtrace)
libc_hidden_def (__backtrace)

117
sysdeps/powerpc/powerpc64/backtrace.c
View File

@ -1,117 +0,0 @@
/* Return backtrace of current program state.
Copyright (C) 1998-2021 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C Library 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
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If
not, see <https://www.gnu.org/licenses/>. */
#include <stddef.h>
#include <string.h>
#include <signal.h>
#include <stdint.h>
#include <execinfo.h>
#include <libc-vdso.h>
/* This is the stack layout we see with every stack frame.
Note that every routine is required by the ABI to lay out the stack
like this.
+----------------+ +-----------------+
%r1 -> | %r1 last frame--------> | %r1 last frame--->... --> NULL
| | | |
| cr save | | cr save |
| | | |
| (unused) | | return address |
+----------------+ +-----------------+
*/
struct layout
{
struct layout *next;
long int condition_register;
void *return_address;
};
/* Since the signal handler is just like any other function it needs to
save/restore its LR and it will save it into callers stack frame.
Since a signal handler doesn't have a caller, the kernel creates a
dummy frame to make it look like it has a caller. */
struct signal_frame_64 {
#define SIGNAL_FRAMESIZE 128
char dummy[SIGNAL_FRAMESIZE];
ucontext_t uc;
/* We don't care about the rest, since the IP value is at 'uc' field. */
};
/* Test if the address match to the inside the trampoline code.
Up to and including kernel 5.8, returning from an interrupt or syscall to a
signal handler starts execution directly at the handler's entry point, with
LR set to address of the sigreturn trampoline (the vDSO symbol).
Newer kernels will branch to signal handler from the trampoline instead, so
checking the stacktrace against the vDSO entrypoint does not work in such
case.
The vDSO branches with a 'bctrl' instruction, so checking either the
vDSO address itself and the next instruction should cover all kernel
versions. */
static inline bool
is_sigtramp_address (void *nip)
{
#ifdef HAVE_SIGTRAMP_RT64
if (nip == GLRO (dl_vdso_sigtramp_rt64) ||
nip == GLRO (dl_vdso_sigtramp_rt64) + 4)
return true;
#endif
return false;
}
int
__backtrace (void **array, int size)
{
struct layout *current;
int count;
/* Force gcc to spill LR. */
asm volatile ("" : "=l"(current));
/* Get the address on top-of-stack. */
asm volatile ("ld %0,0(1)" : "=r"(current));
for ( count = 0;
current != NULL && count < size;
current = current->next, count++)
{
array[count] = current->return_address;
/* Check if the symbol is the signal trampoline and get the interrupted
* symbol address from the trampoline saved area. */
if (is_sigtramp_address (current->return_address))
{
struct signal_frame_64 *sigframe = (struct signal_frame_64*) current;
if (count + 1 == size)
break;
array[++count] = (void*) sigframe->uc.uc_mcontext.gp_regs[PT_NIP];
current = (void*) sigframe->uc.uc_mcontext.gp_regs[PT_R1];
}
}
/* It's possible the second-last stack frame can't return
(that is, it's __libc_start_main), in which case
the CRT startup code will have set its LR to 'NULL'. */
if (count > 0 && array[count-1] == NULL)
count--;
return count;
}
weak_alias (__backtrace, backtrace)
libc_hidden_def (__backtrace)

11
sysdeps/unix/sysv/linux/dl-vdso-setup.c
View File

@ -71,17 +71,6 @@ PROCINFO_CLASS int (*_dl_vdso_clock_getres_time64) (clockid_t,
# ifdef HAVE_GET_TBFREQ
PROCINFO_CLASS uint64_t (*_dl_vdso_get_tbfreq)(void) RELRO;
# endif
/* The sigtramp are used on powerpc backtrace without using
INLINE_VSYSCALL, so there is no need to set their type. */
# ifdef HAVE_SIGTRAMP_RT64
PROCINFO_CLASS void *_dl_vdso_sigtramp_rt64 RELRO;
# endif
# ifdef HAVE_SIGTRAMP_RT32
PROCINFO_CLASS void *_dl_vdso_sigtramp_rt32 RELRO;
# endif
# ifdef HAVE_SIGTRAMP_32
PROCINFO_CLASS void *_dl_vdso_sigtramp_32 RELRO;
# endif
#endif
#undef RELRO

9
sysdeps/unix/sysv/linux/dl-vdso-setup.h
View File

@ -47,15 +47,6 @@ setup_vdso_pointers (void)
#ifdef HAVE_GET_TBFREQ
GLRO(dl_vdso_get_tbfreq) = dl_vdso_vsym (HAVE_GET_TBFREQ);
#endif
#ifdef HAVE_SIGTRAMP_RT64
GLRO(dl_vdso_sigtramp_rt64) = dl_vdso_vsym (HAVE_SIGTRAMP_RT64);
#endif
#ifdef HAVE_SIGTRAMP_RT32
GLRO(dl_vdso_sigtramp_rt32) = dl_vdso_vsym (HAVE_SIGTRAMP_RT32);
#endif
#ifdef HAVE_SIGTRAMP_32
GLRO(dl_vdso_sigtramp_32) = dl_vdso_vsym (HAVE_SIGTRAMP_32);
#endif
}
#endif

7
sysdeps/unix/sysv/linux/powerpc/sysdep.h
View File

@ -255,11 +255,4 @@
#define HAVE_GETTIMEOFDAY_VSYSCALL "__kernel_gettimeofday"
#define HAVE_GET_TBFREQ "__kernel_get_tbfreq"
#if defined(__PPC64__) || defined(__powerpc64__)
# define HAVE_SIGTRAMP_RT64 "__kernel_sigtramp_rt64"
#else
# define HAVE_SIGTRAMP_32 "__kernel_sigtramp32"
# define HAVE_SIGTRAMP_RT32 "__kernel_sigtramp_rt32"
#endif
#endif /* _LINUX_POWERPC_SYSDEP_H */