Greetings,
We use libunwind just for stack traces (I suspect many others do as well).
The use pattern is:
GetStackTrace(void** result, int max_depth)
{
...
unw_getcontext(&uc);
unw_init_local(&cursor, &uc);
while (n < max_depth) {
if (unw_get_reg(&cursor, UNW_REG_IP, (unw_word_t *) &ip) < 0) {
break;
}
result[n++] = ip;
if (unw_step(&cursor) <= 0) {
break;
}
}
Given this usage, it is quite convenient for us to block signals (or
prevent signal handlers from re-entering libunwind by other means) at the
"top level", which makes most of the sigprocmask calls performed by
libunwind itself unneccessary.
The second patch in this series adds a configure option which removes most
of the sigprocmask calls.
Attached patch is a preliminary for it -- consolidating all of the
"sigprocmask; mutex_lock;" sequences into lock_acquire and "mutex_unlock;
sigprocmask;" sequences into lock_release.
Thanks,
--
Paul Pluzhnikov
commit 402d15b123d54a7669db7cf17a76dd315094e472
Author: Paul Pluzhnikov <ppluzhnikov@google.com>
Date: Mon Sep 21 10:18:28 2009 -0700
Replace "sigprocmask + mutext_lock" with a single lock_acquire.
Likewise, replace "mutext_unlock + sigprocmask" with lock_release.
This rule (no IP adjustment on ia64) may be correct for locating the right FDE.
Unfortunately the same adjusted/unadjusted return address is being used also by
__gxx_personality_v0() to locate the right call-site (the try {} block) for
unwinding. And this case is already sensitive for off-by-one PC values.
Unlike the FDE location where the function prologue + epilogue make it immune
against off-by-one PC calculations.
Therefore suggesting to unify it with non-ia64 case.
Signed-off-by: Jan Kratochvil <jan.kratochvil@redhat.com>
Provide a special implementation for ia64, because the unwind
information is such that an IP adjustment is not necessary before
looking up unwind info.
Bad things happen if libunwind only provides parts of the ABI and
the rest come from libgcc.
Signed-off-by: Jan Kratochvil <jan.kratochvil@redhat.com>
getcontext in libc.
Also cleanup the namespace (check-name-space passes on x86_64 now).
Replace uses of offsets.h with ucontext_i.h.
Rename _x86_64_setcontext to _Ux86_64_setcontext.
TBD: Add CFI annotations for get/setcontext.
Signed-off-by: Paul Pluzhnikov <ppluzhnikov@google.com>
Signed-off-by: Arun Sharma <arun.sharma@google.com>
bad/missing unwind information, which could result in libunwind
dereferencing bad pointers. This mechanism is based on msync(2) system
call and significantly reduces the chances of a bad pointer
dereference in libunwind.
The original idea was to turn this mechanism on only when necessary
i.e. libunwind didn't find proper unwind information for a IP.
There are a couple of problems in the current implementation.
* The flag is global and is modified without locking
* The flag isn't reset when starting a new unwind
The attached patch makes ->validate a per-thread setting by moving it
into struct cursor from unw_local_addr_space and resets it to false
when starting a new unwind. As a result, cursor->as_arg points to the
cursor itself instead of the ucontext (for the local case).
This was found to reduce the number of msync() system calls from an
application using libunwind significantly.
Signed-off-by: Paul Pluzhnikov <ppluzhnikov@google.com>
Signed-off-by: Arun Sharma <arun.sharma@google.com>
* src/arm/unwind_i (arm_lock, arm_local_resume): Define.
* src/ptrace/_UPT_find_proc_info.c: Handle ARM like X86 etc.
* tests/flush-cache.S (flush_cache): Add (dummy) ARM-version.
ARM does need executable stack, even on Linux...
Signed-off-by: Anderson Lizardo <anderson.lizardo@indt.org.br>
Signed-off-by: Bruna Moreira <bruna.moreira@indt.org.br>
The current pattern is too restrictive and doesn't work well on
modern glibcs.
Signed-off-by: Paul Pluzhnikov <ppluzhnikov@google.com>
Signed-off-by: Arun Sharma <arun.sharma@google.com>
* Use explicit types for XMM registers
* Support full width (128 bits) access
Signed-off-by: Andrew Cagney <cagney@redhat.com>
Signed-off-by: Arun Sharma <aruns@google.com>
as "weak". Since the elf-support is in the library anyhow, this serves
no purpose and in fact causes problem because the weak reference alone
is not enough to pull in the ELF-code from an archive file, causing to
spurious failures of get_proc_name.
On some systems executable stacks are denied. Since libunwind and the
tests don't actually need executable stacks this patch marks all
assembly files as not needing it.
The original patch comes from frysk:
2007-04-05 Jan Kratochvil <jan.kratochvil@redhat.com>
* src/hppa/getcontext.S, src/hppa/setcontext.S, src/hppa/siglongjmp.S,
src/ia64/Ginstall_cursor.S, src/ia64/Linstall_cursor.S,
src/ia64/dyn_info_list.S, src/ia64/getcontext.S, src/ia64/longjmp.S,
src/ia64/setjmp.S, src/ia64/siglongjmp.S, src/ia64/sigsetjmp.S,
src/ppc64/longjmp.S, src/ppc64/siglongjmp.S, src/x86/longjmp.S,
src/x86/siglongjmp.S, src/x86_64/longjmp.S, src/x86_64/setcontext.S,
src/x86_64/siglongjmp.S: Stack should be non-executable, for SELinux.
I added a couple more markers for new files in current libunwind.
Before this patch you would get the following on selinux enabled
systems without allow_exec_stack: error while loading shared
libraries:
libunwind.so.7: cannot enable executable stack as shared object
requires: Permission denied
After the patch that error disappears and all test results are similar
to the results on systems without executable stack protection.
routine and add address-space argument. This is needed because on
PPC64, a the function-name symbol refers to a function descriptor
(unlike, for example, on ia64, where the @fptr() operator is needed to
refer to a function descriptor). Thus, in order to look up the name
of a function, we need to dereference the function descriptor. To
make matters more "interesting", the function descriptors are normally
resolved by the dynamic linker, so we can't get their values from the
ELF file. Instead, we have to read them from the running image, hence
the need for the address-space argument.
This is so that the source file gets distributed and _ucontext_i.h is
generated properly on the target machine.
Signed-off-by: Arun Sharma <arun.sharma@google.com>
When libunwind is linked with a C++ program that throws exceptions,
the exception that's thrown is passed in %rax. However, libc's
setcontext clears %rax, causing problems.
This patch implements a setcontext that doesn't clobber rax.
TBD: Add dwarf CFI annotations
Signed-off-by: Arun Sharma <arun.sharma@google.com>
Yes, it casts to signed, but then converts right back to
unsigned via the return type. Fixed thus.
Signed-off-by: Richard Henderson <rth@redhat.com>
Signed-off-by: Arun Sharma <arun.sharma@google.com>
CFA should be incremented by 16 in the hope that the previous frame
may have valid unwind info.
Also increase the default frame pointer recognition heuristic from 4k
to 16k.
Signed-off-by: Andrey Veskov <Andrey.Veskov@intel.com>
Signed-off-by: Arun Sharma <arun.sharma@google.com>
Now that dwarf_find_save_locs() not just finds the save-locations but
also updates the cursor-state, document this fact (the function really
is misnamed now).
Be sure to clear pi->unwind_info when looking up the kernel table and
not needing the unwind-info. Otherwise, _UPT_put_unwind_info() may
erroneously call free() on the pointer, even though that space wasn't
malloc'd, leading to crashes..
(maps_next): After reading less than a full buffer of data, copy
remaining data to the top of the buffer so as to maintain the
invariant that all data between mi->buf and mi->buf_end is valid.
This avoids maps_next() parsing uninitialized data.
(get_initial_stack_pointers): Likewise.
(unw_init_local): Use new functions to make code more readable and add
Linux kernel support.
(Logical change 1.296)
Include "libunwind_i.h" instead of "internal.h" and "tdep.h".
Define rbs_cover_and_flush() only for the !UNW_REMOTE_ONLY case.
(ia64_is_big_endian): New macro.
(ia64_get_abi): Likewise.
(ia64_set_abi): Likewise.
(ia64_get_abi_marker): Likewise.
(Logical change 1.294)
Use ia64_get_abi_marker() instead of directly referencing c->last_abi_marker.
(linux_scratch_loc): When accessing an fp-reg, default to IA64_FPREG_LOC.
Handle more registers for the Linux interrupt-frame case.
(tdep_access_reg): Use ia64_get_abi() instead of c->as->abi.
Use ia64_is_big_endian() instead of c->as->big_endian.
(Logical change 1.294)
2005/05/17 14:14:23-07:00 hp.com!davidm
(linux_sigtramp): Add "prev_cfm_loc" argument. Use it to set c->ec_loc.
(linux_interrupt): Likewise.
(hpux_sigtramp): Likewise.
(update_frame_state): Copy old cfm_loc to prev_cfm_loc and pass it to
ABI-specific handlers. Initialize c->ec_loc to c->cfm_loc by default.
(Logical change 1.293)
Abstract ia64-specific code into bsp_match() routine.
Support any platform with at least 2 EH argument registers.
2004/12/06 01:33:16-08:00 mostang.com!davidm
Rename: src/longjmp.c -> src/setjmp/longjmp.c
(Logical change 1.290)
2004/11/17 02:43:39-08:00 mostang.com!davidm
(struct callback_data): New structure.
(linear_search): New function.
(callback): Convert to getting auxiliary info passed via a pointer to
a callback_data structure, rather than an unw_dyn_info_t
structure.
Keep track of the maximum load address in max_load_addr.
If an object doesn't have a binary search-table, fall back
on a linear search.
(dwarf_find_proc_info): Fill in callback-data structure before calling
dl_iterate_phdr(). Upon returning, check whether
cb_data.single_fde is set and, if so, return directly, without
searching the DWARF unwind-table.
(dwarf_search_unwind_table): Adjust for renaming of
dwarf_parse_fde() to dwarf_extract_proc_info_from_fde().
If IP doesn't fall into the IP-range of the FDE-entry found
by the search, return UNW_ENOINFO.
(Logical change 1.290)
2004/12/15 15:40:09-08:00 hp.com!davidm
Include "tdep.h" on ia64 (we need the cursor).
(bsp_match): Fix it so it compiles again.
(resume_restore_sigmask): Likewise.
2004/12/06 10:40:49-08:00 mostang.com!davidm
(Logical change 1.290)
2004/11/23 16:59:56-08:00 mostang.com!davidm
(_UPT_access_reg): If the register is out of range, set errno
to EINVAL.
When encountering an error while accessing a register,
print the corresponding error string.
(Logical change 1.290)
a signal-trampoline, assume that it's a PLT stub.
If non-DWARF stepping fails to change IP and CFA, declare
it a bad frame.
2004/11/23 16:59:56-08:00 mostang.com!davidm
(unw_step): Also print IP as part of the function-trace.
2004/11/23 16:17:37-08:00 mostang.com!davidm
(unw_step): When dwarf_step() fails on a signal-frame, fill in all
the known locations because dwarf_step() fails on older
kernels which don't export the kernel vDSO even though every-
thing else may be providing proper DWARF unwind-info.
2004/10/25 17:43:57+02:00 homeip.net!davidm
Add Debug statement for return-value.
(Logical change 1.290)
