Recover from slightly out-of-bounds wrt. %rsp memory accesses.
When we're unwinding the first frame of a chain, and we start from, eg.
a `pop %rbx` at the end of the function, the DWARF can be out of sync
and still state that eg. `%rbx` is saved at something that simplifies to
`%rsp-8`. Which might not be accessibe through the `access_mem`
abstraction, eg. if we're running perf and it didn't capture the stack
below `%rsp`
A recent commit added code to override the unwind location for the
TOC pointer register r2:
unsigned int *inst = (unw_word_t*)c->dwarf.ip;
if (*inst == (0xE8410000 + 24)) {
// @plt call, restoring R2 from CFA+24
c->dwarf.loc[UNW_PPC64_R2] = DWARF_LOC(c->dwarf.cfa + 24, 0);
}
It is correct that such code is needed, since DWARF CFI does not
describe the unwind location for r2 on PowerPC. However, this
particular bit of code has a number of issues, which are fixed
in this patch.
First of all, the location CFA+24 is correct only for the ELFv2
ABI. In the ELFv1 ABI, the TOC location is actually CFA+40.
More problematically, attempting to read the current instruction
by just dereferencing the address in c->dwarf.ip is wrong, and
may often lead to crashes. In particular:
- During remote unwinding, this is always wrong since we're in
the wrong address space. I've used the fetch32 helper from
remote.h to use the proper access_mem under the covers.
- c->dwarf.ip may be NULL if we've reached the end-of-stack.
I've fixed this by moving the c->dwarf.ip == 0 check down
to after unwinding (instead of before), just like all other
platforms do.
- Even so, c->dwarf.ip may point to some random location if
we've gotten confused during unwinding earlier. One likely
cause for such confusion is that we did not find DWARF CFI
for some earlier frame and attempted to use the stack
backchain. The problem is that this code currently claims
all registers remain unchanges in such a frame, which is
generally wrong. In particular if the function actually
saves and modifies r31, and this is used as frame pointer
by a later frame, things will likely go quite wrong. While
it is not really possibly to completely fix this, I've at
least marked all registers as unavailable after unwinding
a frame via stack backchain.
Tested on powerpc64-linux and powerpc64le-linux. The patch fixes
about a dozen test cases that were crashing before.
Signed-off-by: Ulrich Weigand <ulrich.weigand@de.ibm.com>
By default, the start_ip_offset in libunwind's table_entry struct is
relative to the unw_dyn_info_t's segbase. This presents a problem
for us in conjunction with using LLVM's MCJIT because it likes to
spread text sections and the corresponding eh_frame sections quite
far apart. This represents my attempt to support this use case in the
simplest manner that is backwards compatible, by adding a new format
kind (UNW_INFO_FORMAT_REMOTE_TABLE2) that indicates that the
`start_ip_offset` should be interpreted as relative to `start_ip`
rather than segbase.
Detect if current frame is a signal frame by checking for preceeding
syscall instruction. For signal frames, update the cursor correctly
from user context before calling dwarf_step.
This is similar to commit c90a2e02b3
"Mark run-ptrace-mapper and run-ptrace-misc as XFAIL on MIPS".
Starting with 2.6.39, ARM Linux returns -EIO for PTRACE_SINGLESTEP, so
we need to mark this as XFAIL for ARM too.
The Linux commit that changed this is
commit 425fc47adb5bb69f76285be77a09a3341a30799e
Author: Will Deacon <will.deacon@arm.com>
Date: Mon Feb 14 14:31:09 2011 +0100
ARM: 6668/1: ptrace: remove single-step emulation code
see: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=425fc47adb5bb69f76285be77a09a3341a30799e
Signed-off-by: Gregory Fong <gregory.0xf0@gmail.com>
Due to a bug in the gold linker[1], the .eh_frame and .eh_frame_hdr
sections contains garbage. When dwarf_extract_proc_info_from_fde tried
to look up the begin of the CIE subsection, it would underflow the
.eh_frame segment, resulting in a crash[2].
This patch avoids that crash by checking whether the CIE pointer is
located after the begin of the .eh_frame section. The variable "base"
was misused in various places as a boolean (decode as .debug_frame or
decode as .eh_frame). These instances have been renamed to
is_debug_frame where applicable.
Tested on Linux x86_64.
[1]: https://sourceware.org/bugzilla/show_bug.cgi?id=17639
[2]: http://lists.nongnu.org/archive/html/libunwind-devel/2014-11/msg00009.html
Signed-off-by: Peter Wu <peter@lekensteyn.nl>
- Add autogen.sh to bootstrap autotools generation
- Make generation of man pages optional, and check for
availibity of latex2man if documentation is requested.
Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Signed-off-by: Arun Sharma <asharma@fb.com>
