dwarf: If the dwarf_readu8 call to set op fails, and if there are register
states pushed onto the stack, the stack is not emptied before the function
returns. This change addresses that.
Most of the rest is eliminating ‘goto fail’ from the code.
0-valued hints are used when they are just initial values with no use as
hints. And I think there were some other problems as well.
This patch cleans up and stores hint values with 1 added, so that 0-valued
hints can be ignored.
unw_get_proc_info must always load the unwind info so that unw_resume
works with GNU_args_size expressions, but must not update
use_prev_expr unless we are unw_step()ing.
blame rev: 4b63a536ee
reported-by: Doug Moore <dougm@rice.edu>
libunwind already had support for local unwind on a MIPS. This patch makes
support for remote unwinding on a MIPS.
I should add a few words to the changes to _UPT_access_mem.c: On MIPS, an
unw_word_t is defined as a 64-bit integer whether it's compiled for a 32- or a
64-bit MIPS.
When doing remote unwinding using the default _UPT_accessors, dwarf_readu8()
therefore expects _UPT_access_mem() to return a 64-bit integer. However, if
compiled on a 32-bit MIPS, only 32 bits are valid upon return from
_UPT_access_mem(). The patch detects this and will in this case perform two
calls to ptrace(PTRACE_POKE/PEEK_DATA) and organize the return value according
to endianness.
Centralize gnu_debuglink logic in elfxx. Remove previous duplicated logic
from Gfind_proc_info and os-linux.
Logic is roughly the same as previous load_debug_frame, but uses VLAs
instead of malloc.
This fixes GCC 4.9.3 warnings (Linux/mipsel):
In file included from dwarf/Lfind_unwind_table.c:4:0:
dwarf/Gfind_unwind_table.c: In function '_ULmips_dwarf_find_unwind_table':
dwarf/Gfind_unwind_table.c:140:14: warning: cast from pointer to integer of
different size [-Wpointer-to-int-cast]
addr = (unw_word_t) (hdr + 1);
^
dwarf/Gfind_unwind_table.c:196:50: warning: cast from pointer to integer of
different size [-Wpointer-to-int-cast]
+ (addr - (unw_word_t) edi->ei.image
^
dwarf/Gfind_unwind_table.c:202:40: warning: cast from pointer to integer of
different size [-Wpointer-to-int-cast]
+ ((unw_word_t) hdr - (unw_word_t)
edi->ei.image
^
dwarf/Gfind_unwind_table.c:202:59: warning: cast from pointer to integer of
different size [-Wpointer-to-int-cast]
+ ((unw_word_t) hdr - (unw_word_t)
edi->ei.image
^
```
src/dwarf/Gfind_proc_info-lsb.c:536:16: warning: 'eh_frame' may be used uninitialized in this function [-Wmaybe-uninitialized]
Elf_W (Addr) eh_frame;
^
```
Introduced-in: 25413c729a
It is possible to have multiple CFA_args_size adjustments for a single
frame. If the CFA_args_size adjustment is immediately following the
return from a function which can raise an exception, it is possible to
incorrectly adjust the stack pointer. Consider the following:
...
.cfi_escape 0x2e, 0x00
call f
.Ltmp:
.cfi_escape 0x2e, 0x10
lea label@GOTOFF(%ebx), %eax
...
Because we process the CFI program up to and *INCLUDING* IP, where the
IP is the RA, we would process the associated DW_CFA_GNU_args_size for
the post-call instruction. The result would be a DW_CFA_GNU_args_size
of 0x10 rather than 0x00, resulting in an incorrect stack adjustment.
Handle this by processing the CFI operation but not adjusting the state
record unless we are below the current IP.
Commit 92327a3 "ARM: prefer to unwind using DWARF info"
changes order of unwind info searching to prefer DWARF (.debug_frame)
section in prior to ARM specific (.ARM.exidx). This patch only affects
local process unwinding. Now the same is done for remote unwinding.
Sometimes probing .ARM.exidx first causes backtrace truncation
after __aeabi_ldiv0 (division by 0 handler that generates SIGFPE),
because it hits [cantunwind] generated by cross-gcc for __divsi3
function copied with __aeabi_ldiv0 from libgcc.a. Perhaps, lack of
debug info for __divsi3 causes [cantunwind], or there is a problem
converting DWARF to ARM unwind tables, but when unwinding using
DWARF, it hits proper entry, and backtrace is shown correctly.
Reported-by: Frederic Berat <fberat@de.adit-jv.com>
Signed-off-by: Vitaly Kuzmichev <Vitaly_Kuzmichev@mentor.com>
When adjusting the stack for a DW_CFA_arg_size adjustment, ensure that
we use the target dependent register name as the generic name does not
necessarily map to the same register. For example, on x86, ESP maps to
the eip register, which results in the wrong stack adjustment being
applied.
Debian likes to hive off symbol information to separate -dbg packages,
installing the debug information in a parallel tree rooted at /usr/lib/debug.
libunwind doesn't know how to find these files but it's easy, per the tested,
attached patch, to make it so. I don't see /usr/lib/debug at
http://www.pathname.com/fhs/pub/fhs-2.3.html#USRLIBLIBRARIESFORPROGRAMMINGANDPA
but
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/4/html/Debugging_with_gdb/separate-debug-files.html
says it's not just Debian and hints it might be driven by gdb. I do see mention
of /usr/lib/debug in libunwind already, but only in a DWARF-specific part of
the code. A minor concern might be checking errno to see if the problem is
ENOENT before trying the alternate path. That might be better than flogging a
mmap problem or being out of file handles or whatever.
Add interface for configurable dwarf cache size
* Use item size and round up to nearest power of 2.
* Initial cache still exists in BSS. Without this, it means we would fail
backtrace when out of memory. The test-mem test fails without this
Currently setcontext for x86_64 restores the signal mask, even
though it is never saved anywhere. This means the signal mask
is often garbage after an unw_resume.
(changed in commit f8a15e9679)
It looks like this was a fix for the Gtest-resume-sig function -
testing if signal masks are restored across signal frames. The
root issue looks like that x86_64 only uses sigreturn for the exact
signal frame, and not for any decedant frames as well (as i64 does).
Instead, modify Gresume to use sigreturn if *any* frame on the stack
is a signal frame, so that we correct fixup the signal mask and any
sigaltstacks. The sigreturn os-specific functions are changed slightly
to copy in the saved ucontext structure if we are jumping farther
up the stack.
This should fix sigprocmask reported issues such as
https://github.com/dropbox/pyston/blob/master/libunwind_patches/0002-pyston-stop-x86_64-setcontext-restoring-uninitialize.patch
Tests pass on freebsd, linux
When resuming execution, DW_CFA_GNU_args_size from the current frame
must be added back to the stack pointer. Clang now generates these frequently
at -O3. A simple repro for x86_64, that will crash with clang ~3.9 or newer:
void f(int, int,int,int,int,int,int,int,int);
int main() {
try {
f(0,1,2,3,4,5,6,7,8);
} catch (int) {
return 0;
}
return 1;
}
Where f is something that throws an int, but in a different translation unit to
prevent optimization.
This results in cfi instructions before the call:
.cfi_escape 0x2e, 0x20
Grabbing the args_size means fully parsing the cfi in the current frame, which
is unfortunate because it means nearly twice the work at each step. The logic
to grab args_size can be in unw_step or get_proc_info (since this is always
called before resuming in stack unwinding). Putting it in get_proc_info allows
the more common unw_step code to remain fast.
It would potentially fit in nicely with a proc info cache (as mentioned in the
if0 comment block)
GCC versions 4.9~current will often generate stack alignment prologues like:
lea 0x8(%rsp),%r10
and $0xfffffffffffffff0,%rsp
...
push %rbp
mov %rsp, %rbp
push %r10
resulting in dwarf expressions:
DW_CFA_def_cfa_expression (DW_OP_breg6: -8; DW_OP_deref)
DW_CFA_expression: r6 (rbp) (DW_OP_breg6: 0)
These prologues seem to be generated for SSE/AVX code, but sometimes
other times as well.
tdep_trace fastpath currently falls back to the slow dwarf parsing path
if it encounters any cfa_expressions. Unfortunately this is happening
often enough in our codebase to cause perf issues. We could also fix the
fallback path (make the rs cache bigger, lock-free instead of locking, etc),
but that seems like a separate issue, and it will ever be as fast as the tracing
code. Our binaries each have at least ~100 functions in them like this.
This patch teaches the tdep_trace about the two specific cfa_expressions,
which really just result in a single extra memory dereference of the stack
at a fixed offset from rbp.
next = inote.descdata + align_power (inote.descsz, 2);
this align is missing, leading to parsing errors. In one case
libunwind only found 1 thread out of 4.
Improves support for binaries missing the GNU_EH_FRAME segment
(.eh_frame_hdr section) by adding a function
'dwarf_find_eh_frame_section' that can create a synthetic one.
unw_is_signal_frame() returns <= 0 if not a signal frame. Several places in
code were only checking for a "if (unw_is_signal_frame())", or
"if (!unw_is_signal_frame())".
This fixes GCC 4.9.3 warnings (Linux/mipsel):
dwarf/Gfind_proc_info-lsb.c: In function 'locate_debug_info':
dwarf/Gfind_proc_info-lsb.c:244:23: warning: 'mi.buf_end' may be used
uninitialized in this function [-Wmaybe-uninitialized]
struct map_iterator mi;
^
dwarf/Gfind_proc_info-lsb.c:244:23: warning: 'mi.buf' may be used
uninitialized in this function [-Wmaybe-uninitialized]
In file included from dwarf/Gfind_proc_info-lsb.c:46:0:
./os-linux.h:292:27: warning: 'mi.buf_size' may be used uninitialized in
this function [-Wmaybe-uninitialized]
munmap (mi->buf_end - mi->buf_size, mi->buf_size);
^
dwarf/Gfind_proc_info-lsb.c:244:23: note: 'mi.buf_size' was declared here
struct map_iterator mi;
^
The detection logic introduced in 28f33c8ce0 is
broken, because it tests mincore using an address that is almost certainly not
page-aligned. straces confirms that msync is used all the time.
This patch fixes the logic by page-aligning the test pointer. strace now shows
that mincore is actually used. Furthermore, the return value of mincore is not
sufficient to assess whether the address can be safely dereferenced: we should
also check that the pages are mapped, through the passed mvec array. This patch
also adds this verification.
Tested on a system where unwinding a stack across a JNI boundary would cause
sporadic segfaults; no more crashes were observed after the patch.
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.
