libunwind uses mincore() to validate that memory is mapped and available to the process.
For this purpose, checking the return value of mincore() is sufficient.
The result array tells us if the kernel has swapped out the page or not.
We don't care about this, and the check leads to failure in those
cases where the kernel has swapped out the page.
ASAN will complain about this write call with the following error:
ERROR: AddressSanitizer: stack-buffer-underflow on address
HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext
This is similar to what google's abseil does to work around the issue.
Reported-by: qiwang@fb.com
This adds a port to Linux on the IBM Z platform (a.k.a s390x). It only
supports the 64-bit ABI. Most functionality is working and all the tests
pass with the exception of the coredump tests*.
Unwinding is only supported if DWARF unwind information is present.
libunwind can't currently make use of the backchain (if present).
The getcontext/setcontext functions only preserve/restore a subset of
registers. Currently this only consists of callee-saved registers and
some parameter registers.
Vector registers and access registers are not saved (and aren't callee-
saved) by getcontext and cannot currently be modified. They will however
be restored unmodified after resuming a context from a signal handler.
There is no special libunwind support for setjmp, the functionality is
emulated using glibc (I think all the ports do this for modern Linux
kernels).
* Unwinding on s390x requires floating point register access which the
coredump library doesn't currently support.
DW_CFA_remember_state used memcpy to overwrite state with the value
of rs_current. Unfortunately rs_current was slightly larger than state,
possibly resulting in rs_stack->next being overwritten.
Fix this by making the type of state match the type of rs_current and
using an assigment to perform the copy rather than memcpy. This should
ensure that the types match in future.
If loading debug link is not successful, the initial NULL pointer for
ei->image will eventually be restored, causing segfault during a later
call to valid_object.
Move populating the prev_image and prev_size to after elf_map_image() to
fix this.
Signed-off-by: Hans-Christian Noren Egtvedt <hegtvedt@cisco.com>
During unwinding/resuming execution of a normal call frame,
it is not only necessary to use the previous instruction to lookup the unwind info
but also when executing the cfi program. Although the call usually don't modify
any unwinding state, it can happen for noreturn call or when the callee cleanup the stack.
In these cases, the next instruction after the call may have a cfi adjusting the state
(e.g. stack pointer) and such instruction should be executed.
3d9a694de8 worked around this issue by treating `cfi_restore_state`
specially. It works when the compiler use that instruction to restore the state, i.e.
```
.cfi_remember_state
je .L0
push ...
.cfi_def_cfi_offset <new_value>
call noreturn
.L0
.cfi_restore_state
```
which is what GCC ususally does. However, it is not necessarily the case and clang/LLVM doesn't
do that. Instead LLVM emits the following unwind info which is also perfectly valid but is not
handled by the special case.
```
je .L0
push ...
.cfi_def_cfi_offset <new_value>
call noreturn
.L0
.cfi_def_cfi_offset <old_value>
```
e9e8ed73e3 also worked around this issue for another special case.
This patch fix this issue for all cfi types by adjusting the `end_ip` based on the type of the
current frame instead, similar to what's done in `fetch_proc_info`.
Since this requires using the same `use_prev_instr` value after `fetch_proc_info` returns,
the patch also remove the `need_unwind_info` parameter to the function and move the code updating
`use_prev_instr` after all use of the old value are done.
(At least on x86(_32),) `unw_resume` will call `setcontext` which will modify the signal masks
based on the value in the context. Since the signal mask is not being initialized by
`unw_getcontext`, this cause the signal mask to be set to a random (uninitialized) value after
`unw_resume` which cause the test to fail since it relies on the signal mask for SIGUSR2 being
cleared.
The proper fix is likely to either make `unw_resume` not touch the signal mask if the context
wasn't initialized with a signal ucontext, or to make `unw_getcontext` record the signal mask too.
It's unclear to me which approach should be taken...
In the mean time, the intermittent failure can be fixed simply by zero initialing the context first
which would clear all the signal masks.
When siginfo is available, a more reliable way is to use the `ucontext` passed in
to the signal handler directly and rely on `sigreturn` to reset it.
Unfortunately, this is currently not implemented on all archs either.
* Add `SA_SIGINFO` flag
This is needed to guarantee the availability of the `ucontext` argument
* Mark the `NULL` pointer load as `volatile`
Further prevent any compiler optimization on the load.
We should update locations of the registers after all of them will
be restored. Otherwise some locations will be incorrect.
For example if function stores ebp, edi, esi and ebx registers on
stack in its prologue, compiler can generate following unwind info:
DW_CFA_expression: r5 (ebp) (DW_OP_breg5 (ebp): 0)
DW_CFA_expression: r7 (edi) (DW_OP_breg5 (ebp): -4)
DW_CFA_expression: r6 (esi) (DW_OP_breg5 (ebp): -8)
DW_CFA_expression: r3 (ebx) (DW_OP_breg5 (ebp): -12)
In this case locations of the ebx and ebp will be calculated using
current ebp but locations of the esi and edi will be calculated using
previous (restored) one. Due to it their locations will be incorrect
and it could lead to crash if we will try to get esi or edi value.
This patch fixes this problem.
glibc no longer defines sigreturn, but we want to use it
when unwinding through signal stacks to resture the signal mask,
without forcing all uses of getcontext/setcontext to save and
restore the signal mask
Repro for a multilib binary on host x86_64:
CFLAGS="-m32" LDFLAGS="-m32" ./configure --enable-debug -- host=i686-pc-linux-gnu --target=i686-pc-linux-gnu --libdur=/usr/lib32 --prefix=/usr --disable-documentation
make check
Gtest-init function fails trying to step through libc_start_main. The CFA function is:
DW_CFA_def_cfa_offset: 112
DW_CFA_advance_loc: 5 to ...643
DW_CFA_restore state
Where the return address is 643.
Generally, it appears we apply all ip <= end_ip, which is incorrect in some circumstances.
libgcc only applies ip < end_ip + is_signal_frame, but that seems to break async signal handling
tests in libunwind for unknown reasons.
This is somewhat simlar to the fix in e9e8ed73e for GNU_args_size,
where the same ip check was added.
The calls to mincore() or msync() are not checking for actual accessibility
this could lead to SIGSEGV if the address from a mapped page with the
PROT_NONE property occurs on the stack.
Hence an attempt to write one byte from the checked address to a pipe will
fail if the address is not readable.
I tried to build libunwind for arm target and got a build error. Type
for "uc" argument is inconsistent between unw_init_local2 and
unw_init_local_common.
From 54fb6483e47916836c314a38715e8e0ce8c3da44 Mon Sep 17 00:00:00 2001
From: Guillaume Blanc <guillaume.blanc@parrot.com>
Date: Tue, 22 Aug 2017 16:46:20 +0200
Subject: [PATCH] arm: Fix unw_init_local2 argument type
Attached is a corrected version of my previous patch for aarch64 PLT
entry recognition. The comparison in the is_plt_entry function should
have been:
ret = (((w0 & 0xff0000009f000000) == 0xf900000090000000)
&& ((w1 & 0xffffffffff000000) == 0xd61f022091000000));
We were testing libunwind-coredump and got some warnings about
uninitialized eh_valid_mask.
The code was working fine because the default value of the mask was 0, but
it could potentially take a wrong branch if there's garbage in memory.
If I configure with ./configure --prefix= --enable-shared --disable-static, a
broken symlink lib/libunwind-generic.a is installed that points to a missing
architecture-specific version of that library (e.g. lib/libunwind-x86_64.a). I
suppose that not installing that library is the intended behavior with these
configuration settings, so the symlink should not be there in the first place.
Reported-by: MarcoKoch
Some binaries contain a gnu_debuglink, even though the actual
file it points to doesn't exist. In those cases, continue
to use the existing binary instead of trying to load the debuglink file.
The ARM Thumb implementation of unw_tdep_getcontext switches to ARM
mode (".code 32"), but doesn't switch back to Thumb mode.
In gcc, this is fine (it automatically switches back to Thumb mode
at the end of an asm block), but in clang, this causes bad assembly
output (thumb instructions generated by C/C++ code later on are
interpreted as ARM mode assembly, which can't work).
Switching back to Thumb mode manually fixes clang, and is a no-op for gcc.
If Thumb is used, the least bit of the retrived IP value is set,
which makes the retrived opcode based on the IP invalid.
This patch fixes such behavior and adds a missed condition
found with glibc built for recent ARMv7l with Thumb2.
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
CC: Yvan Roux
CC: Arun Sharma
CC: David Mosberger
Let's not drop error code or zero-return unconditionally.
This has been incurring occasional indefinite loop in
dotnet core when it already had hit the bottom by
continously returning 1 from unw_step();
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
