libunwind

libunwind is a portable and efficient C API for determining the current call chain of ELF program threads of execution and for resuming execution at any point in that call chain. The API supports both local (same process) and remote (other process) operation.

The API ise useful in a number of applications, including but not limited to the following.

• program introspection Either for error messages showing a back trace of the call chain leading to a problem or for performance monitoring and analysis.
• debugging Whether the debugging and analysis of the call chain of a remote program or the post-mortem analysis of a coredump.
• language runtime exception handling libunwind optionally provides an alternative implementation of the Itanium exception handling ABI used by many popular toolchains.
• alternative setjmp()/longjmp() libunwind optionally provides an alternative implementation of the setjmp()/longjmp() functionality of the C standard library.

Supported Systems

This library supports several architecture/operating-system combinations:

Libc Requirements

libunwind depends on getcontext(), setcontext() functions which are missing from C libraries like musl-libc because they are considered to be "obsolescent" API by POSIX document. The following table tries to track current status of such dependencies

• r, requires
• p, provides its own implementation
• empty, no requirement

General Build Instructions

In general, this library can be built and installed with the following commands:

$ autoreconf -i # Needed only for building from git. Depends on libtool.
$ ./configure --prefix=PREFIX
$ make
$ make install

where PREFIX is the installation prefix. By default, a prefix of /usr/local is used, such that libunwind.a is installed in /usr/local/lib and unwind.h is installed in /usr/local/include. For testing, you may want to use a prefix of /usr/local instead.

Building with Intel compiler

Version 8 and later

Starting with version 8, the preferred name for the IA-64 Intel compiler is icc (same name as on x86). Thus, the configure-line should look like this:

$ ./configure CC=icc CFLAGS="-g -O3 -ip" CXX=icc CCAS=gcc CCASFLAGS=-g \
    LDFLAGS="-L$PWD/src/.libs"

Building on HP-UX

For the time being, libunwind must be built with GCC on HP-UX.

libunwind should be configured and installed on HP-UX like this:

$ ./configure CFLAGS="-g -O2 -mlp64" CXXFLAGS="-g -O2 -mlp64"

Caveat: Unwinding of 32-bit (ILP32) binaries is not supported at the moment.

Building for PowerPC64 / Linux

For building for power64 you should use:

$ ./configure CFLAGS="-g -O2 -m64" CXXFLAGS="-g -O2 -m64"

If your power support altivec registers:

$ ./configure CFLAGS="-g -O2 -m64 -maltivec" CXXFLAGS="-g -O2 -m64 -maltivec"

To check if your processor has support for vector registers (altivec):

cat /proc/cpuinfo | grep altivec

and should have something like this:

cpu             : PPC970, altivec supported

If libunwind seems to not work (backtracing failing), try to compile it with -O0, without optimizations. There are some compiler problems depending on the version of your gcc.

Building on FreeBSD

General building instructions apply. To build and execute several tests on older versions of FreeBSD, you need libexecinfo library available in ports as devel/libexecinfo. This port has been removed as of 2017 and is indeed no longer needed.

Regression Testing

After building the library, you can run a set of regression tests with:

$ make check

Expected results on x86 Linux

The following tests are expected to fail on x86 Linux:

• test-ptrace

Expected results on x86-64 Linux

The following tests are expected to fail on x86-64 Linux:

• run-ptrace-misc (see http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18748 and http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18749)

Expected results on PARISC Linux

The following tests are expected to fail on x86-64 Linux:

• Gtest-bt (backtrace truncated at kill() due to lack of unwind-info)
• Ltest-bt (likewise)
• Gtest-resume-sig (Gresume.c:my_rt_sigreturn() is wrong somehow)
• Ltest-resume-sig (likewise)
• Gtest-init (likewise)
• Ltest-init (likewise)
• Gtest-dyn1 (no dynamic unwind info support yet)
• Ltest-dyn1 (no dynamic unwind info support yet)
• test-setjmp (longjmp() not implemented yet)
• run-check-namespace (toolchain doesn't support HIDDEN yet)

Expected results on HP-UX

make check is currently unsupported for HP-UX. You can try to run it, but most tests will fail (and some may fail to terminate). The only test programs that are known to work at this time are:

• tests/bt
• tests/Gperf-simple
• tests/test-proc-info
• tests/test-static-link
• tests/Gtest-init
• tests/Ltest-init
• tests/Gtest-resume-sig
• tests/Ltest-resume-sig

Expected results on PPC64 Linux

make check should run with no more than 10 out of 24 tests failed.

Expected results on Solaris x86-64

make check is passing 27 out of 33 tests. The following six tests are consistently failing:

• Gtest-concurrent
• Ltest-concurrent
• Ltest-init-local-signal
• Lrs-race
• test-setjmp
• x64-unwind-badjmp-signal-frame

Performance Testing

This distribution includes a few simple performance tests which give some idea of the basic cost of various libunwind operations. After building the library, you can run these tests with the following commands:

$ cd tests
$ make perf

Contacting the Developers

Please raise issues and pull requests through the GitHub repository: https://github.com/libunwind/libunwind.