Why Does My C Program With Static Linking and Pthreads Result in a Segmentation Fault?

When g Static Links Pthread, Causing Segmentation Fault: Explanation and Solution

Problem:

When compiling a C program with g and the -pthread flag for linking against the pthread library, but statically (-static), the program encounters a Segmentation Fault.

Explanation:

1. Weak Symbols:

   • pthread and libstdc use weak symbols for certain functions, such as pthread_mutex_lock().
   • Weak symbols can be replaced by strong symbols during linking.

2. Dynamic Linking vs. Static Linking:

   • In dynamic linking, weak symbols are resolved from shared libraries.
   • In static linking, the linker stops at the first symbol (including weak ones) and doesn't search for strong symbols.

3. Incomplete Link Resolution:

   • When using -static, the linker doesn't consider all symbols from the pthread library, as it encounters a weak symbol first.
   • Consequently, the strong symbol for pthread_mutex_lock() is not used.

Solution:

To force the linker to look at all symbols from the pthread library in a statically linked program, use:

g++ -o one one.cpp -Wall -std=c++11 -O3 -static -pthread \
    -Wl,--whole-archive -lpthread -Wl,--no-whole-archive

• -Wl,--whole-archive: Includes all object files in the specified archive.
• -lpthread: Links against the pthread library.
• -Wl,--no-whole-archive: Disables the whole-archive option for subsequent archives.

Additional Notes:

• Some systems may require additional flags, such as -lrt for librt.
• If using Autotools, define the flags in configure.ac and substitute them in Makefile.am. For example:

WL_WHOLE_ARCHIVE_HACK="-Wl,--whole-archive"
WL_NO_WHOLE_ARCHIVE_HACK="-Wl,--no-whole-archive"
AC_SUBST(WL_WHOLE_ARCHIVE_HACK)
AC_SUBST(WL_NO_WHOLE_ARCHIVE_HACK)

mytarget_LDADD = @WL_WHOLE_ARCHIVE_HACK@ -lpthread @WL_NO_WHOLE_ARCHIVE_HACK@

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