1.6.2 Writing reliable code

When compiling and testing Gnulib and Gnulib-using programs, certain compiler options can help improve reliability. First of all, make it a habit to use ‘-Wall’ in all compilation commands. Beyond that, the manywarnings module enables several forms of static checking in GCC and related compilers (see manywarnings).

For dynamic checking, you can run configure with CFLAGS options appropriate for your compiler. For example:

./configure \
 CPPFLAGS='-Wall'\
 CFLAGS='-g3 -O2'\
' -D_FORTIFY_SOURCE=2'\
' -fsanitize=undefined'\
' -fsanitize-undefined-trap-on-error'

Here:

• -D_FORTIFY_SOURCE=2 enables extra security hardening checks in the GNU C library.
• -fsanitize=undefined enables GCC’s undefined behavior sanitizer (ubsan), and
• -fsanitize-undefined-trap-on-error causes ubsan to abort the program (through an “illegal instruction” signal). This measure stops exploit attempts and also allows you to debug the issue.

Without the -fsanitize-undefined-trap-on-error option, -fsanitize=undefined causes messages to be printed, and execution continues after an undefined behavior situation. The message printing causes GCC-like compilers to arrange for the program to dynamically link to libraries it might not otherwise need. With GCC, instead of -fsanitize-undefined-trap-on-error you can use the -static-libubsan option to arrange for two of the extra libraries (libstdc++ and libubsan) to be linked statically rather than dynamically, though this typically bloats the executable and the remaining extra libraries are still linked dynamically.

It is also good to occasionally run the programs under valgrind (see Running self-tests under valgrind).