warning: null format string in stop.c

[astamm]

gcc-ubsan and gcc-asan show

warning: null format string

occurring in stop.c specifically in function nlopt_vsprintf().

According to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116834, the fix is to first check that the pointer to format is not null and abort if it is before calling vsnprintf().

[stevengj]

Where is it being called with a NULL format string? I'm more worried about the call site.

[astamm]

It actually happens at build time of nlopt with gcc-asan, prior to using its functions in nloptr. Three other warnings seem to be raised as well: see full details in 00install.out.txt.

[aitap]

When sanitizers are enabled with GCC, many "middle-end" warnings are unreliable and known to produce false positives (e.g. 1 2).