Counting static __cxa_atexit calls

Florian Weimer fweimer@redhat.com
Tue Aug 23 11:58:30 GMT 2022


We currently have a latent bug in glibc where C++ constructor calls can
fail if they have static or thread storage duration and a non-trivial
destructor.  The reason is that __cxa_atexit (and
__cxa_thread_atexit_impl) may have to allocate memory.  We can avoid
that if we know how many such static calls exist in an object (for C++,
the compiler will never emit these calls repeatedly in a loop).  Then we
can allocate the resources beforehand, either during process and thread
start, or when dlopen is called and new objects are loaded.

What would be the most ELF-flavored way to implement this?  After the
final link, I expect that the count (or counts, we need a separate
counter for thread-local storage) would show up under a new dynamic tag
in the dynamic segment.  This is actually a very good fit because older
loaders will just ignore it.  But the question remains what GCC should
emit into assembler & object files, so that the link editor can compute
the total count from that.

Thanks,
Florian



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