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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