On 16.12.22 10:47, Richard Biener wrote:
No, if you select -fprofile-update=atomic, then the updates shall be
atomic from my point of view. If a fallback is acceptable, then you can
use -fprofile-update=prefer-atomic. Using the fallback in
-fprofile-update=atomic is a bug which prevents the use of gcov for
multi-threaded applications on the lower end targets which do not have
atomic operations in hardware.
Ah, OK. So the fallback there is libatomic calls as well then? Note
not all targets support libatomic, for those the failure mode is likely
a link error (which might be fine, but we eventually might want to
amend documentation to indicate this failure mode).
It seems these library calls caused issues in the past:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77466
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77378
One option could be to emit calls to a new libgcov function:
__gcov_inc_counter(counter) -> updated value
This function could use a __gthread_mutex_t mutex for updates. This ends
up probably with quite a bad performance.
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