tree d093c1599382cd3cfdb3e9bbca78f339fd6310a5
parent f7a9d4a454681d46e668916a38583ade127e40d4
author Willy Tarreau <w@1wt.eu> 1588687080 +0200
committer Christopher Faulet <cfaulet@haproxy.com> 1590387742 +0200

BUG/MINOR: threads: fix multiple use of argument inside HA_ATOMIC_CAS()

When threads are disabled, HA_ATOMIC_CAS() becomes a simple compound
expression. However this expression presents a problem, which is that
its arguments are evaluated multiple times, once for the comparison
and once again for the assignement. This presents a risk of performing
some side-effect operations twice in the non-threaded case (e.g. in
case of auto-increment or function return).

The macro was rewritten using local copies for arguments like the
other macros do.

Fortunately a complete inspection of the code indicates that this case
currently never happens. It was however responsible for the strict-aliasing
warning emitted when building fd.c without threads but with 64-bit CAS.

This may be backported as far as 1.8 though it will not fix any existing
bug and is more of a long-term safety measure in case a future fix would
depend on this behavior.

(cherry picked from commit d66345d6b0639dfc42986a4326e6f6f6d18e053e)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 3b9cef806ed16d3d90243138d0db29509f9cf404)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>