From: Simon Marchi Date: Wed, 17 Aug 2022 15:24:25 +0000 (-0400) Subject: Fix: change method used by _rcu_dereference to strip type constness X-Git-Tag: v0.14.0~18 X-Git-Url: http://git.lttng.org/?a=commitdiff_plain;h=2d466a6397dbc7af397d0fc10e327cc6cac76a5a;hp=2d466a6397dbc7af397d0fc10e327cc6cac76a5a;p=userspace-rcu.git Fix: change method used by _rcu_dereference to strip type constness Commit 1e41ec3b07e4 ("Make temporary variable in _rcu_dereference non-const") used the trick to add 0 to the pointer passed as a parameter to the macro to get rid of its constness, should it be const (with the end goal of avoiding compiler warnings). This is problematic (as shown in [1]) if it is a pointer to an opaque type though, as the compiler cannot perform pointer arithmetic on such a pointer (even though it wouldn't really need to here, as we add 0). Change it to use another trick to strip away the constness, that shouldn't hit this problem. It was found in the same stackoverflow post as the original trick [2]. It consists of using a statement expression like so: __typeof__(({ const int foo; foo; })) The statement expression yields a value of type `int`. Statement expressions are extensions to the C language, but we already use them here. The test_build* binaries now need to be linked against the urcu library, otherwise they would be missing the rcu_dereference_sym symbol. [1] https://lists.lttng.org/pipermail/lttng-dev/2022-August/030247.html [2] https://stackoverflow.com/a/54016713 Change-Id: Ic73590ef4beaa1832161aa05a6df37e467f85116 Signed-off-by: Simon Marchi Signed-off-by: Mathieu Desnoyers ---