Le 29/08/2022 à 07:52, Sathvika Vasireddy a écrit :

objtool is throwing *unannotated intra-function call* warnings in
.c files with a few instructions that are marked unreachable. The
problem comes from the annotate_unreachable() macro that is
called by unreachable(). This annotation is adding a call to a
function with size 0, and objtool does not add such symbols
to the rbtree. Due to this reason, find_call_destination() function
is not able to find the destination symbol for that call.

With the annotation (annotate_unreachable()), gcc seems to
generate a 'bl' to unreachable symbol with size 0. But with
the builtin variant of unreachable (__builtin_unreachable()),
gcc does not emit calls to such symbols and the warnings
go away. Given that the codegen remains same, and that
there are no 'bl' instructions to such symbols emitted, fix
these warnings by replacing unreachable() with it's builtin
variant in __WARN_FLAGS().

How can you say that the codegen remains the same if with the original 
you get stale 'bl' instructions and with the alternative you don't ?

Also, add barrier_before_unreachable() before __builtin_unreachable()
to work around a gcc bug [1], for the problem reported at [2].

Here my comment was not related to the gcc bug [1] but to gcc bug 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365 , which was worked 
around by commit 173a3efd3edb ("bug.h: work around GCC PR82365 in BUG()")

By chance it also solve the problem [1] as you mention.

[1]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106751
[2]: https://lkml.org/lkml/2022/8/25/418

Signed-off-by: Sathvika Vasireddy <redacted>

Reviewed-by: Christophe Leroy <redacted>