Prior to version 4.8, GCC may miscompile READ_ONCE() by erroneously discarding the 'volatile' qualifier: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 We've been working around this using some nasty hacks which make READ_ONCE() both horribly complicated and also prevent us from enforcing that it is only used on scalar types. Since GCC 4.8 is pretty old for kernel builds now, emit a warning if we detect it during the build. Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx> Signed-off-by: Will Deacon <will@xxxxxxxxxx> --- include/linux/compiler-gcc.h | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index d7ee4c6bad48..62afe874073e 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -14,6 +14,10 @@ # error Sorry, your compiler is too old - please upgrade it. #endif +#if GCC_VERSION < 40800 +# warning Your compiler is old and may miscompile the kernel due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 - please upgrade it. +#endif + /* Optimization barrier */ /* The "volatile" is due to gcc bugs */ -- 2.25.0.rc1.283.g88dfdc4193-goog
