Building net-next with powerpc with GCC 14 compiler results in this build error: /home/sfr/next/tmp/ccuSzwiR.s: Assembler messages: /home/sfr/next/tmp/ccuSzwiR.s:2579: Error: operand out of domain (39 is not a multiple of 4) make[5]: *** [/home/sfr/next/next/scripts/Makefile.build:229: net/core/page_pool.o] Error 1 Root caused in this thread: https://lore.kernel.org/netdev/913e2fbd-d318-4c9b-aed2-4d333a1d5cf0@xxxxxxxxxxxxxxxxxx/ We try to access offset 40 in the pointer returned by this function: static inline unsigned long _compound_head(const struct page *page) { unsigned long head = READ_ONCE(page->compound_head); if (unlikely(head & 1)) return head - 1; return (unsigned long)page_fixed_fake_head(page); } The GCC 14 (but not 11) compiler optimizes this by doing: ld page + 39 Rather than: ld (page - 1) + 40 Causing an unaligned read error. Fix this by bitwise operand instead of an arthimetic operation to clear the pointer, which probably communicates the intention of the code a bit better anyway. Cc: Simon Horman <horms@xxxxxxxxxx> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Cc: Jakub Kicinski <kuba@xxxxxxxxxx> Cc: David Miller <davem@xxxxxxxxxxxxx> Cc: Paolo Abeni <pabeni@xxxxxxxxxx> Cc: Networking <netdev@xxxxxxxxxxxxxxx> Cc: Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx> Cc: Linux Next Mailing List <linux-next@xxxxxxxxxxxxxxx> Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: "linuxppc-dev@xxxxxxxxxxxxxxxx" <linuxppc-dev@xxxxxxxxxxxxxxxx> Suggested-by: LEROY Christophe <christophe.leroy2@xxxxxxxxxxxxxxxxxx> Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx> --- include/linux/page-flags.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h index 5769fe6e4950..ea4005d2d1a9 100644 --- a/include/linux/page-flags.h +++ b/include/linux/page-flags.h @@ -239,8 +239,8 @@ static inline unsigned long _compound_head(const struct page *page) { unsigned long head = READ_ONCE(page->compound_head); - if (unlikely(head & 1)) - return head - 1; + if (unlikely(head & 1UL)) + return head & ~1UL; return (unsigned long)page_fixed_fake_head(page); } -- 2.46.0.662.g92d0881bb0-goog
