On Fri, Sep 13, 2024 at 2:33 PM Mina Almasry <almasrymina@xxxxxxxxxx> wrote: > > 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 > > And causing an unaligned load. Get around this by issuing a READ_ONCE as > we convert the page to netmem. That disables the compiler optimizing the > load in this way. > > 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> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > > Suggested-by: Jakub Kicinski <kuba@xxxxxxxxxx> > Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx> > Gah, right after I hit send I realized I missed the 24hr rule. Although I'm unsure about the urgency of build fixes. Sorry about that. -- Thanks, Mina
