Segher Boessenkool <seg...@kernel.crashing.org> writes: > Hi! > > On Mon, Sep 16, 2024 at 10:05:10PM +1000, Michael Ellerman wrote: >> The 'ld' and 'std' instructions require a 4-byte aligned displacement >> because they are DS-form instructions. But the "m" asm constraint >> doesn't enforce that. >> >> That can lead to build errors if the compiler chooses a non-aligned >> displacement, as seen with GCC 14: >> >> /tmp/ccuSzwiR.s: Assembler messages: >> /tmp/ccuSzwiR.s:2579: Error: operand out of domain (39 is not a multiple >> of 4) >> make[5]: *** [scripts/Makefile.build:229: net/core/page_pool.o] Error 1 >> >> Dumping the generated assembler shows: >> >> ld 8,39(8) # MEM[(const struct atomic64_t *)_29].counter, t >> >> Use the YZ constraints to tell the compiler either to generate a DS-form >> displacement, or use an X-form instruction, either of which prevents the >> build error. > > Great explanation text, a perfect commit! :-)
Thanks - I'm sure there's something that could be better, but I do try :) cheers
