Le 08/07/2020 à 16:45, Mathieu Desnoyers a écrit :
Hi,
Reviewing use of the patterns "Un%Xn" with lwz and stw instructions
(where n should be the operand number) within the Linux kernel led
me to spot those 2 weird cases:
arch/powerpc/include/asm/nohash/pgtable.h:__set_pte_at()
__asm__ __volatile__("\
stw%U0%X0 %2,%0\n\
eieio\n\
stw%U0%X0 %L2,%1"
: "=m" (*ptep), "=m" (*((unsigned char *)ptep+4))
: "r" (pte) : "memory");
I would have expected the stw to be:
stw%U1%X1 %L2,%1"
and:
arch/powerpc/include/asm/book3s/32/pgtable.h:__set_pte_at()
__asm__ __volatile__("\
stw%U0%X0 %2,%0\n\
eieio\n\
stw%U0%X0 %L2,%1"
: "=m" (*ptep), "=m" (*((unsigned char *)ptep+4))
: "r" (pte) : "memory");
where I would have expected:
stw%U1%X1 %L2,%1"
Is it a bug or am I missing something ?
Well spotted. I guess it's definitly a bug.
Introduced 12 years ago by commit
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9bf2b5cd
("powerpc: Fixes for CONFIG_PTE_64BIT for SMP support").
It's gone unnoticed until now it seems.
Can you submit a patch for it ?
Christophe
