Re: [PATCH] powerpc/64: Avoid link stack corruption in kexec_wait()
From: Daniel Axtens <hidden>
Date: 2021-08-31 06:17:57
Also in:
lkml
Hi Christophe,
Use bcl 20,31,+4 instead of bl in order to preserve link stack.
See commit c974809a26a1 ("powerpc/vdso: Avoid link stack corruption
in __get_datapage()") for details.From my understanding of that commit message, the change helps to keep the link stack correctly balanced which is helpful for performance, rather than for correctness. If I understand correctly, kexec_wait is not in a hot path - rather it is where CPUs spin while waiting for kexec. Is there any benefit in using the more complicated opcode in this situation?
quoted hunk ↗ jump to hunk
Signed-off-by: Christophe Leroy <redacted> --- arch/powerpc/kernel/misc_64.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/arch/powerpc/kernel/misc_64.S b/arch/powerpc/kernel/misc_64.S index 4b761a18a74d..613509907166 100644 --- a/arch/powerpc/kernel/misc_64.S +++ b/arch/powerpc/kernel/misc_64.S@@ -255,7 +255,7 @@ _GLOBAL(scom970_write) * Physical (hardware) cpu id should be in r3. */ _GLOBAL(kexec_wait) - bl 1f + bcl 20,31,1f 1: mflr r5
Would it be better to create a macro of some sort to wrap this unusual special form so that the meaning is more clear? Kind regards, Daniel
addi r5,r5,kexec_flag-1b -- 2.25.0