Re: [PATCH] x86/mm: fix objtool failure with KMSAN enabled

[Thomas Gleixner]

On Thu, Jul 02 2026 at 21:46, Thomas Gleixner wrote:
> On Thu, Jul 02 2026 at 13:15, Peter Zijlstra wrote:
>> A quick test with folio_zero_user() seems to suggest the
>> ASM_CALL_CONSTRAINT movement (your patch) generates the same code for
>> defconfg as does the unmodified code. The change from the thread linked
>> above (input constraint on __builtin_frame_address(0)) generates
>> different code.
>>
>> A third option is to force FRAME_POINTER=y for KMSAN builds -- for now,
>> until clang is taught to be less insane.
>
> With FRAME_POINTER=y I get now with clang-22
>
> vmlinux.o: warning: objtool: folio_zero_user+0xa7b: stack state mismatch: reg1[4]=-1+0 reg2[4]=-2-336
> vmlinux.o: warning: objtool: set_ftrace_ops_ro+0x64: relocation to !ENDBR: machine_kexec_prepare+0x8f0
>
> That's with your objtool patch applied. When I remove that then the
> folio_zero_user one goes away. The relocation to !ENDBR stays.
>
> Oh well...

And none of this boots when KMSAN=y ....