Alan Modra wrote:
On Tue, May 17, 2022 at 10:32:09PM +1000, Michael Ellerman wrote:
"Naveen N. Rao" <naveen.n....@linux.ibm.com> writes:
> Michael Ellerman wrote:
>>
>> diff --git a/arch/powerpc/kernel/vdso/gettimeofday.S
b/arch/powerpc/kernel/vdso/gettimeofday.S
>> index eb9c81e1c218..0aee255e9cbb 100644
>> --- a/arch/powerpc/kernel/vdso/gettimeofday.S
>> +++ b/arch/powerpc/kernel/vdso/gettimeofday.S
>> @@ -22,12 +22,15 @@
>> .macro cvdso_call funct call_time=0
>> .cfi_startproc
>> PPC_STLU r1, -PPC_MIN_STKFRM(r1)
>> + .cfi_adjust_cfa_offset PPC_MIN_STKFRM
>> mflr r0
>> - .cfi_register lr, r0
>> PPC_STLU r1, -PPC_MIN_STKFRM(r1)
>> + .cfi_adjust_cfa_offset PPC_MIN_STKFRM
>> PPC_STL r0, PPC_MIN_STKFRM + PPC_LR_STKOFF(r1)
>
> <snip>
>
>> @@ -46,6 +50,7 @@
>> mtlr r0
>> .cfi_restore lr
>> addi r1, r1, 2 * PPC_MIN_STKFRM
>> + .cfi_def_cfa_offset 0
>
> Should this be .cfi_adjust_cfa_offset, given that we used that at the
> start of the function?
AIUI "adjust x" is offset += x, whereas "def x" is offset = x.
Yes.
So we could use adjust here, but we'd need to adjust by -(2 * PPC_MIN_STKFRM).
Yes.
It seemed clearer to just set the offset back to 0, which is what it is
at the start of the function.
Yes. In detail, both .cfi_def_cfa_offset and .cfi_adjust_cfa_offset
are interpreteted by the assembler into DW_CFA_def_cfa_offset byte
codes, so you should get the same .eh_frame contents if using Naveen's
suggestion. It boils down to style really, and the most common style
is to use ".cfi_def_cfa_offset 0" here.
Thank you, that clarifies things.
- Naveen
