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SubjectRe: [RFC PATCH 3/3] objtool/mcount: Add powerpc specific functions
Peter Zijlstra wrote:
> On Sat, May 21, 2022 at 09:38:35AM +0000, Christophe Leroy wrote:
>
>> I gave it a try this morning, I selected HAVE_OBJTOOL and
>> HAVE_OBJTOOL_MCOUNT from arch/powerpc/Kconfig
>>
>>
>> Seems like there are still some x86 arch specific stuff in common common
>> code and I get the following errors.
>
> I'm assuming there's a metric ton of x86 specific stuff in there.
> That'll take a while to clean out.
>
> Mostly Josh's rewrite was centered around splitting out the runtime
> options, but objtool is still always build with all options included,
> even the ones you're not using for your arch, which is what's triggering
> the problems you see here, I suppose...
>
>> Also, is it normal to get those functions built allthough I have not
>> selected HAVE_STACK_VALIDATION ?
>>
>> CC /home/chleroy/linux-powerpc/tools/objtool/check.o
>> check.c: In function 'has_valid_stack_frame':
>> check.c:2369:30: error: 'CFI_BP' undeclared (first use in this
>> function); did you mean 'CFI_SP'?
>> 2369 | if (cfi->cfa.base == CFI_BP &&
>> | ^~~~~~
>> | CFI_SP
>> check.c:2369:30: note: each undeclared identifier is reported only once
>> for each function it appears in
>> check.c:2371:44: error: 'CFI_RA' undeclared (first use in this
>> function); did you mean 'CFI_R3'?
>> 2371 | check_reg_frame_pos(&cfi->regs[CFI_RA],
>> -cfi->cfa.offset + 8))
>> | ^~~~~~
>> | CFI_R3
>> check.c: In function 'update_cfi_state':
>> check.c:2499:70: error: 'CFI_BP' undeclared (first use in this
>> function); did you mean 'CFI_SP'?
>> 2499 | if (op->src.reg == CFI_SP &&
>> op->dest.reg == CFI_BP &&
>> |
>> ^~~~~~
>> |
>> CFI_SP
>> make[3]: *** [/home/chleroy/linux-powerpc/tools/build/Makefile.build:97:
>> /home/chleroy/linux-powerpc/tools/objtool/check.o] Error 1
>> make[2]: *** [Makefile:54:
>> /home/chleroy/linux-powerpc/tools/objtool/objtool-in.o] Error 2
>> make[1]: *** [Makefile:69: objtool] Error 2
>> make: *** [Makefile:1337: tools/objtool] Error 2
>>
>>
>> What would be the best approach to fix that ?
>
> Define CFI_BP to your frame register (r2, afaict) I suppose. If you're
> only using OBJTOOL_MCOUNT this code will never run, so all you have to
> ensure is that it compiles, not that it makes sense (-:

Sathvika has been looking into this.

>
> The very long and complicated way would be to propagate the various
> CONFIG_HAVE_* build time things to the objtool build and librally
> sprinkle a lot of #ifdef around.

I think there were just a couple of unrelated checks/warnings that were
causing problems on powerpc. So, we likely won't need too many #ifdefs,
at least for mcount purposes.

Sathvika,
Can you post what you have?


- Naveen

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