Re: [RFC PATCH 3/3] objtool/mcount: Add powerpc specific functions

[Naveen N. Rao]

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