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SubjectRe: [RFC PATCH] perf report: add sort by file lines
Em Thu, Mar 31, 2011 at 04:45:55PM +0800, Lin Ming escreveu:
> On Wed, 2011-03-30 at 09:04 +0800, Masami Hiramatsu wrote:
> > > foo:
> > > .cfi_startproc
> > > pushq %rbp
> > > .cfi_def_cfa_offset 16
> > > movq %rsp, %rbp
> > > .cfi_offset 6, -16
> > > .cfi_def_cfa_register 6
> > > movq %rdi, -8(%rbp)
> > > movq %rsi, -16(%rbp)
> > > movq -8(%rbp), %rax /* load foo arg from stack */
> > > movq 24(%rax), %rax /* load foo->bar */
> > > movq -16(%rbp), %rdx /* load tmp arg from stack */
> > > movl 32(%rdx), %edx /* load tmp->blah */
> > > movl %edx, 20(%rax) /* store bar->fubar */ <<==(1)
> > > leave
> > > ret
> > > .cfi_endproc
> >
> > At (1), dwarf tells us the location of 'foo' is -8(%rbp) and 'tmp' is
> > -16(%rbp), but doesn't know to what 20(%rax) is mapped, because
> > foo->bar->fubar is not a real variable.
>
> I am considering if it is possible to do "instruction unwind" to get a
> map from (temporarily used) register to a specific member of a data
> structure pointed by a pointer.
>
> 4004a0: movq -8(%rbp), %rax /* load foo arg from stack */
> 4004a4: movq 24(%rax), %rax /* load foo->bar */
> 4004a8: movq -16(%rbp), %rdx /* load tmp arg from stack */
> 4004ac: movl 32(%rdx), %edx /* load tmp->blah */
> 4004af: movl %edx, 20(%rax) /* store bar->fubar */
>
> foo: -8(%rbp)
> tmp: -16(%rbp)
>
> Assume we are now at ip 4004af, from the instruction decoder, we know
> it's a store operation, and we want to find out what %rax is.
>
> 1. unwind to 4004ac
> Ignore this, because it does not touch %rax
>
> 2. unwind to 4004a8
> Ignore this, because it does not touch %rax
>
> 3. unwind to 4004a4
> 20(%rax) => 20(24(%rax)), continue to unwind because we still
> have no idea what %rax is
>
> 4. unwind to 4004a0
> 20(24(%rax)) => 20(24(-8(%rbp))), stop unwind, because we now know
> -8(%rbp) is foo.
>
> So the original 20(%rax) is replace as 20(24(-8(%rbp))), and it means
> foo->bar->fubar
>
> Does this make sense?

I think it does, so we do just like with annotation, but parsing objdump
-S output, is that what you're planning?

After we have the members we can do data annotation, in much the same
way we do with code annotation, i.e. augmenting pahole output.

- Arnaldo


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