Messages in this thread | | | Date | Thu, 31 Mar 2011 10:46:38 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [RFC PATCH] perf report: add sort by file lines |
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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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