Re: [RFC PATCH] perf report: add sort by file lines

[Lin Ming]

On Thu, 2011-03-31 at 21:46 +0800, Arnaldo Carvalho de Melo wrote:
> 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?

I mean to use libopcodes to decode the instructions.
But to parse objdump -S output maybe a better and simpler idea.

> 
> 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.

What is data annotation? Is it to list the percentage of access for each
member of the structure? For example,

struct bar {
        int poekoe[5];      //10%
        int fubar;          //20%
};

Lin Ming

> 
> - Arnaldo


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