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SubjectRe: Implement dwarf variable/type resolving for perf script
Hi Andi,

On Mon, 27 Nov 2017 16:23:09 -0800
Andi Kleen <andi@firstfloor.org> wrote:

> This patchkit extends perf script to query dwarf information for variable
> names or types/structure fields accessed from code.

Very interesting! so it is a kind of revert query interface.

>
> The dwarf resolution is all on top of Masami's perf probe dwarf code.
>
> It supports multiple use cases:
> - When we sample registers it can use the dwarf information to resolve
> the registers to names.
> - When we sample any instruction the instruction can be decoded and
> we can determine the type/struct field to make an estimate of the
> memory access patterns in data structures.
> - When we sample the new PTWRITE instruction the logged value from
> the PT log can be associated with a variable.
> - Various cleanups and fixes to make the one above all possible.

OK, I'll review that.

Thanks!

>
> It is all implemented with new output formats in perf script:
> iregval (map register values to names) and insnvar (decode instruction
> and map back memory operand to dwarf operation)
>
> There are some limitations, it cannot decode everything, and is
> somewhat slow, but it's already quite useful for typical code
>
>
> % perf record -Idi,si ./targ
> % perf script -F +iregvals
> ...
> targ 8584 169763.761843: 2091795 cycles:ppp: 40041a main (targ)
> targ 8584 169763.762520: 1913932 cycles:ppp: 400534 f1 (targ) { b = 0x2, int } { a = 0x1, int }
> targ 8584 169763.763141: 1638913 cycles:ppp: 400523 f2 (targ) { b = 0x1, int } { a = 0x2, int }
> targ 8584 169763.763672: 1516522 cycles:ppp: 400522 f2 (targ) { b = 0x1, int } { a = 0x2, int }
> targ 8584 169763.764165: 1335501 cycles:ppp: 400523 f2 (targ) { b = 0x1, int } { a = 0x2, int }
> targ 8584 169763.764598: 1253289 cycles:ppp: 400522 f2 (targ) { b = 0x2, int } { a = 0x1, int }
> targ 8584 169763.765005: 1135131 cycles:ppp: 400534 f1 (targ) { b = 0x2, int } { a = 0x1, int }
> targ 8584 169763.765373: 1080325 cycles:ppp: 400522 f2 (targ) { b = 0x2, int } { a = 0x1, int }
> targ 8584 169763.765724: 1036999 cycles:ppp: 400522 f2 (targ) { b = 0x1, int } { a = 0x2, int }
> targ 8584 169763.766061: 971213 cycles:ppp: 400534 f1 (targ) { b = 0x2, int } { a = 0x1, int }
>
>
> % perf record -e intel_pt//u -a sleep 1
> % perf script --itrace=i0ns -F insnvar,insn,ip,sym -f 2>&1 | xed -F insn: -A -64 | less
> ...
> 4f7e61 xyarray__max_y pushq %rbp
> 4f7e62 xyarray__max_y mov %rsp, %rbp
> 4f7e65 xyarray__max_y sub $0x20, %rsp
> 4f7e69 xyarray__max_y movq %rdi, -0x18(%rbp) { -24(xy), struct xyarray* }
> 4f7e6d xyarray__max_y movq %fs:0x28, %rax
> 4f7e76 xyarray__max_y movq %rax, -0x8(%rbp) { -8(xy), struct xyarray* }
> 4f7e7a xyarray__max_y xor %eax, %eax
> 4f7e7c xyarray__max_y movq -0x18(%rbp), %rax { -24(xy), struct xyarray* }
> 4f7e80 xyarray__max_y movq 0x20(%rax), %rax
> 4f7e84 xyarray__max_y movq -0x8(%rbp), %rdx { -8(xy), struct xyarray* }
> 4f7e88 xyarray__max_y xorq %fs:0x28, %rdx
> 4f7e91 xyarray__max_y jz 0x7
> 4f7e98 xyarray__max_y leaveq
> 4f7e99 xyarray__max_y retq
>
> In this example we now know that this function accesses two fields in struct xyarray *
>
> Available from
>
> git://git.kernel.org/pub/scm/linux/kernel/git/ak/linux-misc perf/var-resolve-2
>
> v1: Initial post


--
Masami Hiramatsu <mhiramat@kernel.org>

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