linux-kernel - Re: [PATCH] Properly interpret indirect call in perf annotate.

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Date:   Tue, 28 Aug 2018 11:18:43 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Martin Liška <mliska@...e.cz>
Cc:     linux-perf-users@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH] Properly interpret indirect call in perf annotate.

Em Tue, Aug 28, 2018 at 11:10:47AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Mon, Aug 27, 2018 at 11:06:21AM +0200, Martin Liška escreveu:
> > On 08/23/2018 04:12 PM, Arnaldo Carvalho de Melo wrote:
> > > Em Thu, Aug 23, 2018 at 02:29:34PM +0200, Martin Liška escreveu:
> > >> The patch changes interpretation of:
> > >> callq  *0x8(%rbx)
> > >>
> > >> from:
> > >>   0.26 │     → callq  *8
> > >> to:
> > >>   0.26 │     → callq  *0x8(%rbx)

<SNIP>

> > > Please mention one or two functions where such sequence appears, so that
> > > others can reproduce your before/after more quickly,

> > Sure, there's self-contained example on can compile (-O2) and test.
> > It's following call in test function:

> > test:
> > .LFB1:
> >         .cfi_startproc
> >         movq    %rdi, %rax
> >         subq    $8, %rsp
> >         .cfi_def_cfa_offset 16
> >         movq    %rsi, %rdi
> >         movq    %rdx, %rsi
> >         call    *8(%rax) <---- here
> >         cmpl    $1, %eax
> >         adcl    $-1, %eax
> >         addq    $8, %rsp
> >         .cfi_def_cfa_offset 8
> >         ret
> >         .cfi_endproc
> 
> Here I'm getting:
> 
> Samples: 2K of event 'cycles:uppp', 4000 Hz, Event count (approx.): 1808551484
> test  /home/acme/c/perf-callq [Percent: local period]
>   0.17 │      mov    %rdx,-0x28(%rbp)
>   0.58 │      mov    -0x18(%rbp),%rax
>   7.90 │      mov    0x8(%rax),%rax
>   8.67 │      mov    -0x28(%rbp),%rcx
>        │      mov    -0x20(%rbp),%rdx
>   0.08 │      mov    %rcx,%rsi
>   6.28 │      mov    %rdx,%rdi
>  10.50 │    → callq  *%rax
>   1.67 │      mov    %eax,-0x4(%rbp)
>  11.95 │      cmpl   $0x0,-0x4(%rbp)
>   8.14 │    ↓ je     3d
>        │      mov    -0x4(%rbp),%eax
>        │      sub    $0x1,%eax
>        │    ↓ jmp    42
>        │3d:   mov    $0x0,%eax
>   7.84 │42:   leaveq
>        │    ← retq
> 
> Without the patch, will check if something changes with it.

No changes with the patch, but then I did another test, ran a system
wide record for a while, then tested without/with your patch, with
--stdio2 redirecting to /tmp/{before,after} and got the expected
results, see below.

Thanks, applying,

- Arnaldo

--- /tmp/before 2018-08-28 11:16:03.238384143 -0300
+++ /tmp/after  2018-08-28 11:15:39.335341042 -0300
@@ -13274,7 +13274,7 @@
              ↓ jle    128     
                hash_value = hash_table->hash_func (key);
                mov    0x8(%rsp),%rdi
-  0.91       → callq  *30     
+  0.91       → callq  *0x30(%r12)
                mov    $0x2,%r8d
                cmp    $0x2,%eax
                node_hash = hash_table->hashes[node_index];
@@ -13848,7 +13848,7 @@
                 mov    %r14,%rdi
                 sub    %rbx,%r13
                 mov    %r13,%rdx
-              → callq  *38      
+              → callq  *0x38(%r15)
                 cmp    %rax,%r13
   1.91        ↓ je     240      
          1b4:   mov    $0xffffffff,%r13d
@@ -14026,7 +14026,7 @@
                 mov    %rcx,-0x500(%rbp)
                 mov    %r15,%rsi
                 mov    %r14,%rdi
-              → callq  *38      
+              → callq  *0x38(%rax)
                 mov    -0x500(%rbp),%rcx
                 cmp    %rax,%rcx
               ↓ jne    9b0
<SNIP tons of other such cases>