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

From: Martin LiÅka
Date: Tue Aug 28 2018 - 13:55:57 EST

On 08/28/2018 04:18 PM, Arnaldo Carvalho de Melo wrote:
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 LiÅka escreveu:
On 08/23/2018 04:12 PM, Arnaldo Carvalho de Melo wrote:
Em Thu, Aug 23, 2018 at 02:29:34PM +0200, Martin LiÅka escreveu:
The patch changes interpretation of:
callq *0x8(%rbx)

0.26 â â callq *8
0.26 â â callq *0x8(%rbx)


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:

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

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 â mov %rdx,-0x28(%rbp)
0.58 â mov -0x18(%rbp),%rax
7.90 â mov 0x8(%rax),%rax
8.67 â mov -0x28(%rbp),%rcx
â mov -0x20(%rbp),%rdx
0.08 â mov %rcx,%rsi
6.28 â mov %rdx,%rdi
10.50 â â callq *%rax
1.67 â mov %eax,-0x4(%rbp)
11.95 â cmpl $0x0,-0x4(%rbp)
8.14 â â je 3d
â mov -0x4(%rbp),%eax
â sub $0x1,%eax
â â jmp 42
â3d: mov $0x0,%eax
7.84 â42: leaveq
â â retq

Without the patch, will check if something changes with it.

Hi Arnaldo.

Thanks for re-sending of the patch and for the testing. The example I sent
is dependent on version of GCC compiler.

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 @@
â jle 128
hash_value = hash_table->hash_func (key);
mov 0x8(%rsp),%rdi
- 0.91 â callq *30
+ 0.91 â 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
- â callq *38
+ â callq *0x38(%r15)
cmp %rax,%r13
1.91 â je 240
1b4: mov $0xffffffff,%r13d
@@ -14026,7 +14026,7 @@
mov %rcx,-0x500(%rbp)
mov %r15,%rsi
mov %r14,%rdi
- â callq *38
+ â callq *0x38(%rax)
mov -0x500(%rbp),%rcx
cmp %rax,%rcx
â jne 9b0
<SNIP tons of other such cases>