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>
