On Wed, Mar 02, 2016 at 04:53:36PM +0100, Sedat Dilek wrote:
> ffffffff8110f570 <del_timer_sync>:
> ffffffff8110f570:     55                      push   %rbp
> ffffffff8110f571:     48 89 e5                mov    %rsp,%rbp
> ffffffff8110f574:     41 57                   push   %r15
> ffffffff8110f576:     41 56                   push   %r14
> ffffffff8110f578:     53                      push   %rbx
> ffffffff8110f579:     48 83 ec 28             sub    $0x28,%rsp

stack offset is 0x28 bytes [*]

> ffffffff8110f57d:     48 89 fb                mov    %rdi,%rbx
> ffffffff8110f580:     e8 6b 6e 80 00          callq  ffffffff819163f0 <mcount>
> ffffffff8110f585:     e8 66 6e 80 00          callq  ffffffff819163f0 <mcount>
> ffffffff8110f58a:     e8 61 6e 80 00          callq  ffffffff819163f0 <mcount>
> ffffffff8110f58f:     e8 5c 6e 80 00          callq  ffffffff819163f0 <mcount>

Your compiler is on drugs!

> ffffffff8110f594:     9c                      pushfq 
> ffffffff8110f595:     8f 45 e0                popq   -0x20(%rbp)

Saves flags in -0x20(%rbp)

> ffffffff8110f598:     4c 8b 7d e0             mov    -0x20(%rbp),%r15

And in %r15

/me wonders what's wrong with: popf %r15

> ffffffff8110f59c:     e8 4f 6e 80 00          callq  ffffffff819163f0 <mcount>
> ffffffff8110f5a1:     e8 4a 6e 80 00          callq  ffffffff819163f0 <mcount>
> ffffffff8110f5a6:     fa                      cli    
> ffffffff8110f5a7:     e8 84 cb fc ff          callq  ffffffff810dc130 
> <trace_hardirqs_off>
> ffffffff8110f5ac:     4c 8d 73 50             lea    0x50(%rbx),%r14
> ffffffff8110f5b0:     48 c7 04 24 b0 f5 10    movq   
> $0xffffffff8110f5b0,(%rsp)
> ffffffff8110f5b7:     81 
> ffffffff8110f5b8:     31 f6                   xor    %esi,%esi
> ffffffff8110f5ba:     31 d2                   xor    %edx,%edx
> ffffffff8110f5bc:     31 c9                   xor    %ecx,%ecx
> ffffffff8110f5be:     41 b8 01 00 00 00       mov    $0x1,%r8d
> ffffffff8110f5c4:     45 31 c9                xor    %r9d,%r9d
> ffffffff8110f5c7:     4c 89 f7                mov    %r14,%rdi
> ffffffff8110f5ca:     e8 c1 e5 fc ff          callq  ffffffff810ddb90 
> <lock_acquire>
> ffffffff8110f5cf:     be 01 00 00 00          mov    $0x1,%esi
> ffffffff8110f5d4:     48 c7 c2 cf f5 10 81    mov    $0xffffffff8110f5cf,%rdx
> ffffffff8110f5db:     4c 89 f7                mov    %r14,%rdi
> ffffffff8110f5de:     e8 8d 08 fd ff          callq  ffffffff810dfe70 
> <lock_release>
> ffffffff8110f5e3:     e8 08 6e 80 00          callq  ffffffff819163f0 <mcount>

> ffffffff8110f5e8:     4c 89 f8                mov    %r15,%rax
> ffffffff8110f5eb:     49 89 c6                mov    %rax,%r14

Moves r15 into r14 through rax


> ffffffff8110f5ee:     f6 c4 02                test   $0x2,%ah
> ffffffff8110f5f1:     75 19                   jne    ffffffff8110f60c 
> <del_timer_sync+0x9c>
> ffffffff8110f5f3:     e8 f8 6d 80 00          callq  ffffffff819163f0 <mcount>
> ffffffff8110f5f8:     e8 f3 6d 80 00          callq  ffffffff819163f0 <mcount>


> ffffffff8110f5fd:     4c 89 75 d0             mov    %r14,-0x30(%rbp)
> ffffffff8110f601:     ff 75 d0                pushq  -0x30(%rbp)
> ffffffff8110f604:     9d                      popfq  

put r14 into -0x30(rbp) and pushes/pops that, see [*] this is 8 bytes
over stack ?!

> ffffffff8110f605:     e8 26 cb fc ff          callq  ffffffff810dc130 
> <trace_hardirqs_off>
> ffffffff8110f60a:     eb 17                   jmp    ffffffff8110f623 
> <del_timer_sync+0xb3>
> ffffffff8110f60c:     e8 2f cb fc ff          callq  ffffffff810dc140 
> <trace_hardirqs_on>
> ffffffff8110f611:     e8 da 6d 80 00          callq  ffffffff819163f0 <mcount>
> ffffffff8110f616:     e8 d5 6d 80 00          callq  ffffffff819163f0 <mcount>
> ffffffff8110f61b:     4c 89 75 d8             mov    %r14,-0x28(%rbp)
> ffffffff8110f61f:     ff 75 d8                pushq  -0x28(%rbp)
> ffffffff8110f622:     9d                      popfq  

puts r14 into -0x28(rbp) and pushes/pops that

> ffffffff8110f623:     e8 c8 6d 80 00          callq  ffffffff819163f0 <mcount>
> ffffffff8110f628:     65 8b 04 25 d4 ae 00    mov    %gs:0xaed4,%eax
> ffffffff8110f62f:     00 
> ffffffff8110f630:     a9 00 00 0f 00          test   $0xf0000,%eax
> ffffffff8110f635:     74 25                   je     ffffffff8110f65c 
> <del_timer_sync+0xec>
> ffffffff8110f637:     f6 43 2a 20             testb  $0x20,0x2a(%rbx)
> ffffffff8110f63b:     75 1f                   jne    ffffffff8110f65c 
> <del_timer_sync+0xec>
> ffffffff8110f63d:     48 c7 c7 04 54 c5 81    mov    $0xffffffff81c55404,%rdi
> ffffffff8110f644:     be 61 04 00 00          mov    $0x461,%esi
> ffffffff8110f649:     e8 12 c4 f6 ff          callq  ffffffff8107ba60 
> <warn_slowpath_null>
> ffffffff8110f64e:     eb 0c                   jmp    ffffffff8110f65c 
> <del_timer_sync+0xec>
> ffffffff8110f650:     e8 9b 6d 80 00          callq  ffffffff819163f0 <mcount>
> ffffffff8110f655:     e8 96 6d 80 00          callq  ffffffff819163f0 <mcount>
> ffffffff8110f65a:     f3 90                   pause  
> ffffffff8110f65c:     48 89 df                mov    %rbx,%rdi
> ffffffff8110f65f:     e8 4c fe ff ff          callq  ffffffff8110f4b0 
> <try_to_del_timer_sync>
> ffffffff8110f664:     85 c0                   test   %eax,%eax
> ffffffff8110f666:     78 e8                   js     ffffffff8110f650 
> <del_timer_sync+0xe0>
> ffffffff8110f668:     48 83 c4 28             add    $0x28,%rsp
> ffffffff8110f66c:     5b                      pop    %rbx
> ffffffff8110f66d:     41 5e                   pop    %r14
> ffffffff8110f66f:     41 5f                   pop    %r15
> ffffffff8110f671:     5d                      pop    %rbp
> ffffffff8110f672:     c3                      retq   
> ffffffff8110f673:     66 66 66 66 2e 0f 1f    data32 data32 data32 nopw 
> %cs:0x0(%rax,%rax,1)
> ffffffff8110f67a:     84 00 00 00 00 00 


That LLVM generate disgusting code, as a contrast, this is what my GCC
makes of this:

ffffffff81155f50 <del_timer_sync>:
ffffffff81155f50:       e8 bb 02 9c 00          callq  ffffffff81b16210 
<__fentry__>
ffffffff81155f55:       55                      push   %rbp
ffffffff81155f56:       48 89 e5                mov    %rsp,%rbp
ffffffff81155f59:       41 55                   push   %r13
ffffffff81155f5b:       41 54                   push   %r12
ffffffff81155f5d:       53                      push   %rbx
ffffffff81155f5e:       48 89 fb                mov    %rdi,%rbx
ffffffff81155f61:       48 83 ec 08             sub    $0x8,%rsp
ffffffff81155f65:       9c                      pushfq 
ffffffff81155f66:       41 5c                   pop    %r12
ffffffff81155f68:       fa                      cli    
ffffffff81155f69:       e8 72 5c fd ff          callq  ffffffff8112bbe0 
<trace_hardirqs_off>
ffffffff81155f6e:       4c 8d 6b 50             lea    0x50(%rbx),%r13
ffffffff81155f72:       45 31 c9                xor    %r9d,%r9d
ffffffff81155f75:       31 c9                   xor    %ecx,%ecx
ffffffff81155f77:       31 d2                   xor    %edx,%edx
ffffffff81155f79:       31 f6                   xor    %esi,%esi
ffffffff81155f7b:       4c 89 ef                mov    %r13,%rdi
ffffffff81155f7e:       48 c7 04 24 55 5f 15    movq   
$0xffffffff81155f55,(%rsp)
ffffffff81155f85:       81 
ffffffff81155f86:       41 b8 01 00 00 00       mov    $0x1,%r8d
ffffffff81155f8c:       e8 3f b3 fd ff          callq  ffffffff811312d0 
<lock_acquire>
ffffffff81155f91:       48 c7 c2 55 5f 15 81    mov    $0xffffffff81155f55,%rdx
ffffffff81155f98:       be 01 00 00 00          mov    $0x1,%esi
ffffffff81155f9d:       4c 89 ef                mov    %r13,%rdi
ffffffff81155fa0:       e8 0b b5 fd ff          callq  ffffffff811314b0 
<lock_release>
ffffffff81155fa5:       41 f7 c4 00 02 00 00    test   $0x200,%r12d
ffffffff81155fac:       75 52                   jne    ffffffff81156000 
<del_timer_sync+0xb0>
ffffffff81155fae:       41 54                   push   %r12
ffffffff81155fb0:       9d                      popfq  
ffffffff81155fb1:       e8 2a 5c fd ff          callq  ffffffff8112bbe0 
<trace_hardirqs_off>
ffffffff81155fb6:       65 8b 05 5b 66 eb 7e    mov    
%gs:0x7eeb665b(%rip),%eax        # c618 <__preempt_count>
ffffffff81155fbd:       a9 00 00 0f 00          test   $0xf0000,%eax
ffffffff81155fc2:       74 25                   je     ffffffff81155fe9 
<del_timer_sync+0x99>
ffffffff81155fc4:       f6 43 2a 20             testb  $0x20,0x2a(%rbx)
ffffffff81155fc8:       75 1f                   jne    ffffffff81155fe9 
<del_timer_sync+0x99>
ffffffff81155fca:       be 61 04 00 00          mov    $0x461,%esi
ffffffff81155fcf:       48 c7 c7 09 87 f3 81    mov    $0xffffffff81f38709,%rdi
ffffffff81155fd6:       e8 15 03 f8 ff          callq  ffffffff810d62f0 
<warn_slowpath_null>
ffffffff81155fdb:       48 89 df                mov    %rbx,%rdi
ffffffff81155fde:       e8 fd fe ff ff          callq  ffffffff81155ee0 
<try_to_del_timer_sync>
ffffffff81155fe3:       85 c0                   test   %eax,%eax
ffffffff81155fe5:       79 0e                   jns    ffffffff81155ff5 
<del_timer_sync+0xa5>
ffffffff81155fe7:       f3 90                   pause  
ffffffff81155fe9:       48 89 df                mov    %rbx,%rdi
ffffffff81155fec:       e8 ef fe ff ff          callq  ffffffff81155ee0 
<try_to_del_timer_sync>
ffffffff81155ff1:       85 c0                   test   %eax,%eax
ffffffff81155ff3:       78 f2                   js     ffffffff81155fe7 
<del_timer_sync+0x97>
ffffffff81155ff5:       48 83 c4 08             add    $0x8,%rsp
ffffffff81155ff9:       5b                      pop    %rbx
ffffffff81155ffa:       41 5c                   pop    %r12
ffffffff81155ffc:       41 5d                   pop    %r13
ffffffff81155ffe:       5d                      pop    %rbp
ffffffff81155fff:       c3                      retq   
ffffffff81156000:       e8 4b 8b fd ff          callq  ffffffff8112eb50 
<trace_hardirqs_on>
ffffffff81156005:       41 54                   push   %r12
ffffffff81156007:       9d                      popfq  
ffffffff81156008:       eb ac                   jmp    ffffffff81155fb6 
<del_timer_sync+0x66>
ffffffff8115600a:       66 0f 1f 44 00 00       nopw   0x0(%rax,%rax,1)
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