D14302: Don't block forever in ensureKdeinitRunning

[Thiago Macieira]

thiago added a comment.


  In D14302#297159 <https://phabricator.kde.org/D14302#297159>, @jtamate wrote:
  
  >   (gdb) disass
  >   Dump of assembler code for function _ZN9QLockFile7tryLockEi:
  >      0x00007f54be8bc752 <+2>:     mov    $0xffffffff,%eax
  >   ...
  >      0x00007f54be8bc76d <+29>:    test   %esi,%esi
  >   ...
  >      0x00007f54be8bc772 <+34>:    cmovs  %eax,%esi
  >   ...
  >      0x00007f54be8bc78c <+60>:    movslq %esi,%rsi
  >      0x00007f54be8bc78f <+63>:    callq  0x7f54be962150 <QDeadlineTimer::QDeadlineTimer(long long, Qt::TimerType)>
  >
  
  
  This is entirely correct: in +29 it checks  parameter (in %esi) and in +34 if it has the sign bit set (read: is negative), moves -1 to it. Then it does a sign extension from 32- to 64-bit in +60, before placing the call.
  
  qMax is working properly.
  
  >   Dump of assembler code for function _ZN16KDEInitInterface20ensureKdeinitRunningEv:
  >   ...
  >      0x00007f54c0a23ae1 <+497>:   xor    %esi,%esi
  >      0x00007f54c0a23ae3 <+499>:   mov    %r12,%rdi
  >      0x00007f54c0a23ae6 <+502>:   callq  0x7f54c0a1e960 <_ZN9QLockFile7tryLockEi at plt>
  
  Also correct: this passed a zero as the parameter to tryLock().
  
  Now here's the interesting thing:
  
  >      0x00007f54c0a23aeb <+507>:   test   %al,%al
  >      0x00007f54c0a23aed <+509>:   jne    0x7f54c0a23b8d <_ZN16KDEInitInterface20ensureKdeinitRunningEv+669>
  >      0x00007f54c0a23af3 <+515>:   mov    %r12,%rdi
  >      0x00007f54c0a23af6 <+518>:   callq  0x7f54c0a1e9c0 <_ZN9QLockFile4lockEv at plt>
  >   => 0x00007f54c0a23afb <+523>:   mov    %rbx,%rdi
  
  Note where the => is pointing to. It's not to the return from tryLock(), but to the return to lock(). We've been looking at the wrong line.
  
  That also means the patch doesn't make sense, because it's changing the line that is already working.

REPOSITORY
  R271 KDBusAddons

REVISION DETAIL
  https://phabricator.kde.org/D14302

To: jtamate, dfaure, #frameworks, thiago
Cc: lvsouza, kde-frameworks-devel, michaelh, ngraham, bruns
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