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Malloc Debugging

The GNU C library itself has some debugging features and hooks you can use to add your own.

For documentation on a Linux system type info libc and then g Heap<TAB>. Another useful info node is “Hooks for Malloc”, you can get there with g Hooks<TAB>

Recent versions of Linux libc (later than 5.4.23) and glibc (2.x) include a malloc() implementation which is tunable via environment variables. For details, see mallopt(3).

[blyth@belle7 debugging]$ MALLOC_CHECK_=1 ls
malloc: using debugging hooks

Got some more info using MALLOC_CHECK_=1 (continuing beyond the first corruption).

Now GDB fails:

GiGaRunActionGDML::BeginOfRunAction i 0 c D
FreeFilePath  return /data1/env/local/env/geant4/geometry/gdml/DVGX_20131203-2016/g4_00.dae i 1
GiGaRunActionGDML::WriteDAE to /data1/env/local/env/geant4/geometry/gdml/DVGX_20131203-2016/g4_00.dae recreatePoly 0
/data1/env/local/dyb/external/Python/2.7/i686-slc5-gcc41-dbg/bin/python: symbol lookup error: /data1/env/local/dyb/NuWa-trunk/lhcb/InstallArea/i686-slc5-gcc41-dbg/lib/ undefined symbol: _ZN10G4DAEWrite5WriteERK8G4StringPK15G4LogicalVolumeS2_ibb

Program exited with code 0177.

[blyth@belle7 DVGX_20131203-1719]$ c++filt _ZN10G4DAEWrite5WriteERK8G4StringPK15G4LogicalVolumeS2_ibb
G4DAEWrite::Write(G4String const&, G4LogicalVolume const*, G4String const&, int, bool, bool)

Redirecting Malloc messages doesnt work

The reason you can't redirect it is that it gets written specifically to
/dev/tty, unless you have set the environment variable LIBC_FATAL_STDERR_. (I'm
not sure this is documented anywhere, but the relevant code can be found here.)


single quotes needed for GDB breakpoint tab completion

(gdb) b 'G4VSceneHandler::G4VSceneHandler(G4VGraphicsSystem&, int, G4String const&)'
Breakpoint 2 at 0x7ed79b1: file src/, line 84.

Resolved by getting rid of fSummary in G4VRML2FileSceneHandler.hh

The culprit looks to be inconsisent class definition, due to not recompiling all the other classes that access this one. Moral of the story:

  • if possible avoid changing headers of classes under test when debugging those classes
  • instead prefer to take notes in other debug only structures