Difference between revisions of "Development/malloc check"

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(Jazz up the MALLOC_CHECK_ page)
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{{Template:I18n/Language Navigation Bar|MALLOC_CHECK_}}
 
{{Template:I18n/Language Navigation Bar|MALLOC_CHECK_}}
The MALLOC_CHECK_ environment variable is used in malloc(3), to decide which implementation use. It could have 4 different values:
 
  
*MALLOC_CHECK_ is not set: When MALLOC_CHECK_ has not been set, then malloc(3) have the usual behavior, nothing special happens.
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= MALLOC_CHECK_ =
*MALLOC_CHECK_ = 0: All errors are silently ignored.
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*MALLOC_CHECK_ = 1: On error, a diagnostic message is printed on stderr.
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*MALLOC_CHECK_ = 2: On error, abort(3) is called without a diagnostic message.
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*MALLOC_CHECK_ = 3: abort(3) is called, and a diagnostic message is printed.
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MALLOC_CHECK_ is an environment variable used by the [http://www.gnu.org/software/libc/ GNU C Library] (glibc) to automatically enable an extensive suite of debugging functions, which check for proper memory allocation, usage, and deallocation.  It includes options to enable aborting a program as soon as corruption is detection and for printing out error messages.
  
startkde script set this variable to 2 in trunk, so maybe you'll have crashes because of that.
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== KDE's usage ==
  
Notice that, the faster implementation is which is used when MALLOC_CHECK_ is not defined.
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KDE enables MALLOC_CHECK_ by default in development versions of KDE by setting the environment variable in the startkde script, from among the following possibilities:
  
More information in malloc(3).
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* MALLOC_CHECK_ is not set: When MALLOC_CHECK_ has not been set, then memory is used as normal with no special behavior.  If bugs exist you may still receive "Segmentation faults" after the corruption has become severe enough to trip an operating system error routine.
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* MALLOC_CHECK_ = 0: Memory check code is enabled.  However all errors are silently ignored without so much as a warning.
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* MALLOC_CHECK_ = 1: On error, a diagnostic message is printed on stderr.
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* MALLOC_CHECK_ = 2: On error, abort(3) is called without a diagnostic message.  This is the value set by startkde for glibc versions less than 2.9.
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* MALLOC_CHECK_ = 3: abort(3) is called, and a diagnostic message is printed.  This is the value set by startkde for glibc versions greater than or equal to 2.9.  Earlier glibc versions were unnecessarily "noisy" with this variable set to 3.
  
[[Development/malloc_check_crashExample | Example of crash because of this variable.]]
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{{note|An exception to the automatic variable setting is that if MALLOC_CHECK_ is already set to a value when startkde is run, startkde will not change that value.}}
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More information is available in the man page for malloc(3), and in the "Heap Consistency Checking" GNU info page for libc. (Konqueror users can open info:/libc/Heap Consistency Checking)
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== Crashes ==
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This checking may reveal bugs in programs, with a " *** glibc: corruption detected" message (or similar).  See
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[[Development/malloc_check_crashExample | an example of a crash because of this variable.]]
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Note that these crashes are '''not''' bugs with MALLOC_CHECK_, but a bug in the program which has gone unnoticed up to this point.
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{{note|There ''is'' a possible bug with glibc 2.10.1's memory checking for x86_64 systems using KDE 4 and glib. See KDE bug 196207.}}
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If you are a developer experiencing crashes due to this checking and you are unable to diagnose the source of the bug, it may be fruitful to use the [[Development/Tools/Valgrind|Valgrind]] tool to search for the source of the error.

Revision as of 02:43, 16 July 2009


MALLOC_CHECK_


MALLOC_CHECK_

MALLOC_CHECK_ is an environment variable used by the GNU C Library (glibc) to automatically enable an extensive suite of debugging functions, which check for proper memory allocation, usage, and deallocation. It includes options to enable aborting a program as soon as corruption is detection and for printing out error messages.

KDE's usage

KDE enables MALLOC_CHECK_ by default in development versions of KDE by setting the environment variable in the startkde script, from among the following possibilities:

  • MALLOC_CHECK_ is not set: When MALLOC_CHECK_ has not been set, then memory is used as normal with no special behavior. If bugs exist you may still receive "Segmentation faults" after the corruption has become severe enough to trip an operating system error routine.
  • MALLOC_CHECK_ = 0: Memory check code is enabled. However all errors are silently ignored without so much as a warning.
  • MALLOC_CHECK_ = 1: On error, a diagnostic message is printed on stderr.
  • MALLOC_CHECK_ = 2: On error, abort(3) is called without a diagnostic message. This is the value set by startkde for glibc versions less than 2.9.
  • MALLOC_CHECK_ = 3: abort(3) is called, and a diagnostic message is printed. This is the value set by startkde for glibc versions greater than or equal to 2.9. Earlier glibc versions were unnecessarily "noisy" with this variable set to 3.
noframe
 
Note
An exception to the automatic variable setting is that if MALLOC_CHECK_ is already set to a value when startkde is run, startkde will not change that value.

More information is available in the man page for malloc(3), and in the "Heap Consistency Checking" GNU info page for libc. (Konqueror users can open info:/libc/Heap Consistency Checking)

Crashes

This checking may reveal bugs in programs, with a " *** glibc: corruption detected" message (or similar). See an example of a crash because of this variable.

Note that these crashes are not bugs with MALLOC_CHECK_, but a bug in the program which has gone unnoticed up to this point.

noframe
 
Note
There is a possible bug with glibc 2.10.1's memory checking for x86_64 systems using KDE 4 and glib. See KDE bug 196207.

If you are a developer experiencing crashes due to this checking and you are unable to diagnose the source of the bug, it may be fruitful to use the Valgrind tool to search for the source of the error.


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