MALLOCSS(3) MALLOCSS(3)
NAME
malloc, free, realloc, calloc, memalign, valloc, ssmalloc_error -
SpeedShop memory allocation library
SYNOPSIS
#include <stdlib.h>
void *malloc (sizet size);
void free (void *ptr);
void *realloc (void *ptr, sizet size);
void *calloc (sizet nelem, sizet elsize);
void *memalign (sizet alignment, sizet size);
void *valloc (sizet size);
void ssmallocerror (char *message);
DESCRIPTION
The SpeedShop Performance Tools contain a malloc library, -lmalloc_ss,
which provides tracing and error detection around calls to the various
malloc routines.
The library provides an intercept layer for calls to malloc, free,
realloc, memalign, and valloc; the intercept allows tracing of all calls
with the SpeedShop performance tools.
Calls to malloc, free, and realloc are passed through to whatever memory
allocation library the program is linked with. Calls to calloc are
actually not intercepted, but rely on the underlying calloc to call
malloc to get the space allocated. Calls to memalign are implemented by
allocating a block large enough to hold the aligned area asked for by the
user, as well as a guard area that holds a flag indicating that the user
block was obtained through memalign, and the address of the larger block.
Calls to valloc are translated into a call to getpagesize, followed by a
memalign call.
The last function, ssmalloc_error is not a user-accessible function, it
is an internal static function. It is called whenever any error is
detected, so that a debugger trap may be placed at exit from that routine
to interactively examine malloc errors.
MALLOC TRACING
The library provides for tracing of all calls to any of the entry points
listed above, as well as any of the errors listed below. The trace is
normally captured using a SpeedShop performance experiment. It may be
written in ASCII to stderr by enabling the environment variable
_SSMALLOC_TRACING, although this typically produces a great deal of
output.
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MALLOCSS(3) MALLOCSS(3)
ERROR DETECTION
The library will detect some errors under all conditions, and others if
_SSMALLOC_FASTCHK error detection is enabled. All errors pass through
the routine ssmalloc_error and a trap can be placed at the exit from that
routine to catch the problem. Errors are also traced.
The errors that are always detected are:
malloc call failing (returning NULL).
realloc call failing (returning NULL).
realloc call with an address outside the range of heap addresses
returned by malloc or memalign.
memalign call with an improper alignment.
free call with an address that is improperly aligned.
free call with an address outside the range of heap addresses
returned by malloc or memalign.
If _SSMALLOC_FASTCHK is enabled, the library will also detect:
free or realloc calls where the words prior to the user block have
been corrupted.
free or realloc calls where the words following the user block have
been corrupted.
free or realloc calls where the address is that of a block that has
already been freed. This error may not always be detected if the
area around the block is reallocated after it was first freed.
The behavior of the library is governed by various environment variables:
SPEEDSHOPVERBOSE
If set to a zero-length string, messages are printed to stderr only
when an error occurs. If set to a non-zero length string), detailed
information about all traced events, including the callstack at the
time the error was detected, is printed. This option is not
normally used by the end user, as it can produce a huge volume of
output.
SSMALLOCTRACING
enables tracing of all calls through the library. Tracing is
normally done in the course of a performance experiment; the
variable need not be set in such cases, as the running of the
experiment will automatically enable it. If the option is enabled
when the program is run independently, and _SSMALLOC_VERBOSE is set
to 2 or greater, the trace events and program call stacks will be
written to stderr.
SSMALLOCFASTCHK
enables corruption detection for library calls. Corruption
detection is done by allocating a space larger than the requested
area, and putting specific patterns in front of and behind the area
returned to the caller. When free is called, the patterns are
checked, and if the area was overwritten, an error message is
printed using an internal call to the routine ssmalloc_error. Under
the debugger, a trap may be set at exit from this routine to catch
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the program at the error.
SSMALLOCFULLWARN
enables detection of some calls that are not strictly errors, but
represent sloppy programming, including free(NULL), malloc(0), and
realloc(ptr,0).
SSMALLOCMAXMALLOC n
(where n is a non-zero integer, in any base) sets a maximum size for
any malloc or realloc or memalign allocation. Any request exceeding
that size will be flagged as an error, and return a NULL pointer.
Setting _SSMALLOC_MAXMALLOC to zero disables the test. Note that
the size argument to malloc is an unsigned variable, and a small
negative number will be treated as a very large unsigned number, and
will typically trigger this error if _SSMALLOC_MAXMALLOC is set.
SSMALLOCNOREUSE
specifies that no area that has been freed will be reused. With
this option enabled, no actual free calls are really made, and the
process space and swap requirements can grow quite large.
SSMALLOCCLEARFREE
will clear the data upon any free call. It will only work if
_SSMALLOC_FASTCHK is also enabled.
SSMALLOCCLEARFREEPATTERN <pattern>
specifies a pattern to clear the data if _SSMALLOC_CLEAR_FREE is
enabled. The default pattern is 0xcafebeef for the 32-bit version,
and 0xcafebeefcafebeef for the 64-bit versions. Only full words
(double words for 64-bits) are cleared to the pattern.
SSMALLOCCLEARMALLOC
will clear the memory area upon each allocation. It also requires
_SSMALLOC_FASTCHK be enabled.
SSMALLOCCLEARMALLOCPATTERN <pattern>
specifies a pattern to clear the data if _SSMALLOC_CLEAR_MALLOC is
enabled. The default pattern is 0xfacebeef for the 32-bit version,
and 0xfacebeeffacebeef for the 64-bit versions. Only full words
(double words for 64-bits) are cleared to the pattern.
SEE ALSO
malloc(3C), malloc(3X), ssrun(1), prof(1), ssdump(1), ssrt(3).
DIAGNOSTICS
As ouput from the library routines.
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