NAME

umem_debug - debugging features of the umem library

SYNOPSIS

cc [ flag... ] file... -lumem [ library... ]
#include <umem.h>

DESCRIPTION

The libumem library provides debugging features that detect memory leaks, buffer overruns, multiple frees, use of uninitialized data, use of freed data, and many other common programming errors. The activation of the run-time debugging features is controlled by environment variables.

When the library detects an error, it writes a description of the error to an internal buffer that is readable with the ::umem_status mdb(1) dcmd and then calls abort(3C).

When using the debugging features of the library, a program may opt into changing the failure rate of memory allocation. This is often useful for test code that would like to force memory allocation failures in a controlled fashion. See the umem_setmtbf(3MALLOC) function for more information.

ENVIRONMENT VARIABLES

UMEM_DEBUG

This variable contains a list of comma-separated options. Unrecognized options are ignored. Possible options include:

audit[=frames]

This option enables the recording of auditing information, including thread ID, high-resolution time stamp, and stack trace for the last action (allocation or free) on every allocation. If transaction logging (see UMEM_LOGGING) is enabled, this auditing information is also logged.

The frames parameter sets the number of stack frames recorded in the auditing structure. The upper bound for frames is implementation-defined. If a larger value is requested, the upper bound is used instead.

If frames is not specified or is not an integer, the default value of 15 is used.

This option also enables the guards option.

contents[=count]

If auditing and contents logging (see UMEM_LOGGING) are enabled, the first count bytes of each buffer are logged when they are freed. If a buffer is shorter than count bytes, it is logged in its entirety.

If count is not specified or is not an integer, the default value of 256 is used.

default

This option is equivalent to audit,contents,guards.

guards

This option enables filling allocated and freed buffers with special patterns to help detect the use of uninitialized data and previously freed buffers. It also enables an 8-byte redzone after each buffer that contains 0xfeedfacefeedfaceULL.

When an object is freed, it is filled with 0xdeadbeef. When an object is allocated, the 0xdeadbeef pattern is verified and replaced with 0xbaddcafe. The redzone is checked every time a buffer is allocated or freed.

For caches with either constructors or destructors, or both, umem_cache_alloc(3MALLOC) and umem_cache_free(3MALLOC) apply the cache's constructor and destructor, respectively, instead of caching constructed objects. The presence of assert(3C)s in the destructor verifying that the buffer is in the constructed state can be used to detect any objects returned in an improper state. See umem_cache_create(3MALLOC) for details.

verbose

The library writes error descriptions to standard error before aborting. These messages are not localized.

UMEM_LOGGING

To be enabled, this variable should be set to a comma-separated list of in-memory logs. The logs available are:

transaction[=size]

If the audit debugging option is set (see UMEM_DEBUG), the audit structures from previous transactions are entered into this log.

contents[=size]

If the audit debugging option is set, the contents of objects are recorded in this log as they are freed.

If the "contents" debugging option was not set, 256 bytes of each freed buffer are saved.

fail[=size]

Records are entered into this log for every failed allocation.

For any of these options, if size is not specified, the default value of 64k is used. The size parameter must be an integer that can be qualified with K, M, G, or T to specify kilobytes, megabytes, gigabytes, or terabytes, respectively.

Logs that are not listed or that have either a size of 0 or an invalid size are disabled.

The log is disabled if during initialization the requested amount of storage cannot be allocated.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Unstable
MT-Level	MT-Safe

WARNINGS

When libumem aborts the process using abort(3C), any existing signal handler for SIGABRT is called. If the signal handler performs allocations, undefined behavior can result.

NOTES

Some of the debugging features work only for allocations smaller than 16 kilobytes in size. Allocations larger than 16 kilobytes could have reduced support.

Activating any of the library's debugging features could significantly increase the library's memory footprint and decrease its performance.