mcheck

Heap consistency checking for malloc

TLDR

Enable heap checking in a C program (call before any malloc)

$ mcheck(NULL)

Enable heap checking with a custom error handler

$ mcheck([handler_func])

Enable pedantic checking on every allocation

$ mcheck_pedantic(NULL)

Check all allocated blocks immediately

$ mcheck_check_all()

Explicitly check a specific allocated block

$ mprobe([ptr])

Link with mcheck to enable automatic checking

$ cc [program.c] -lmcheck

$ #include <mcheck.h>

int mcheck(void (*abortfunc)(enum mcheck_status mstatus));
int mcheck_pedantic(void (*abortfunc)(enum mcheck_status mstatus));
void mcheck_check_all(void);
enum mcheck_status mprobe(void *ptr);

DESCRIPTION

The mcheck family of functions installs debugging hooks for the malloc(3) memory allocation functions in glibc. These hooks perform consistency checks on the heap, detecting common errors such as double-free, buffer overruns that corrupt malloc bookkeeping data, and use of freed memory.The mcheck() function must be called before the first call to malloc(). Linking the program with -lmcheck inserts an implicit call to mcheck(NULL) before the first allocation, which is easier than modifying source code.The mprobe() function returns a status indicating the block's state: MCHECK_OK (no inconsistency), MCHECK_HEAD (memory before the block was clobbered), MCHECK_TAIL (memory after the block was clobbered), or MCHECK_FREE (the block was freed twice).

PARAMETERS

mcheck abortfunc

Install debugging hooks for malloc. Pass NULL to use the default handler that prints a message and calls abort(). Must be called before the first malloc().

mcheck_pedantic abortfunc

Like mcheck(), but performs consistency checks on all allocated blocks on every call to malloc(), realloc(), or free(). Very slow.

mcheck_check_all

Trigger an immediate consistency check on all allocated blocks. Only effective if mcheck() was called first.

mprobe ptr

Explicitly check the block pointed to by ptr for consistency.

CAVEATS

The mcheck() function must be called before any memory allocation; otherwise it returns -1. These functions are glibc-specific and non-portable. The MALLOC_CHECK_ environment variable provides similar functionality without recompilation. The mcheck_pedantic() function is very slow and should only be used for targeted debugging. Deprecated in newer glibc versions in favor of MALLOC_CHECK_ and tools like valgrind.

HISTORY

The mcheck functions are part of the GNU C Library (glibc) and originate from early Unix malloc debugging facilities. They are documented in the glibc manual under "Heap Consistency Checking".