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# glibc
## malloc tracer [`mtrace(3)`][mtrace]
Trace memory allocation and de-allocation to detect memory leaks.
Need to call `mtrace(3)` to install the tracing hooks.
If we can't modify the binary to call `mtrace` we can create a small shared
library and pre-load it.
```c
// libmtrace.c
#include <mcheck.h>
__attribute__((constructor)) static void init_mtrace() { mtrace(); }
```
Compile as:
```bash
gcc -shared -fPIC -o libmtrace.so libmtrace.c
```
To generate the trace file run:
```bash
export MALLOC_TRACE=<file>
LD_PRELOAD=./libmtrace.so <binary>
```
**Note**: If `MALLOC_TRACE` is not set `mtrace` won't install tracing hooks.
To get the results of the trace file:
```bash
mtrace <binary> $MALLOC_TRACE
```
## malloc check [`mallopt(3)`][mallopt]
Configure action when glibc detects memory error.
```bash
export MALLOC_CHECK_=<N>
```
Useful values:
```markdown
1 print detailed error & continue
3 print detailed error + stack trace + memory mappings & abort
7 print simple error message + stack trace + memory mappings & abort
```
[mtrace]: http://man7.org/linux/man-pages/man3/mtrace.3.html
[mallopt]: http://man7.org/linux/man-pages/man3/mallopt.3.html
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