valgrind leak-check aracı

Giriş
valgrind yerine mcheck aracını kullanmak daha kolay olabilir.

gdb
memcheck ile gdb'yi beraber kullanmak için şöyle yaparız.

valgrind --vgdb=yes --vgdb-error=0 app

leak-check
Şöyledir.

--leak-check=<no|summary|yes|full> [default: summary]

Bu aracın çıktısında iki tane başlık var

1. Heap Summary

2. Leak Summary

Her ikisine de bakmak gerekir.

leak-check= full
leak-check = full ise diğer seçenekler devreye girer. Açıklaması şöyle.

Once this option is set, you can use several other options to specify which kinds of memory leaks you want detailed reports for:

--show-leak-kinds=definite,possible only reports unfreed blocks with no pointers or that depend on interior pointers (the default)
--show-possibly-lost=no or --show-leak-kinds=definite only reports unfreed blocks with no pointers
--show-reachable=yes or --show-leak-kinds=all reports all forms of unfreed blocks, even trivial ones with clear pointers

show_leak_kinds seçeneği
leak-check = full ile etkindir. definite,indirect,possible,reachable,all,none seçeneklerinden birisini alır. Şöyle yaparız.

1.show-leak-kinds = definite, possible seçeneği - sadece kaybolan pointer'lar
Şöyle yaparız.

$ valgrind --leak-check=full -v ./a.out 

Şöyle yaparız.

$ valgrind --leak-check=full ./leak

Örnek
Definitely lost hatası yoksa çıktı olarak şuna benzer bir şey alırız.

==9145== HEAP SUMMARY:
==9145==     in use at exit: 64 bytes in 2 blocks
==9145==   total heap usage: 8 allocs, 6 frees, 300 bytes allocated
==9145== 
...
==9145== LEAK SUMMARY:
==9145==    definitely lost: 0 bytes in 0 blocks
==9145==    indirectly lost: 0 bytes in 0 blocks
==9145==      possibly lost: 0 bytes in 0 blocks
==9145==    still reachable: 64 bytes in 2 blocks
==9145==         suppressed: 0 bytes in 0 blocks
...
==9145== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
==9145== 
==9145== 1 errors in context 1 of 1:
==9145== Syscall param rt_sigaction(act->sa_mask) points to uninitialised byte(s)
==9145==    at 0x4E6D3F1: __libc_sigaction (sigaction.c:62)
==9145==    by 0x401061: main (in /home/dac/ClionProjects/openshell/a.out)
==9145==  Address 0xffeffefc8 is on thread 1's stack
==9145== 

Örnek
Definitely lost hatası varsa çıktı olarak şuna benzer bir şey alırız. Hatanın yerini de gösterilir. Hata malloc()'lanan belleğin silinmemesidir.

==32091== HEAP SUMMARY:
==32091==     in use at exit: 1 bytes in 1 blocks
==32091==   total heap usage: 1 allocs, 0 frees, 1 bytes allocated
==32091==
==32091== 1 bytes in 1 blocks are definitely lost in loss record 1 of 1
==32091==    at 0x4C29110: malloc (in /usr/lib64/....)
==32091==    by 0x40056A: f (leak.c:1)
==32091==    by 0x40057A: main (leak.c:2)
==32091==
==32091== LEAK SUMMARY:
==32091==    definitely lost: 1 bytes in 1 blocks
==32091==    indirectly lost: 0 bytes in 0 blocks
==32091==      possibly lost: 0 bytes in 0 blocks
==32091==    still reachable: 0 bytes in 0 blocks
==32091==         suppressed: 0 bytes in 0 blocks
==32091==

Örnek
Elimizde şöyle bir kod olsun.

A a = *getA();

Şuna benzer bir şey alırız. Bu sefer hata new()'lenen belleğin silinmemesidir.

==13832== 16 bytes in 1 blocks are definitely lost in loss record 1 of 1
==13832==    at 0x4C2D25F: operator new(unsigned long) (in /usr/lib/valgrind/...)
==13832==    by 0x108AAC: getA() (48538032.cpp:18)
==13832==    by 0x108AD4: doSomething() (48538032.cpp:22)
==13832==    by 0x108B3B: main (48538032.cpp:27)

2. show-leak-kinds= all seçeneği - herşey
Şöyle yaparız.

valgrind --leak-check=full --show-leak-kinds=all <prog_name>

Çıktı olarak şuna benzer bir şey alırız.

$cat main.cpp
int main(){}
$g++ -std=c++1z -o main main.cpp                         
$valgrind --leak-check=full --show-leak-kinds=all ./main
==26823== Memcheck, a memory error detector
==26823== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==26823== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==26823== Command: ./main
==26823== 
==26823== 
==26823== HEAP SUMMARY:
==26823==     in use at exit: 72,704 bytes in 1 blocks
==26823==   total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated
==26823== 
==26823== 72,704 bytes in 1 blocks are still reachable in loss record 1 of 1
==26823==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/...
==26823==    by 0x4E9D62F: ??? (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.22)
==26823==    by 0x4010109: call_init.part.0 (dl-init.c:78)
==26823==    by 0x40101F2: call_init (dl-init.c:36)
==26823==    by 0x40101F2: _dl_init (dl-init.c:126)
==26823==    by 0x4001309: ??? (in /lib/x86_64-linux-gnu/ld-2.19.so)
==26823== 
==26823== LEAK SUMMARY:
==26823==    definitely lost: 0 bytes in 0 blocks
==26823==    indirectly lost: 0 bytes in 0 blocks
==26823==      possibly lost: 0 bytes in 0 blocks
==26823==    still reachable: 72,704 bytes in 1 blocks
==26823==         suppressed: 0 bytes in 0 blocks
==26823== 
==26823== For counts of detected and suppressed errors, rerun with: -v
==26823== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)