参考资料：http://www.redhat.com/magazine/015jan06/features/valgrind/
http://www.stlinux.com/devel/debug/mudflap
我们用C语言在做大型服务器程序的时候，不可避免的要面对内存错误的问题。典型的问题是内存泄漏，越界，随机乱写等问题。 在linux下valgrind是个很好的工具，大部分问题都可以查的到的。但是对于更微妙的越界问题，valgrind有时候也是无能为力的。比如下面的问题。
[admin@my174 ~]$ cat bug.c
[admin@my174 ~]$ gcc -g -o bug bug.c |
[admin@my174 ~]$ valgrind ./bug |
==5791== Memcheck, a memory error detector. |
==5791== Copyright (C) 2002-2006, and GNU GPL'd, by Julian Seward et al. |
==5791== Using LibVEX rev 1658, a library for dynamic binary translation. |
==5791== Copyright (C) 2004-2006, and GNU GPL'd, by OpenWorks LLP. |
==5791== Using valgrind-3.2.1, a dynamic binary instrumentation framework. |
==5791== Copyright (C) 2000-2006, and GNU GPL'd, by Julian Seward et al. |
==5791== For more details, rerun with: -v |
==5791== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 4 from 1) |
==5791== malloc/free: in use at exit: 0 bytes in 0 blocks. |
==5791== malloc/free: 0 allocs, 0 frees, 0 bytes allocated. |
==5791== For counts of detected errors, rerun with: -v |
==5791== All heap blocks were freed -- no leaks are possible. |
valgrind报告一切安好。
[admin@my174 ~]$ gcc -o bug bug.c -g -fmudflap -lmudflap |
mudflap violation 1 (check/read): time=1285386334.204054 ptr=0x700e00 size=48 |
pc=0x2b6c3013c4c1 location=`bug.c:5 (main)' |
/usr/lib64/libmudflap.so.0(__mf_check+0x41) [0x2b6c3013c4c1] |
./bug(main+0x7a) [0x400952] |
/lib64/libc.so.6(__libc_start_main+0xf4) [0x39ea21d994] |
Nearby object 1: checked region begins 0B into and ends 8B after |
mudflap object 0x16599370: name=`bug.c:1 a' |
bounds=[0x700e00,0x700e27] size=40 area=static check=3r/0w liveness=3 |
alloc time=1285386334.204025 pc=0x2b6c3013bfe1 |
number of nearby objects: 1 |
mudflap就很顺利的检查出来了。
[admin@my174 ~]$ gcc -v
…
gcc version 4.1.2 20080704 (Red Hat 4.1.2-46)
当然我们的这个例子很简单，典型的服务器要比这个复杂很多， 而且mudflap的运行开销也非常高，我们在定位此类bug的时候不妨实验下。
Have fun!
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