glibc ,pthread库中 __read_nocancel, __write_nocancel 等函数冲突及调用问题

最新推荐文章于 2023-11-06 15:36:45 发布

最新推荐文章于 2023-11-06 15:36:45 发布 · 802 阅读

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本文通过一个简单的程序示例，探讨了在使用pthread库时，read和write系统调用如何从glibc库变为libpthread库的问题。当添加-pthread编译选项后，read和write调用来源于libpthread。解决方法是在编译时显式链接glibc动态库-lc。实际上，pthread是glibc的一部分，因此仅需glibc库即可解决冲突。

从一个简单程序开始了解下情况:

#include <stdio.h> #include <fcntl.h> int main() { FILE* fp = open("./1", O_WRONLY); char a[100]; while (1){ write(fp,"aaaa",4); read(fp, a, 100); } close(fp); }

其它sys call不看,主要是write和read,linux中它们两个是来自glibc库。我们编译这段程序看看函数调用情况。

^_^[/home/Crazybaby/]#gcc main.c ^_^[/home/Crazybaby/]#valgrind --tool=callgrind a.out ->C-c ^_^[/home/Crazybaby/]#callgrind_annotate callgrind.out.9150 ...省略... Ir file:function -------------------------------------------------------------------------------- 4,534,175 ???:main [/home/Crazybaby/WelcomeC/a.out] 4,534,167 ???:__write_nocancel [/lib64/libc-2.5.so] 4,534,160 ???:__read_nocancel [/lib64/libc-2.5.so] 824,404 ???:read [/lib64/libc-2.5.so] 824,394 ???:write [/lib64/libc-2.5.so]

可以看出正常编译下(不加线程库pthread)时 read 和 write 来自 libc ,很正常

来看看加上-pthread的情况.

^_^[/home/Crazybaby/]#gcc main.c -lpthread ^_^[/home/Crazybaby/]#valgrind --tool=callgrind a.out ->C-c ^_^[/home/Crazybaby/]#callgrind_annotate callgrind.out.9150 ...省略... Ir file:function -------------------------------------------------------------------------------- 2,769,176 ???:main [/home/Crazybaby/WelcomeC/a.out] 2,769,162 ???:__read_nocancel [/lib64/libpthread-2.5.so] 2,769,162 ???:__write_nocancel [/lib64/libpthread-2.5.so] 503,499 ???:read [/lib64/ld-2.5.so] 503,484 ???:write [/lib64/libpthread-2.5.so] 33,527 ???:do_lookup_x [/lib64/ld-2.5.so]

可以看出 write 和 read 都来自libpthread库了。

解决方法是: 在编译时显示的加上 -lc 这个glibc动态库

^_^[/home/Crazybaby/]#gcc main.c -lc -lpthread ^_^[/home/Crazybaby/]#valgrind --tool=callgrind a.out ->C-c ^_^[/home/Crazybaby/]#callgrind_annotate callgrind.out.9276 ...省略... -------------------------------------------------------------------------------- Ir file:function -------------------------------------------------------------------------------- 2,183,618 ???:main [/home/Crazybaby/WelcomeC/a.out] 2,183,610 ???:__write_nocancel [/lib64/libc-2.5.so] 2,183,599 ???:__read_nocancel [/lib64/libc-2.5.so] 397,033 ???:read [/lib64/libc-2.5.so] 397,020 ???:write [/lib64/libc-2.5.so] 28,297 ???:do_lookup_x [/lib64/ld-2.5.so] 22,899 ???:_dl_lookup_symbol_x [/lib64/ld-2.5.so]

今早又分析了下发现pthread是glibc的组成部分，所以只需要glibc库即可