c++ - gcc dynamic linking dependency missing library? -

main.cc

#include <stdio.h> #include <thread> int output() {     printf("thread\n"); } int keke(); int main() {     //keke();     std::thread th(output);     th.join();     return 0; } 

keke.cc

#include <unistd.h> #include <pthread.h> int keke() {     pthread_attr_t attr;     return pthread_attr_init(&attr); } 

makefile

haha: libkeke.so     g++ -std=c++11 -o haha main.cc -l. -lkeke -pthread  libkeke.so: keke.cc     g++ -o libkeke.so -fpic -shared keke.cc -pthread clean:     rm libkeke.so haha 

make , result haha not load pthread.so,

(link)$ ldd haha     linux-vdso.so.1 =>  (0x00007fff65972000)     libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f9dee04a000)     libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f9dede34000)     libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f9deda6f000)     libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f9ded769000)     /lib64/ld-linux-x86-64.so.2 (0x00007f9dee34e000) 

ldd shows executable not depends on pthread library , crash. if uncomment call keke main.cc, program works well.

in conclusion, gcc not write dependency library(pthread) dynamic section if previous shared library(libkeke.so) depend on it. however, if executable not refer symbol in specific library(does not call keke), ld not write library(libkeke.so) dynamic section either. in consequence, ld.so not load dependency library(pthread) , executable(haha) crash.

the problem why not gcc write depend in dynamic section no matter whether included in previous depends msvc does? there drawback this?