Archivi tag: linking

autotools and latest gcc version

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Running an old autotools build I just found it didn’t work no more. The command in error was:
# gcc -lpthread -o foo foo.o

Manually putting -lpthread at the end was ok but as I was using autotools I couldn’t just change the order and – above all – it was fine for gcc to expect the library *after* the object file!

The solution – suggested on #gcc by ngladitz – was to use the right autotools variable for adding libraries.

After RTFM I just:
– foo_LDFLAGS=-lpthread # autotools put flags before …
+ foo_LDADD=-lpthread # … and libraries after

cleaning up and rebuilding fixed everything!

Mixing static and dynamic linking

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Due to some limitation of profiling software, it may be useful to link statically some libs into our programs. The following command links statically only lcrypto – while using dynamic linking on all other libs.

# gcc test.c -o test -Wl,-Bstatic -lcrypto -Wl,-Bdynamic

If you forget the ending -Wl,-Bdynamic you’ll get the following error:

 /usr/bin/ld: cannot find -lgcc_s
collect2: ld returned 1 exit status

This because gcc tries to link statically libgcc too – but using the wrong file: libgcc_s.a. To link statically libgcc you have to add the -static-libgcc flag

# gcc test.c -o test -Wl,-Bstatic -lcrypto  -static-libgcc