GNU build system question

Question

How to find the library, which contains the definition of particular function? I am getting linker error.

Answer 1

You can use the nm command-line tool to list exported symbols in binaries:

~/src> cat nm-test.c

static int plus_four(int x)
{
        return x + 4;
}

int sum_plus_four(int a, int b)
{
        return plus_four(a + b);
}

int product_plus_four(int a, int b)
{
        return plus_four(a * b);
}
~/src> gcc -c nm-test.c
~/src> nm ./nm-test.o
00000000 t plus_four
00000023 T product_plus_four
0000000b T sum_plus_four

According to the manual, 't' means that the symbol is in the code (text) segment, and uppercase means it's public.

If you have a symbol that you're looking for, you can use nm to make the symbols exported by a library accessible to e.g. grep:

$ find -name lib*.a /example/library/path | xargs nm | grep -E "T $SYMBOL_TO_FIND"

This command-line is an untested sketch, but it should show the concept.

Answer 2

If it's part of the C standard API then just run man, it should clearly state where the function is defined.