How to set the dynamic linker path for a shared library?

I want to compile a shared library with an .interp segment.

#include <stdio.h>

int foo(int argc, char** argv) {

    printf("Hello, world!\n");
    return 0;

}

I'm using the following commands.

gcc -c -o test.o test.c
ld --dynamic-linker=blah -shared -o test.so test.o

I end up without an INTERP segment, as if I never passed the --dynamic-linker=blah option. C开发者_运维百科heck with readelf -l test.so. When building an executable, the linker processes the option correctly and puts an INTERP segment in the program header. How to do I make it work for shared libraries too?

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ld doesn't include a .interp section if -shared is used, as @MichaelDillon already said. You can however provide this section yourself.

const char interp_section[] __attribute__((section(".interp"))) = "/path/to/dynamic/linker";

The line above will save the string "/path/to/dynamic/linker" in the .interp section using GCC attributes.

If you're trying to build a shared object that's also executable by itself, check this question out. It has a more comprehensive description of the process.

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The INTERP segment only goes into binaries which need to load the ELF interpreter (ld.so) in the first place. A shared library has no INTERP segment because the ELF interpreter is already loaded before the shared library is loaded.

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In most linux systems the ldconfig is run at every system boot and it looks definitions in /etc/ld.so.conf for looking in directories that have shared libraries. In the file /etc/ld.so.cache there are mappings for shared libraries sonames and the library full path. Consider reading this article: http://grahamwideman.wordpress.com/2009/02/09/the-linux-loader-and-how-it-finds-libraries/#comment-164