Compile error: relocation R_X86_64_PC32 against undefined symbol [duplicate]

Question

I try to make functions in assembly language and put them in a dynamic library so I create .o with .S with this command:
nasm -f elf64 hello.S -o hello.o
but when I want to create the lib with gcc:
gcc -fPIC -shared hello.o -o libasm.so
and it displays me this error:
/usr/bin/ld: hello.o: relocation R_X86_64_PC32 against undefined symbol printf@@GLIBC_2.2.5 can not be used when making a shared object; recompile with -fPIC

Comedienne

See nasm.us/xdoc/2.10rc8/html/nasmdoc9.html#section-9.2.5 (Calling procedures outside the library) – Corned

Answer 1

From http://www.nasm.us/xdoc/2.10rc8/html/nasmdoc9.html#section-9.2.5:

To call an external routine, you must use another special PIC relocation type, WRT ..plt. This is much easier than the GOT-based ones: you simply replace calls such as CALL printf with the PLT-relative version CALL printf WRT ..plt.

so instead of

; ...
call     printf

use

; ...
call     printf WRT ..plt

and compile and link as normal.

BTW, "WRT" means "With Respect To ...", i.e, "in the context of ..."

Wesson

Or better, call [rel printf wrt ..got] like gcc -fno-plt uses. Full details in Can't call C standard library function on 64-bit Linux from assembly (yasm) code – Jolenejolenta

maybe this should be closed as duplicate of that if the justification for ..got appears there? – Wesson

I already did close it as a duplicate, right after updating my answer on the linked question to include a TL:DR at the top :P And yes, my answer there describes the fact that using the GOT pointer directly removes the layer of indirection through the PLT. – Jolenejolenta

ah, way ahead of me – Wesson