linker - Linking error using gcc in Ubuntu 11.10

Question

I'm trying to compile and run a simple "Hello World" program in C, and I get a strange error of multiple definition of some C stdlib functions

The .c file is:

#include <stdio.h>
#include <stdlib.h>

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

  printf("hello world
");
  return 0;
}

the commands I use to compile and create an executable are:

gcc -Werror -Wall src/main.c -o bin/m.o
gcc -Werror -Wall bin/m.o -o bin/m

The compilation part goes fine, but in the second command, where I invoke the GCC Linker to create an executable I get the following errors:

bin/m.o: In function `_fini':
(.fini+0x0): multiple definition of `_fini'
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../x86_64-linux-gnu/crti.o:(.fini+0x0): first defined here
bin/m.o: In function `__data_start':
(.data+0x0): multiple definition of `__data_start'
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 0 has invalid symbol index 10
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 1 has invalid symbol index 11
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 2 has invalid symbol index 2
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 3 has invalid symbol index 2
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 4 has invalid symbol index 10
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 5 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 6 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 7 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 8 has invalid symbol index 2
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 9 has invalid symbol index 2
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 10 has invalid symbol index 11
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 11 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 12 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 13 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 14 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 15 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 16 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 17 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 18 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 19 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 20 has invalid symbol index 19
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../x86_64-linux-gnu/crt1.o:(.data+0x0): first defined here
bin/m.o: In function `__data_start':
(.data+0x8): multiple definition of `__dso_handle'
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/crtbegin.o:(.data+0x0): first defined here
bin/m.o:(.rodata+0x0): multiple definition of `_IO_stdin_used'
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../x86_64-linux-gnu/crt1.o:             (.rodata.cst4+0x0): first defined here
bin/m.o: In function `_start':
(.text+0x0): multiple definition of `_start'
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_line): relocation 0 has invalid symbol index 2
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../x86_64-linux-gnu/crt1.o:/build/buildd    /eglibc-2.13/csu/../sysdeps/x86_64/elf/start.S:109: first defined here
bin/m.o: In function `_init':
(.init+0x0): multiple definition of `_init'
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/../../../x86_64-linux-gnu/crti.o:(.init+0x0): first     defined here
/usr/lib/gcc/x86_64-linux-gnu/4.6.1/crtend.o:(.dtors+0x0): multiple definition of     `__DTOR_END__'
bin/m.o:(.dtors+0x8): first defined here
/usr/bin/ld: error in bin/m.o(.eh_frame); no .eh_frame_hdr table will be created.
collect2: ld returned 1 exit status

by the way, when I run the m.o file with the bash executing prefix, it works just fine

never programed in C or anything, I'm trying to start, but this holds me back

Answer 1

You need a -c in the compile step, or else your m.o object will be a fully linked executable. Example:

gcc -Werror -Wall -c src/main.c -o bin/m.o
gcc -Werror -Wall bin/m.o -o bin/m

The difference would be immediately obvious if your program was composed of more than just the single translation unit. If you had file1.c and file2.c, for example:

gcc -c file1.c -o file1.o
gcc -c file2.c -o file2.o
gcc file1.o file2.o -o app

Is correct, whereas if you had:

gcc file1.c -o file1.o
gcc file2.c -o file2.o
gcc file1.o file2.o -o app

Both the first and second lines would fail before you even got to the final link stage, since they would be missing symbols.