CODEWITHSUNDEEP
cgccassemblygnu-assembler
shebaw
shebaw

Reputation: 1925

Symbol name conflicts when using gas

I'm using gcc to generate assembly files from multiple c files. When I try to use gas to assemble the generated assembly files, it spits out this error because it finds the symbols defined in multiple files.

Error: symbol '.L???' is already defined

Looking at the documentation, .L prefixed files are supposed to be local symbol names so why is gas complaining when it finds the same symbol name in different files?

Upvotes: 0

Views: 456

Answers (1)

user35443
user35443

Reputation: 6413

I don't know what procedure are you using when compiling those files, but I ran into similar problems when I tried to compile output listing improperly.

Let's say you've got two files, main.c and foo.c:

/* main.c */
#include <stdio.h>
int main() {
    printf("Hello");
    if(5==7);
    else printf("Yes");
}

/* foo.c */
#include <stdio.h>
int foo() {
    printf("Single!");
    if(7==5);
    else printf("Yes");
}

If you produce assembly listing for every file individually, you can see...

    .file   "main.c"
    .def    ___main;    .scl    2;  .type   32; .endef
    .section .rdata,"dr"
LC0:
    .ascii "Hello\0"
LC1:
    .ascii "Yes\0"
    .text
    .globl  _main
    .def    _main;  .scl    2;  .type   32; .endef
_main:
....

    .file   "foo.c"
    .section .rdata,"dr"
LC0:
    .ascii "Single!\0"
LC1:
    .ascii "Yes\0"
    .text
    .globl  _foo
    .def    _foo;   .scl    2;  .type   32; .endef
_foo:
....

...that string constants used in the C code are also numbered individually for each file (LC0 and LC1 are present in both files, but they don't have the same content).

Now, if you try to compile these listings together...

as main.s foo.s

you get your errors...

foo.s:3: Error: Symbol `LC0` is already defined
foo.s:5: Error: Symbol `LC1` is already defined

The solution is not only to produce listings for each file separately, but also to compile every listing into separate object file and then link them.

as main.s -o main.o
as foo.s -o foo.o
gcc main.o foo.o

Upvotes: 1

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