How do I compile the asm generated by GCC?

Question

I\'m playing around with some asm code, and something is bothering me.

I compile this:

#include 

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


        

Answer 1

You can embed the assembly code in a normal C program. Here's a good introduction. Using the appropriate syntax, you can also tell GCC you want to interact with variables declared in C. The program below instructs gcc that:

• eax shall be foo
• ebx shall be bar
• the value in eax shall be stored in foo after the assembly code executed

\n

int main(void)
{
        int foo = 10, bar = 15;
        __asm__ __volatile__("addl  %%ebx,%%eax"
                             :"=a"(foo)
                             :"a"(foo), "b"(bar)
                             );
        printf("foo+bar=%d\n", foo);
        return 0;
}

Answer 2

nasm -f bin -o 2_hello 2_hello.asm

Answer 3

gcc can use an assembly file as input, and invoke the assembler as needed. There is a subtlety, though:

• If the file name ends with ".s" (lowercase 's'), then gcc calls the assembler.
• If the file name ends with ".S" (uppercase 'S'), then gcc applies the C preprocessor on the source file (i.e. it recognizes directives such as #if and replaces macros), and then calls the assembler on the result.

So, on a general basis, you want to do things like this:

gcc -S file.c -o file.s
gcc -c file.s

Answer 4

Yes, gcc can also compile assembly source code. Alternatively, you can invoke as, which is the assembler. (gcc is just a "driver" program that uses heuristics to call C compiler, C++ compiler, assembler, linker, etc..)

Answer 5

You can use GAS, which is gcc's backend assembler:

http://linux.die.net/man/1/as

Answer 6

Yes, You can use gcc to compile your asm code. Use -c for compilation like this:

gcc -c file.S -o file.o

This will give object code file named file.o. To invoke linker perform following after above command:

gcc file.o -o file