Porting to .intel_syntax Inline Assembly / "m" Constraint with .intel_syntax / Targeting -fPIC

[Daniel Yek <dyek at real dot com>]

Hi,

I have several questions regarding GCC Inline Assembly support.

(1)
I'm porting (reasonably big) blocks of Intel-syntax Inline Assembly to 
GCC/Linux.

I would like to find out if it is a good idea to utilize GCC's 
.intel_syntax Inline Assembly support (for non-trivial blocks), or to 
convert them to GAS or NASM assembly functions, .S files.

(2)
The source Inline Assembly blocks make full use of available x86 
registers, thus causing out-of-registers problem when -fPIC is used, 
where one register is used for GOT addressing.

Is there a way I can use the memory constraint, "m", effectively in 
.intel_syntax Inline Assembly?

In the following Inline Assembly sample, how can I specify "m" memory 
constraint in .intel_syntax (and has the proper syntax generated)?

   asm __volatile__ (
       ".intel_syntax noprefix       \n\t"
       "mov     ebp, eax             \n\t"
       "mov     ebp, %8              \n\t"
       ...
       ".att_syntax noprefix         \n\t"
   : /* Output operands */
       "=a" (dummy)
     //, "=b" (dummy)
     , "=D" (dummy)
     , "=S" (dummy)
     , "=c" (dummy)
   : /* Input operands */
       "0" (param0)
     //, "1" (var0)
     , "1" (var1)
     , "2" (param1)
     , "3" (var2)

     , "m" (var0)
   );

COMMAND LINE:
gcc -fPIC -DPIC -S -o temp.S temp.c

OUTPUT:
#APP
   .intel_syntax noprefix      
   mov     ebp, eax            
   mov     ebp, -28(%ebp)       // Trouble: AT&T syntax in .intel_syntax!

See attached files for complete .c and .S files.

(3) Is there any document providing information how I can create a 
single version of assembly code (Inline Assembly or pure assembly) and 
have it compiled with or without -fPIC correctly?

Thanks for any help.

--
Daniel.

#include <stdio.h>

int func(unsigned int param0, unsigned int param1, unsigned int param2, unsigned int param3)
{
    unsigned int dummy = 0;
    unsigned int var0 = 10;
    unsigned int var1 = 20;
    unsigned int var2 = 30;
    unsigned int var3 = 40;

    asm __volatile__ (
        ".intel_syntax noprefix       \n\t"
        //"mov     eax, param0          \n\t"
        //"mov     ebx, var0            \n\t"
        //"mov     edi, var1            \n\t"
        //"mov     esi, param1          \n\t"
        //"mov     ecx, var2            \n\t"
        "mov     ebp, eax             \n\t"
        "mov     ebp, %8              \n\t"
        "mov     ebp, edi             \n\t"
        "mov     ebp, esi             \n\t"
        "mov     ebp, ecx             \n\t"
        ".att_syntax noprefix         \n\t"
    : /* Output operands */
        "=a" (dummy)
      //, "=b" (dummy)
      , "=D" (dummy)
      , "=S" (dummy)
      , "=c" (dummy)
    : /* Input operands */
        "0" (param0)
      //, "1" (var0)
      , "1" (var1)
      , "2" (param1)
      , "3" (var2)

      , "m" (var0)
    : /* Clobbered registers */
        "memory"
    );
    return 0;
}

int main(int argc, char **argv)
{
    return 0;
}


	.file	"temp.c"
	.text
.globl func
	.type	func, @function
func:
	pushl	%ebp
	movl	%esp, %ebp
	pushl	%edi
	pushl	%esi
	subl	$32, %esp
	movl	$0, -24(%ebp)
	movl	$10, -28(%ebp)
	movl	$20, -20(%ebp)
	movl	$30, -16(%ebp)
	movl	$40, -12(%ebp)
	movl	8(%ebp), %eax
	movl	-20(%ebp), %edi
	movl	12(%ebp), %esi
	movl	-16(%ebp), %ecx
#APP
	.intel_syntax noprefix       
	mov     ebp, eax             
	mov     ebp, -28(%ebp)              
	mov     ebp, edi             
	mov     ebp, esi             
	mov     ebp, ecx             
	.att_syntax noprefix         
	
#NO_APP
	movl	%eax, -24(%ebp)
	movl	%edi, -24(%ebp)
	movl	%esi, -24(%ebp)
	movl	%ecx, -24(%ebp)
	movl	$0, %eax
	addl	$32, %esp
	popl	%esi
	popl	%edi
	popl	%ebp
	ret
	.size	func, .-func
.globl main
	.type	main, @function
main:
	leal	4(%esp), %ecx
	andl	$-16, %esp
	pushl	-4(%ecx)
	pushl	%ebp
	movl	%esp, %ebp
	pushl	%ecx
	movl	$0, %eax
	popl	%ecx
	popl	%ebp
	leal	-4(%ecx), %esp
	ret
	.size	main, .-main
	.ident	"GCC: (GNU) 4.1.1"
	.section	.note.GNU-stack,"",@progbits