compilefunc var-arg.c

Session

# Grab 'compilefunc' here:
# https://github.com/scottt/scottt-bin/blob/master/compilefunc

$ CFLAGS='-O0' compilefunc -s -l var-arg.c main
28	{
   0x0000000000400823 <+0>:	push   %rbp
   0x0000000000400824 <+1>:	mov    %rsp,%rbp

29		/* See 3.5.7 Variable Arugment Lists in http://www.x86-64.org/documentation/abi.pdf
30		 * "When a function taking variable-arguments is called, %rax must be set to the
31		 * total number of floating point parameters passed to the function in vector registers".
32		 */
33		f1("", 1l, -1.0);
   0x0000000000400827 <+4>:	movsd  0xe1(%rip),%xmm0        # 0x400910
   0x000000000040082f <+12>:	mov    $0x1,%esi
   0x0000000000400834 <+17>:	mov    $0x40090a,%edi
   0x0000000000400839 <+22>:	mov    $0x1,%eax
   0x000000000040083e <+27>:	callq  0x400536 <f1>

34		f2("", 1l, -1.0, 0.0);
   0x0000000000400843 <+32>:	pxor   %xmm1,%xmm1
   0x0000000000400847 <+36>:	movsd  0xc1(%rip),%xmm0        # 0x400910
   0x000000000040084f <+44>:	mov    $0x1,%esi
   0x0000000000400854 <+49>:	mov    $0x40090a,%edi
   0x0000000000400859 <+54>:	mov    $0x2,%eax
   0x000000000040085e <+59>:	callq  0x40067b <f2>

35		return 0;
   0x0000000000400863 <+64>:	mov    $0x0,%eax

36	}
   0x0000000000400868 <+69>:	pop    %rbp
   0x0000000000400869 <+70>:	retq   

$ CFLAGS='-O3' compilefunc -s -l var-arg.c main
28	{
   0x0000000000400440 <+0>:	sub    $0x8,%rsp

29		/* See 3.5.7 Variable Arugment Lists in http://www.x86-64.org/documentation/abi.pdf
30		 * "When a function taking variable-arguments is called, %rax must be set to the
31		 * total number of floating point parameters passed to the function in vector registers".
32		 */
33		f1("", 1l, -1.0);
   0x0000000000400444 <+4>:	mov    $0x1,%esi
   0x0000000000400449 <+9>:	mov    $0x400794,%edi
   0x000000000040044e <+14>:	movsd  0x34a(%rip),%xmm0        # 0x4007a0
   0x0000000000400456 <+22>:	mov    $0x1,%eax
   0x000000000040045b <+27>:	callq  0x400590 <f1>

34		f2("", 1l, -1.0, 0.0);
   0x0000000000400460 <+32>:	pxor   %xmm1,%xmm1
   0x0000000000400464 <+36>:	mov    $0x1,%esi
   0x0000000000400469 <+41>:	movsd  0x32f(%rip),%xmm0        # 0x4007a0
   0x0000000000400471 <+49>:	mov    $0x400794,%edi
   0x0000000000400476 <+54>:	mov    $0x2,%eax
   0x000000000040047b <+59>:	callq  0x400620 <f2>

35		return 0;
36	}
   0x0000000000400480 <+64>:	xor    %eax,%eax
   0x0000000000400482 <+66>:	add    $0x8,%rsp
   0x0000000000400486 <+70>:	retq   

$ CFLAGS='-Os' compilefunc -s -l var-arg.c main
28	{
   0x0000000000400440 <+0>:	push   %rax

29		/* See 3.5.7 Variable Arugment Lists in http://www.x86-64.org/documentation/abi.pdf
30		 * "When a function taking variable-arguments is called, %rax must be set to the
31		 * total number of floating point parameters passed to the function in vector registers".
32		 */
33		f1("", 1l, -1.0);
   0x0000000000400441 <+1>:	mov    $0x1,%esi
   0x0000000000400446 <+6>:	mov    $0x400754,%edi
   0x000000000040044b <+11>:	mov    $0x1,%al
   0x000000000040044d <+13>:	movsd  0x30b(%rip),%xmm0        # 0x400760
   0x0000000000400455 <+21>:	callq  0x400576 <f1>

34		f2("", 1l, -1.0, 0.0);
   0x000000000040045a <+26>:	xorps  %xmm1,%xmm1
   0x000000000040045d <+29>:	mov    $0x1,%esi
   0x0000000000400462 <+34>:	movsd  0x2f6(%rip),%xmm0        # 0x400760
   0x000000000040046a <+42>:	mov    $0x400754,%edi
   0x000000000040046f <+47>:	mov    $0x2,%al
   0x0000000000400471 <+49>:	callq  0x4005f4 <f2>

35		return 0;
36	}
   0x0000000000400476 <+54>:	xor    %eax,%eax
   0x0000000000400478 <+56>:	pop    %rdx
   0x0000000000400479 <+57>:	retq 

var-arg.c

/* Demonstrate stdarg ABI */

#include <stdarg.h>
#include <stdio.h>

int f1(const char *fmt, ...)
{
	va_list args;
	va_start(args, fmt);
	printf("%ld\n", va_arg(args, long));
	printf("%lf\n", va_arg(args, double));
	va_end(args);
	return 0;
}

int f2(const char *fmt, ...)
{
	va_list args;
	va_start(args, fmt);
	printf("%ld\n", va_arg(args, long));
	printf("%lf\n", va_arg(args, double));
	printf("%lf\n", va_arg(args, double));
	va_end(args);
	return 0;
}

int main()
{
	/* See 3.5.7 Variable Arugment Lists in http://www.x86-64.org/documentation/abi.pdf
	 * "When a function taking variable-arguments is called, %rax must be set to the
	 * total number of floating point parameters passed to the function in vector registers".
	 */
	f1("", 1l, -1.0);
	f2("", 1l, -1.0, 0.0);
	return 0;
}