language

understand gcc assembly output

0x00 generate assembly code when compile

gcc -S -o test.s test.c

sample code

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#include <stdio.h>

int main(int argc, char* argv[])
{
	int i = 0;
	for (i=0; i<10; i++) {
		printf("hello123");
	}
	return 0;
}

assembly code:

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	.file	"test.c"
	.section	.rodata
.LC0:
	.string	"hello123"
	.text
	.globl	main
	.type	main, @function
main:
.LFB0:
	.cfi_startproc
	pushq	%rbp
	.cfi_def_cfa_offset 16
	.cfi_offset 6, -16
	movq	%rsp, %rbp
	.cfi_def_cfa_register 6
	subq	$32, %rsp
	movl	%edi, -20(%rbp)
	movq	%rsi, -32(%rbp)
	movl	$0, -4(%rbp)
	movl	$0, -4(%rbp)
	jmp	.L2
.L3:
	movl	$.LC0, %edi
	movl	$0, %eax
	call	printf
	addl	$1, -4(%rbp)
.L2:
	cmpl	$9, -4(%rbp)
	jle	.L3
	movl	$0, %eax
	leave
	.cfi_def_cfa 7, 8
	ret
	.cfi_endproc
.LFE0:
	.size	main, .-main
	.ident	"GCC: (Ubuntu 4.8.4-2ubuntu1~14.04.1) 4.8.4"
	.section	.note.GNU-stack,"",@progbits

0x01 basic acknowledge of assembly [AT&T]

  • Register
  • Move

0x02 Reference