Otokon C - Tartışma

decompiled-binary-opt-0.asm.md

Optimization Level 0 ( none )

foo function

Offset	Data	Command
00000ED0	55	pushq %rbp
00000ED1	488900000	movq %rsp, %rbp
00000ED4	4883EC10	subq $0x10, %rsp
00000ED8	48897DF8	movq %rdi, -0x8(%rbp)
00000EDC	488B7DF8	movq -0x8(%rbp), %rdi
00000EE0	8B07	movl (%rdi), %eax
00000EE2	8945F4	movl %eax, -0xc(%rbp)
00000EE5	48817DF800000000	cmpq $0x0, -0x8(%rbp)
00000EED	0F8505000000	jne 0x100000EF8
00000EF3	E905000000	jmpq 0x100000EFD
00000EF8	E843000000	callq "0x100000F40 (_bar)"
00000EFD	4883C410	addq $0x10, %rsp
00000F01	5D	popq %rbp
00000F02	C3	ret
00000F03	666666662E0F1F840000000000	nopw %cs: (%rax,%rax)

main function

Offset	Data	Command
00000F10	55	pushq %rbp
00000F11	4889E5	movq %rsp, %rbp
00000F14	4883EC10	subq $0x10, %rsp
00000F18	C745FC00000000	movl $0x0, -0x4(%rbp)
00000F1F	48C745F000000000	movq $0x0, -0x10(%rbp)
00000F27	488B7DF0	movq -0x10(%rbp), %rdi
00000F2B	E8A0FFFFFF	callq "0x100000ED0 (_foo)"
00000F30	31C0	xorl %eax, %eax
00000F32	4883C410	addq $0x10, %rsp
00000F36	5D	popq %rbp
00000F37	C3	ret
00000F38	90	nop
00000F39	90	nop
00000F3A	90	nop
00000F3B	90	nop
00000F3C	90	nop
00000F3D	90	nop
00000F3E	90	nop
00000F3F	90	nop

bar function

Offset	Data	Command
00000F40	55	pushq %rbp
00000F41	4889E5	movq %rsp, %rbp
00000F44	4883EC10	subq $0x10, %rsp
00000F48	488D3D33000000	leaq "0x1000000F82: "bar\n""(%rip), %rdi
00000F4F	B000	movb $0x0, %al
00000F51	E80A000000	callq "[0x100000F60->_printf]"
00000F56	8945FC	movl %eax, -0x4(%rbp)
00000F59	4883C410	addq $0x10, %rsp
00000F5D	5D	popq %rbp
00000F5E	C3	ret

decompiled-binary-opt-1.asm.md

Optimization Level 1 (min)

foo function

Offset	Data	Command
00000F10	55	pushq %rbp
00000F11	4889E5	movq %rsp, %rbp
00000F14	4885FF	testq %rdi, %rdi
00000F17	7406	je 0x100000f1f
00000F19	5D	popq %rbp
00000F1A	E921000000	jmpq "0x100000F40 (_bar)"
00000F1F	5D	popq %rbp
00000F20	C3	ret
00000F21	6666666666662E0F1F840000000000	nopw %cs:(%rax,%rax)

main function

Offset	Data	Command
00000F30	55	pushq %rbp
00000F31	4889E5	movq %rsp, %rbp
00000F34	31FF	xorl %edi, %edi
00000F36	E8D5FFFFFF	callq "0x100000F10 (_foo)"
00000F3B	31C0	xorl %eax, %eax
00000F3D	5D	popq %rbp
00000F3E	C3	ret
00000F3F	90	nop

bar function

Offset	Data	Command
00000F40	55	pushq %rbp
00000F41	4889E5	movq %rsp, %rbp
00000F44	488D3D2C000000	leaq "0x1000000F77:"bar""(%rip), %rdi
00000F4B	5D	popq %rbp
00000F4C	E901000000	jmpq "[0x100000F52->_puts]"

decompiled-binary-opt-2.asm.md

Optimization Level 2 (mid)

foo function

Offset	Data	Command
00000F20	55	pushq %rbp
00000F21	4889E5	movq %rsp, %rbp
00000F24	4885FF	testq %rdi, %rdi
00000F27	7406	je 0x100000f2f
00000F29	5D	popq %rbp
00000F2A	E921000000	jmpq "0x100000F50 (_bar)"
00000F2F	5D	popq %rbp
00000F30	C3	ret
00000F31	6666666666662E0F1F840000000000	nopw %cs:(%rax,%rax)

main function

Offset	Data	Command
00000F40	55	pushq %rbp
00000F41	4889E5	movq %rsp, %rbp
00000F44	31C0	xorl %eax, %eax
00000F46	5D	popq %rbp
00000F47	C3	ret
00000F48	90	nop
00000F49	90	nop
00000F4A	90	nop
00000F4B	90	nop
00000F4C	90	nop
00000F4D	90	nop
00000F4E	90	nop
00000F4F	90	nop

bar function

Offset	Data	Command
00000F50	55	pushq %rbp
00000F51	4889E5	movq %rsp, %rbp
00000F54	488D3D27000000	leaq "0x1000000F82:"bar""(%rip), %rdi
00000F5B	5D	popq %rbp
00000F5C	E901000000	jmpq "[0x100000F62->_puts]"

decompiled-binary-opt-3.asm.md

Optimization Level 3 (max)

same as opt-level-2

foo function

Offset	Data	Command
00000F20	55	pushq %rbp
00000F21	4889E5	movq %rsp, %rbp
00000F24	4885FF	testq %rdi, %rdi
00000F27	7406	je 0x100000f2f
00000F29	5D	popq %rbp
00000F2A	E921000000	jmpq "0x100000F50 (_bar)"
00000F2F	5D	popq %rbp
00000F30	C3	ret
00000F31	6666666666662E0F1F840000000000	nopw %cs:(%rax,%rax)

main function

Offset	Data	Command
00000F40	55	pushq %rbp
00000F41	4889E5	movq %rsp, %rbp
00000F44	31C0	xorl %eax, %eax
00000F46	5D	popq %rbp
00000F47	C3	ret
00000F48	90	nop
00000F49	90	nop
00000F4A	90	nop
00000F4B	90	nop
00000F4C	90	nop
00000F4D	90	nop
00000F4E	90	nop
00000F4F	90	nop

bar function

Offset	Data	Command
00000F50	55	pushq %rbp
00000F51	4889E5	movq %rsp, %rbp
00000F54	488D3D27000000	leaq "0x1000000F82:"bar""(%rip), %rdi
00000F5B	5D	popq %rbp
00000F5C	E901000000	jmpq "[0x100000F62->_puts]"

idonotknow-extern.c

#include<stdio.h>
void bar(void){
    printf("bar\n");
}

idonotknow.c

#include<stdio.h>
extern void bar(void);
void foo(int *x)
{
    int y = *x;  /* (1) */
    if(!x)       /* (2) */
    {
        return;    /* (3) */
    }
    bar();
    return;
}
int main(void){
    int* temp=NULL;
    foo(temp);
    return 0;
}

Örnek derleme ve linkleme

gcc idontknow.c idontknow-extern.c -o question2.run --> decompile --> decompiled-binary-opt-0.asm.md

Gcc optimizasyonu etkinleştirerek aynı işlemi 3 farklı şekilde yapabiliyoruz.

gcc -O1 idontknow.c idontknow-extern.c -o question2.run
gcc -O2 idontknow.c idontknow-extern.c -o question2.run
gcc -O3 idontknow.c idontknow-extern.c -o question2.run

her farklı çalıştırılabilir dosyayı de-compile edip 4 farklı assembly dosyası elde edebiliriz.

Sırasıyla

• decompiled-binary-opt-0.asm.md ( sıfır optimizasyon )
• decompiled-binary-opt-1.asm.md
• decompiled-binary-opt-2.asm.md
• decompiled-binary-opt-3.asm.md ( maximum optimizasyon )