前置知识

系统调用

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指令级别

_FFFFFF,t_70,g_se,x_16)

参数传值顺序

EBX,EXC,EDX,ESI,EDI,EBP

系统调用

time系统调用

time_asm.c

#include<stdio.h>
#include<time.h>

int main(){
	time_t tt;
	struct tm *t;
	asm volatile(
		"mov $0,%%ebx\n\t"
		"mov $0xd,%%eax\n\t"
		"int 0x80\n\t"
		"mov %%eax,%0\n\t"
		:"=m"(tt)
	);
	t = localtime(&tt);
	printf("time:%d:%d:%d:%d:%d:%d:\n",t->tm_year+1900,t->tm_mon,t->tm_mday,t->tm_hour,t->tm_min,t->tm_sec);
	return 0;
}

这个代码有个地方好像是错的
t->tm_mda===>t->tm_mday

rename 系统调用

rename.c

#include<stdio.h>
int main(){
	int ret;//承接系统返回值
	char *oldname="hello.c";
	char *newname="newhello.c";
	ret = rename(oldname,newname);
	if(ret == 0)
		printf("Rename ok");
	else
		printf("Rename failed");
	
	return 0;
}

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rename_asm.c

#include<stdio.h>
int main(){
	int ret;
	char *oldname="hello.c";
	char *newname="newhello.c";
	asm volatile(
		"movl %2,%%ecx\n\t" //newname是第二个值，所以赋给ecx 
		"movl %1,%%ebx\n\t" //oldname 是第一个值，所以赋给ebx
		"movl $0x26,%%eax\n\t" //rename的系统调用号是38
		："=a"(ret)
		:"b"(oldname),"c"(newname)
	);
	if(ret ==0 )
		printf("Rename ok!");
	else
		printf("Rename failed");
		return 0;
}

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syscall.c

#include<stdio.h>
#include<sys/syscall.h>
int main(){
	int ret;
	char *oldname="hello.c";
	char *newname="newhello.c";
	ret = syscall(SYS_reanme,oldname,newname);
		if(ret ==0 )
		printf("Rename ok!");
	else
		printf("Rename failed");
		return 0;