© / Posted in Linux / May 30, 2008
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网上有很多文档介绍如何添加自定义的系统调用的，说的都特别详细，但是定义好自定义的系统调用后，察看新生成的内核符号表System.map中也出现了自己定义的系统调用，但是在编写用户程序进行测试时，发现问题了：
_syscall0–_syscall6宏在linux/unistd.h中没有了。致使用户测试程序没法进行。
我查阅了内核源码和Changelogs,发现在Linux2.6.19.1中这些宏还在,如下：
#include
/*
* user-visible error numbers are in the range -1 - -MAX_ERRNO: see
*
*/
#define __syscall_return(type, res) \
do { \
if ((unsigned long)(res) >= (unsigned long)(-MAX_ERRNO)) { \
errno = -(res); \
res = -1; \
} \
return (type) (res); \
} while (0)
/* XXX - _foo needs to be __foo, while __NR_bar could be _NR_bar. */
#define _syscall0(type,name) \
type name(void) \
{ \
long __res; \
__asm__ volatile (”int $0×80” \
: “=a” (__res) \
: “0” (__NR_##name)); \
__syscall_return(type,__res); \
}
#define _syscall1(type,name,type1,arg1) \
type name(type1 arg1) \
{ \
long __res; \
__asm__ volatile (”push %%ebx ; movl %2,%%ebx ; int $0×80 ; pop %%ebx” \
: “=a” (__res) \
: “0” (__NR_##name),”ri” ((long)(arg1)) : “memory”); \
__syscall_return(type,__res); \
}
#define _syscall2(type,name,type1,arg1,type2,arg2) \
type name(type1 arg1,type2 arg2) \
{ \
long __res; \
__asm__ volatile (”push %%ebx ; movl %2,%%ebx ; int $0×80 ; pop %%ebx” \
: “=a” (__res) \
: “0” (__NR_##name),”ri” ((long)(arg1)),”c” ((long)(arg2)) \
: “memory”); \
__syscall_return(type,__res); \
}
#define _syscall3(type,name,type1,arg1,type2,arg2,type3,arg3) \
type name(type1 arg1,type2 arg2,type3 arg3) \
{ \
long __res; \
__asm__ volatile (”push %%ebx ; movl %2,%%ebx ; int $0×80 ; pop %%ebx” \
: “=a” (__res) \
: “0” (__NR_##name),”ri” ((long)(arg1)),”c” ((long)(arg2)), \
“d” ((long)(arg3)) : “memory”); \
__syscall_return(type,__res); \
}
#define _syscall4(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4) \
type name (type1 arg1, type2 arg2, type3 arg3, type4 arg4) \
{ \
long __res; \
__asm__ volatile (”push %%ebx ; movl %2,%%ebx ; int $0×80 ; pop %%ebx” \
: “=a” (__res) \
: “0” (__NR_##name),”ri” ((long)(arg1)),”c” ((long)(arg2)), \
“d” ((long)(arg3)),”S” ((long)(arg4)) : “memory”); \
__syscall_return(type,__res); \
}
#define _syscall5(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4, \
type5,arg5) \
type name (type1 arg1,type2 arg2,type3 arg3,type4 arg4,type5 arg5) \
{ \
long __res; \
__asm__ volatile (”push %%ebx ; movl %2,%%ebx ; movl %1,%%eax ; ” \
“int $0×80 ; pop %%ebx” \
: “=a” (__res) \
: “i” (__NR_##name),”ri” ((long)(arg1)),”c” ((long)(arg2)), \
“d” ((long)(arg3)),”S” ((long)(arg4)),”D” ((long)(arg5)) \
: “memory”); \
__syscall_return(type,__res); \
}
#define _syscall6(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4, \
type5,arg5,type6,arg6) \
type name (type1 arg1,type2 arg2,type3 arg3,type4 arg4,type5 arg5,type6 arg6) \
{ \
long __res; \
struct { long __a1; long __a6; } __s = { (long)arg1, (long)arg6 }; \
__asm__ volatile (”push %%ebp ; push %%ebx ; movl 4(%2),%%ebp ; ” \
“movl 0(%2),%%ebx ; movl %1,%%eax ; int $0×80 ; ” \
“pop %%ebx ; pop %%ebp” \
: “=a” (__res) \
: “i” (__NR_##name),”0” ((long)(&__s)),”c” ((long)(arg2)), \
“d” ((long)(arg3)),”S” ((long)(arg4)),”D” ((long)(arg5)) \
: “memory”); \
__syscall_return(type,__res); \
}
但是到了Linux2.6.20,这些宏就没有定义了。Changelog中有说是Remove these macros.原因是这些宏会导致系统安全漏洞，网上也有利用此漏洞的例子。
那我们以后自定义系统调用后如何调用呢？我将这些宏加入程序程序后，发现可以很好的运行。
下面是一个例子：
#include
#include
#include
/*
* user-visible error numbers are in the range -1 - -MAX_ERRNO: see
*
*/
#define __syscall_return(type, res) \
do { \
if ((unsigned long)(res) >= (unsigned long)(-MAX_ERRNO)) { \
errno = -(res); \
res = -1; \
} \
return (type) (res); \
} while (0)
/* XXX - _foo needs to be __foo, while __NR_bar could be _NR_bar. */
#define _syscall0(type,name) \
type name(void) \
{ \
long __res; \
__asm__ volatile (”int $0×80” \
: “=a” (__res) \
: “0” (__NR_##name)); \
__syscall_return(type,__res); \
}
#define _syscall1(type,name,type1,arg1) \
type name(type1 arg1) \
{ \
long __res; \
__asm__ volatile (”push %%ebx ; movl %2,%%ebx ; int $0×80 ; pop %%ebx” \
: “=a” (__res) \
: “0” (__NR_##name),”ri” ((long)(arg1)) : “memory”); \
__syscall_return(type,__res); \
}
#define _syscall2(type,name,type1,arg1,type2,arg2) \
type name(type1 arg1,type2 arg2) \
{ \
long __res; \
__asm__ volatile (”push %%ebx ; movl %2,%%ebx ; int $0×80 ; pop %%ebx” \
: “=a” (__res) \
: “0” (__NR_##name),”ri” ((long)(arg1)),”c” ((long)(arg2)) \
: “memory”); \
__syscall_return(type,__res); \
}
#define _syscall3(type,name,type1,arg1,type2,arg2,type3,arg3) \
type name(type1 arg1,type2 arg2,type3 arg3) \
{ \
long __res; \
__asm__ volatile (”push %%ebx ; movl %2,%%ebx ; int $0×80 ; pop %%ebx” \
: “=a” (__res) \
: “0” (__NR_##name),”ri” ((long)(arg1)),”c” ((long)(arg2)), \
“d” ((long)(arg3)) : “memory”); \
__syscall_return(type,__res); \
}
#define _syscall4(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4) \
type name (type1 arg1, type2 arg2, type3 arg3, type4 arg4) \
{ \
long __res; \
__asm__ volatile (”push %%ebx ; movl %2,%%ebx ; int $0×80 ; pop %%ebx” \
: “=a” (__res) \
: “0” (__NR_##name),”ri” ((long)(arg1)),”c” ((long)(arg2)), \
“d” ((long)(arg3)),”S” ((long)(arg4)) : “memory”); \
__syscall_return(type,__res); \
}
#define _syscall5(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4, \
type5,arg5) \
type name (type1 arg1,type2 arg2,type3 arg3,type4 arg4,type5 arg5) \
{ \
long __res; \
__asm__ volatile (”push %%ebx ; movl %2,%%ebx ; movl %1,%%eax ; ” \
“int $0×80 ; pop %%ebx” \
: “=a” (__res) \
: “i” (__NR_##name),”ri” ((long)(arg1)),”c” ((long)(arg2)), \
“d” ((long)(arg3)),”S” ((long)(arg4)),”D” ((long)(arg5)) \
: “memory”); \
__syscall_return(type,__res); \
}
#define _syscall6(type,name,type1,arg1,type2,arg2,type3,arg3,type4,arg4, \
type5,arg5,type6,arg6) \
type name (type1 arg1,type2 arg2,type3 arg3,type4 arg4,type5 arg5,type6 arg6) \
{ \
long __res; \
struct { long __a1; long __a6; } __s = { (long)arg1, (long)arg6 }; \
__asm__ volatile (”push %%ebp ; push %%ebx ; movl 4(%2),%%ebp ; ” \
“movl 0(%2),%%ebx ; movl %1,%%eax ; int $0×80 ; ” \
“pop %%ebx ; pop %%ebp” \
: “=a” (__res) \
: “i” (__NR_##name),”0” ((long)(&__s)),”c” ((long)(arg2)), \
“d” ((long)(arg3)),”S” ((long)(arg4)),”D” ((long)(arg5)) \
: “memory”); \
__syscall_return(type,__res); \
}
#define __NR_mycall 325
_syscall1(int,mycall,int,rtvalue)
int main()
{
printf(”mycall(100)=%d\n”,mycall(100));
}
自定义的系统调用原型是
asmlinkage sys_mycall(int number)
{
return number;
}
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