glibc中fork系统调用传参

因为想跟踪下在新建进程时，如何处理新建进程的vruntime，所以跟踪了下fork。

 

以glic-2.17中ARM为例（unicore架构的没找到）,实际上通过寄存器向系统调用传递的参数为：

r7: __NR_clone 120

r0: CLONE_CHILD_SETTID | CLONE_CHILD_CLEARTID | SIGCHLD

r1: NULL

r2: NULL

r3: NULL

r4: &THREAD_SELF->tid

fork()---->__fork()---->__libc_fork()



__libc_fork()---->INLINE_SYSCALL (clone, 5, \

                                  CLONE_CHILD_SETTID | \

                                  CLONE_CHILD_CLEARTID | \

                                  SIGCHLD, \

                                  NULL, NULL, NULL, &THREAD_SELF->tid)

 

#define INLINE_SYSCALL(name, nr, args...)  \

      ({ unsigned int _sys_result = \
                  INTERNAL_SYSCALL (name, , nr, args); \

            if (__builtin_expect \
                (INTERNAL_SYSCALL_ERROR_P (_sys_result, ), 0)) \

            {       \       

                __set_errno (INTERNAL_SYSCALL_ERRNO \
                            (_sys_result, )); \       

                _sys_result = (unsigned int) -1;  \       

            }    \       

         (int) _sys_result; })

 

#define INTERNAL_SYSCALL(name, err, nr, args...)   \       

            INTERNAL_SYSCALL_RAW(SYS_ify(name), err, nr, args)



//#define __NR_clone 120

#define SYS_ify(syscall_name)   (__NR_##syscall_name)

 

//err没用使用，也没有传递宏参，第一次见到
# define INTERNAL_SYSCALL_RAW(name, err, nr, args...)           \       

  ({                                                            \       

          register int _a1 asm ("r0"), _nr asm ("r7");          \       

          LOAD_ARGS_##nr (args)                                 \       

          _nr = name;                                           \       

          asm volatile ("swi       0x0     @ syscall " #name    \       

                        : "=r" (_a1)                            \       

                        : "r" (_nr) ASM_ARGS_##nr               \       

                        : "memory");                            \       

    _a1; })                                                                                                        

关于宏INTERAL_SYSCALL_RAW还是满有意思的，写了个函数测试下，真实的看下库如何向系统调用传参：

#define LOAD_ARGS_0()

#define ASM_ARGS_0





#define LOAD_ARGS_1(a1) \

    int _a1tmp = (int)(a1); \

    LOAD_ARGS_0 () \

    _a1 = _a1tmp;



#define ASM_ARGS_1 ASM_ARGS_0, "r" (_a1)







#define LOAD_ARGS_2(a1, a2) \

    int _a2tmp = (int)(a2); \

    LOAD_ARGS_1(a1) \

    register int _a2 asm ("a2") = _a2tmp;



#define ASM_ARGS_2 ASM_ARGS_1, "r" (_a2)







#define LOAD_ARGS_3(a1, a2, a3) \

    int _a3tmp = (int)(a3); \

    LOAD_ARGS_2 (a1, a2) \

    register int _a3 asm ("a3") = _a3tmp;



#define ASM_ARGS_3 ASM_ARGS_2, "r" (_a3)







#define LOAD_ARGS_4(a1, a2, a3, a4) \

    int _a4tmp = (int) (a4); \

    LOAD_ARGS_3 (a1, a2, a3) \

    register int _a4 asm ("a4") = _a4tmp;



#define ASM_ARGS_4 ASM_ARGS_3, "r" (_a4)







#define LOAD_ARGS_5(a1, a2, a3, a4, a5) \

    int _v1tmp = (int)(a5); \

    LOAD_ARGS_4 (a1, a2, a3, a4) \

    register int _v1 asm ("v1") = _v1tmp; 



#define ASM_ARGS_5 ASM_ARGS_4, "r" (_v1)



#define INTERNAL_SYSCALL_RAW(name, err, nr, args...) \

    ({ \

        register int _a1 asm("r0"), _nr asm("r7"); \

        LOAD_ARGS_5 (args) \

        _nr = name; \

        asm volatile ("swi 0x0" \

                      : "=r" (_a1) \

                      : "r" (_nr) ASM_ARGS_##nr \

                      : "memory" \

                     ); \

        _a1; \

     })



void test(void)

{

    INTERNAL_SYSCALL_RAW(120, , 5,  6, 7, 8, 9, 0);

}                                                                                                                  

 

预处理后即为：

void test(void)                                                                                                    

{

 ({ 

      register int _a1 asm("r0"), _nr asm("r7"); 

      int _v1tmp = (int)(0); 

      int _a4tmp = (int) (9); 

      int _a3tmp = (int)(8); 

      int _a2tmp = (int)(7); 

      int _a1tmp = (int)(6); 

      _a1 = _a1tmp; 

      register int _a2 asm ("a2") = _a2tmp; 

      register int _a3 asm ("a3") = _a3tmp; 

      register int _a4 asm ("a4") = _a4tmp; 

      register int _v1 asm ("v1") = _v1tmp; 

      _nr = 120;  

      asm volatile (

                      "swi 0x0" 

                      : "=r" (_a1) 

                      : "r" (_nr) , "r" (_a1), "r" (_a2),
                        "r" (_a3), "r" (_a4), "r" (_v1) 

                      : "memory" 

                  );      

      _a1;    

    });

}

相应的汇编代码：

test:                                                                                                              

    stmfd   sp!, {r4, r7, fp}

    add fp, sp, #8

    sub sp, sp, #28



    mov r3, #0

    str r3, [fp, #-32]



    mov r3, #9

    str r3, [fp, #-28]



    mov r3, #8

    str r3, [fp, #-24]



    mov r3, #7

    str r3, [fp, #-20]



    mov r3, #6

    str r3, [fp, #-16]



    ldr r0, [fp, #-16]

    ldr r1, [fp, #-20]

    ldr r2, [fp, #-24]

    ldr r3, [fp, #-28]

    ldr r4, [fp, #-32]

    mov r7, #120

#APP

@ 16 "go.c" 1

    swi 0x0

@ 0 "" 2

    sub sp, fp, #8

    ldmfd   sp!, {r4, r7, fp}

    bx  lr