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, , \
                                  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, ), )) \
            {       \
                __set_errno (INTERNAL_SYSCALL_ERRNO \
                            (_sys_result, )); \
                _sys_result = (unsigned int) -;  \
            }    \
         (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(, , ,  , , , , );
}                                                                                                                  

预处理后即为：

void test(void)
{
 ({
      register int _a1 asm("r0"), _nr asm("r7");
      int _v1tmp = (int)();
      int _a4tmp = (int) ();
      int _a3tmp = (int)();
      int _a2tmp = (int)();
      int _a1tmp = (int)();
      _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 = ;
      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, #
    sub sp, sp, #
 
    mov r3, #
    str r3, [fp, #-]
 
    mov r3, #
    str r3, [fp, #-]
 
    mov r3, #
    str r3, [fp, #-]
 
    mov r3, #
    str r3, [fp, #-]
 
    mov r3, #
    str r3, [fp, #-]
 
    ldr r0, [fp, #-]
    ldr r1, [fp, #-]
    ldr r2, [fp, #-]
    ldr r3, [fp, #-]
    ldr r4, [fp, #-]
    mov r7, #
#APP
@  "go.c"
    swi 0x0
@  ""
    sub sp, fp, #
    ldmfd   sp!, {r4, r7, fp}
    bx  lr