os_kernel/lib/user/syscall.c

#include "syscall.h"

#define _syscall0(NUMBER) ({                                           \
    int retval;                                                        \
    asm volatile("int $0x80" : "=a"(retval) : "a"(NUMBER) : "memory"); \
    retval;                                                            \
})
#define _syscall1(NUMBER, ARG1) ({ \
    int retval;                    \
    asm volatile(                  \
        "int $0x80"                \
        : "=a"(retval)             \
        : "a"(NUMBER), "b"(ARG1)   \
        : "memory");               \
    retval;                        \
})

#define _syscall2(NUMBER, ARG1, ARG2) ({    \
    int retval;                             \
    asm volatile(                           \
        "int $0x80"                         \
        : "=a"(retval)                      \
        : "a"(NUMBER), "b"(ARG1), "c"(ARG2) \
        : "memory");                        \
    retval;                                 \
})

#define _syscall3(NUMBER, ARG1, ARG2, ARG3) ({         \
    int retval;                                        \
    asm volatile(                                      \
        "int $0x80"                                    \
        : "=a"(retval)                                 \
        : "a"(NUMBER), "b"(ARG1), "c"(ARG2), "d"(ARG3) \
        : "memory");                                   \
    retval;                                            \
})

uint32_t getpid(void)
{
    return _syscall0(SYS_GETPID);
}