70 lines
1.4 KiB
C
70 lines
1.4 KiB
C
struct syscall_result {
|
|
long val;
|
|
int errno;
|
|
};
|
|
|
|
static struct syscall_result syscall_return(long result)
|
|
{
|
|
struct syscall_result res;
|
|
if (((unsigned long)result) >= ((unsigned long)-125)) {
|
|
res.errno = - result;
|
|
res.val = -1;
|
|
} else {
|
|
res.errno = 0;
|
|
res.val = result;
|
|
}
|
|
return res;
|
|
}
|
|
static struct syscall_result syscall1(unsigned long nr, unsigned long arg1)
|
|
{
|
|
long res;
|
|
asm volatile(
|
|
"int $0x80"
|
|
: "=a" (res)
|
|
: "a" (nr), "b" (arg1));
|
|
return syscall_return(res);
|
|
|
|
}
|
|
|
|
static struct syscall_result syscall3(unsigned long nr, unsigned long arg1, unsigned long arg2,
|
|
unsigned long arg3)
|
|
{
|
|
long res;
|
|
asm volatile(
|
|
"int $0x80"
|
|
: "=a" (res)
|
|
: "a" (nr), "b" (arg1), "c" (arg2), "d" (arg3));
|
|
return syscall_return(res);
|
|
|
|
}
|
|
|
|
#define NR_exit 1
|
|
#define NR_write 4
|
|
/* Standard file descriptors */
|
|
#define STDIN_FILENO 0 /* Standard input */
|
|
#define STDOUT_FILENO 1 /* Standard output */
|
|
#define STDERR_FILENO 2 /* Standard error output */
|
|
|
|
typedef long ssize_t;
|
|
typedef unsigned long size_t;
|
|
|
|
static ssize_t write(int fd, const void *buf, size_t count)
|
|
{
|
|
struct syscall_result res;
|
|
res = syscall3(NR_write, fd, (unsigned long)buf, count);
|
|
return res.val;
|
|
}
|
|
|
|
static void _exit(int status)
|
|
{
|
|
struct syscall_result res;
|
|
res = syscall1(NR_exit, status);
|
|
}
|
|
|
|
static void main(void)
|
|
{
|
|
static const char msg[] = "hello world\r\n";
|
|
write(STDOUT_FILENO, msg, sizeof(msg));
|
|
_exit(0);
|
|
}
|