syscall.c

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#include <sys/syscall.h>
#include <stddef.h>
#include <sys/types.h>
#include <stdio.h>
#include <stdarg.h>
#include <errno.h>

static inline int syscall0(int fn)
{
        int ret;

        asm volatile (
                "movl %1, %%eax\n"
                "movl $0, %%ecx\n"
                "int $0x31\n"
                "movl %%eax, %0\n"
                : "=m"(ret)
                : "m"(fn)
                : "memory", "%eax", "%ecx"
        );

        return ret;
}

static inline int syscall1(int fn, int arg)
{
        int ret;

        asm volatile (
                "pushl %1\n"
                "movl %2, %%eax\n"
                "movl $1, %%ecx\n"
                "int $0x31\n"
                "addl $4, %%esp\n"
                "movl %%eax, %0\n"
                : "=m"(ret)
                : "m"(arg), "m"(fn)
                : "memory", "%eax", "%ecx", "%esp"
        );

        return ret;
}

static inline int syscall2(int fn, int arg[2])
{
        int ret;

        asm volatile (
                "pushl %1\n"
                "pushl %2\n"
                "movl %3, %%eax\n"
                "movl $2, %%ecx\n"
                "int $0x31\n"
                "addl $8, %%esp\n"
                "movl %%eax, %0\n"
                : "=m"(ret)
                : "m"(arg[0]), "m"(arg[1])
                : "memory", "%eax", "%ecx", "%esp"
        );

        return ret;
}

static inline int syscall3(int fn, int arg[3])
{
        int ret;

        asm volatile (
                "pushl %1\n"
                "pushl %2\n"
                "pushl %3\n"
                "movl %4, %%eax\n"
                "movl $3, %%ecx\n"
                "int $0x31\n"
                "addl $12, %%esp\n"
                "movl %%eax, %0\n"
                : "=m"(ret)
                : "m"(arg[0]), "m"(arg[1]), "m"(arg[2]), "m"(fn)
                : "memory", "%eax", "%ecx", "%esp"
        );

        return ret;
}

int syscall(int fn, ...)
{
        va_list ap;
        int arg[3];
        int ret;

        switch (fn) {
        case SYS_NR_OPEN: /* 3 */
        case SYS_NR_READ: /* 3 */
        case SYS_NR_WRITE: /* 3 */
        case SYS_NR_SEEK: /* 3 */
                va_start(ap, fn);
                arg[0] = (int)va_arg(ap, int);
                arg[1] = (int)va_arg(ap, int);
                arg[2] = (int)va_arg(ap, int);
                ret = syscall3(fn, arg);
                va_end(ap);
                break;
        case SYS_NR_CLOSE: /* 1 */
        case SYS_NR_OPENDIR: /* 1 */
        case SYS_NR_CLOSEDIR: /* 1 */
        case SYS_NR_READDIR: /* 1 */
                va_start(ap, fn);
                arg[0] = (int)va_arg(ap, int);
                ret = syscall1(fn, arg[0]);
                va_end(ap);
                break;
        case SYS_NR_YIELD: /* 0 */
                ret = syscall0(fn);
                break;
        default:
                ret = -ENOSYS;
                break;
        }

        return ret;
}

/* End of a file */