1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * vdso_test.c: Sample code to test parse_vdso.c on x86
  4 * Copyright (c) 2011-2014 Andy Lutomirski
  5 *
  6 * You can amuse yourself by compiling with:
  7 * gcc -std=gnu99 -nostdlib
  8 *     -Os -fno-asynchronous-unwind-tables -flto -lgcc_s
  9 *      vdso_standalone_test_x86.c parse_vdso.c
 10 * to generate a small binary.  On x86_64, you can omit -lgcc_s
 11 * if you want the binary to be completely standalone.
 12 */
 13
 14#include <sys/syscall.h>
 15#include <sys/time.h>
 16#include <unistd.h>
 17#include <stdint.h>
 18
 19#include "parse_vdso.h"
 20
 21/* We need a libc functions... */
 22int strcmp(const char *a, const char *b)
 23{
 24	/* This implementation is buggy: it never returns -1. */
 25	while (*a || *b) {
 26		if (*a != *b)
 27			return 1;
 28		if (*a == 0 || *b == 0)
 29			return 1;
 30		a++;
 31		b++;
 32	}
 33
 34	return 0;
 35}
 36
 37/* ...and two syscalls.  This is x86-specific. */
 38static inline long x86_syscall3(long nr, long a0, long a1, long a2)
 39{
 40	long ret;
 41#ifdef __x86_64__
 42	asm volatile ("syscall" : "=a" (ret) : "a" (nr),
 43		      "D" (a0), "S" (a1), "d" (a2) :
 44		      "cc", "memory", "rcx",
 45		      "r8", "r9", "r10", "r11" );
 46#else
 47	asm volatile ("int $0x80" : "=a" (ret) : "a" (nr),
 48		      "b" (a0), "c" (a1), "d" (a2) :
 49		      "cc", "memory" );
 50#endif
 51	return ret;
 52}
 53
 54static inline long linux_write(int fd, const void *data, size_t len)
 55{
 56	return x86_syscall3(__NR_write, fd, (long)data, (long)len);
 57}
 58
 59static inline void linux_exit(int code)
 60{
 61	x86_syscall3(__NR_exit, code, 0, 0);
 62}
 63
 64void to_base10(char *lastdig, time_t n)
 65{
 66	while (n) {
 67		*lastdig = (n % 10) + '0';
 68		n /= 10;
 69		lastdig--;
 70	}
 71}
 72
 73__attribute__((externally_visible)) void c_main(void **stack)
 74{
 75	/* Parse the stack */
 76	long argc = (long)*stack;
 77	stack += argc + 2;
 78
 79	/* Now we're pointing at the environment.  Skip it. */
 80	while(*stack)
 81		stack++;
 82	stack++;
 83
 84	/* Now we're pointing at auxv.  Initialize the vDSO parser. */
 85	vdso_init_from_auxv((void *)stack);
 86
 87	/* Find gettimeofday. */
 88	typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
 89	gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday");
 90
 91	if (!gtod)
 92		linux_exit(1);
 93
 94	struct timeval tv;
 95	long ret = gtod(&tv, 0);
 96
 97	if (ret == 0) {
 98		char buf[] = "The time is                     .000000\n";
 99		to_base10(buf + 31, tv.tv_sec);
100		to_base10(buf + 38, tv.tv_usec);
101		linux_write(1, buf, sizeof(buf) - 1);
102	} else {
103		linux_exit(ret);
104	}
105
106	linux_exit(0);
107}
108
109/*
110 * This is the real entry point.  It passes the initial stack into
111 * the C entry point.
112 */
113asm (
114	".text\n"
115	".global _start\n"
116	".type _start,@function\n"
117	"_start:\n\t"
118#ifdef __x86_64__
119	"mov %rsp,%rdi\n\t"
120	"jmp c_main"
121#else
122	"push %esp\n\t"
123	"call c_main\n\t"
124	"int $3"
125#endif
126	);