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
 19extern void *vdso_sym(const char *version, const char *name);
 20extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
 21extern void vdso_init_from_auxv(void *auxv);
 22
 23/* We need a libc functions... */
 24int strcmp(const char *a, const char *b)
 25{
 26	/* This implementation is buggy: it never returns -1. */
 27	while (*a || *b) {
 28		if (*a != *b)
 29			return 1;
 30		if (*a == 0 || *b == 0)
 31			return 1;
 32		a++;
 33		b++;
 34	}
 35
 36	return 0;
 37}
 38
 39/* ...and two syscalls.  This is x86-specific. */
 40static inline long x86_syscall3(long nr, long a0, long a1, long a2)
 41{
 42	long ret;
 43#ifdef __x86_64__
 44	asm volatile ("syscall" : "=a" (ret) : "a" (nr),
 45		      "D" (a0), "S" (a1), "d" (a2) :
 46		      "cc", "memory", "rcx",
 47		      "r8", "r9", "r10", "r11" );
 48#else
 49	asm volatile ("int $0x80" : "=a" (ret) : "a" (nr),
 50		      "b" (a0), "c" (a1), "d" (a2) :
 51		      "cc", "memory" );
 52#endif
 53	return ret;
 54}
 55
 56static inline long linux_write(int fd, const void *data, size_t len)
 57{
 58	return x86_syscall3(__NR_write, fd, (long)data, (long)len);
 59}
 60
 61static inline void linux_exit(int code)
 62{
 63	x86_syscall3(__NR_exit, code, 0, 0);
 64}
 65
 66void to_base10(char *lastdig, time_t n)
 67{
 68	while (n) {
 69		*lastdig = (n % 10) + '0';
 70		n /= 10;
 71		lastdig--;
 72	}
 73}
 74
 75__attribute__((externally_visible)) void c_main(void **stack)
 76{
 77	/* Parse the stack */
 78	long argc = (long)*stack;
 79	stack += argc + 2;
 80
 81	/* Now we're pointing at the environment.  Skip it. */
 82	while(*stack)
 83		stack++;
 84	stack++;
 85
 86	/* Now we're pointing at auxv.  Initialize the vDSO parser. */
 87	vdso_init_from_auxv((void *)stack);
 88
 89	/* Find gettimeofday. */
 90	typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
 91	gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday");
 92
 93	if (!gtod)
 94		linux_exit(1);
 95
 96	struct timeval tv;
 97	long ret = gtod(&tv, 0);
 98
 99	if (ret == 0) {
100		char buf[] = "The time is                     .000000\n";
101		to_base10(buf + 31, tv.tv_sec);
102		to_base10(buf + 38, tv.tv_usec);
103		linux_write(1, buf, sizeof(buf) - 1);
104	} else {
105		linux_exit(ret);
106	}
107
108	linux_exit(0);
109}
110
111/*
112 * This is the real entry point.  It passes the initial stack into
113 * the C entry point.
114 */
115asm (
116	".text\n"
117	".global _start\n"
118	".type _start,@function\n"
119	"_start:\n\t"
120#ifdef __x86_64__
121	"mov %rsp,%rdi\n\t"
122	"jmp c_main"
123#else
124	"push %esp\n\t"
125	"call c_main\n\t"
126	"int $3"
127#endif
128	);