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98eedc3a9d
It turns out that parsing the vDSO is nontrivial if you don't already have an ELF dynamic loader around. So document it in Documentation/ABI and add a reference CC0-licenced parser. This code is dedicated to Go issue 1933: http://code.google.com/p/go/issues/detail?id=1933 Signed-off-by: Andy Lutomirski <luto@mit.edu> Link: http://lkml.kernel.org/r/a315a9514cd71bcf29436cc31e35aada21a5ff21.1310563276.git.luto@mit.edu Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
112 lines
2.4 KiB
C
112 lines
2.4 KiB
C
/*
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* vdso_test.c: Sample code to test parse_vdso.c on x86_64
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* Copyright (c) 2011 Andy Lutomirski
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* Subject to the GNU General Public License, version 2
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*
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* You can amuse yourself by compiling with:
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* gcc -std=gnu99 -nostdlib
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* -Os -fno-asynchronous-unwind-tables -flto
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* vdso_test.c parse_vdso.c -o vdso_test
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* to generate a small binary with no dependencies at all.
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*/
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#include <sys/syscall.h>
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#include <sys/time.h>
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#include <unistd.h>
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#include <stdint.h>
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extern void *vdso_sym(const char *version, const char *name);
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extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
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extern void vdso_init_from_auxv(void *auxv);
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/* We need a libc functions... */
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int strcmp(const char *a, const char *b)
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{
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/* This implementation is buggy: it never returns -1. */
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while (*a || *b) {
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if (*a != *b)
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return 1;
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if (*a == 0 || *b == 0)
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return 1;
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a++;
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b++;
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}
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return 0;
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}
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/* ...and two syscalls. This is x86_64-specific. */
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static inline long linux_write(int fd, const void *data, size_t len)
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{
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long ret;
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asm volatile ("syscall" : "=a" (ret) : "a" (__NR_write),
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"D" (fd), "S" (data), "d" (len) :
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"cc", "memory", "rcx",
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"r8", "r9", "r10", "r11" );
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return ret;
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}
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static inline void linux_exit(int code)
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{
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asm volatile ("syscall" : : "a" (__NR_exit), "D" (code));
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}
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void to_base10(char *lastdig, uint64_t n)
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{
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while (n) {
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*lastdig = (n % 10) + '0';
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n /= 10;
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lastdig--;
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}
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}
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__attribute__((externally_visible)) void c_main(void **stack)
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{
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/* Parse the stack */
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long argc = (long)*stack;
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stack += argc + 2;
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/* Now we're pointing at the environment. Skip it. */
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while(*stack)
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stack++;
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stack++;
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/* Now we're pointing at auxv. Initialize the vDSO parser. */
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vdso_init_from_auxv((void *)stack);
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/* Find gettimeofday. */
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typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
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gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday");
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if (!gtod)
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linux_exit(1);
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struct timeval tv;
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long ret = gtod(&tv, 0);
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if (ret == 0) {
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char buf[] = "The time is .000000\n";
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to_base10(buf + 31, tv.tv_sec);
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to_base10(buf + 38, tv.tv_usec);
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linux_write(1, buf, sizeof(buf) - 1);
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} else {
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linux_exit(ret);
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}
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linux_exit(0);
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}
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/*
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* This is the real entry point. It passes the initial stack into
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* the C entry point.
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*/
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asm (
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".text\n"
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".global _start\n"
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".type _start,@function\n"
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"_start:\n\t"
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"mov %rsp,%rdi\n\t"
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"jmp c_main"
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);
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