mirror of
https://github.com/torvalds/linux.git
synced 2024-11-17 17:41:44 +00:00
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
/*
|
|
* vdso_test.c: Sample code to test parse_vdso.c on x86_64
|
|
* Copyright (c) 2011 Andy Lutomirski
|
|
* Subject to the GNU General Public License, version 2
|
|
*
|
|
* You can amuse yourself by compiling with:
|
|
* gcc -std=gnu99 -nostdlib
|
|
* -Os -fno-asynchronous-unwind-tables -flto
|
|
* vdso_test.c parse_vdso.c -o vdso_test
|
|
* to generate a small binary with no dependencies at all.
|
|
*/
|
|
|
|
#include <sys/syscall.h>
|
|
#include <sys/time.h>
|
|
#include <unistd.h>
|
|
#include <stdint.h>
|
|
|
|
extern void *vdso_sym(const char *version, const char *name);
|
|
extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
|
|
extern void vdso_init_from_auxv(void *auxv);
|
|
|
|
/* We need a libc functions... */
|
|
int strcmp(const char *a, const char *b)
|
|
{
|
|
/* This implementation is buggy: it never returns -1. */
|
|
while (*a || *b) {
|
|
if (*a != *b)
|
|
return 1;
|
|
if (*a == 0 || *b == 0)
|
|
return 1;
|
|
a++;
|
|
b++;
|
|
}
|
|
|
|
return 0;
|
|
}
|
|
|
|
/* ...and two syscalls. This is x86_64-specific. */
|
|
static inline long linux_write(int fd, const void *data, size_t len)
|
|
{
|
|
|
|
long ret;
|
|
asm volatile ("syscall" : "=a" (ret) : "a" (__NR_write),
|
|
"D" (fd), "S" (data), "d" (len) :
|
|
"cc", "memory", "rcx",
|
|
"r8", "r9", "r10", "r11" );
|
|
return ret;
|
|
}
|
|
|
|
static inline void linux_exit(int code)
|
|
{
|
|
asm volatile ("syscall" : : "a" (__NR_exit), "D" (code));
|
|
}
|
|
|
|
void to_base10(char *lastdig, uint64_t n)
|
|
{
|
|
while (n) {
|
|
*lastdig = (n % 10) + '0';
|
|
n /= 10;
|
|
lastdig--;
|
|
}
|
|
}
|
|
|
|
__attribute__((externally_visible)) void c_main(void **stack)
|
|
{
|
|
/* Parse the stack */
|
|
long argc = (long)*stack;
|
|
stack += argc + 2;
|
|
|
|
/* Now we're pointing at the environment. Skip it. */
|
|
while(*stack)
|
|
stack++;
|
|
stack++;
|
|
|
|
/* Now we're pointing at auxv. Initialize the vDSO parser. */
|
|
vdso_init_from_auxv((void *)stack);
|
|
|
|
/* Find gettimeofday. */
|
|
typedef long (*gtod_t)(struct timeval *tv, struct timezone *tz);
|
|
gtod_t gtod = (gtod_t)vdso_sym("LINUX_2.6", "__vdso_gettimeofday");
|
|
|
|
if (!gtod)
|
|
linux_exit(1);
|
|
|
|
struct timeval tv;
|
|
long ret = gtod(&tv, 0);
|
|
|
|
if (ret == 0) {
|
|
char buf[] = "The time is .000000\n";
|
|
to_base10(buf + 31, tv.tv_sec);
|
|
to_base10(buf + 38, tv.tv_usec);
|
|
linux_write(1, buf, sizeof(buf) - 1);
|
|
} else {
|
|
linux_exit(ret);
|
|
}
|
|
|
|
linux_exit(0);
|
|
}
|
|
|
|
/*
|
|
* This is the real entry point. It passes the initial stack into
|
|
* the C entry point.
|
|
*/
|
|
asm (
|
|
".text\n"
|
|
".global _start\n"
|
|
".type _start,@function\n"
|
|
"_start:\n\t"
|
|
"mov %rsp,%rdi\n\t"
|
|
"jmp c_main"
|
|
);
|