memcheck/tests/amd64-linux/access_below_sp.c

   1
   2 #include <stdio.h>
   3
   4
   5 #define COMPILER_BARRIER  __asm__ __volatile("":::"cc","memory")
   6
   7 /* force the kernel to map in 15k below SP, so we can safely poke
   8    around there. */
   9 __attribute__((noinline)) void make_below_sp_safe ( void )
  10 {
  11    const int N = 15000;
  12    unsigned char a[N];
  13    int i;
  14
  15    for (i = 0; i < N; i++) {
  16       a[i] = i & 0xFF;
  17    }
  18
  19    COMPILER_BARRIER;
  20
  21    unsigned int r = 0;
  22    for (i = 0; i < N; i++) {
  23       r = (r << 1) | (r >> 31);
  24       r ^= (unsigned int)a[i];
  25    }
  26    fprintf(stderr, "Checksum: %08x\n", r);
  27 }
  28
  29
  30 int main ( void )
  31 {
  32    make_below_sp_safe();
  33
  34    unsigned int res;
  35    __asm__ __volatile__("movl -8192(%%rsp), %0"
  36                         : "=r"(res) : : "memory","cc");
  37    fprintf(stderr, "Got %08x\n", res);
  38    return 0;
  39 }