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#include <stdio.h>
#define COMPILER_BARRIER __asm__ __volatile("":::"cc","memory")
/* force the kernel to map in 15k below SP, so we can safely poke
around there. */
__attribute__((noinline)) void make_below_sp_safe ( void )
{
const int N = 15000;
unsigned char a[N];
int i;
for (i = 0; i < N; i++) {
a[i] = i & 0xFF;
}
COMPILER_BARRIER;
unsigned int r = 0;
for (i = 0; i < N; i++) {
r = (r << 1) | (r >> 31);
r ^= (unsigned int)a[i];
}
fprintf(stderr, "Checksum: %08x\n", r);
}
int main ( void )
{
make_below_sp_safe();
unsigned int res;
__asm__ __volatile__("movl -8192(%%rsp), %0"
: "=r"(res) : : "memory","cc");
fprintf(stderr, "Got %08x\n", res);
return 0;
}
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