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SubjectRe: mprotect() failed: Cannot allocate memory
Date
On Wednesday 21 April 2010 01:17:22 Mike Frysinger wrote:
> On Tuesday 20 April 2010 19:05:20 Paweł Sikora wrote:
> > i'm trying to debug an ugly application with ElectricFence.
>
> electricfence does a lot of ugly memory tricks to do its thing, including,
> but not limited to, overriding memory related symbols. best to seek help
> from the electricfence authors.

so, let's avoid EF and run following test:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/mman.h>

void* my_alloc( size_t n )
{
size_t ps = getpagesize();
printf( "request for %Zd bytes => ", n );
/* alloc PAGE_SIZE + n */
char* p = mmap( 0, ps + n, PROT_READ | PROT_WRITE, MAP_SHARED |
MAP_ANONYMOUS, -1, 0 );
if ( p == MAP_FAILED )
__builtin_abort();
/* block guard page */
int rc = mprotect( p, ps, PROT_NONE );
if ( rc != 0 )
__builtin_abort();
char* q = p + ps;
printf( "guard page @ %p, allocated region @ %p\n", p, q );
return q;
}

int main()
{
#define N 100
size_t NN = 4*100*100;
size_t kmax = 100;
int i;

double **bm = (double **)my_alloc( NN * sizeof( double* ) );
for( i = 0; i < NN; ++i )
{
bm[ i ] = (double*)my_alloc( kmax * sizeof( double ) );
}
// leak...
return 0;
}

and the result is...

(...)
mmap(NULL, 4896, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0) =
0x7f5fd97df000
mprotect(0x7f5fd97df000, 4096, PROT_NONE) = -1 ENOMEM (Cannot allocate memory)
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