Re: 64-bit question
Re: 64-bit question
- Subject: Re: 64-bit question
- From: Mike Fischer <email@hidden>
- Date: Wed, 9 Nov 2005 02:12:26 +0100
Am 08.11.2005 um 21:03 schrieb Sam Hart <email@hidden>:
I think it is a bug in the 32bit handling too, albeit less dramatic.
The process b0rked with a bus error rather than an "Out Of Memory".
Given the source snippet Bob originally posted on this list I think
it might simply be one of the following bugs in his code:
- The stack gets overwritten when i > ARRAY_SIZE.
- It tries to copy from NULL after malloc failed.
- The strcpy function will copy an unspecified amount of data because
buf is not a \0 terminated C string. Depending what comes after buf
on the stack this will overwrite more or less dynamic memory which
might also cause a crash. strncpy or memset would have been better.
Oh and some other non crashing bugs or oddities in that code are:
- The display of the allocated memory dosn't include the initial
allocation of bigbuf so it is off by about 8MB (for 64-bit, or 4MB
for 32-bit).
- The choice of 1000000 is somewhat arbitrary, given that the page
size of the VM system is 4096 bytes. I'd use 1MB or 1024*1024.
Here is a more correct version of said code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define BUFFER_SIZE (1024*1024)
int main(int argc, const char * argv[])
{
long long int i = 0,
total = 0;
while (++i)
{
char *bp = malloc(BUFFER_SIZE * sizeof(char));
if (bp == NULL)
{
printf("Internal malloc failed!\n");
break; // When this happens then the situation will
not get better. Give up right away.
}
else
{
memset(bp, 'A', BUFFER_SIZE * sizeof(char)); //
Access the memory so the VM system will actually allocate
//
physical memory, not just logical address space.
//
Note: it would be enough to touch one byte of every memory
// page
but the speed difference will not justify the more
//
complicated code as the VM thrashing will hide any
//
small perfomance gains made here.
total = i; // Keep track of the total.
if (i % 1000 == 0) // Don't print too much.
{
printf("MB allocated: %lld\n",i);
}
}
}
printf("Done! Total MB allocated: %lld\n", total);
while (1) { } // So it doesn't exit! Really bad style to use
an infinite loop but ok for this test!
return 0;
}
Does this version crash with a bus error as well?
Mike
--
Mike Fischer Softwareentwicklung, EDV-Beratung
Schulung, Vertrieb
Address: Bundesstrasse 9, D-20146 Hamburg, Germany
Phone: +49 (0)40/45038886, Fax: +49 (0)40/45038887
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