Date: Fri, 10 Jun 2005 15:40:58 -0700 From: Mike Hunter <mhunter@ack.berkeley.edu> To: freebsd-hackers@freebsd.org Subject: unitialized memory is all zeros...why not garbage instead? Message-ID: <20050610224058.GA11336@malcolm.berkeley.edu>
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Hey everybody, I have a feeling that I'm missing something really obvious, but I'm having trouble understanding why the following program: #include <stdlib.h> #include <stdio.h> int main (int argc, char * argv[]) { void * ptr = malloc(65536); size_t i; for (i = 0; i < 65536; i++) { printf ("%x", *((unsigned char *)ptr + i)); if ((i % 16) == 0) { puts("\n"); } } return 0; } Never prints anything but "0"'s. I ran less up to my hw.physmem by feeding it /dev/random and watching top, and then ran the program, so I "know" there was tons of non-zero bits in memory. I'm curious because I am worried about information leaks between processes on the same machine...did somebody decide to solve this problem while I wasn't paying attention? :) %gcc -v Using built-in specs. Configured with: FreeBSD/i386 system compiler Thread model: posix gcc version 3.4.2 [FreeBSD] 20040728 %uname -a FreeBSD mylabtop.berkeley.edu 5.4-STABLE FreeBSD 5.4-STABLE #1: Wed May 11 12:05:39 PDT 2005
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