From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <329de470156ae34054ae5f9314a37c49@mail.gmx.net>
To: 9fans@cse.psu.edu
From: sretzki@gmx.de
Date: Fri,  5 Jan 2007 15:36:32 +0100
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Subject: [9fans] memory woes
Topicbox-Message-UUID: fde64948-ead1-11e9-9d60-3106f5b1d025


Hi all,

I got this code:
#include <u.h>
#include <libc.h>


void main(int argc, char **argv) {
	int i;
	char *m00;

	for(i=0; i<=5; i++) {
		if((m00 = malloc(strlen("Hello World"))) == nil) {
			print("drama! [%d]\n",i);
			exits("malloc");
		}
		strcpy(m00,"Hello World");
		print("%d> %s\n",i,m00);
		free(m00);
	}
	exits(nil);
}

If I run that, I get:
term% 8c foo.c && 8l foo.8
term% 8.out
0> Hello World
mem user overflow
pool sbrkmem block a460
hdr 0a110c09 00000040 0000104f 00000000 6c6c6548 6f57206f
tail 00000000 00000000 00000000 00000000 00000000 00000000 | ef2d00be 00000040
user data 6c 6f 20 57  6f 72 6c 64 | 00 fe f1 f0  00 00 00 00
panic: pool panic
8.out 1430: suicide: sys: trap: fault read addr=0x0 pc=0x0000324a
term%


Without the free()-call in the loop, it does not crash - why is that? Also, I see programs just get killed without any warning/error-message anywhere - commenting out random free() calls seem to help ^^

Can somebody explain what is going on?


Mfg, Sascha