Re: [B.A.T.M.A.N.] Debug Malloc Problem

[Sven Eckelmann <sven.eckelmann@gmx.de>]

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On Tuesday 26 May 2009 20:50:56 Nathan Wharton wrote:
> I added the following patch:
> =========================================
> --- batmand-r1269/batman/allocate.c     2009-05-20 13:54:18.000000000 -0500
> +++ batmand-r1269.mod/batman/allocate.c 2009-05-26 12:25:07.000000000 -0500
> @@ -206,6 +206,10 @@
>        struct chunkHeader *chunkHeader;
>        struct chunkTrailer *chunkTrailer;
>        unsigned char *chunk;
> +       uint32_t remainder = length % 4;
> +
> +       if (remainder > 0)
> +         length += 4 - remainder;
>
>  /*     printf("sizeof(struct chunkHeader) = %u, sizeof (struct
> chunkTrailer) = %u\n", sizeof (struct chunkHeader), sizeof (struct
> chunkTrailer)); */
Please don't introduce more magic numbers. If you need an alignment on integer 
granularity then please use sizeof(int) instead of a simple constant.
The rest looks quite good and logical. I assumed that the only architecture 
without automatic catching of alignment problems is mips with load operators 
to the fp registers (never had such problems on simple arm machine nor could I 
produce that problem on them). Is there any other documentation about such 
problems on xscale or can you proof this with an test program (malloc 6 byte, 
write uint32_t to first 4 byte, write another uint32_t to byte 2-5, compare 
bytes with input - don't forget to set it volatile)? Your current proof if 
concept test only shows that the "overriden" bytes will not get overriden 
after moving them some bytes higher.

=========================================
#include <stdio.h>
#include <stdlib.h>

#define x_moved(pos) ((int*)&x[pos])[0]
static const int value1 = 0x01234567;
static const int value2 = 0x89abcdef;

int main() {
	volatile char *x = (char*)malloc(sizeof(int) * 2);
	x_moved(0) = value1;
	x_moved(2) = value2;

	if (x_moved(2) != value2) {
		printf("ERROR Value: ");
	} else {
		printf("Value: ");
	}
	printf("%x %x\n", x_moved(0) , x_moved(2));

	free(x);
	return 0;
}
=========================================


Best regards,
	Sven

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