strncpy (maybe others) broken on Alpha

[Mathieu Chouquet-Stringer <mchouque@free.fr>]

[ some background here: this started as a kobject_add error from the
scsi subsystem, now it appears the strncpy routine on Alpha is broken
see http://lkml.org/lkml/fancy/2006/4/19/305 or
msgid 20060419213129.GA9148@localhost ]

On Thu, Apr 20, 2006 at 12:14:48PM +0200, Mathieu Chouquet-Stringer wrote:
> So I guess the strncpy routine on alpha is fscked up or gcc is doing
> something crazy. The function is under arch/alpha/lib/strncpy.S, time to
> learn assembly.

Replying to myself here, i've created the following test program and
redefined strncpy to mystrncpy (I used strncpy.S and stxncpy.S from
arch/alpha/lib):

=============================================================================
#include <stdio.h>
#include <string.h>
#define FOO 50

extern char *mystrncpy(char *dest, const char *src, size_t count);

int main(int argc, char **argv)
{

	char src[FOO] = "";
	char dest[FOO];
	char letter[] = "a";
	int i;

	for (i = 0; i < FOO - 1; i++) {
		size_t beflen, aftlen;

		letter[0] = 'a' + i;
		strncat(src, letter, FOO);
		beflen = strlen(src);

		mystrncpy(dest, src, FOO);
		aftlen = strlen(dest);
		if (beflen != aftlen)
			printf("fails for strlen = %ld (copied %ld)\n",
				beflen, aftlen);
	}


	return 0;
}
=============================================================================

And here's the output using gcc version 3.4.4 (Gentoo 3.4.4-r1,
ssp-3.4.4-1.0, pie-8.7.8), note i didn't use flag except -Wall:

fails for strlen = 3 (copied 2)
fails for strlen = 4 (copied 2)
fails for strlen = 5 (copied 2)
fails for strlen = 6 (copied 2)
fails for strlen = 7 (copied 2)
fails for strlen = 11 (copied 10)
fails for strlen = 12 (copied 10)
fails for strlen = 13 (copied 10)
fails for strlen = 14 (copied 10)
fails for strlen = 15 (copied 10)
fails for strlen = 19 (copied 18)
fails for strlen = 20 (copied 18)
fails for strlen = 21 (copied 18)
fails for strlen = 22 (copied 18)
fails for strlen = 23 (copied 18)
fails for strlen = 27 (copied 26)
fails for strlen = 28 (copied 26)
fails for strlen = 29 (copied 26)
fails for strlen = 30 (copied 26)
fails for strlen = 31 (copied 26)
fails for strlen = 35 (copied 34)
fails for strlen = 36 (copied 34)
fails for strlen = 37 (copied 34)
fails for strlen = 38 (copied 34)
fails for strlen = 39 (copied 34)
fails for strlen = 43 (copied 42)
fails for strlen = 44 (copied 42)
fails for strlen = 45 (copied 42)
fails for strlen = 46 (copied 42)
fails for strlen = 47 (copied 42)


So much for this function...  I'll look at the assembly to see if I can
understand what's going on: it always copy a multiple of 8 + 2 bytes (as
in 8x + 2).
-- 
Mathieu Chouquet-Stringer                           mchouque@free.fr

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