Re: [linuxsh-dev] Fixup for the fast SH4 memcpy

[David M. <da...@sn...>]

Jivin Stuart Menefy lays it down ...
> > Attached is a patch,  and the changed original just in case.  I would
> > appreciate any feedback on the correctness/speed implications.  I ran
> > it through an extensive alignment/boundary case test without any problems
> > and it fixed my original crash :-)
> 
> Once I had a test case to throw at it, I fixed it independently, and
> came up with an almost identical fix, a copy of which is
> attached. Either will fix it, and I can't see any correctness
> problems with either.

Sorry to say this but the registers are the wrong way around :-)

The line:

-	cmp/hs	r1, r2		!  58 MT

Needs to be

+	cmp/hs	r2, r1		!  58 MT

My test code showed the problem,  included below for reference, it's
not pretty but it brute force tests memcpy fairly well, it is also way
slow ;-)

Cheers,
Davidm



static unsigned char buffer[256 * 5];
static unsigned char *buf0    = buffer + 256 * 0;
static unsigned char *buf1    = buffer + 256 * 1;
static unsigned char *buf2    = buffer + 256 * 2;
static unsigned char *buf_src = buffer + 256 * 3;

static void memcpy_test()
{
	int i, j, k;
	int c1;

	memset(buf_src, 0xff, 512);
	for (c1 = 0; c1 < 512; c1++)
		buf_src[c1] = (c1 & 0xff);


	for (i = 0; i < 256; i++)
		for (j = 0; j < 256; j++)
			for (k = 0; k + i < 256; k++) {
				memset(buf0, 0x0, 256);
				memset(buf1, 0x0, 256);
				memset(buf2, 0x0, 256);
				memcpy(&buf1[i], &buf_src[j], k);

				for (c1 = 0; c1 < 256; c1++) {
					if (buf0[c1])
						printk("buf0 corrupted at %d (%d,%d,%d)\n",c1,i,j,k);
					if ((c1 < i || c1 >= i + k) && buf1[c1])
						printk("buf1 corrupted at %d (%d,%d,%d)\n",c1,i,j,k);
					if (c1 >= i && c1 < i + k && buf1[c1] != buf_src[j+(c1-i)])
						printk("buf1 not copied   %d (%d,%d,%d,0x%02x)\n",
									c1, i, j, k, buf1[c1]);
					if (buf2[c1])
						printk("buf2 corrupted at %d (%d,%d,%d)\n",c1,i,j,k);
				}
			}
}


-- 
David McCullough:    Ph: +61 7 3435 2815  http://www.SnapGear.com
da...@sn...  Fx: +61 7 3891 3630  Custom Embedded Solutions + Security