Re: [ANNOUNCE] Git v2.23.0-rc0 - Initial test failures on NonStop

From

Jeff King <peff@peff.net>

Date

Jul 30, 2019, 20:02 UTC

Message-ID

<20190730200203.GA4882@sigill.intra.peff.net>

In-Reply-To

<20190730194938.GZ4545@pobox.com>

On Tue, Jul 30, 2019 at 03:49:38PM -0400, Todd Zullinger wrote:

> > Subtest 6 had an ordering issue. We do not know whether
> > the problem is the code or the test result not keeping up
> > with the code changes.
> >
> > --- expect      2019-07-30 16:56:36 +0000
> > +++ actual      2019-07-30 16:56:36 +0000
> > @@ -1,6 +1,6 @@
> >  NULL
> >  NULL
> >  NULL
> > +7c7cd714e262561f73f3079dfca4e8724682ac21 3
> >  139b20d8e6c5b496de61f033f642d0e3dbff528d 2
> >  d79ce1670bdcb76e6d1da2ae095e890ccb326ae9 1
> > -7c7cd714e262561f73f3079dfca4e8724682ac21 3
> 
> I hit the same failure while building for Fedora on the
> s390x architecture.  I have not dug into it much yet, but
> perhaps this is an endianess issue?

We _could_ reconcile that like this:

diff --git a/hashmap.h b/hashmap.h
index 8424911566..493229ac54 100644
--- a/hashmap.h
+++ b/hashmap.h
@@ -116,19 +116,11 @@ unsigned int memihash_cont(unsigned int hash_seed, const void *buf, size_t len);
  * Converts a cryptographic hash (e.g. SHA-1) into an int-sized hash code
  * for use in hash tables. Cryptographic hashes are supposed to have
  * uniform distribution, so in contrast to `memhash()`, this just copies
- * the first `sizeof(int)` bytes without shuffling any bits. Note that
- * the results will be different on big-endian and little-endian
- * platforms, so they should not be stored or transferred over the net.
+ * the first `sizeof(int)` bytes without shuffling any bits.
  */
 static inline unsigned int oidhash(const struct object_id *oid)
 {
-	/*
-	 * Equivalent to 'return *(unsigned int *)oid->hash;', but safe on
-	 * platforms that don't support unaligned reads.
-	 */
-	unsigned int hash;
-	memcpy(&hash, oid->hash, sizeof(hash));
-	return hash;
+	return get_be32(oid->hash);
 }
 
 /*
diff --git a/t/t0016-oidmap.sh b/t/t0016-oidmap.sh
index bbe719e950..6656db9d69 100755
--- a/t/t0016-oidmap.sh
+++ b/t/t0016-oidmap.sh
@@ -93,9 +93,9 @@ put three 3
 iterate" "NULL
 NULL
 NULL
+$(git rev-parse three) 3
 $(git rev-parse two) 2
-$(git rev-parse one) 1
-$(git rev-parse three) 3"
+$(git rev-parse one) 1"
 
 '
 

which not only fixes this test but any other hash-based oddities. I
wonder if it's appreciably less efficient. I'll bet I could nerd-snipe
René into doing a bunch of measurements and explorations of the
disassembled code. ;)

-Peff