diff options
| author | Ævar Arnfjörð Bjarmason <avarab@gmail.com> | 2022-08-31 12:18:43 +0300 |
|---|---|---|
| committer | Junio C Hamano <gitster@pobox.com> | 2022-09-01 00:37:31 +0300 |
| commit | 9dc523aa0e20271cfe1474bef9fafbe62b7ff603 (patch) | |
| tree | 9e75110b9b63173053fadb0d7c9a2f02e7961b27 /INSTALL | |
| parent | d42b38dfb5edf1a7fddd9542d722f91038407819 (diff) | |
Makefile + hash.h: remove PPC_SHA1 implementation
Remove the PPC_SHA1 implementation added in a6ef3518f9a ([PATCH] PPC
assembly implementation of SHA1, 2005-04-22). When this was added
Apple consumer hardware used the PPC architecture, and the
implementation was intended to improve SHA-1 speed there.
Since it was added we've moved to using sha1collisiondetection by
default, and anyone wanting hard-rolled non-DC SHA-1 implementation
can use OpenSSL's via the OPENSSL_SHA1 knob.
The PPC_SHA1 originally originally targeted 32 bit PPC, and later the
64 bit PPC 970 (a.k.a. Apple PowerPC G5). See 926172c5e48 (block-sha1:
improve code on large-register-set machines, 2009-08-10) for a
reference about the performance on G5 (a comment in block-sha1/sha1.c
being removed here).
I can't get it to do anything but segfault on both the BE and LE POWER
machines in the GCC compile farm[1]. Anyone who's concerned about
performance on PPC these days is likely to be using the IBM POWER
processors.
There have been proposals to entirely remove non-sha1collisiondetection
implementations from the tree[2]. I think per [3] that would be a bit
overzealous. I.e. there are various set-ups git's speed is going to be
more important than the relatively implausible SHA-1 collision attack,
or where such attacks are entirely mitigated by other means (e.g. by
incoming objects being checked with DC_SHA1).
But that really doesn't apply to PPC_SHA1 in particular, which seems
to have outlived its usefulness.
As this gets rid of the only in-tree *.S assembly file we can remove
the small bits of logic from the Makefile needed to build objects
from *.S (as opposed to *.c)
The code being removed here was also throwing warnings with the
"-pedantic" flag, it could have been fixed as 544d93bc3b4 (block-sha1:
remove use of obsolete x86 assembly, 2022-03-10) did for block-sha1/*,
but as noted above let's remove it instead.
1. https://cfarm.tetaneutral.net/machines/list/
Tested on gcc{110,112,135,203}, a mixture of POWER [789] ppc64 and
ppc64le. All segfault in anything needing object
hashing (e.g. t/t1007-hash-object.sh) when compiled with
PPC_SHA1=Y.
2. https://lore.kernel.org/git/20200223223758.120941-1-mh@glandium.org/
3. https://lore.kernel.org/git/20200224044732.GK1018190@coredump.intra.peff.net/
Acked-by: brian m. carlson" <sandals@crustytoothpaste.net>
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'INSTALL')
| -rw-r--r-- | INSTALL | 3 |
1 files changed, 1 insertions, 2 deletions
@@ -135,8 +135,7 @@ Issues of note: By default, git uses OpenSSL for SHA1 but it will use its own library (inspired by Mozilla's) with either NO_OPENSSL or - BLK_SHA1. Also included is a version optimized for PowerPC - (PPC_SHA1). + BLK_SHA1. - "libcurl" library is used for fetching and pushing repositories over http:// or https://, as well as by |