git/INSTALL
Ævar Arnfjörð Bjarmason 9dc523aa0e Makefile + hash.h: remove PPC_SHA1 implementation
Remove the PPC_SHA1 implementation added in a6ef3518f9 ([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 926172c5e4 (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 544d93bc3b (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>
2022-08-31 14:37:31 -07:00

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Git installation
Normally you can just do "make" followed by "make install", and that
will install the git programs in your own ~/bin/ directory. If you want
to do a global install, you can do
$ make prefix=/usr all doc info ;# as yourself
# make prefix=/usr install install-doc install-html install-info ;# as root
(or prefix=/usr/local, of course). Just like any program suite
that uses $prefix, the built results have some paths encoded,
which are derived from $prefix, so "make all; make prefix=/usr
install" would not work.
The beginning of the Makefile documents many variables that affect the way
git is built. You can override them either from the command line, or in a
config.mak file.
Alternatively you can use autoconf generated ./configure script to
set up install paths (via config.mak.autogen), so you can write instead
$ make configure ;# as yourself
$ ./configure --prefix=/usr ;# as yourself
$ make all doc ;# as yourself
# make install install-doc install-html;# as root
If you're willing to trade off (much) longer build time for a later
faster git you can also do a profile feedback build with
$ make prefix=/usr profile
# make prefix=/usr PROFILE=BUILD install
This will run the complete test suite as training workload and then
rebuild git with the generated profile feedback. This results in a git
which is a few percent faster on CPU intensive workloads. This
may be a good tradeoff for distribution packagers.
Alternatively you can run profile feedback only with the git benchmark
suite. This runs significantly faster than the full test suite, but
has less coverage:
$ make prefix=/usr profile-fast
# make prefix=/usr PROFILE=BUILD install
Or if you just want to install a profile-optimized version of git into
your home directory, you could run:
$ make profile-install
or
$ make profile-fast-install
As a caveat: a profile-optimized build takes a *lot* longer since the
git tree must be built twice, and in order for the profiling
measurements to work properly, ccache must be disabled and the test
suite has to be run using only a single CPU. In addition, the profile
feedback build stage currently generates a lot of additional compiler
warnings.
Issues of note:
- Ancient versions of GNU Interactive Tools (pre-4.9.2) installed a
program "git", whose name conflicts with this program. But with
version 4.9.2, after long hiatus without active maintenance (since
around 1997), it changed its name to gnuit and the name conflict is no
longer a problem.
NOTE: When compiled with backward compatibility option, the GNU
Interactive Tools package still can install "git", but you can build it
with --disable-transition option to avoid this.
- You can use git after building but without installing if you want
to test drive it. Simply run git found in bin-wrappers directory
in the build directory, or prepend that directory to your $PATH.
This however is less efficient than running an installed git, as
you always need an extra fork+exec to run any git subcommand.
It is still possible to use git without installing by setting a few
environment variables, which was the way this was done
traditionally. But using git found in bin-wrappers directory in
the build directory is far simpler. As a historical reference, the
old way went like this:
GIT_EXEC_PATH=`pwd`
PATH=`pwd`:$PATH
GITPERLLIB=`pwd`/perl/build/lib
export GIT_EXEC_PATH PATH GITPERLLIB
- By default (unless NO_PERL is provided) Git will ship various perl
scripts. However, for simplicity it doesn't use the
ExtUtils::MakeMaker toolchain to decide where to place the perl
libraries. Depending on the system this can result in the perl
libraries not being where you'd like them if they're expected to be
used by things other than Git itself.
Manually supplying a perllibdir prefix should fix this, if this is
a problem you care about, e.g.:
prefix=/usr perllibdir=/usr/$(/usr/bin/perl -MConfig -wle 'print substr $Config{installsitelib}, 1 + length $Config{siteprefixexp}')
Will result in e.g. perllibdir=/usr/share/perl/5.26.1 on Debian,
perllibdir=/usr/share/perl5 (which we'd use by default) on CentOS.
- Unless NO_PERL is provided Git will ship various perl libraries it
needs. Distributors of Git will usually want to set
NO_PERL_CPAN_FALLBACKS if NO_PERL is not provided to use their own
copies of the CPAN modules Git needs.
- Git is reasonably self-sufficient, but does depend on a few external
programs and libraries. Git can be used without most of them by adding
the appropriate "NO_<LIBRARY>=YesPlease" to the make command line or
config.mak file.
- "zlib", the compression library. Git won't build without it.
- "ssh" is used to push and pull over the net.
- A POSIX-compliant shell is required to run some scripts needed
for everyday use (e.g. "bisect", "request-pull").
- "Perl" version 5.8 or later is needed to use some of the
features (e.g. preparing a partial commit using "git add -i/-p",
interacting with svn repositories with "git svn"). If you can
live without these, use NO_PERL. Note that recent releases of
Redhat/Fedora are reported to ship Perl binary package with some
core modules stripped away (see http://lwn.net/Articles/477234/),
so you might need to install additional packages other than Perl
itself, e.g. Digest::MD5, File::Spec, File::Temp, Net::Domain,
Net::SMTP, and Time::HiRes.
- git-imap-send needs the OpenSSL library to talk IMAP over SSL if
you are using libcurl older than 7.34.0. Otherwise you can use
NO_OPENSSL without losing git-imap-send.
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.
- "libcurl" library is used for fetching and pushing
repositories over http:// or https://, as well as by
git-imap-send if the curl version is >= 7.34.0. If you do
not need that functionality, use NO_CURL to build without
it.
Git requires version "7.19.4" or later of "libcurl" to build
without NO_CURL. This version requirement may be bumped in
the future.
- "expat" library; git-http-push uses it for remote lock
management over DAV. Similar to "curl" above, this is optional
(with NO_EXPAT).
- "wish", the Tcl/Tk windowing shell is used in gitk to show the
history graphically, and in git-gui. If you don't want gitk or
git-gui, you can use NO_TCLTK.
- A gettext library is used by default for localizing Git. The
primary target is GNU libintl, but the Solaris gettext
implementation also works.
We need a gettext.h on the system for C code, gettext.sh (or
Solaris gettext(1)) for shell scripts, and libintl-perl for Perl
programs.
Set NO_GETTEXT to disable localization support and make Git only
use English. Under autoconf the configure script will do this
automatically if it can't find libintl on the system.
- Python version 2.7 or later is needed to use the git-p4 interface
to Perforce.
- Some platform specific issues are dealt with Makefile rules,
but depending on your specific installation, you may not
have all the libraries/tools needed, or you may have
necessary libraries at unusual locations. Please look at the
top of the Makefile to see what can be adjusted for your needs.
You can place local settings in config.mak and the Makefile
will include them. Note that config.mak is not distributed;
the name is reserved for local settings.
- To build and install documentation suite, you need to have
the asciidoc/xmlto toolchain. Because not many people are
inclined to install the tools, the default build target
("make all") does _not_ build them.
"make doc" builds documentation in man and html formats; there are
also "make man", "make html" and "make info". Note that "make html"
requires asciidoc, but not xmlto. "make man" (and thus make doc)
requires both.
"make install-doc" installs documentation in man format only; there
are also "make install-man", "make install-html" and "make
install-info".
Building and installing the info file additionally requires
makeinfo and docbook2X. Version 0.8.3 is known to work.
Building and installing the pdf file additionally requires
dblatex. Version >= 0.2.7 is known to work.
All formats require at least asciidoc 8.4.1. Alternatively, you can
use Asciidoctor (requires Ruby) by passing USE_ASCIIDOCTOR=YesPlease
to make. You need at least Asciidoctor version 1.5.
There are also "make quick-install-doc", "make quick-install-man"
and "make quick-install-html" which install preformatted man pages
and html documentation. To use these build targets, you need to
clone two separate git-htmldocs and git-manpages repositories next
to the clone of git itself.
The minimum supported version of docbook-xsl is 1.74.
Users attempting to build the documentation on Cygwin may need to ensure
that the /etc/xml/catalog file looks something like this:
<?xml version="1.0"?>
<!DOCTYPE catalog PUBLIC
"-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
"http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd"
>
<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
<rewriteURI
uriStartString = "http://docbook.sourceforge.net/release/xsl/current"
rewritePrefix = "/usr/share/sgml/docbook/xsl-stylesheets"
/>
<rewriteURI
uriStartString="http://www.oasis-open.org/docbook/xml/4.5"
rewritePrefix="/usr/share/sgml/docbook/xml-dtd-4.5"
/>
</catalog>
This can be achieved with the following two xmlcatalog commands:
xmlcatalog --noout \
--add rewriteURI \
http://docbook.sourceforge.net/release/xsl/current \
/usr/share/sgml/docbook/xsl-stylesheets \
/etc/xml/catalog
xmlcatalog --noout \
--add rewriteURI \
http://www.oasis-open.org/docbook/xml/4.5/xsl/current \
/usr/share/sgml/docbook/xml-dtd-4.5 \
/etc/xml/catalog