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compat: auto-detect if zlib has uncompress2()

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We have a copy of uncompress2() implementation in compat/ so that we
can build with an older version of zlib that lack the function, and
the build procedure selects if it is used via the NO_UNCOMPRESS2
$(MAKE) variable.  This is yet another "annoying" knob the porters
need to tweak on platforms that are not common enough to have the
default set in the config.mak.uname file.

Attempt to instead ask the system header <zlib.h> to decide if we
need the compatibility implementation.  This is a deviation from the
way we have been handling the "compatiblity" features so far, and if
it can be done cleanly enough, it could work as a model for features
that need compatibility definition we discover in the future.  With
that goal in mind, avoid expedient but ugly hacks, like shoving the
code that is conditionally compiled into an unrelated .c file, which
may not work in future cases---instead, take an approach that uses a
file that is independently compiled and stands on its own.

Compile and link compat/zlib-uncompress2.c file unconditionally, but
conditionally hide the implementation behind #if/#endif when zlib
version is 1.2.9 or newer, and unconditionally archive the resulting
object file in the libgit.a to be picked up by the linker.

There are a few things to note in the shape of the code base after
this change:

 - We no longer use NO_UNCOMPRESS2 knob; if the system header
   <zlib.h> claims a version that is more cent than the library
   actually is, this would break, but it is easy to add it back when
   we find such a system.

 - The object file compat/zlib-uncompress2.o is always compiled and
   archived in libgit.a, just like a few other compat/ object files
   already are.

 - The inclusion of <zlib.h> is done in <git-compat-util.h>; we used
   to do so from <cache.h> which includes <git-compat-util.h> as the
   first thing it does, so from the *.c codes, there is no practical
   change.

 - Until objects in libgit.a that is already used gains a reference
   to the function, the reftable code will be the only one that
   wants it, so libgit.a on the linker command line needs to appear
   once more at the end to satisify the mutual dependency.

 - Beat found a trick used by OpenSSL to avoid making the
   conditionally-compiled object truly empty (apparently because
   they had to deal with compilers that do not want to see an
   effectively empty input file).  Our compat/zlib-uncompress2.c
   file borrows the same trick for portabilty.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Helped-by: Beat Bolli <dev+git@drbeat.li>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Ævar Arnfjörð Bjarmason 2022-01-24 10:27:59 -08:00 committed by Junio C Hamano
parent 297ca895a2
commit 07564773c2
8 changed files with 21 additions and 46 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

11
Makefile
View file

@ -256,8 +256,6 @@ all::
#
# Define NO_DEFLATE_BOUND if your zlib does not have deflateBound.
#
# Define NO_UNCOMPRESS2 if your zlib does not have uncompress2.
#
# Define NO_NORETURN if using buggy versions of gcc 4.6+ and profile feedback,
# as the compiler can crash (http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49299)
#
@ -862,6 +860,7 @@ LIB_OBJS += commit-reach.o
LIB_OBJS += commit.o
LIB_OBJS += compat/obstack.o
LIB_OBJS += compat/terminal.o
LIB_OBJS += compat/zlib-uncompress2.o
LIB_OBJS += config.o
LIB_OBJS += connect.o
LIB_OBJS += connected.o
@ -1194,7 +1193,8 @@ THIRD_PARTY_SOURCES += compat/regex/%
THIRD_PARTY_SOURCES += sha1collisiondetection/%
THIRD_PARTY_SOURCES += sha1dc/%
GITLIBS = common-main.o $(LIB_FILE) $(XDIFF_LIB) $(REFTABLE_LIB)
# xdiff and reftable libs may in turn depend on what is in libgit.a
GITLIBS = common-main.o $(LIB_FILE) $(XDIFF_LIB) $(REFTABLE_LIB) $(LIB_FILE)
EXTLIBS =
GIT_USER_AGENT = git/$(GIT_VERSION)
@ -1726,11 +1726,6 @@ ifdef NO_DEFLATE_BOUND
BASIC_CFLAGS += -DNO_DEFLATE_BOUND
endif
ifdef NO_UNCOMPRESS2
BASIC_CFLAGS += -DNO_UNCOMPRESS2
REFTABLE_OBJS += compat/zlib-uncompress2.o
endif
ifdef NO_POSIX_GOODIES
BASIC_CFLAGS += -DNO_POSIX_GOODIES
endif

1
cache.h
View file

@ -18,7 +18,6 @@
#include "repository.h"
#include "mem-pool.h"
#include <zlib.h>
typedef struct git_zstream {
z_stream z;
unsigned long avail_in;

1
ci/lib.sh
View file

@ -197,7 +197,6 @@ esac
case "$jobname" in
linux32)
CC=gcc
MAKEFLAGS="$MAKEFLAGS NO_UNCOMPRESS2=1"
;;
linux-musl)
CC=gcc

11
compat/zlib-uncompress2.c
View file

@ -1,3 +1,6 @@
#include "git-compat-util.h"
#if ZLIB_VERNUM < 0x1290
/* taken from zlib's uncompr.c
commit cacf7f1d4e3d44d871b605da3b647f07d718623f
@ -8,16 +11,11 @@
*/
#include "../reftable/system.h"
#define z_const
/*
* Copyright (C) 1995-2003, 2010, 2014, 2016 Jean-loup Gailly, Mark Adler
* For conditions of distribution and use, see copyright notice in zlib.h
*/
#include <zlib.h>
/* clang-format off */
/* ===========================================================================
@ -93,3 +91,6 @@ int ZEXPORT uncompress2 (
err == Z_BUF_ERROR && left + stream.avail_out ? Z_DATA_ERROR :
err;
}
#else
static void *dummy_variable = &dummy_variable;
#endif

7
config.mak.uname
View file

@ -66,7 +66,6 @@ ifeq ($(uname_S),Linux)
# centos7/rhel7 provides gcc 4.8.5 and zlib 1.2.7.
ifneq ($(findstring .el7.,$(uname_R)),)
BASIC_CFLAGS += -std=c99
NO_UNCOMPRESS2 = YesPlease
endif
endif
ifeq ($(uname_S),GNU/kFreeBSD)
@ -266,10 +265,6 @@ ifeq ($(uname_S),FreeBSD)
FILENO_IS_A_MACRO = UnfortunatelyYes
endif
ifeq ($(uname_S),OpenBSD)
# Versions < 7.0 need compatibility layer
ifeq ($(shell expr "$(uname_R)" : "[1-6]\."),2)
NO_UNCOMPRESS2 = UnfortunatelyYes
endif
NO_STRCASESTR = YesPlease
NO_MEMMEM = YesPlease
USE_ST_TIMESPEC = YesPlease
@ -525,7 +520,6 @@ ifeq ($(uname_S),Interix)
endif
endif
ifeq ($(uname_S),Minix)
NO_UNCOMPRESS2 = YesPlease
NO_IPV6 = YesPlease
NO_ST_BLOCKS_IN_STRUCT_STAT = YesPlease
NO_NSEC = YesPlease
@ -581,7 +575,6 @@ ifeq ($(uname_S),NONSTOP_KERNEL)
NO_SETENV = YesPlease
NO_UNSETENV = YesPlease
NO_MKDTEMP = YesPlease
NO_UNCOMPRESS2 = YesPlease
# Currently libiconv-1.9.1.
OLD_ICONV = UnfortunatelyYes
NO_REGEX = NeedsStartEnd

13
configure.ac
View file

@ -664,22 +664,9 @@ AC_LINK_IFELSE([ZLIBTEST_SRC],
NO_DEFLATE_BOUND=yes])
LIBS="$old_LIBS"
AC_DEFUN([ZLIBTEST_UNCOMPRESS2_SRC], [
AC_LANG_PROGRAM([#include <zlib.h>],
[uncompress2(NULL,NULL,NULL,NULL);])])
AC_MSG_CHECKING([for uncompress2 in -lz])
old_LIBS="$LIBS"
LIBS="$LIBS -lz"
AC_LINK_IFELSE([ZLIBTEST_UNCOMPRESS2_SRC],
[AC_MSG_RESULT([yes])],
[AC_MSG_RESULT([no])
NO_UNCOMPRESS2=yes])
LIBS="$old_LIBS"
GIT_UNSTASH_FLAGS($ZLIB_PATH)
GIT_CONF_SUBST([NO_DEFLATE_BOUND])
GIT_CONF_SUBST([NO_UNCOMPRESS2])
#
# Define NEEDS_SOCKET if linking with libc is not enough (SunOS,

12
git-compat-util.h
View file

@ -1386,6 +1386,18 @@ void unleak_memory(const void *ptr, size_t len);
#define UNLEAK(var) do {} while (0)
#endif
#define z_const
#include <zlib.h>
#if ZLIB_VERNUM < 0x1290
/*
* This is uncompress2, which is only available in zlib >= 1.2.9
* (released as of early 2017). See compat/zlib-uncompress2.c.
*/
int uncompress2(Bytef *dest, uLongf *destLen, const Bytef *source,
uLong *sourceLen);
#endif
/*
* This include must come after system headers, since it introduces macros that
* replace system names.

11
reftable/system.h
View file

@ -16,17 +16,6 @@ license that can be found in the LICENSE file or at
#include "hash.h" /* hash ID, sizes.*/
#include "dir.h" /* remove_dir_recursively, for tests.*/
#include <zlib.h>
#ifdef NO_UNCOMPRESS2
/*
* This is uncompress2, which is only available in zlib >= 1.2.9
* (released as of early 2017)
*/
int uncompress2(Bytef *dest, uLongf *destLen, const Bytef *source,
uLong *sourceLen);
#endif
int hash_size(uint32_t id);
#endif