liblzma: Disable external SHA-256 by default.
This is the sane thing to do. The conflict with OpenSSL
on some OSes and especially that the OS-provided versions
can be significantly slower makes it clear that it was
a mistake to have the external SHA-256 support enabled by
default.
Those who want it can now pass --enable-external-sha256 to
configure. INSTALL was updated with notes about OSes where
this can be a bad idea.
The SHA-256 detection code in configure.ac had some bugs that
could lead to a build failure in some situations. These were
fixed, although it doesn't matter that much now that the
external SHA-256 is disabled by default.
MINIX >= 3.2.0 uses NetBSD's libc and thus has SHA256_Init
in libc instead of libutil. Support for the libutil version
was removed.
diff --git a/INSTALL b/INSTALL
index 22ef077..fb2b6d7 100644
--- a/INSTALL
+++ b/INSTALL
@@ -246,6 +246,42 @@
the liblzma ABI, so this option should be used only when
it is known to not cause problems.
+ --enable-external-sha256
+ Try to use SHA-256 code from the operating system libc
+ or similar base system libraries. This doesn't try to
+ use OpenSSL or libgcrypt or such libraries.
+
+ The reasons to use this option:
+
+ - It makes liblzma slightly smaller.
+
+ - It might improve SHA-256 speed if the implementation
+ in the operating is very good (but see below).
+
+ External SHA-256 is disabled by default for two reasons:
+
+ - On some operating systems the symbol names of the
+ SHA-256 functions conflict with OpenSSL's libcrypto.
+ This causes weird problems such as decompression
+ errors if an application is linked against both
+ liblzma and libcrypto. This problem affects at least
+ FreeBSD 10 and older and MINIX 3.3.0 and older, but
+ other OSes that provide a function "SHA256_Init" might
+ also be affected. FreeBSD 11 has the problem fixed.
+ NetBSD had the problem but it was fixed it in 2009
+ already. OpenBSD uses "SHA256Init" and thus never had
+ a conflict with libcrypto.
+
+ - The SHA-256 code in liblzma is faster than the SHA-256
+ code provided by some operating systems. If you are
+ curious, build two copies of xz (internal and external
+ SHA-256) and compare the decompression (xz --test)
+ times:
+
+ dd if=/dev/zero bs=1024k count=1024 \
+ | xz -v -0 -Csha256 > foo.xz
+ time xz --test foo.xz
+
--disable-xz
--disable-xzdec
--disable-lzmadec
diff --git a/configure.ac b/configure.ac
index 86322dc..4a3e010 100644
--- a/configure.ac
+++ b/configure.ac
@@ -275,6 +275,20 @@
[AM_CONDITIONAL(COND_CHECK_[]m4_toupper(NAME), test "x$enable_check_[]NAME" = xyes)
])dnl
+AC_MSG_CHECKING([if external SHA-256 should be used])
+AC_ARG_ENABLE([external-sha256], AS_HELP_STRING([--enable-external-sha256],
+ [Use SHA-256 code from the operating system.
+ See INSTALL for possible subtle problems.]),
+ [], [enable_external_sha256=no])
+if test "x$enable_check_sha256" != "xyes"; then
+ enable_external_sha256=no
+fi
+if test "x$enable_external_sha256" = xyes; then
+ AC_MSG_RESULT([yes])
+else
+ AC_MSG_RESULT([no])
+fi
+
###########################
# Assembler optimizations #
@@ -645,48 +659,34 @@
TUKLIB_CPUCORES
TUKLIB_MBSTR
-# Check for system-provided SHA-256. The supported implementations are listed
-# below. The detection for the ones marked with [*] has been intentionally
-# disabled because they have symbol name conflicts with OpenSSL's libcrypto
-# which can cause weird problems (clean namespaces would make things too
-# boring, I guess).
+# If requsted, check for system-provided SHA-256. At least the following
+# implementations are supported:
#
# OS Headers Library Type Function
-# FreeBSD sys/types.h + sha256.h libmd SHA256_CTX SHA256_Init [*]
+# FreeBSD sys/types.h + sha256.h libmd SHA256_CTX SHA256_Init
# NetBSD sys/types.h + sha2.h SHA256_CTX SHA256_Init
# OpenBSD sys/types.h + sha2.h SHA2_CTX SHA256Init
# Solaris sys/types.h + sha2.h libmd SHA256_CTX SHA256Init
-# MINIX 3 sys/types.h + minix/sha2.h libutil SHA256_CTX SHA256_Init [*]
+# MINIX 3 sys/types.h + sha2.h SHA256_CTX SHA256_Init
# Darwin CommonCrypto/CommonDigest.h CC_SHA256_CTX CC_SHA256_Init
#
-# Notes:
+# Note that Darwin's CC_SHA256_Update takes buffer size as uint32_t instead
+# of size_t.
#
-# - NetBSD's SHA256_Init doesn't conflict with libcrypto because
-# libcrypto on NetBSD was made to use the libc implementation to avoid
-# this exact symbol conflict problem:
-# http://ftp.netbsd.org/pub/NetBSD/security/advisories/NetBSD-SA2009-012.txt.asc
-#
-# - As of 2016-03-10, FreeBSD seems to have the issue fixed in SVN head
-# but not in the FreeBSD 10 branch.
-#
-# - Darwin's CC_SHA256_Update takes buffer size as uint32_t instead
-# of size_t.
-#
-# We don't check for e.g. OpenSSL or libgcrypt because we don't want
-# to introduce dependencies to other packages by default. Maybe such
-# libraries could be supported via additional configure options though.
-#
-if test "x$enable_check_sha256" = "xyes"; then
+sha256_header_found=no
+sha256_type_found=no
+sha256_func_found=no
+if test "x$enable_external_sha256" = "xyes"; then
# Test for Common Crypto before others, because Darwin has sha256.h
# too and we don't want to use that, because on older versions it
# uses OpenSSL functions, whose SHA256_Init is not guaranteed to
# succeed.
- sha256_header_found=no
AC_CHECK_HEADERS(
- [CommonCrypto/CommonDigest.h sha256.h sha2.h minix/sha2.h],
+ [CommonCrypto/CommonDigest.h sha256.h sha2.h],
[sha256_header_found=yes ; break])
if test "x$sha256_header_found" = xyes; then
- AC_CHECK_TYPES([CC_SHA256_CTX, SHA256_CTX, SHA2_CTX], [], [],
+ AC_CHECK_TYPES([CC_SHA256_CTX, SHA256_CTX, SHA2_CTX],
+ [sha256_type_found=yes], [],
[[#ifdef HAVE_SYS_TYPES_H
# include <sys/types.h>
#endif
@@ -698,21 +698,19 @@
#endif
#ifdef HAVE_SHA2_H
# include <sha2.h>
- #endif
- #ifdef HAVE_MINIX_SHA2_H
- # include <minix/sha2.h>
#endif]])
- dnl Omit detection of the FreeBSD and MINIX 3 versions:
- dnl AC_SEARCH_LIBS([SHA256_Init], [md util])
- AC_SEARCH_LIBS([SHA256Init], [md])
- AC_CHECK_FUNCS([CC_SHA256_Init SHA256_Init SHA256Init],
- [break])
+ if test "x$sha256_type_found" = xyes ; then
+ AC_SEARCH_LIBS([SHA256Init], [md])
+ AC_SEARCH_LIBS([SHA256_Init], [md])
+ AC_CHECK_FUNCS([CC_SHA256_Init SHA256Init SHA256_Init],
+ [sha256_func_found=yes ; break])
+ fi
fi
fi
-AM_CONDITIONAL([COND_INTERNAL_SHA256],
- [test "x$ac_cv_func_SHA256_Init" != xyes \
- && test "x$ac_cv_func_SHA256Init" != xyes \
- && test "x$ac_cv_func_CC_SHA256_Init" != xyes])
+AM_CONDITIONAL([COND_INTERNAL_SHA256], [test "x$sha256_func_found" = xno])
+if test "x$enable_external_sha256$sha256_func_found" = xyesno; then
+ AC_MSG_ERROR([--enable-external-sha256 was specified but no supported external SHA-256 implementation was found])
+fi
# Check for SSE2 intrinsics.
AC_CHECK_DECL([_mm_movemask_epi8],
diff --git a/src/liblzma/check/check.h b/src/liblzma/check/check.h
index b8902f0..3007d88 100644
--- a/src/liblzma/check/check.h
+++ b/src/liblzma/check/check.h
@@ -15,13 +15,12 @@
#include "common.h"
-// If either the data type or the function for external SHA-256 is missing,
-// use the internal SHA-256 code.
-#if !(defined(HAVE_CC_SHA256_CTX) || defined(HAVE_SHA256_CTX) \
- || defined(HAVE_SHA2_CTX)) \
- || !(defined(HAVE_CC_SHA256_INIT) \
- || defined(HAVE_SHA256_INIT) \
- || defined(HAVE_SHA256INIT))
+// If the function for external SHA-256 is missing, use the internal SHA-256
+// code. Due to how configure works, these defines can only get defined when
+// both a usable header and a type have already been found.
+#if !(defined(HAVE_CC_SHA256_INIT) \
+ || defined(HAVE_SHA256_INIT) \
+ || defined(HAVE_SHA256INIT))
# define HAVE_INTERNAL_SHA256 1
#endif
@@ -35,9 +34,6 @@
#elif defined(HAVE_SHA2_H)
# include <sys/types.h>
# include <sha2.h>
-#elif defined(HAVE_MINIX_SHA2_H)
-# include <sys/types.h>
-# include <minix/sha2.h>
#endif
#if defined(HAVE_INTERNAL_SHA256)
