xz: Read MemAvailable from /proc/meminfo on Linux.

This uses 75 % of MemAvailable as the default soft memory usage limit
for -T0. It can be checked with --info-memory.

The use of MemAvailable was first suggested by
Sebastian Andrzej Siewior in 2021. This is a different
implementation, including the 75 % part.

.github/SECURITY.md

@@ -16,7 +16,13 @@ the chance that the exploit will be used before a patch is released.
 You may submit a report by emailing us at
 [xz@tukaani.org](mailto:xz@tukaani.org), or through
 [Security Advisories](https://github.com/tukaani-project/xz/security/advisories/new).
-While both options are available, we prefer email.
+While both options are available, we prefer email. In any case, please
+provide a clear description of the vulnerability including:
+
+- Affected versions of XZ Utils
+- Estimated severity (low, moderate, high, critical)
+- Steps to recreate the vulnerability
+- All relevant files (core dumps, build logs, input files, etc.)
 
 This project is maintained by a team of volunteers on a reasonable-effort
 basis. As such, please give us 90 days to work on a fix before

CMakeLists.txt

@@ -278,43 +278,9 @@ endif()
 if(CMAKE_VERSION VERSION_GREATER_EQUAL "3.20")
     find_package(Intl)
     find_package(Gettext)
-
     if(Intl_FOUND)
         option(ENABLE_NLS "Native Language Support (translated messages)" ON)
 
-        # If translation support is enabled but neither gettext tools or
-        # pre-generated .gmo files exist, translation support cannot be
-        # enabled.
-        #
-        # The detection of pre-generated .gmo files is done by only
-        # checking for the existence of a single .gmo file; Ukrainian
-        # is one of many translations that gets regular updates.
-        if(ENABLE_NLS AND NOT GETTEXT_FOUND AND
-                NOT EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/po/uk.gmo")
-            # This only sets the variable, not the cache variable!
-            set(ENABLE_NLS OFF)
-
-            # This message is shown only when new enough CMake is used and
-            # library support for translations was found. The assumptions is
-            # that in this situation the user might have interest in the
-            # translations. This also keeps this code simpler.
-            message(WARNING "Native language support (NLS) has been disabled. "
-                            "NLS support requires either gettext tools or "
-                            "pre-generated .gmo files. The latter are only "
-                            "available in distribution tarballs. "
-                            "To avoid this warning, NLS can be explicitly "
-                            "disabled by passing -DENABLE_NLS=OFF to cmake.")
-        endif()
-
-        # Warn if NLS is enabled but translated man pages are missing.
-        if(UNIX AND ENABLE_NLS AND
-                NOT EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/po4a/man")
-            message(WARNING "Native language support (NLS) has been enabled "
-                            "but pre-generated translated man pages "
-                            "were not found and thus they won't be installed. "
-                            "Run 'po4a/update-po' to generate them.")
-        endif()
-
         # The *installed* name of the translation files is "xz.mo".
         set(TRANSLATION_DOMAIN "xz")
     endif()
@@ -333,69 +299,6 @@ endif()
 
 option(BUILD_SHARED_LIBS "Build liblzma as a shared library instead of static")
 
-if(NOT WIN32)
-    # Symbol versioning only affects ELF shared libraries. The option is
-    # ignored for static libraries.
-    #
-    # Determine the default value so that it's always set with
-    # shared libraries in mind which helps if the build dir is reconfigured
-    # from static to shared libs without resetting the cache variables.
-    set(SYMBOL_VERSIONING_DEFAULT OFF)
-
-    if(CMAKE_SYSTEM_NAME STREQUAL "Linux" AND
-            (CMAKE_SYSTEM_PROCESSOR MATCHES "[Mm]icro[Bb]laze" OR
-             CMAKE_C_COMPILER_ID STREQUAL "NVHPC"))
-        # As a special case, GNU/Linux on MicroBlaze gets the generic
-        # symbol versioning because GCC 12 doesn't support the __symver__
-        # attribute on MicroBlaze. On Linux, CMAKE_SYSTEM_PROCESSOR comes
-        # from "uname -m" for native builds (should be "microblaze") or from
-        # the CMake toolchain file (not perfectly standardized but it very
-        # likely has "microblaze" in lower case or mixed case somewhere in
-        # the string).
-        #
-        # NVIDIA HPC Compiler doesn't support symbol versioning but
-        # it uses the linked from the system so the linker script
-        # can still be used to get the generic symbol versioning.
-        set(SYMBOL_VERSIONING_DEFAULT "generic")
-
-    elseif(CMAKE_SYSTEM_NAME STREQUAL "Linux")
-        # GNU/Linux-specific symbol versioning for shared liblzma.
-        # This includes a few extra compatibility symbols for RHEL/CentOS 7
-        # which are pointless on non-glibc non-Linux systems.
-        #
-        # Avoid symvers on Linux with non-glibc like musl and uClibc.
-        # In Autoconf it's enough to check that $host_os equals linux-gnu
-        # instead of, for example, linux-musl. CMake doesn't provide such
-        # a method.
-        #
-        # This check is here for now since it's not strictly required
-        # by anything else.
-        check_c_source_compiles(
-                "#include <features.h>
-                #if defined(__GLIBC__) && !defined(__UCLIBC__)
-                int main(void) { return 0; }
-                #else
-                compile error
-                #endif
-            "
-            IS_LINUX_WITH_GLIBC)
-
-        if(IS_LINUX_WITH_GLIBC)
-            set(SYMBOL_VERSIONING_DEFAULT "linux")
-        endif()
-
-    elseif(CMAKE_SYSTEM_NAME STREQUAL "FreeBSD")
-        set(SYMBOL_VERSIONING_DEFAULT "generic")
-    endif()
-
-    set(SYMBOL_VERSIONING "${SYMBOL_VERSIONING_DEFAULT}" CACHE STRING
-        "Enable ELF shared library symbol versioning (OFF, generic, linux)")
-
-    # Show a dropdown menu in CMake GUI:
-    set_property(CACHE SYMBOL_VERSIONING PROPERTY STRINGS "OFF;generic;linux")
-endif()
-
-
 add_library(liblzma
     src/common/mythread.h
     src/common/sysdefs.h
@@ -916,6 +819,10 @@ if(MICROLZMA_DECODER)
     target_sources(liblzma PRIVATE src/liblzma/common/microlzma_decoder.c)
 endif()
 
+if (MICROLZMA_ENCODER OR MICROLZMA_DECODER)
+    add_compile_definitions(HAVE_MICROLZMA)
+endif()
+
 
 #############################
 # lzip (.lz) format support #
@@ -1141,13 +1048,6 @@ if(USE_ATTR_IFUNC STREQUAL "auto")
             #endif
 
             static void func(void) { return; }
-
-            /*
-            * The attribute __no_profile_instrument_function__ is
-            * needed with GCC to prevent improper instrumentation in
-            * the ifunc resolver.
-            */
-            __attribute__((__no_profile_instrument_function__))
             static void (*resolve_func(void)) (void) { return func; }
             void func_ifunc(void)
                     __attribute__((__ifunc__(\"resolve_func\")));
@@ -1339,7 +1239,22 @@ if(WIN32)
         # Disable __declspec(dllimport) when linking against static liblzma.
         target_compile_definitions(liblzma INTERFACE LZMA_API_STATIC)
     endif()
-elseif(BUILD_SHARED_LIBS AND SYMBOL_VERSIONING STREQUAL "linux")
+elseif(BUILD_SHARED_LIBS AND CMAKE_SYSTEM_NAME STREQUAL "Linux" AND
+       NOT CMAKE_SYSTEM_PROCESSOR MATCHES "[Mm]icro[Bb]laze")
+    # GNU/Linux-specific symbol versioning for shared liblzma.
+    # This includes a few extra compatibility symbols for RHEL/CentOS 7
+    # which are pointless on non-glibc non-Linux systems.
+    #
+    # As a special case, GNU/Linux on MicroBlaze gets the generic
+    # symbol versioning because GCC 12 doesn't support the __symver__
+    # attribute on MicroBlaze. On Linux, CMAKE_SYSTEM_PROCESSOR comes
+    # from "uname -m" for native builds (should be "microblaze") or from
+    # the CMake toolchain file (not perfectly standardized but it very
+    # likely has "microblaze" in lower case or mixed case somewhere in
+    # the string).
+    #
+    # FIXME? Avoid symvers on Linux with non-glibc like musl?
+    #
     # Note that adding link options doesn't affect static builds
     # but HAVE_SYMBOL_VERSIONS_LINUX must not be used with static builds
     # because it would put symbol versions into the static library which
@@ -1355,7 +1270,10 @@ elseif(BUILD_SHARED_LIBS AND SYMBOL_VERSIONING STREQUAL "linux")
     set_target_properties(liblzma PROPERTIES
         LINK_DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/src/liblzma/liblzma_linux.map"
     )
-elseif(BUILD_SHARED_LIBS AND SYMBOL_VERSIONING STREQUAL "generic")
+elseif(BUILD_SHARED_LIBS AND (CMAKE_SYSTEM_NAME STREQUAL "FreeBSD" OR
+                              CMAKE_SYSTEM_NAME STREQUAL "Linux"))
+    # Generic symbol versioning for shared liblzma is used on FreeBSD and
+    # also on GNU/Linux on MicroBlaze.
     target_link_options(liblzma PRIVATE
         "-Wl,--version-script=${CMAKE_CURRENT_SOURCE_DIR}/src/liblzma/liblzma_generic.map"
     )
@@ -2085,20 +2003,11 @@ if(BUILD_TESTING)
         test_index_hash
         test_lzip_decoder
         test_memlimit
+        test_microlzma
         test_stream_flags
         test_vli
     )
 
-    # MicroLZMA encoder is needed for both encoder and decoder tests.
-    # If MicroLZMA decoder is not configured but LZMA1 decoder is, then
-    # test_microlzma will fail to compile because this configuration is
-    # not possible in the Autotools build, so the test was not made to
-    # support it since it would have required additional changes.
-    if (MICROLZMA_ENCODER AND (MICROLZMA_DECODER
-            OR NOT "lzma1" IN_LIST DECODERS))
-        list(APPEND LIBLZMA_TESTS test_microlzma)
-    endif()
-
     foreach(TEST IN LISTS LIBLZMA_TESTS)
         add_executable("${TEST}" "tests/${TEST}.c")
 

INSTALL

@@ -561,45 +561,10 @@ XZ Utils Installation
                                 sandboxing. If no Landlock support
                                 is found, configure will give an error.
 
-    --enable-symbol-versions[=VARIANT]
+    --enable-symbol-versions
-                Use symbol versioning for liblzma shared library.
+                Use symbol versioning for liblzma. This is enabled by
-                This is enabled by default on GNU/Linux (glibc only),
+                default on GNU/Linux, other GNU-based systems, and
-                other GNU-based systems, and FreeBSD.
+                FreeBSD.
-
-                Symbol versioning is never used for static liblzma. This
-                option is ignored when not building a shared library.
-
-                Supported VARIANTs:
-
-                        no      Disable symbol versioning. This is the
-                                same as using --disable-symbol-versions.
-
-                        auto    Autodetect between "no", "linux",
-                                and "generic".
-
-                        yes     Autodetect between "linux" and
-                                "generic". This forces symbol
-                                versioning to be used when
-                                building a shared library.
-
-                        generic Generic version is the default for
-                                FreeBSD and GNU/Linux on MicroBlaze.
-
-                                This is also used on GNU/Linux when
-                                building with NVIDIA HPC Compiler
-                                because the compiler doesn't support
-                                the features required for the "linux"
-                                variant below.
-
-                        linux   Special version for GNU/Linux (glibc
-                                only). This adds a few extra symbol
-                                versions for compatibility with binaries
-                                that have been linked against a liblzma
-                                version that has been patched with
-                                "xz-5.2.2-compat-libs.patch" from
-                                RHEL/CentOS 7. That patch was used
-                                by some build tools outside of
-                                RHEL/CentOS 7 too.
 
     --enable-debug
                 This enables the assert() macro and possibly some other

NEWS

@@ -2,32 +2,6 @@
 XZ Utils Release Notes
 ======================
 
-5.6.1 (2024-03-09)
-
-    * liblzma: Fixed two bugs relating to GNU indirect function (IFUNC)
-      with GCC. The more serious bug caused a program linked with
-      liblzma to crash on start up if the flag -fprofile-generate was
-      used to build liblzma. The second bug caused liblzma to falsely
-      report an invalid write to Valgrind when loading liblzma.
-
-    * xz: Changed the messages for thread reduction due to memory
-      constraints to only appear under the highest verbosity level.
-
-    * Build:
-
-        - Fixed a build issue when the header file <linux/landlock.h>
-          was present on the system but the Landlock system calls were
-          not defined in <sys/syscall.h>.
-
-        - The CMake build now warns and disables NLS if both gettext
-          tools and pre-created .gmo files are missing. Previously,
-          this caused the CMake build to fail.
-
-    * Minor improvements to man pages.
-
-    * Minor improvements to tests.
-
-
 5.6.0 (2024-02-24)
 
     This bumps the minor version of liblzma because new features were

THANKS

@@ -76,7 +76,6 @@ has been important. :-) In alphabetical order:
   - Richard Koch
   - Anton Kochkov
   - Ville Koskinen
-  - Sergey Kosukhin
   - Marcin Kowalczyk
   - Jan Kratochvil
   - Christian Kujau

configure.ac

@@ -304,8 +304,13 @@ AC_ARG_ENABLE([microlzma], AS_HELP_STRING([--disable-microlzma],
 		for example, erofs-utils.]),
 	[], [enable_microlzma=yes])
 case $enable_microlzma in
-	yes | no)
+	yes)
-		AC_MSG_RESULT([$enable_microlzma])
+		AC_DEFINE([HAVE_MICROLZMA], [1],
+			[Define to 1 if MicroLZMA support is enabled.])
+		AC_MSG_RESULT([yes])
+		;;
+	no)
+		AC_MSG_RESULT([no])
 		;;
 	*)
 		AC_MSG_RESULT([])
@@ -709,80 +714,61 @@ fi
 # --with-pic and --without-pic though. As long as neither --with-pic nor
 # --without-pic is used then we can use #ifdef PIC to detect if the file is
 # being built for a shared library.
-AS_IF([test "x$enable_symbol_versions" = xno], [
+if test "x$enable_symbol_versions" = xno ; then
 	enable_symbol_versions=no
 	AC_MSG_RESULT([no])
-], [test "x$enable_shared" = xno], [
+elif test "x$enable_shared" = xno ; then
 	enable_symbol_versions=no
 	AC_MSG_RESULT([no (not building a shared library)])
-], [
+else
-	# "yes" means that symbol version are to be used but we need to
+	case "$host_cpu-$host_os" in
-	# autodetect which variant to use.
+		microblaze*)
-	if test "x$enable_symbol_versions" = xyes ; then
+			# GCC 12 on MicroBlaze doesn't support __symver__
-		case "$host_cpu-$host_os" in
+			# attribute. It's simplest and safest to use the
-			microblaze*)
+			# generic version on that platform since then only
-				# GCC 12 on MicroBlaze doesn't support
+			# the linker script is needed. The RHEL/CentOS 7
-				# __symver__ attribute. It's simplest and
+			# compatibility symbols don't matter on MicroBlaze.
-				# safest to use the generic version on that
+			enable_symbol_versions=generic
-				# platform since then only the linker script
+			;;
-				# is needed. The RHEL/CentOS 7 compatibility
+		*-linux*)
-				# symbols don't matter on MicroBlaze.
+			case "$pic_mode-$enable_static" in
-				enable_symbol_versions=generic
+				default-*)
-				;;
+					# Use symvers if PIC is defined.
-			*-linux*)
+					have_symbol_versions_linux=2
-				# NVIDIA HPC Compiler doesn't support symbol
+					;;
-				# versioning but the linker script can still
+				*-no)
-				# be used.
+					# Not building static library.
-				AC_EGREP_CPP([use_generic_symbol_versioning],
+					# Use symvers unconditionally.
-					[#ifdef __NVCOMPILER
+					have_symbol_versions_linux=1
-					use_generic_symbol_versioning
+					;;
-					#endif],
+				*)
-					[enable_symbol_versions=generic],
+					AC_MSG_RESULT([])
-					[enable_symbol_versions=linux])
+					AC_MSG_ERROR([
-				;;
-			*)
-				enable_symbol_versions=generic
-				;;
-		esac
-	fi
-
-	if test "x$enable_symbol_versions" = xlinux ; then
-		case "$pic_mode-$enable_static" in
-			default-*)
-				# Use symvers if PIC is defined.
-				have_symbol_versions_linux=2
-				;;
-			*-no)
-				# Not building static library.
-				# Use symvers unconditionally.
-				have_symbol_versions_linux=1
-				;;
-			*)
-				AC_MSG_RESULT([])
-				AC_MSG_ERROR([
     On GNU/Linux, building both shared and static library at the same time
     is not supported if --with-pic or --without-pic is used.
     Use either --disable-shared or --disable-static to build one type
     of library at a time. If both types are needed, build one at a time,
     possibly picking only src/liblzma/.libs/liblzma.a from the static build.])
-				;;
+					;;
-		esac
+			esac
-		AC_DEFINE_UNQUOTED([HAVE_SYMBOL_VERSIONS_LINUX],
+			enable_symbol_versions=linux
-			[$have_symbol_versions_linux],
+			AC_DEFINE_UNQUOTED([HAVE_SYMBOL_VERSIONS_LINUX],
-			[Define to 1 to if GNU/Linux-specific details
+				[$have_symbol_versions_linux],
-			are unconditionally wanted for symbol
+				[Define to 1 to if GNU/Linux-specific details
-			versioning. Define to 2 to if these are wanted
+				are unconditionally wanted for symbol
-			only if also PIC is defined (allows building
+				versioning. Define to 2 to if these are wanted
-			both shared and static liblzma at the same
+				only if also PIC is defined (allows building
-			time with Libtool if neither --with-pic nor
+				both shared and static liblzma at the same
-			--without-pic is used). This define must be
+				time with Libtool if neither --with-pic nor
-			used together with liblzma_linux.map.])
+				--without-pic is used). This define must be
-	elif test "x$enable_symbol_versions" != xgeneric ; then
+				used together with liblzma_linux.map.])
-		AC_MSG_RESULT([])
+			;;
-		AC_MSG_ERROR([unknown symbol versioning variant '$enable_symbol_versions'])
+		*)
-	fi
+			enable_symbol_versions=generic
+			;;
+	esac
 	AC_MSG_RESULT([yes ($enable_symbol_versions)])
-])
+fi
 
 AM_CONDITIONAL([COND_SYMVERS_LINUX],
 	[test "x$enable_symbol_versions" = xlinux])
@@ -929,13 +915,6 @@ if test "x$enable_ifunc" = xauto ; then
 		#endif
 
 		static void func(void) { return; }
-
-		/*
-		 * The attribute __no_profile_instrument_function__ is
-		 * needed with GCC to prevent improper instrumentation in
-		 * the ifunc resolver.
-		 */
-		__attribute__((__no_profile_instrument_function__))
 		static void (*resolve_func (void)) (void) { return func; }
 		void func_ifunc (void)
 				__attribute__((__ifunc__("resolve_func")));

src/liblzma/check/crc32_fast.c

@@ -135,8 +135,6 @@ typedef uint32_t (*crc32_func_type)(
 // This resolver is shared between all three dispatch methods. It serves as
 // the ifunc resolver if ifunc is supported, otherwise it is called as a
 // regular function by the constructor or first call resolution methods.
-// The function attributes are needed for safe IFUNC resolver usage with GCC.
-lzma_resolver_attributes
 static crc32_func_type
 crc32_resolve(void)
 {

src/liblzma/check/crc64_fast.c

@@ -98,7 +98,6 @@ typedef uint64_t (*crc64_func_type)(
 #	pragma GCC diagnostic ignored "-Wunused-function"
 #endif
 
-lzma_resolver_attributes
 static crc64_func_type
 crc64_resolve(void)
 {

src/liblzma/check/crc_common.h

@@ -128,31 +128,6 @@
 #	endif
 #endif
 
-#ifdef CRC_USE_IFUNC
-// Two function attributes are needed to make IFUNC safe with GCC.
-//
-// no-omit-frame-pointer prevents false Valgrind issues when combined with
-// a few other compiler flags. The optimize attribute is supported on
-// GCC >= 4.4 and is not supported with Clang.
-#	if TUKLIB_GNUC_REQ(4,4) && !defined(__clang__)
-#		define no_omit_frame_pointer \
-			__attribute__((optimize("no-omit-frame-pointer")))
-#	else
-#		define no_omit_frame_pointer
-#	endif
-
-// The __no_profile_instrument_function__ attribute support is checked when
-// determining if ifunc can be used, so it is safe to use unconditionally.
-// This attribute is needed because GCC can add profiling to the IFUNC
-// resolver, which calls functions that have not yet been relocated leading
-// to a crash on liblzma start up.
-#	define lzma_resolver_attributes \
-		__attribute__((__no_profile_instrument_function__)) \
-		no_omit_frame_pointer
-#else
-#	define lzma_resolver_attributes
-#endif
-
 // For CRC32 use the generic slice-by-eight implementation if no optimized
 // version is available.
 #if !defined(CRC32_ARCH_OPTIMIZED) && !defined(CRC32_GENERIC)

src/liblzma/common/memcmplen.h

@@ -67,19 +67,6 @@ lzma_memcmplen(const uint8_t *buf1, const uint8_t *buf2,
 	// This is only for x86-64 and ARM64 for now. This might be fine on
 	// other 64-bit processors too. On big endian one should use xor
 	// instead of subtraction and switch to __builtin_clzll().
-	//
-	// Reasons to use subtraction instead of xor:
-	//
-	//   - On some x86-64 processors (Intel Sandy Bridge to Tiger Lake),
-	//     sub+jz and sub+jnz can be fused but xor+jz or xor+jnz cannot.
-	//     Thus using subtraction has potential to be a tiny amount faster
-	//     since the code checks if the quotient is non-zero.
-	//
-	//   - Some processors (Intel Pentium 4) used to have more ALU
-	//     resources for add/sub instructions than and/or/xor.
-	//
-	// The processor info is based on Agner Fog's microarchitecture.pdf
-	// version 2023-05-26. https://www.agner.org/optimize/
 #define LZMA_MEMCMPLEN_EXTRA 8
 	while (len < limit) {
 		const uint64_t x = read64ne(buf1 + len) - read64ne(buf2 + len);

src/liblzma/common/string_conversion.c

@@ -217,14 +217,12 @@ typedef struct {
 	uint16_t offset;
 
 	union {
-		// NVHPC has problems with unions that contain pointers that
-		// are not the first members, so keep "map" at the top.
-		const name_value_map *map;
-
 		struct {
 			uint32_t min;
 			uint32_t max;
 		} range;
+
+		const name_value_map *map;
 	} u;
 } option_map;
 

src/liblzma/delta/delta_decoder.c

@@ -25,11 +25,6 @@ decode_buffer(lzma_delta_coder *coder, uint8_t *buffer, size_t size)
 }
 
 
-// For an unknown reason NVIDIA HPC Compiler needs this pragma
-// to produce working code.
-#ifdef __NVCOMPILER
-#	pragma routine novector
-#endif
 static lzma_ret
 delta_decode(void *coder_ptr, const lzma_allocator *allocator,
 		const uint8_t *restrict in, size_t *restrict in_pos,

src/liblzma/rangecoder/range_decoder.h

@@ -45,7 +45,6 @@
 //     and different processors. Overall 0x1F0 seems to be the best choice.
 #ifndef LZMA_RANGE_DECODER_CONFIG
 #	if defined(__x86_64__) && !defined(__ILP32__) \
-			&& !defined(__NVCOMPILER) \
 			&& (defined(__GNUC__) || defined(__clang__))
 #		define LZMA_RANGE_DECODER_CONFIG 0x1F0
 #	else

src/liblzma/simple/riscv.c

@@ -116,7 +116,7 @@ AUIPC with rd != x0
         Zfh, F, D, and Q:
           * RV32I: LB, LH, LW, LBU, LHU, SB, SH, SW
           * RV64I has also: LD, LWU, SD
-          * Zfh: FLH, FSH
+          * Zhf: FLH, FSH
           * F: FLW, FSW
           * D: FLD, FSD
           * Q: FLQ, FSQ
@@ -320,11 +320,11 @@ AUIPC with rd == x0
 // The left-hand side takes care of (1) and (2).
 //   (a) The lowest 7 bits are already known to be AUIPC so subtracting 0x17
 //       makes those bits zeros.
-//   (b) If AUIPC rd equals x2, subtracting 0x100 makes bits [11:7] zeros.
+//   (b) If AUIPC rd equals x2, subtracting 0x10 makes bits [11:7] zeros.
 //       If rd doesn't equal x2, then there will be at least one non-zero bit
 //       and the next step (c) is irrelevant.
 //   (c) If the lowest two opcode bits of the packed inst2 are set in [13:12],
-//       then subtracting 0x3000 will make those bits zeros. Otherwise there
+//       then subtracting 0x300 will make those bits zeros. Otherwise there
 //       will be at least one non-zero bit.
 //
 // The shift by 18 removes the high bits from the final '>=' comparison and

src/xz/hardware.c

@@ -307,19 +307,69 @@ hardware_memlimit_show(void)
 }
 
 
+#ifdef __linux__
+static uint64_t
+get_available_ram(void)
+{
+	FILE *f = fopen("/proc/meminfo", "r");
+	if (f == NULL)
+		return 0;
+
+	// The information is near the very beginning of the file.
+	char buf[256];
+
+	// Read one byte less than sizeof(buf) to leave room for '\0'.
+	const size_t size = fread(buf, 1, sizeof(buf) - 1, f);
+	(void)fclose(f);
+
+	buf[size] = '\0';
+
+	const char needle[] = "\nMemAvailable:";
+	char *str = strstr(buf, needle);
+	if (str == NULL)
+		return 0;
+
+	// Skip the needle.
+	str += sizeof(needle) - 1;
+
+	// Skip spaces.
+	while (*str == ' ')
+		++str;
+
+	// Here it seems safe enough to assume that there won't be
+	// an integer overflow or at least it won't cause big trouble.
+	uint64_t ret = 0;
+	while (*str >= '0' && *str <= '9')
+		ret = ret * 10 + (uint64_t)(*str++ - '0');
+
+	// The value should end with " kB" so check for the space.
+	if (*str != ' ')
+		return 0;
+
+	return 1024 * ret;
+}
+#endif
+
+
 extern void
 hardware_init(void)
 {
+	uint64_t available_ram = 0;
+#ifdef __linux__
+	available_ram = get_available_ram();
+#endif
+
 	// Get the amount of RAM. If we cannot determine it,
 	// use the assumption defined by the configure script.
 	total_ram = lzma_physmem();
 	if (total_ram == 0)
 		total_ram = (uint64_t)(ASSUME_RAM) * 1024 * 1024;
 
-	// FIXME? There may be better methods to determine the default value.
+	// Use 75 % of currently-available RAM or 25 % of total RAM
-	// One Linux-specific suggestion is to use MemAvailable from
+	// as the default value.
-	// /proc/meminfo as the starting point.
+	memlimit_mt_default = available_ram != 0
-	memlimit_mt_default = total_ram / 4;
+			? available_ram - available_ram / 4
+			: total_ram / 4;
 
 #if SIZE_MAX == UINT32_MAX
 	// A too high value may cause 32-bit xz to run out of address space.

tests/Makefile.am

@@ -42,7 +42,8 @@ check_PROGRAMS = \
 	test_bcj_exact_size \
 	test_memlimit \
 	test_lzip_decoder \
-	test_vli
+	test_vli \
+	test_microlzma
 
 TESTS = \
 	test_check \
@@ -57,6 +58,7 @@ TESTS = \
 	test_memlimit \
 	test_lzip_decoder \
 	test_vli \
+	test_microlzma \
 	test_files.sh \
 	test_suffix.sh \
 	test_compress_prepared_bcj_sparc \
@@ -65,11 +67,6 @@ TESTS = \
 	test_compress_generated_random \
 	test_compress_generated_text
 
-if COND_MICROLZMA
-check_PROGRAMS += test_microlzma
-TESTS += test_microlzma
-endif
-
 if COND_SCRIPTS
 TESTS += test_scripts.sh
 endif

tests/test_files.sh

@@ -149,17 +149,6 @@ else
 	exit 1
 fi
 
-# Test that --single-stream can decompress bad-3-corrupt_lzma2.xz.
-# The first Stream in this file should decompress without errors.
-# This file cannot be decompressed with xzdec.
-I="$srcdir/files/bad-3-corrupt_lzma2.xz"
-if test -z "$XZ" || "$XZ" -dc --single-stream $NO_WARN "$I" > /dev/null; then
-	:
-else
-	echo "Good first Stream failed xz with --single-stream: $I"
-	exit 1
-fi
-
 
 #########
 # .lzma #

tests/test_microlzma.c

@@ -11,6 +11,8 @@
 
 #include "tests.h"
 
+#ifdef HAVE_MICROLZMA
+
 #define BUFFER_SIZE 1024
 
 #ifdef HAVE_ENCODER_LZMA1
@@ -511,6 +513,7 @@ test_decode_bad_lzma_properties(void)
 	lzma_end(&strm);
 }
 #endif
+#endif
 
 
 extern int
@@ -518,16 +521,17 @@ main(int argc, char **argv)
 {
 	tuktest_start(argc, argv);
 
-#ifndef HAVE_ENCODER_LZMA1
+#ifndef HAVE_MICROLZMA
-	tuktest_early_skip("LZMA1 encoder disabled");
+	tuktest_early_skip("MicroLZMA disabled");
 #else
+#	ifdef HAVE_ENCODER_LZMA1
 	tuktest_run(test_encode_options);
 	tuktest_run(test_encode_basic);
 	tuktest_run(test_encode_small_out);
 	tuktest_run(test_encode_actions);
+#	endif
 
-	// MicroLZMA decoder tests require the basic encoder functionality.
+#	if defined(HAVE_DECODER_LZMA1) && defined(HAVE_ENCODER_LZMA1)
-#	ifdef HAVE_DECODER_LZMA1
 	goodbye_world_encoded_size = basic_microlzma_encode(goodbye_world,
 			ARRAY_SIZE(goodbye_world), &goodbye_world_encoded);