liblzma: Use symbol versioning.

Symbol versioning is enabled by default on GNU/Linux,
other GNU-based systems, and FreeBSD.

I'm not sure how stable this is, so it may need
backward-incompatible changes before the next release.

The idea is that alpha and beta symbols are considered
unstable and require recompiling the applications that
use those symbols. Once a symbol is stable, it may get
extended with new features in ways that don't break
compatibility with older ABI & API.

The mydist target runs validate_map.sh which should
catch some probable problems in liblzma.map. Otherwise
I would forget to update the map file for new releases.

Makefile.am

@@ -87,6 +87,7 @@ dist-hook:
 
 # This works with GNU tar and gives cleaner package than normal 'make dist'.
 mydist:
+	sh "$(srcdir)/src/liblzma/validate_map.sh"
 	VERSION=$(VERSION); \
 	if test -d "$(srcdir)/.git" && type git > /dev/null 2>&1; then \
 		SNAPSHOT=`cd "$(srcdir)" && git describe --abbrev=4 | cut -b2-`; \

configure.ac

@@ -403,6 +403,27 @@ AC_ARG_ENABLE([scripts], [AC_HELP_STRING([--disable-scripts],
 AM_CONDITIONAL([COND_SCRIPTS], [test x$enable_scripts != xno])
 
 
+#####################
+# Symbol versioning #
+#####################
+
+AC_ARG_ENABLE([symbol-versions], [AC_HELP_STRING([--enable-symbol-versions],
+		[Use symbol versioning for liblzma. Enabled by default on
+		GNU/Linux, other GNU-based systems, and FreeBSD.])],
+	[], [enable_symbol_versions=auto])
+if test "x$enable_symbol_versions" = xauto; then
+	case $host_os in
+		gnu* | *-gnu* | freebsd*)
+			enable_symbol_versions=yes
+			;;
+		*)
+			enable_symbol_versions=no
+			;;
+	esac
+fi
+AM_CONDITIONAL([COND_SYMVERS], [test "x$enable_symbol_versions" = xyes])
+
+
 ###############################################################################
 # Checks for programs.
 ###############################################################################

src/liblzma/Makefile.am

@@ -26,6 +26,12 @@ liblzma_la_CPPFLAGS = \
 	-DTUKLIB_SYMBOL_PREFIX=lzma_
 liblzma_la_LDFLAGS = -no-undefined -version-info 5:99:0
 
+if COND_SYMVERS
+EXTRA_DIST += liblzma.map
+liblzma_la_LDFLAGS += \
+	-Wl,--version-script=$(top_srcdir)/src/liblzma/liblzma.map
+endif
+
 include $(srcdir)/common/Makefile.inc
 include $(srcdir)/check/Makefile.inc
 

src/liblzma/liblzma.map

@@ -0,0 +1,105 @@
+XZ_5.0 {
+global:
+	lzma_alone_decoder;
+	lzma_alone_encoder;
+	lzma_auto_decoder;
+	lzma_block_buffer_bound;
+	lzma_block_buffer_decode;
+	lzma_block_buffer_encode;
+	lzma_block_compressed_size;
+	lzma_block_decoder;
+	lzma_block_encoder;
+	lzma_block_header_decode;
+	lzma_block_header_encode;
+	lzma_block_header_size;
+	lzma_block_total_size;
+	lzma_block_unpadded_size;
+	lzma_check_is_supported;
+	lzma_check_size;
+	lzma_code;
+	lzma_crc32;
+	lzma_crc64;
+	lzma_easy_buffer_encode;
+	lzma_easy_decoder_memusage;
+	lzma_easy_encoder;
+	lzma_easy_encoder_memusage;
+	lzma_end;
+	lzma_filter_decoder_is_supported;
+	lzma_filter_encoder_is_supported;
+	lzma_filter_flags_decode;
+	lzma_filter_flags_encode;
+	lzma_filter_flags_size;
+	lzma_filters_copy;
+	lzma_filters_update;
+	lzma_get_check;
+	lzma_index_append;
+	lzma_index_block_count;
+	lzma_index_buffer_decode;
+	lzma_index_buffer_encode;
+	lzma_index_cat;
+	lzma_index_checks;
+	lzma_index_decoder;
+	lzma_index_dup;
+	lzma_index_encoder;
+	lzma_index_end;
+	lzma_index_file_size;
+	lzma_index_hash_append;
+	lzma_index_hash_decode;
+	lzma_index_hash_end;
+	lzma_index_hash_init;
+	lzma_index_hash_size;
+	lzma_index_init;
+	lzma_index_iter_init;
+	lzma_index_iter_locate;
+	lzma_index_iter_next;
+	lzma_index_iter_rewind;
+	lzma_index_memusage;
+	lzma_index_memused;
+	lzma_index_size;
+	lzma_index_stream_count;
+	lzma_index_stream_flags;
+	lzma_index_stream_padding;
+	lzma_index_stream_size;
+	lzma_index_total_size;
+	lzma_index_uncompressed_size;
+	lzma_lzma_preset;
+	lzma_memlimit_get;
+	lzma_memlimit_set;
+	lzma_memusage;
+	lzma_mf_is_supported;
+	lzma_mode_is_supported;
+	lzma_physmem;
+	lzma_properties_decode;
+	lzma_properties_encode;
+	lzma_properties_size;
+	lzma_raw_buffer_decode;
+	lzma_raw_buffer_encode;
+	lzma_raw_decoder;
+	lzma_raw_decoder_memusage;
+	lzma_raw_encoder;
+	lzma_raw_encoder_memusage;
+	lzma_stream_buffer_bound;
+	lzma_stream_buffer_decode;
+	lzma_stream_buffer_encode;
+	lzma_stream_decoder;
+	lzma_stream_encoder;
+	lzma_stream_flags_compare;
+	lzma_stream_footer_decode;
+	lzma_stream_footer_encode;
+	lzma_stream_header_decode;
+	lzma_stream_header_encode;
+	lzma_version_number;
+	lzma_version_string;
+	lzma_vli_decode;
+	lzma_vli_encode;
+	lzma_vli_size;
+};
+
+XZ_5.1.1alpha {
+global:
+	lzma_stream_encoder_mt;
+	lzma_stream_encoder_mt_memusage;
+
+local:
+	*;
+} XZ_5.0;

src/liblzma/validate_map.sh

@@ -0,0 +1,68 @@
+#!/bin/sh
+
+###############################################################################
+#
+# Check liblzma.map for certain types of errors
+#
+# Author: Lasse Collin
+#
+# This file has been put into the public domain.
+# You can do whatever you want with this file.
+#
+###############################################################################
+
+LC_ALL=C
+export LC_ALL
+
+STATUS=0
+
+cd "$(dirname "$0")"
+
+# Get the list of symbols that aren't defined in liblzma.map.
+SYMS=$(sed -n 's/^extern LZMA_API([^)]*) \([a-z0-9_]*\)(.*$/\1;/p' \
+		api/lzma/*.h \
+	| sort \
+	| grep -Fve "$(sed '/[{}:*]/d;/^$/d;s/^	//' liblzma.map)")
+
+# Check that there are no old alpha or beta versions listed.
+VER=$(cd ../.. && sh build-aux/version.sh)
+NAMES=
+case $VER in
+	*alpha | *beta)
+		NAMES=$(sed -n 's/^.*XZ_\([^ ]*\)\(alpha\|beta\) .*$/\1\2/p' \
+			liblzma.map | grep -Fv "$VER")
+		;;
+esac
+
+# Check for duplicate lines. It can catch missing dependencies.
+DUPS=$(sort liblzma.map | sed '/^$/d;/^global:$/d' | uniq -d)
+
+# Print error messages if needed.
+if test -n "$SYMS$NAMES$DUPS"; then
+	echo
+	echo 'validate_map.sh found problems from liblzma.map:'
+	echo
+
+	if test -n "$SYMS"; then
+		echo 'liblzma.map lacks the following symbols:'
+		echo "$SYMS"
+		echo
+	fi
+
+	if test -n "$NAMES"; then
+		echo 'Obsolete alpha or beta version names:'
+		echo "$NAMES"
+		echo
+	fi
+
+	if test -n "$DUPS"; then
+		echo 'Duplicate lines:'
+		echo "$DUPS"
+		echo
+	fi
+
+	STATUS=1
+fi
+
+# Exit status is 1 if problems were found, 0 otherwise.
+exit "$STATUS"