Library not linked against libdl for multilib build on Linux

[djcj]

When using the script build/linux/multilib.sh to build a multilib version of x265, the resulting shared library uses symbols from libdl but isn't linked against it. This caused some problems when I tried to configure ffmpeg with libx265 enabled.

Afaik BSD-like systems don't have a separate libdl file so I guess this is a Linux-specific issue.

I recommend something like the following changes:

--- multilib.sh.orig    2015-10-17 16:22:20.088480771 +0200
+++ multilib.sh 2015-10-17 16:22:10.840480613 +0200
@@ -10,16 +10,21 @@
 cmake ../../../source -DHIGH_BIT_DEPTH=ON -DEXPORT_C_API=OFF -DENABLE_SHARED=OFF -DENABLE_CLI=OFF
 make ${MAKEFLAGS}

+uname=`uname`
+
 cd ../8bit
 ln -sf ../10bit/libx265.a libx265_main10.a
 ln -sf ../12bit/libx265.a libx265_main12.a
-cmake ../../../source -DEXTRA_LIB="x265_main10.a;x265_main12.a" -DEXTRA_LINK_FLAGS=-L. -DLINKED_10BIT=ON -DLINKED_12BIT=ON
+if [ "$uname" = "Linux" ]; then
+  # On Linux, we need to link against libdl
+  libdl=";-ldl"
+fi
+cmake ../../../source -DEXTRA_LIB="x265_main10.a;x265_main12.a$libdl" -DEXTRA_LINK_FLAGS=-L. -DLINKED_10BIT=ON -DLINKED_12BIT=ON
 make ${MAKEFLAGS}

 # rename the 8bit library, then combine all three into libx265.a
 mv libx265.a libx265_main.a

-uname=`uname`
 if [ "$uname" = "Linux" ]
 then

[Sebastian Ramacher]

The shared objects are already linked with -ldl, but it's at the wrong place. The order of objects matters when linking. The following patch also fixes the issue:

diff --git a/source/CMakeLists.txt b/source/CMakeLists.txt
index 3da6865..dbb1af1 100644
--- a/source/CMakeLists.txt
+++ b/source/CMakeLists.txt
@@ -455,6 +455,9 @@ option(ENABLE_SHARED "Build shared library" ON)
 if(ENABLE_SHARED)
     add_library(x265-shared SHARED "${PROJECT_BINARY_DIR}/x265.def" ${YASM_OBJS}
                 ${X265_RC_FILE} $<TARGET_OBJECTS:encoder> $<TARGET_OBJECTS:common>)
+    if(EXTRA_LIB)
+        target_link_libraries(x265-shared ${EXTRA_LIB})
+    endif()
     target_link_libraries(x265-shared ${PLATFORM_LIBS})
     if(MSVC)
         set_target_properties(x265-shared PROPERTIES OUTPUT_NAME libx265)
@@ -480,9 +483,6 @@ if(ENABLE_SHARED)
                 ARCHIVE DESTINATION ${LIB_INSTALL_DIR}
                 RUNTIME DESTINATION ${BIN_INSTALL_DIR})
     endif()
-    if(EXTRA_LIB)
-        target_link_libraries(x265-shared ${EXTRA_LIB})
-    endif()
     if(LINKER_OPTIONS)
         # set_target_properties can't do list expansion
         string(REPLACE ";" " " LINKER_OPTION_STR "${LINKER_OPTIONS}")

It would also be nice if the code using dlopen wouldn't be built for the multilib build as it will never be used.

[Deepthi Nandakumar]

cmake: correct order of linking, fixes #202

First, the library which needs symbols. Next, the library which resolves symbols.

→ <<cset b6d0c1ce70f5>>