diff options
| -rw-r--r-- | CMakeLists.txt | 26 |
1 files changed, 22 insertions, 4 deletions
diff --git a/CMakeLists.txt b/CMakeLists.txt index ac89b2e6..3a3ec41d 100644 --- a/CMakeLists.txt +++ b/CMakeLists.txt @@ -1144,10 +1144,28 @@ if(ALLOW_ARM64_CRC32) endif() -# Support -fvisiblity=hidden when building shared liblzma. -# These lines do nothing on Windows (even under Cygwin). -# HAVE_VISIBILITY should always be defined to 0 or 1. -if(BUILD_SHARED_LIBS) +# Symbol visibility support: +# +# The C_VISIBILITY_PRESET property takes care of adding the compiler +# option -fvisibility=hidden (or equivalent) if and only if it is supported. +# +# HAVE_VISIBILITY should always be defined to 0 or 1. It tells liblzma +# if __attribute__((__visibility__("default"))) +# and __attribute__((__visibility__("hidden"))) are supported. +# Those are useful only when the compiler supports -fvisibility=hidden +# or such option so HAVE_VISIBILITY should be 1 only when both option and +# the attribute support are present. HAVE_VISIBILITY is ignored on Windows +# and Cygwin by the liblzma C code; __declspec(dllexport) is used instead. +# +# CMake's GenerateExportHeader module is too fancy since liblzma already +# has the necessary macros. Instead, check CMake's internal variable +# CMAKE_C_COMPILE_OPTIONS_VISIBILITY (it's the C-specific variant of +# CMAKE_<LANG>_COMPILE_OPTIONS_VISIBILITY) which contains the compiler +# command line option for visibility support. It's empty or unset when +# visibility isn't supported. (It was added to CMake 2.8.12 in the commit +# 0e9f4bc00c6b26f254e74063e4026ac33b786513 in 2013.) This way we don't +# set HAVE_VISIBILITY to 1 when visibility isn't actually supported. +if(BUILD_SHARED_LIBS AND CMAKE_C_COMPILE_OPTIONS_VISIBILITY) set_target_properties(liblzma PROPERTIES C_VISIBILITY_PRESET hidden) target_compile_definitions(liblzma PRIVATE HAVE_VISIBILITY=1) else() |