CMake: Option to build static library with PIC, default ON

The static library must be compiled with POSITION_INDEPENDENT_CODE=ON in
order to link it into shared libraries.

But some compilers cannot generate position independent code for static
libraries.

To solve for both use cases, this commit adds a new CMake option
`ENABLE_STATIC_LIB_IS_PIC` that is ON by default.

You may need to build with `-D ENABLE_STATIC_LIB_IS_PIC=OFF` if your
compiler fails to generate position independent code when compiling the
static library.

Resolves: https://gitlab.com/bzip2/bzip2/-/issues/47

CMakeLists.txt

@@ -305,8 +305,10 @@ if(ENABLE_SHARED_LIB)
                   ${CMAKE_CURRENT_SOURCE_DIR}/libbz2.def
         PUBLIC    ${CMAKE_CURRENT_SOURCE_DIR}/bzlib_private.h
         INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/bzlib.h)
+
     # Always use '-fPIC'/'-fPIE' option for shared libraries.
     set_property(TARGET bz2 PROPERTY POSITION_INDEPENDENT_CODE ON)
+
     set_target_properties(bz2 PROPERTIES
         COMPILE_FLAGS "${WARNCFLAGS}"
         VERSION ${LT_VERSION} SOVERSION ${LT_SOVERSION})
@@ -321,7 +323,7 @@ if(ENABLE_SHARED_LIB)
             add_library(bz2_old_soname SHARED ${BZ2_RES})
             target_sources(bz2_old_soname
                 PRIVATE   ${BZ2_SOURCES}
-                        ${CMAKE_CURRENT_SOURCE_DIR}/libbz2.def
+                          ${CMAKE_CURRENT_SOURCE_DIR}/libbz2.def
                 PUBLIC    ${CMAKE_CURRENT_SOURCE_DIR}/bzlib_private.h
                 INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/bzlib.h
             )
@@ -342,6 +344,13 @@ if(ENABLE_STATIC_LIB)
         PRIVATE     ${BZ2_SOURCES}
         PUBLIC      ${CMAKE_CURRENT_SOURCE_DIR}/bzlib_private.h
         INTERFACE   ${CMAKE_CURRENT_SOURCE_DIR}/bzlib.h)
+
+    # Use '-fPIC'/'-fPIE' option for static libraries by default.
+    # You may build with ENABLE_STATIC_LIB_IS_PIC=OFF to disable PIC for the static library.
+    if(ENABLE_STATIC_LIB_IS_PIC)
+        set_property(TARGET bz2_static PROPERTY POSITION_INDEPENDENT_CODE ON)
+    endif()
+
     set_target_properties(bz2_static PROPERTIES
         COMPILE_FLAGS       "${WARNCFLAGS}"
         VERSION             ${LT_VERSION}

CMakeOptions.txt

@@ -23,3 +23,5 @@ option(ENABLE_STATIC_LIB "Build libbz2 in static mode also")
 option(ENABLE_SHARED_LIB "Build libbz2 as a shared library" ON)
 
 option(USE_OLD_SONAME "Use libbz2.so.1.0 for compatibility with old Makefiles" OFF)
+
+option(ENABLE_STATIC_LIB_IS_PIC "Enable position independent code for the static library" ON)

COMPILING.md

@@ -269,3 +269,13 @@ mkdir build && cd build
 cmake .. -DUSE_OLD_SONAME=ON
 cmake --build .
 ```
+
+`ENABLE_STATIC_LIB_IS_PIC`: Default: `ON`
+Disabling this option will make it so that building the static library will not
+use the '-fPIC'/'-fPIE' compiler options. You may need to disable this option if
+your compiler cannot generate position-independent code for your platform. E.g.:
+```sh
+mkdir build && cd build
+cmake .. -DENABLE_STATIC_LIB_IS_PIC=OFF
+cmake --build .
+```