From 65e616728bacf70a4e907eb3c9a84bad2587bfbe Mon Sep 17 00:00:00 2001
From: Phil Greenland <40036098+pgreenland@users.noreply.github.com>
Date: Wed, 21 Feb 2024 08:50:18 +0000
Subject: [PATCH] Make position independent code flag optional for static
 libraries (#27)

* Make PIC optional for static libraries. Make compile definitions private

* Correct comment

* Remove note on fixed PIC
---
 CMakeLists.txt | 18 +++++++++++++-----
 README.md      |  2 --
 isotp_config.h |  2 +-
 3 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3324654..49d0092 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -7,6 +7,7 @@ project(isotp LANGUAGES C VERSION 1.0.1 DESCRIPTION "A platform-agnostic ISOTP i
 
 option(isotpc_USE_INCLUDE_DIR "Copy header files to separate include directory in current binary dir for better separation of header files to combat potential naming conflicts." OFF)
 option(isotpc_STATIC_LIBRARY "Compile libisotpc as a static library, instead of a shared library." OFF)
+option(isotpc_STATIC_LIBRARY_PIC "Make use of position independent code (PIC), when compiling as a static library (enabled automatically when building shared libraries)." OFF)
 option(isotpc_PAD_CAN_FRAMES "Pad CAN frames to their full size." ON)
 set(isotpc_CAN_FRAME_PAD_VALUE "0xAA" CACHE STRING "Padding byte value to be used in CAN frames if enabled")
 
@@ -20,13 +21,20 @@ endif()
 # Strict building policies
 ###
 target_compile_options(
-    isotp PUBLIC
-    -fPIC
+    isotp PRIVATE
     -Werror
     -Wall
     -Wno-unknown-pragmas # ignore unknown pragmas, such as #pragma region
 )
 
+###
+# Enable position independent code (PIC) if required
+###
+if (NOT isotpc_STATIC_LIBRARY OR isotpc_STATIC_LIBRARY_PIC)
+    # Building a shared library or a static library with PIC enabled
+    target_compile_options(isotp PRIVATE -fPIC)
+endif()
+
 ###
 # Provide padding configuration
 ###
@@ -38,10 +46,10 @@ endif()
 # Check for debug builds
 ###
 if (CMAKE_BUILD_TYPE STREQUAL "Debug")
-    target_compile_options(isotp PUBLIC -O0 -g) # don't optimise and add debugging symbols
+    target_compile_options(isotp PRIVATE -O0 -g) # don't optimise and add debugging symbols
 else()
-    target_compile_options(isotp PUBLIC -O2) # optimise code
-    target_link_libraries(isotp PUBLIC -s) # strip the library
+    target_compile_options(isotp PRIVATE -O2) # optimise code
+    target_link_libraries(isotp PRIVATE -s) # strip the library
 endif()
 
 if (isotpc_USE_INCLUDE_DIR)
diff --git a/README.md b/README.md
index 6c5756f..5705737 100644
--- a/README.md
+++ b/README.md
@@ -38,8 +38,6 @@ If your projects use a different build system, you are more than welcome to incl
 
 The Makefile generator for isotpc will automatically detect whether or not your build system is using the `Debug` or `Release` build type and will adjust compiler parameters accordingly.
 
-> **NOTE**: Regardless of build type, the library will be compiled as position-independant code.
-
 #### Debug Build
 If your project is configured to build as `Debug`, then the library will be compiled with **no** optimisations and **with** debug symbols.  
 `-DCMAKE_BUILD_TYPE=Debug`
diff --git a/isotp_config.h b/isotp_config.h
index cda4bbb..13c4c91 100644
--- a/isotp_config.h
+++ b/isotp_config.h
@@ -23,7 +23,7 @@
 
 /* Private: Determines if by default, padding is added to ISO-TP message frames.
  */
-//#define ISO_TP_FRAME_PADDING 0xAA
+//#define ISO_TP_FRAME_PADDING
 
 /* Private: Value to use when padding frames if enabled by ISO_TP_FRAME_PADDING
  */