From 2f6d2e5795382f0d6e22f5aea52e8104110d24ad Mon Sep 17 00:00:00 2001
From: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Date: Sun, 19 Jul 2020 16:29:15 +0200
Subject: [PATCH] cmake/compilerFlags.cmake: properly detect availability of
 flags

Instead of relying on fragile and complex logic to decide if a
compiler flag is available or not, use the check_c_compiler_flag()
macro provided by the CMake standard library.

This for example avoids using -fcf-protection on architectures that
don't support this option.

[Upstream: https://github.com/Exiv2/exiv2/pull/1252. The submitted
patch is slightly different than this one, due to other changes
between 0.27.3 and master.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
---
 cmake/compilerFlags.cmake | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/cmake/compilerFlags.cmake b/cmake/compilerFlags.cmake
index 0418aa61..be430977 100644
--- a/cmake/compilerFlags.cmake
+++ b/cmake/compilerFlags.cmake
@@ -1,4 +1,5 @@
 # These flags applies to exiv2lib, the applications, and to the xmp code
+include(CheckCCompilerFlag)
 
 if ( MINGW OR UNIX OR MSYS ) # MINGW, Linux, APPLE, CYGWIN
     if (${CMAKE_CXX_COMPILER_ID} STREQUAL GNU)
@@ -25,13 +26,16 @@ if ( MINGW OR UNIX OR MSYS ) # MINGW, Linux, APPLE, CYGWIN
 
         # This fails under Fedora, MinGW GCC 8.3.0 and CYGWIN/MSYS 9.3.0
         if (NOT (MINGW OR CMAKE_HOST_SOLARIS OR CYGWIN OR MSYS) )
-            if (COMPILER_IS_GCC AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 8.0)
-                add_compile_options(-fstack-clash-protection -fcf-protection)
-            endif()
-
-            if( (COMPILER_IS_GCC   AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 5.0) # Not in GCC 4.8
-            OR  (COMPILER_IS_CLANG AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 3.7) # Not in Clang 3.4.2
-            )
+            check_c_compiler_flag(-fstack-clash-protection HAS_FSTACK_CLASH_PROTECTION)
+            check_c_compiler_flag(-fcf-protection HAS_FCF_PROTECTION)
+            check_c_compiler_flag(-fstack-protector-strong HAS_FSTACK_PROTECTOR_STRONG)
+            if(HAS_FSTACK_CLASH_PROTECTION)
+                add_compile_options(-fstack-clash-protection)
+            endif()
+            if(GCC_HAS_FCF_PROTECTION)
+                add_compile_options(-fcf-protection)
+            endif()
+            if(GCC_HAS_FSTACK_PROTECTOR_STRONG)
                 add_compile_options(-fstack-protector-strong)
             endif()
         endif()
--- 
2.26.2