ENH: Improve robustness of compiler INFO strings

Compiler INFO strings built at preprocessing time encode information
that must appear as a string literal in the resulting binary.  We must
make sure the strings appear in the final binary no matter what compiler
and flags are used.  The previous implementation worked in most places
but failed with the GNU linker's --gc-sections option which managed to
discard the string.  Instead we make the program return value depend on
an element of the string indexed by a runtime program parameter, which
absolutely requires the string to be present.

1 files changed, 15 insertions, 6 deletions

diff --git a/Modules/CMakeCCompilerId.c.in b/Modules/CMakeCCompilerId.c.in
index ecbe431..35d7df7 100644
--- a/Modules/CMakeCCompilerId.c.in
+++ b/Modules/CMakeCCompilerId.c.in
@@ -2,15 +2,9 @@
 # error "A C++ compiler has been selected for C."
 #endif
 
-/* Provide main() so the program can link.  */
 #if defined(__18CXX)
 # define ID_VOID_MAIN
 #endif
-#ifdef ID_VOID_MAIN
-void main() {}
-#else
-int main() { return 0; }
-#endif
 
 #if defined(__INTEL_COMPILER) || defined(__ICC)
 # define COMPILER_ID "Intel"
@@ -82,3 +76,18 @@ int main() { return 0; }
 char* info_compiler = "INFO" ":" "compiler[" COMPILER_ID "]";
 
 @CMAKE_C_COMPILER_ID_PLATFORM_CONTENT@
+
+/*--------------------------------------------------------------------------*/
+
+#ifdef ID_VOID_MAIN
+void main() {}
+#else
+int main(int argc, char* argv[])
+{
+  int require = 0;
+  require += info_compiler[argc];
+  require += info_platform[argc];
+  (void)argv;
+  return require;
+}
+#endif