Issue #369: Introduced COMMON flag to support GCC-10 and header-only.…

… LIBXSMM now compiles in any case, however header-only applications will duplicated symbols per each object-file if -fcommon is not the default. GCC-10 changed from -fcommon to -fno-common, i.e., duplicated symbols cause linker errors instead of being quietly dropped.

Makefile

@@ -211,6 +211,9 @@ endif
 # avoid to link with C++ standard library
 FORCE_CXX = 0
 
+# GCC-10 style linkage (error for duplicate symbols)
+COMMON = 0
+
 # include common Makefile artifacts
 include $(ROOTDIR)/Makefile.inc
 

Makefile.inc

@@ -787,6 +787,17 @@ else # fallback
 endif
 endif
 
+COMMON ?= 1
+ifneq (0,$(COMMON))
+  ifneq (,$(call ctest,$(LD),-fcommon))
+    CFLAGS += -fcommon
+  endif
+else
+  ifneq (,$(call ctest,$(LD),-fno-common))
+    CFLAGS += -fno-common
+  endif
+endif
+
 FREEFORM ?= 1
 ifeq (,$(strip $(GFC)))
   ifneq (0,$(INTEL))
@@ -1039,7 +1050,9 @@ ifneq (0,$(INTEL))
   CPEDANTIC += -diag-disable 177,1419,1572,2547,10382
   CWARNEXTRA = -Wremarks
   ifeq (1,$(PEDANTIC))
-    CSTD = -std=c99
+    ifeq (0,$(FORCE_CXX))
+      CSTD = -std=c99
+    endif
     CFLAGS += $(CSTD)
     ifeq (,$(strip $(GFC)))
       FSTD = -std03
@@ -1281,7 +1294,9 @@ else # GCC assumed
     endif
     FPEDANTIC += $(FWARNEXTRA)
     ifeq (1,$(PEDANTIC))
-      CSTD = -std=c99
+      ifeq (0,$(FORCE_CXX))
+        CSTD = -std=c99
+      endif
       CXXFLAGS += $(CPEDANTIC) -Wno-long-long
       #CXXFLAGS += -Wno-missing-field-initializers
       CFLAGS += $(CSTD) $(CPEDANTIC)
@@ -1301,7 +1316,9 @@ else # GCC assumed
         CPEDANTIC += -Wno-long-long
         CXXFLAGS += $(CPEDANTIC)
       else # Clang may run into ICEs under macOS
-        CSTD = -std=c99
+        ifeq (0,$(FORCE_CXX))
+          CSTD = -std=c99
+        endif
         CXXFLAGS += $(CPEDANTIC) -Wno-long-long
       endif
       #CXXFLAGS += -Wno-missing-field-initializers #-Wzero-as-null-pointer-constant

version.txt

@@ -1 +1 @@
-master-1.14-1180
+master-1.14-1181