properly fix failing test with missing CLOCK_BOOTTIME support

- detect older kernel versions in makefile
  and skip ClockType.bootTime tests for those
- turn DFLAGS and UDFLAGS into simply expanded variables
  (makes them settable individually and is easier to understand)
  https://www.gnu.org/software/make/manual/html_node/Flavors.html

posix.mak

@@ -27,7 +27,7 @@ INSTALL_DIR=../install
 DOCDIR=doc
 IMPDIR=import
 
-override PIC:=$(if $(PIC),-fPIC,)
+OPTIONAL_PIC:=$(if $(PIC),-fPIC,)
 
 ifeq (osx,$(OS))
 	DOTDLL:=.dylib
@@ -54,13 +54,13 @@ ifeq (solaris,$(OS))
 endif
 
 # Set DFLAGS
-UDFLAGS=-conf= -Isrc -Iimport -w -dip25 $(MODEL_FLAG) $(PIC)
+UDFLAGS:=-conf= -Isrc -Iimport -w -dip25 $(MODEL_FLAG) $(OPTIONAL_PIC)
 ifeq ($(BUILD),debug)
 	UDFLAGS += -g -debug
-	DFLAGS=$(UDFLAGS)
+	DFLAGS:=$(UDFLAGS)
 else
 	UDFLAGS += -O -release
-	DFLAGS=$(UDFLAGS) -inline # unittests don't compile with -inline
+	DFLAGS:=$(UDFLAGS) -inline # unittests don't compile with -inline
 endif
 
 ROOT_OF_THEM_ALL = generated
@@ -168,8 +168,7 @@ $(ROOT)/threadasm.o : src/core/threadasm.S
 
 ######################## Create a shared library ##############################
 
-$(DRUNTIMESO) $(DRUNTIMESOLIB) dll: override PIC:=-fPIC
-$(DRUNTIMESO) $(DRUNTIMESOLIB) dll: DFLAGS+=-version=Shared
+$(DRUNTIMESO) $(DRUNTIMESOLIB) dll: DFLAGS+=-version=Shared -fPIC
 dll: $(DRUNTIMESOLIB)
 
 $(DRUNTIMESO): $(OBJS) $(SRCS)
@@ -201,6 +200,13 @@ unittest-%:
 	$(MAKE) -f $(MAKEFILE) unittest OS=$(OS) MODEL=$(MODEL) DMD=$(DMD) BUILD=$*
 endif
 
+ifeq ($(OS),linux)
+  old_kernel:=$(shell [ "$$(uname -r | cut -d'-' -f1)" \< "2.6.39" ] && echo 1)
+  ifeq ($(old_kernel),1)
+    UDFLAGS+=-version=Linux_Pre_2639
+  endif
+endif
+
 ifeq ($(OS),freebsd)
 DISABLED_TESTS =
 else
@@ -219,8 +225,7 @@ else
 
 UT_DRUNTIME:=$(ROOT)/unittest/libdruntime-ut$(DOTDLL)
 
-$(UT_DRUNTIME): override PIC:=-fPIC
-$(UT_DRUNTIME): UDFLAGS+=-version=Shared
+$(UT_DRUNTIME): UDFLAGS+=-version=Shared -fPIC
 $(UT_DRUNTIME): $(OBJS) $(SRCS)
 	$(DMD) $(UDFLAGS) -shared -unittest -of$@ $(SRCS) $(OBJS) $(LINKDL) -debuglib= -defaultlib=
 

src/core/time.d

@@ -157,7 +157,7 @@ version(CoreDdoc) enum ClockType
     /++
         $(BLUE Linux-Only)
 
-        Uses $(D CLOCK_MONOTONIC_BOOTTIME).
+        Uses $(D CLOCK_BOOTTIME).
       +/
     bootTime = 1,
 
@@ -2714,15 +2714,20 @@ unittest
     auto norm2 = MonoTimeImpl!(ClockType.normal).currTime;
     assert(norm1 <= norm2);
 
+    static bool clockSupported(ClockType c)
+    {
+        version (Linux_Pre_2639) // skip CLOCK_BOOTTIME on older linux kernels
+            return c != ClockType.second && c != ClockType.bootTime;
+        else
+            return c != ClockType.second; // second doesn't work with MonoTimeImpl
+
+    }
+
     foreach(typeStr; __traits(allMembers, ClockType))
     {
-        // ClockType.second is currently the only clock type that doesn't work
-        // with MonoTimeImpl.
-        static if(typeStr != "second")
+        mixin("alias type = ClockType." ~ typeStr ~ ";");
+        static if (clockSupported(type))
         {
-            mixin("alias type = ClockType." ~ typeStr ~ ";");
-            version (linux) if (typeStr == "bootTime" && !MonoTimeImpl!type.ticksPerSecond)
-                continue;
             auto v1 = MonoTimeImpl!type.currTime;
             auto v2 = MonoTimeImpl!type.currTime;
             scope(failure)
@@ -2737,11 +2742,9 @@ unittest
 
             foreach(otherStr; __traits(allMembers, ClockType))
             {
-                static if(otherStr != "second")
+                mixin("alias other = ClockType." ~ otherStr ~ ";");
+                static if (clockSupported(other))
                 {
-                    mixin("alias other = ClockType." ~ otherStr ~ ";");
-                    version (linux) if (typeStr == "bootTime" && !MonoTimeImpl!other.ticksPerSecond)
-                        continue;
                     static assert(is(typeof({auto o1 = MonTimeImpl!other.currTime; auto b = v1 <= o1;})) ==
                                   is(type == other));
                 }