BUILD: makefile: move the fwrapv option to STD_CFLAGS

We now have a separate CFLAGS variable for sensitive options that affect
code generation and/or standard compliance. This one must not be mixed
with the warnings auto-detection because changing such warnings can
result in losing the options. Now it's easier to affect them separately.
The option was not listed in the series of variables useful to packagers
because they're not supposed to touch it.

diff --git a/Makefile b/Makefile
index c308a8fdeb7f320822883c0c55022b76c21158ed..af4a04a49d5b4e6a6126e93e9f46d7af39801f64 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -192,17 +192,22 @@ ERR =
 REG_TEST_FILES =
 REG_TEST_SCRIPT=./scripts/run-regtests.sh
 
-#### Compiler-specific flags that may be used to disable some negative over-
-# optimization or to silence some warnings.
-# We rely on signed integer wraparound on overflow, however clang think it
-# can do whatever it wants since it's an undefined behavior, so use -fwrapv
-# to be sure we get the intended behavior.
+#### Standard C definition
+# Compiler-specific flags that may be used to set the standard behavior we
+# rely on and to disable some negative over-optimization. More specifically,
+# we rely on signed integer wraparound on overflow, however recently clang and
+# gcc decided to change their code generation regarding this and abuse the
+# undefined behavior to silently produce invalid code. For this reason we have
+# to use -fwrapv or -fno-strict-overflow to guarantee the intended behavior.
+# It is preferable not to change this option in order to avoid breakage.
+STD_CFLAGS  := $(call cc-opt-alt,-fwrapv,-fno-strict-overflow)
+
+#### Compiler-specific flags to enable/disable certain classes of warnings.
 WARN_CFLAGS := -Wtype-limits -Wshift-negative-value -Wshift-overflow=2 \
                -Wduplicated-cond -Wnull-dereference
 SPEC_CFLAGS := -Wall -Wextra -Wundef -Wdeclaration-after-statement -Wfatal-errors
 SPEC_CFLAGS += $(call cc-all-fast,$(WARN_CFLAGS))
 
-SPEC_CFLAGS += $(call cc-opt-alt,-fwrapv,-fno-strict-overflow)
 SPEC_CFLAGS += $(cc-wnouwo)
 SPEC_CFLAGS += $(call cc-nowarn,address-of-packed-member)
 SPEC_CFLAGS += $(call cc-nowarn,unused-label)
@@ -471,7 +476,7 @@ $(set_target_defaults)
 # linking with it by default as it's not always available nor deployed
 # (especially on archs which do not need it).
 ifneq ($(USE_THREAD:0=),)
-  ifneq ($(shell $(CC) $(OPT_CFLAGS) $(ARCH_FLAGS) $(CPU_CFLAGS) $(DEBUG_CFLAGS) $(SPEC_CFLAGS) $(CFLAGS) -dM -E -xc - </dev/null 2>/dev/null | grep -c 'LOCK_FREE.*1'),0)
+  ifneq ($(shell $(CC) $(OPT_CFLAGS) $(ARCH_FLAGS) $(CPU_CFLAGS) $(DEBUG_CFLAGS) $(STD_CFLAGS) $(SPEC_CFLAGS) $(CFLAGS) -dM -E -xc - </dev/null 2>/dev/null | grep -c 'LOCK_FREE.*1'),0)
     USE_LIBATOMIC   = implicit
   endif
 endif
@@ -840,10 +845,10 @@ endif
 $(collect_opts_flags)
 
 #### Global compile options
-VERBOSE_CFLAGS = $(OPT_CFLAGS) $(ARCH_FLAGS) $(CPU_CFLAGS) $(DEBUG_CFLAGS) $(SPEC_CFLAGS) $(TARGET_CFLAGS) $(CFLAGS) $(DEFINE)
+VERBOSE_CFLAGS = $(OPT_CFLAGS) $(ARCH_FLAGS) $(CPU_CFLAGS) $(DEBUG_CFLAGS) $(STD_CFLAGS) $(SPEC_CFLAGS) $(TARGET_CFLAGS) $(CFLAGS) $(DEFINE)
 COPTS  = -Iinclude
 
-COPTS += $(OPT_CFLAGS) $(ARCH_FLAGS) $(CPU_CFLAGS) $(DEBUG_CFLAGS) $(SPEC_CFLAGS) $(TARGET_CFLAGS) $(DEFINE) $(SILENT_DEFINE)
+COPTS += $(OPT_CFLAGS) $(ARCH_FLAGS) $(CPU_CFLAGS) $(DEBUG_CFLAGS) $(STD_CFLAGS) $(SPEC_CFLAGS) $(TARGET_CFLAGS) $(DEFINE) $(SILENT_DEFINE)
 COPTS += $(DEBUG) $(OPTIONS_CFLAGS) $(CFLAGS) $(ADDINC)
 
 ifneq ($(VERSION)$(SUBVERS)$(EXTRAVERSION),)
@@ -1152,6 +1157,7 @@ opts:
        @echo -n 'ARCH_FLAGS="$(strip $(ARCH_FLAGS))" '
        @echo -n 'CPU_CFLAGS="$(strip $(CPU_CFLAGS))" '
        @echo -n 'DEBUG_CFLAGS="$(strip $(DEBUG_CFLAGS))" '
+       @echo -n 'STD_CFLAGS="$(strip $(STD_CFLAGS))" '
        @echo -n 'CFLAGS="$(strip $(CFLAGS))" '
        @#echo "$(strip $(BUILD_OPTIONS))"
        @$(foreach opt,$(enabled_opts),\