BUILD: makefile: allow to use CFLAGS to append build options

CFLAGS has always been a troublemaker because the variable was preset
based on other options, including dynamically detected ones, so
overriding it would just lose the original contents, forcing users
to resort to various alternatives such as DEFINE, ADDINC or SMALL_OPTS.

Now that the variable's usage was cleared, let's just preset it to
empty (and it MUST absolutely remain like this) and append it at the
end of the compiler's options. This will now allow to change an
optimization level, force a CPU type or disable a warning as users
commonly expect from CFLAGS passed to a makefile, and not to override
*all* the compiler flags as it has progressively become.

diff --git a/INSTALL b/INSTALL
index 07eda87df0f9a4c1a0497a1acddc6d382ddf4f77..f94cc0bb846f9d5e0b076c39fd7f3819787751fe 100644 (file)
--- a/INSTALL
+++ b/INSTALL
@@ -582,6 +582,10 @@ number of defines and compiler options usually for small systems. For better
 clarity it's recommended to pass the options which result in a smaller binary
 (like memory limits or -Os) into this variable.
 
+A generic CFLAGS variable may be set to append any option to pass to the C
+compiler. These flags are passed last so the variable may be used to override
+other options such as warnings, optimization levels, include paths etc.
+
 If you are building for a different system than the one you're building on,
 this is called "cross-compiling". HAProxy supports cross-compilation pretty
 well and tries to ease it by letting you adjust paths to all libraries (please

diff --git a/Makefile b/Makefile
index 77f22a1bde0632357514dc6fc161f28f935cffc0..40d89cbb9a83553b3f67d6b37e555683beb6059f 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -76,6 +76,7 @@
 #   CC is set to "cc" by default and is used for compilation only.
 #   LD is set to "cc" by default and is used for linking only.
 #   ARCH may be useful to force build of 32-bit binary on 64-bit systems
+#   CFLAGS may be used to append any flags for the C compiler.
 #   LDFLAGS is automatically set to -g and may be overridden.
 #   DEP may be cleared to ignore changes to include files during development
 #   SMALL_OPTS may be used to specify some options to shrink memory usage.
@@ -284,6 +285,13 @@ ARCH_FLAGS.i686   = -m32 -march=i686
 ARCH_FLAGS.x86_64 = -m64 -march=x86-64
 ARCH_FLAGS        = $(ARCH_FLAGS.$(ARCH))
 
+#### Extra CFLAGS
+# These CFLAGS are empty by default and are appended at the end of all the
+# flags passed to the compiler, so that it is possible to use them to force
+# some optimization levels, architecture types and/or disable certain warnings.
+# Just set CFLAGS to the desired ones on the "make" command line.
+CFLAGS =
+
 #### Common LDFLAGS
 # These LDFLAGS are used as the first "ld" options, regardless of any library
 # path or any other option. They may be changed to add any linker-specific
@@ -464,7 +472,7 @@ $(set_target_defaults)
 # linking with it by default as it's not always available nor deployed
 # (especially on archs which do not need it).
 ifneq ($(USE_THREAD:0=),)
-  ifneq ($(shell $(CC) $(ARCH_FLAGS) $(CPU_CFLAGS) $(DEBUG_CFLAGS) $(SPEC_CFLAGS) -dM -E -xc - </dev/null 2>/dev/null | grep -c 'LOCK_FREE.*1'),0)
+  ifneq ($(shell $(CC) $(ARCH_FLAGS) $(CPU_CFLAGS) $(DEBUG_CFLAGS) $(SPEC_CFLAGS) $(CFLAGS) -dM -E -xc - </dev/null 2>/dev/null | grep -c 'LOCK_FREE.*1'),0)
     USE_LIBATOMIC   = implicit
   endif
 endif
@@ -833,11 +841,11 @@ endif
 $(collect_opts_flags)
 
 #### Global compile options
-VERBOSE_CFLAGS = $(ARCH_FLAGS) $(CPU_CFLAGS) $(DEBUG_CFLAGS) $(SPEC_CFLAGS) $(TARGET_CFLAGS) $(SMALL_OPTS) $(DEFINE)
+VERBOSE_CFLAGS = $(ARCH_FLAGS) $(CPU_CFLAGS) $(DEBUG_CFLAGS) $(SPEC_CFLAGS) $(TARGET_CFLAGS) $(SMALL_OPTS) $(CFLAGS) $(DEFINE)
 COPTS  = -Iinclude
 
 COPTS += $(ARCH_FLAGS) $(CPU_CFLAGS) $(DEBUG_CFLAGS) $(SPEC_CFLAGS) $(TARGET_CFLAGS) $(SMALL_OPTS) $(DEFINE) $(SILENT_DEFINE)
-COPTS += $(DEBUG) $(OPTIONS_CFLAGS) $(ADDINC)
+COPTS += $(DEBUG) $(OPTIONS_CFLAGS) $(CFLAGS) $(ADDINC)
 
 ifneq ($(VERSION)$(SUBVERS)$(EXTRAVERSION),)
   COPTS += -DCONFIG_HAPROXY_VERSION=\"$(VERSION)$(SUBVERS)$(EXTRAVERSION)\"
@@ -1147,6 +1155,7 @@ opts:
        @echo -n 'ARCH_FLAGS="$(strip $(ARCH_FLAGS))" '
        @echo -n 'CPU_CFLAGS="$(strip $(CPU_CFLAGS))" '
        @echo -n 'DEBUG_CFLAGS="$(strip $(DEBUG_CFLAGS))" '
+       @echo -n 'CFLAGS="$(strip $(CFLAGS))" '
        @#echo "$(strip $(BUILD_OPTIONS))"
        @$(foreach opt,$(enabled_opts),\
                $(if $(subst command line,,$(origin USE_$(opt))),,\