include/make/compiler.mk - haproxy - Gitiles

 # WARNING: Do not change cc-opt, cc-opt-alt or cc-warning without checking if
 #          clang bug #49364 is fixed. stderr is redirected to /dev/null on
 #          purpose, to work around a clang 11 bug that crashes if stderr is
 #          redirected to stdin.
 #
 # Function used to detect support of a given option by the compiler.
 # Usage: CFLAGS += $(call cc-opt,option). Eg: $(call cc-opt,-fwrapv)
 # Note: ensure the referencing variable is assigned using ":=" and not "=" to
 #       call it only once.
 cc-opt = $(shell set -e; if $(CC) -Werror $(1) -E -xc - -o /dev/null </dev/null >&0 2>/dev/null; then echo "$(1)"; fi;)

 # same but tries with $2 if $1 is not supported
 cc-opt-alt = $(if $(shell set -e; if $(CC) -Werror $(1) -E -xc - -o /dev/null </dev/null >&0 2>/dev/null; then echo 1;fi),$(1),$(call cc-opt,$(2)))

 # validate a list of options one at a time
 cc-all-opts  = $(foreach a,$(1),$(call cc-opt,$(a)))

 # try to pass plenty of options at once, take them on success or try them
 # one at a time on failure and keep successful ones. This is handy to quickly
 # validate most common options.
 cc-all-fast = $(if $(call cc-opt,$(1)),$(1),$(call cc-all-opts,$(1)))

 # Below we verify that the compiler supports any -Wno-something option to
 # disable any warning, or if a special option is needed to achieve that. This
 # will allow to get rid of testing when the compiler doesn't care. The result
 # is made of two variables:
 #  - cc-anywno that's non-empty if the compiler supports disabling anything
 #  - cc-wnouwo that may contain an option needed to enable this behavior
 # Gcc 4.x and above do not need any option but will still complain about unknown
 # options if another warning or error happens, and as such they're not testable.
 # Clang needs a special option -Wno-unknown-warning-option. Compilers not
 # supporting this option will check all warnings individually.
 cc-anywno := $(call cc-opt,-Wno-haproxy-warning)
 cc-wnouwo := $(if $(cc-anywno),,$(call cc-opt,-Wno-unknown-warning-option))
 cc-anywno := $(if $(cc-anywno)$(cc-wnouwo),1)

 # Disable a warning when supported by the compiler. Don't put spaces around the
 # warning! And don't use cc-opt which doesn't always report an error until
 # another one is also returned. If "cc-anywno" is set, the compiler supports
 # -Wno- followed by anything so we don't even need to start the compiler.
 # Usage: CFLAGS += $(call cc-nowarn,warning). Eg: $(call cc-opt,format-truncation)
 cc-nowarn = $(if $(cc-anywno),-Wno-$(1),$(shell set -e; if $(CC) -Werror -W$(1) -E -xc - -o /dev/null </dev/null >&0 2>/dev/null; then echo "-Wno-$(1)"; fi;))
	# WARNING: Do not change cc-opt, cc-opt-alt or cc-warning without checking if
	# clang bug #49364 is fixed. stderr is redirected to /dev/null on
	# purpose, to work around a clang 11 bug that crashes if stderr is
	# redirected to stdin.
	#
	# Function used to detect support of a given option by the compiler.
	# Usage: CFLAGS += $(call cc-opt,option). Eg: $(call cc-opt,-fwrapv)
	# Note: ensure the referencing variable is assigned using ":=" and not "=" to
	# call it only once.
	cc-opt = $(shell set -e; if $(CC) -Werror $(1) -E -xc - -o /dev/null </dev/null >&0 2>/dev/null; then echo "$(1)"; fi;)

	# same but tries with $2 if $1 is not supported
	cc-opt-alt = $(if $(shell set -e; if $(CC) -Werror $(1) -E -xc - -o /dev/null </dev/null >&0 2>/dev/null; then echo 1;fi),$(1),$(call cc-opt,$(2)))

	# validate a list of options one at a time
	cc-all-opts = $(foreach a,$(1),$(call cc-opt,$(a)))

	# try to pass plenty of options at once, take them on success or try them
	# one at a time on failure and keep successful ones. This is handy to quickly
	# validate most common options.
	cc-all-fast = $(if $(call cc-opt,$(1)),$(1),$(call cc-all-opts,$(1)))

	# Below we verify that the compiler supports any -Wno-something option to
	# disable any warning, or if a special option is needed to achieve that. This
	# will allow to get rid of testing when the compiler doesn't care. The result
	# is made of two variables:
	# - cc-anywno that's non-empty if the compiler supports disabling anything
	# - cc-wnouwo that may contain an option needed to enable this behavior
	# Gcc 4.x and above do not need any option but will still complain about unknown
	# options if another warning or error happens, and as such they're not testable.
	# Clang needs a special option -Wno-unknown-warning-option. Compilers not
	# supporting this option will check all warnings individually.
	cc-anywno := $(call cc-opt,-Wno-haproxy-warning)
	cc-wnouwo := $(if $(cc-anywno),,$(call cc-opt,-Wno-unknown-warning-option))
	cc-anywno := $(if $(cc-anywno)$(cc-wnouwo),1)

	# Disable a warning when supported by the compiler. Don't put spaces around the
	# warning! And don't use cc-opt which doesn't always report an error until
	# another one is also returned. If "cc-anywno" is set, the compiler supports
	# -Wno- followed by anything so we don't even need to start the compiler.
	# Usage: CFLAGS += $(call cc-nowarn,warning). Eg: $(call cc-opt,format-truncation)
	cc-nowarn = $(if $(cc-anywno),-Wno-$(1),$(shell set -e; if $(CC) -Werror -W$(1) -E -xc - -o /dev/null </dev/null >&0 2>/dev/null; then echo "-Wno-$(1)"; fi;))