Makefile.flags - busybox - Git at Google

 # ==========================================================================
 # Build system
 # ==========================================================================

 BB_VER = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)
 export BB_VER
 SKIP_STRIP ?= n

 # -std=gnu99 needed for [U]LLONG_MAX on some systems
 CPPFLAGS += $(call cc-option,-std=gnu99,)

 CPPFLAGS += \
 	-Iinclude -Ilibbb \
 	$(if $(KBUILD_SRC),-Iinclude2 -I$(srctree)/include -I$(srctree)/libbb) \
 	-include include/autoconf.h \
 	-D_GNU_SOURCE -DNDEBUG \
 	$(if $(CONFIG_LFS),-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64) \
 	-D"BB_VER=KBUILD_STR($(BB_VER))"

 CFLAGS += $(call cc-option,-Wall,)
 CFLAGS += $(call cc-option,-Wshadow,)
 CFLAGS += $(call cc-option,-Wwrite-strings,)
 CFLAGS += $(call cc-option,-Wundef,)
 CFLAGS += $(call cc-option,-Wstrict-prototypes,)
 CFLAGS += $(call cc-option,-Wunused -Wunused-parameter,)
 CFLAGS += $(call cc-option,-Wunused-function -Wunused-value,)
 CFLAGS += $(call cc-option,-Wmissing-prototypes -Wmissing-declarations,)
 CFLAGS += $(call cc-option,-Wno-format-security,)
 # warn about C99 declaration after statement
 CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
 # If you want to add more -Wsomething above, make sure that it is
 # still possible to build bbox without warnings.

 ifeq ($(CONFIG_WERROR),y)
 CFLAGS += $(call cc-option,-Werror,)
 ## TODO:
 ## gcc version 4.4.0 20090506 (Red Hat 4.4.0-4) (GCC) is a PITA:
 ## const char *ptr; ... off_t v = *(off_t*)ptr; -> BOOM
 ## and no easy way to convince it to shut the hell up.
 ## We have a lot of such things all over the place.
 ## Classic *(off_t*)(void*)ptr does not work,
 ## and I am unwilling to do crazy gcc specific ({ void *ppp = ...; })
 ## stuff in macros. This would obfuscate the code too much.
 ## Maybe try __attribute__((__may_alias__))?
 #CFLAGS += $(call cc-ifversion, -eq, 0404, -fno-strict-aliasing)
 endif
 # gcc 3.x emits bogus "old style proto" warning on find.c:alloc_action()
 CFLAGS += $(call cc-ifversion, -ge, 0400, -Wold-style-definition)

 ifneq ($(CC),clang)
 # "clang-9: warning: optimization flag '-finline-limit=0' is not supported
 CFLAGS += $(call cc-option,-finline-limit=0,)
 endif

 CFLAGS += $(call cc-option,-fno-builtin-strlen -fomit-frame-pointer -ffunction-sections -fdata-sections,)
 # -fno-guess-branch-probability: prohibit pseudo-random guessing
 # of branch probabilities (hopefully makes bloatcheck more stable):
 CFLAGS += $(call cc-option,-fno-guess-branch-probability,)
 CFLAGS += $(call cc-option,-funsigned-char,)

 ifneq ($(CC),clang)
 # "clang-9: warning: argument unused during compilation: '-static-libgcc'"
 CFLAGS += $(call cc-option,-static-libgcc,)
 endif

 CFLAGS += $(call cc-option,-falign-functions=1,)
 ifneq ($(CC),clang)
 # "clang-9: warning: optimization flag '-falign-jumps=1' is not supported" (and same for other two)
 CFLAGS += $(call cc-option,-falign-jumps=1 -falign-labels=1 -falign-loops=1,)
 endif

 # Defeat .eh_frame bloat (gcc 4.6.3 x86-32 defconfig: 20% smaller busybox binary):
 CFLAGS += $(call cc-option,-fno-unwind-tables,)
 CFLAGS += $(call cc-option,-fno-asynchronous-unwind-tables,)
 # No automatic printf->puts,putchar conversions
 # (try disabling this and comparing assembly, it's instructive)
 CFLAGS += $(call cc-option,-fno-builtin-printf,)

 # clang-9 does not like "str" + N and "if (CONFIG_ITEM && cond)" constructs
 CFLAGS += $(call cc-option,-Wno-string-plus-int -Wno-constant-logical-operand)

 # FIXME: These warnings are at least partially to be concerned about and should
 # be fixed..
 #CFLAGS += $(call cc-option,-Wconversion,)

 ifneq ($(CONFIG_DEBUG),y)
 CFLAGS += $(call cc-option,-Os,$(call cc-option,-O2,))
 else
 CFLAGS += $(call cc-option,-g,)
 #CFLAGS += "-D_FORTIFY_SOURCE=2"
 ifeq ($(CONFIG_DEBUG_PESSIMIZE),y)
 CFLAGS += $(call cc-option,-O0,)
 else
 CFLAGS += $(call cc-option,-Os,$(call cc-option,-O2,))
 endif
 endif
 ifeq ($(CONFIG_DEBUG_SANITIZE),y)
 CFLAGS += $(call cc-option,-fsanitize=address,)
 CFLAGS += $(call cc-option,-fsanitize=leak,)
 CFLAGS += $(call cc-option,-fsanitize=undefined,)
 endif

 # If arch/$(ARCH)/Makefile did not override it (with, say, -fPIC)...
 ARCH_FPIC ?= -fpic
 ARCH_FPIE ?= -fpie
 ARCH_PIE ?= -pie

 # Usage: $(eval $(call pkg_check_modules,VARIABLE-PREFIX,MODULES))
 define pkg_check_modules
 $(1)_CFLAGS := $(shell $(PKG_CONFIG) $(PKG_CONFIG_FLAGS) --cflags $(2))
 $(1)_LIBS := $(shell $(PKG_CONFIG) $(PKG_CONFIG_FLAGS) --libs $(2))
 endef

 ifeq ($(CONFIG_BUILD_LIBBUSYBOX),y)
 # on i386: 14% smaller libbusybox.so
 # (code itself is 9% bigger, we save on relocs/PLT/GOT)
 CFLAGS += $(ARCH_FPIC)
 # and another 4% reduction of libbusybox.so:
 # (external entry points must be marked EXTERNALLY_VISIBLE)
 CFLAGS += $(call cc-option,-fvisibility=hidden)
 endif

 ifeq ($(CONFIG_STATIC),y)
 CFLAGS_busybox += -static
 PKG_CONFIG_FLAGS += --static
 endif

 ifeq ($(CONFIG_PIE),y)
 CFLAGS_busybox += $(ARCH_PIE)
 CFLAGS += $(ARCH_FPIE)
 endif

 ifneq ($(CONFIG_EXTRA_CFLAGS),)
 CFLAGS += $(strip $(subst ",,$(CONFIG_EXTRA_CFLAGS)))
 #"))
 endif

 # Note: both "" (string consisting of two quote chars) and empty string
 # are possible, and should be skipped below.
 ifneq ($(subst "",,$(CONFIG_SYSROOT)),)
 CFLAGS += --sysroot=$(CONFIG_SYSROOT)
 export SYSROOT=$(CONFIG_SYSROOT)
 endif

 # Android has no separate crypt library
 # gcc-4.2.1 fails if we try to feed C source on stdin:
 #  echo 'int main(void){return 0;}' | $(CC) $(CFLAGS) -lcrypt -o /dev/null -xc -
 # fall back to using a temp file:
 CRYPT_AVAILABLE := $(shell echo 'int main(void){return 0;}' >crypttest.c; $(CC) $(CFLAGS) -lcrypt -o /dev/null crypttest.c >/dev/null 2>&1 && echo "y"; rm crypttest.c)
 ifeq ($(CRYPT_AVAILABLE),y)
 LDLIBS += m rt crypt
 else
 LDLIBS += m rt
 endif
 # libm may be needed for dc, awk, ntpd
 # librt may be needed for clock_gettime()

 # libpam may use libpthread, libdl and/or libaudit.
 # On some platforms that requires an explicit -lpthread, -ldl, -laudit.
 # However, on *other platforms* it fails when some of those flags
 # given needlessly. On some systems, crypt needs pthread.
 #
 # I even had a system where a runtime test for pthread
 # (similar to CRYPT_AVAILABLE test above) was not reliable.
 #
 # Do not propagate this mess by adding libraries to CONFIG_PAM/CRYPT_AVAILABLE blocks.
 # Add libraries you need to CONFIG_EXTRA_LDLIBS instead.

 ifeq ($(CONFIG_PAM),y)
 LDLIBS += pam pam_misc
 endif

 ifeq ($(CONFIG_SELINUX),y)
 SELINUX_PC_MODULES = libselinux libsepol
 $(eval $(call pkg_check_modules,SELINUX,$(SELINUX_PC_MODULES)))
 CPPFLAGS += $(SELINUX_CFLAGS)
 LDLIBS += $(if $(SELINUX_LIBS),$(SELINUX_LIBS:-l%=%),$(SELINUX_PC_MODULES:lib%=%))
 endif

 ifeq ($(CONFIG_FEATURE_NSLOOKUP_BIG),y)
 LDLIBS += resolv
 endif

 ifeq ($(CONFIG_EFENCE),y)
 LDLIBS += efence
 endif

 ifeq ($(CONFIG_DMALLOC),y)
 LDLIBS += dmalloc
 endif

 # If a flat binary should be built, CFLAGS_busybox="-elf2flt"
 # env var should be set for make invocation.
 # Here we check whether CFLAGS_busybox indeed contains that flag.
 # (For historical reasons, we also check LDFLAGS, which doesn't
 # seem to be entirely correct variable to put "-elf2flt" into).
 W_ELF2FLT = -elf2flt
 ifneq (,$(findstring $(W_ELF2FLT),$(LDFLAGS) $(CFLAGS_busybox)))
 SKIP_STRIP = y
 endif

 ifneq ($(CONFIG_EXTRA_LDFLAGS),)
 LDFLAGS += $(strip $(subst ",,$(CONFIG_EXTRA_LDFLAGS)))
 #"))
 endif

 ifneq ($(CONFIG_EXTRA_LDLIBS),)
 LDLIBS += $(strip $(subst ",,$(CONFIG_EXTRA_LDLIBS)))
 #"))
 endif

 # Busybox is a stack-fatty so make sure we increase default size
 # TODO: use "make stksizes" to find & fix big stack users
 # (we stole scripts/checkstack.pl from the kernel... thanks guys!)
 # Reduced from 20k to 16k in 1.9.0.
 FLTFLAGS += -s 16000
	# ==========================================================================
	# Build system
	# ==========================================================================

	BB_VER = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)
	export BB_VER
	SKIP_STRIP ?= n

	# -std=gnu99 needed for [U]LLONG_MAX on some systems
	CPPFLAGS += $(call cc-option,-std=gnu99,)

	CPPFLAGS += \
	-Iinclude -Ilibbb \
	$(if $(KBUILD_SRC),-Iinclude2 -I$(srctree)/include -I$(srctree)/libbb) \
	-include include/autoconf.h \
	-D_GNU_SOURCE -DNDEBUG \
	$(if $(CONFIG_LFS),-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64) \
	-D"BB_VER=KBUILD_STR($(BB_VER))"

	CFLAGS += $(call cc-option,-Wall,)
	CFLAGS += $(call cc-option,-Wshadow,)
	CFLAGS += $(call cc-option,-Wwrite-strings,)
	CFLAGS += $(call cc-option,-Wundef,)
	CFLAGS += $(call cc-option,-Wstrict-prototypes,)
	CFLAGS += $(call cc-option,-Wunused -Wunused-parameter,)
	CFLAGS += $(call cc-option,-Wunused-function -Wunused-value,)
	CFLAGS += $(call cc-option,-Wmissing-prototypes -Wmissing-declarations,)
	CFLAGS += $(call cc-option,-Wno-format-security,)
	# warn about C99 declaration after statement
	CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
	# If you want to add more -Wsomething above, make sure that it is
	# still possible to build bbox without warnings.

	ifeq ($(CONFIG_WERROR),y)
	CFLAGS += $(call cc-option,-Werror,)
	## TODO:
	## gcc version 4.4.0 20090506 (Red Hat 4.4.0-4) (GCC) is a PITA:
	## const char ptr; ... off_t v = (off_t*)ptr; -> BOOM
	## and no easy way to convince it to shut the hell up.
	## We have a lot of such things all over the place.
	## Classic (off_t)(void*)ptr does not work,
	## and I am unwilling to do crazy gcc specific ({ void *ppp = ...; })
	## stuff in macros. This would obfuscate the code too much.
	## Maybe try __attribute__((__may_alias__))?
	#CFLAGS += $(call cc-ifversion, -eq, 0404, -fno-strict-aliasing)
	endif
	# gcc 3.x emits bogus "old style proto" warning on find.c:alloc_action()
	CFLAGS += $(call cc-ifversion, -ge, 0400, -Wold-style-definition)

	ifneq ($(CC),clang)
	# "clang-9: warning: optimization flag '-finline-limit=0' is not supported
	CFLAGS += $(call cc-option,-finline-limit=0,)
	endif

	CFLAGS += $(call cc-option,-fno-builtin-strlen -fomit-frame-pointer -ffunction-sections -fdata-sections,)
	# -fno-guess-branch-probability: prohibit pseudo-random guessing
	# of branch probabilities (hopefully makes bloatcheck more stable):
	CFLAGS += $(call cc-option,-fno-guess-branch-probability,)
	CFLAGS += $(call cc-option,-funsigned-char,)

	ifneq ($(CC),clang)
	# "clang-9: warning: argument unused during compilation: '-static-libgcc'"
	CFLAGS += $(call cc-option,-static-libgcc,)
	endif

	CFLAGS += $(call cc-option,-falign-functions=1,)
	ifneq ($(CC),clang)
	# "clang-9: warning: optimization flag '-falign-jumps=1' is not supported" (and same for other two)
	CFLAGS += $(call cc-option,-falign-jumps=1 -falign-labels=1 -falign-loops=1,)
	endif

	# Defeat .eh_frame bloat (gcc 4.6.3 x86-32 defconfig: 20% smaller busybox binary):
	CFLAGS += $(call cc-option,-fno-unwind-tables,)
	CFLAGS += $(call cc-option,-fno-asynchronous-unwind-tables,)
	# No automatic printf->puts,putchar conversions
	# (try disabling this and comparing assembly, it's instructive)
	CFLAGS += $(call cc-option,-fno-builtin-printf,)

	# clang-9 does not like "str" + N and "if (CONFIG_ITEM && cond)" constructs
	CFLAGS += $(call cc-option,-Wno-string-plus-int -Wno-constant-logical-operand)

	# FIXME: These warnings are at least partially to be concerned about and should
	# be fixed..
	#CFLAGS += $(call cc-option,-Wconversion,)

	ifneq ($(CONFIG_DEBUG),y)
	CFLAGS += $(call cc-option,-Os,$(call cc-option,-O2,))
	else
	CFLAGS += $(call cc-option,-g,)
	#CFLAGS += "-D_FORTIFY_SOURCE=2"
	ifeq ($(CONFIG_DEBUG_PESSIMIZE),y)
	CFLAGS += $(call cc-option,-O0,)
	else
	CFLAGS += $(call cc-option,-Os,$(call cc-option,-O2,))
	endif
	endif
	ifeq ($(CONFIG_DEBUG_SANITIZE),y)
	CFLAGS += $(call cc-option,-fsanitize=address,)
	CFLAGS += $(call cc-option,-fsanitize=leak,)
	CFLAGS += $(call cc-option,-fsanitize=undefined,)
	endif

	# If arch/$(ARCH)/Makefile did not override it (with, say, -fPIC)...
	ARCH_FPIC ?= -fpic
	ARCH_FPIE ?= -fpie
	ARCH_PIE ?= -pie

	# Usage: $(eval $(call pkg_check_modules,VARIABLE-PREFIX,MODULES))
	define pkg_check_modules
	$(1)_CFLAGS := $(shell $(PKG_CONFIG) $(PKG_CONFIG_FLAGS) --cflags $(2))
	$(1)_LIBS := $(shell $(PKG_CONFIG) $(PKG_CONFIG_FLAGS) --libs $(2))
	endef

	ifeq ($(CONFIG_BUILD_LIBBUSYBOX),y)
	# on i386: 14% smaller libbusybox.so
	# (code itself is 9% bigger, we save on relocs/PLT/GOT)
	CFLAGS += $(ARCH_FPIC)
	# and another 4% reduction of libbusybox.so:
	# (external entry points must be marked EXTERNALLY_VISIBLE)
	CFLAGS += $(call cc-option,-fvisibility=hidden)
	endif

	ifeq ($(CONFIG_STATIC),y)
	CFLAGS_busybox += -static
	PKG_CONFIG_FLAGS += --static
	endif

	ifeq ($(CONFIG_PIE),y)
	CFLAGS_busybox += $(ARCH_PIE)
	CFLAGS += $(ARCH_FPIE)
	endif

	ifneq ($(CONFIG_EXTRA_CFLAGS),)
	CFLAGS += $(strip $(subst ",,$(CONFIG_EXTRA_CFLAGS)))
	#"))
	endif

	# Note: both "" (string consisting of two quote chars) and empty string
	# are possible, and should be skipped below.
	ifneq ($(subst "",,$(CONFIG_SYSROOT)),)
	CFLAGS += --sysroot=$(CONFIG_SYSROOT)
	export SYSROOT=$(CONFIG_SYSROOT)
	endif

	# Android has no separate crypt library
	# gcc-4.2.1 fails if we try to feed C source on stdin:
	# echo 'int main(void){return 0;}' \| $(CC) $(CFLAGS) -lcrypt -o /dev/null -xc -
	# fall back to using a temp file:
	CRYPT_AVAILABLE := $(shell echo 'int main(void){return 0;}' >crypttest.c; $(CC) $(CFLAGS) -lcrypt -o /dev/null crypttest.c >/dev/null 2>&1 && echo "y"; rm crypttest.c)
	ifeq ($(CRYPT_AVAILABLE),y)
	LDLIBS += m rt crypt
	else
	LDLIBS += m rt
	endif
	# libm may be needed for dc, awk, ntpd
	# librt may be needed for clock_gettime()

	# libpam may use libpthread, libdl and/or libaudit.
	# On some platforms that requires an explicit -lpthread, -ldl, -laudit.
	# However, on other platforms it fails when some of those flags
	# given needlessly. On some systems, crypt needs pthread.
	#
	# I even had a system where a runtime test for pthread
	# (similar to CRYPT_AVAILABLE test above) was not reliable.
	#
	# Do not propagate this mess by adding libraries to CONFIG_PAM/CRYPT_AVAILABLE blocks.
	# Add libraries you need to CONFIG_EXTRA_LDLIBS instead.

	ifeq ($(CONFIG_PAM),y)
	LDLIBS += pam pam_misc
	endif

	ifeq ($(CONFIG_SELINUX),y)
	SELINUX_PC_MODULES = libselinux libsepol
	$(eval $(call pkg_check_modules,SELINUX,$(SELINUX_PC_MODULES)))
	CPPFLAGS += $(SELINUX_CFLAGS)
	LDLIBS += $(if $(SELINUX_LIBS),$(SELINUX_LIBS:-l%=%),$(SELINUX_PC_MODULES:lib%=%))
	endif

	ifeq ($(CONFIG_FEATURE_NSLOOKUP_BIG),y)
	LDLIBS += resolv
	endif

	ifeq ($(CONFIG_EFENCE),y)
	LDLIBS += efence
	endif

	ifeq ($(CONFIG_DMALLOC),y)
	LDLIBS += dmalloc
	endif

	# If a flat binary should be built, CFLAGS_busybox="-elf2flt"
	# env var should be set for make invocation.
	# Here we check whether CFLAGS_busybox indeed contains that flag.
	# (For historical reasons, we also check LDFLAGS, which doesn't
	# seem to be entirely correct variable to put "-elf2flt" into).
	W_ELF2FLT = -elf2flt
	ifneq (,$(findstring $(W_ELF2FLT),$(LDFLAGS) $(CFLAGS_busybox)))
	SKIP_STRIP = y
	endif

	ifneq ($(CONFIG_EXTRA_LDFLAGS),)
	LDFLAGS += $(strip $(subst ",,$(CONFIG_EXTRA_LDFLAGS)))
	#"))
	endif

	ifneq ($(CONFIG_EXTRA_LDLIBS),)
	LDLIBS += $(strip $(subst ",,$(CONFIG_EXTRA_LDLIBS)))
	#"))
	endif

	# Busybox is a stack-fatty so make sure we increase default size
	# TODO: use "make stksizes" to find & fix big stack users
	# (we stole scripts/checkstack.pl from the kernel... thanks guys!)
	# Reduced from 20k to 16k in 1.9.0.
	FLTFLAGS += -s 16000