source: drbl_ui/backup/test_busybox/busybox-1.7.2/Makefile.flags @ 59

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

BB_VER = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)
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))" -DBB_BT=AUTOCONF_TIMESTAMP

# flag checks are grouped together to speed the checks up a bit..
CFLAGS += $(call cc-option,-Wall -Wshadow -Wwrite-strings,)
CFLAGS += $(call cc-option,-Wundef -Wstrict-prototypes,)
# If you want to add "-Wmissing-prototypes -Wmissing-declarations" above
# (or anything else for that matter) make sure that it is still possible
# to build bbox without warnings. Current offender: find.c:alloc_action().
# Looks more like gcc bug: gcc will warn on it with or without prototype.
# But still, warning-free compile is a must, or else we will drown
# in warnings pretty soon.

ifeq ($(CONFIG_WERROR),y)
CFLAGS += $(call cc-option,-Werror,)
else
# for development, warn a little bit about unused results..
CPPFLAGS += -D_FORTIFY_SOURCE=2
endif
# gcc 3.x emits bogus "old style proto" warning on find.c:alloc_action()
CFLAGS += $(call cc-ifversion, -ge, 0400, -Wold-style-definition)

# gcc emits bogus "no prev proto" warning on find.c:alloc_action()
ifneq ($(CONFIG_WERROR),y)
CFLAGS += $(call cc-option,-Wmissing-prototypes -Wmissing-declarations,)
endif

CFLAGS += $(call cc-option,-Os -fno-builtin-strlen -finline-limit=0 -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 -static-libgcc,)
CFLAGS += $(call cc-option,-falign-functions=1 -falign-jumps=1 -falign-labels=1 -falign-loops=1,)

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

ifeq ($(CONFIG_DEBUG),y)
CFLAGS += $(call cc-option,-g)
endif

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

BBOX_LIB_LIST = m crypt

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

ifeq ($(CONFIG_SELINUX),y)
BBOX_LIB_LIST += selinux sepol
endif

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

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

# For scripts/trylink
export BBOX_LIB_LIST

#LDFLAGS += -nostdlib

LDFLAGS_ELF2FLT = -Wl,-elf2flt
ifneq (,$(findstring $(LDFLAGS_ELF2FLT),$(LDFLAGS)))
SKIP_STRIP = y
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!)
FLTFLAGS += -s 20000