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busybox/Makefile.flags
Denys Vlasenko 9b80b903c7 build system: stop .eh_frame generation 
From Rich Felker:

By default, modern GCC generates DWARF2 debug/unwind tables in the
.eh_frame section of the object files/binaries. This adds significant
bloat (as much as 15%) to the size of the busybox binary, including
the portion mapped/loaded into memory at runtime (possibly a big issue
for NOMMU targets), and the section is not strippable with the strip
command due to being part of the loaded program text.

I've since done some further checking - both testing and asking the
GCC developers about it - and it seems the solution is to add to the
CFLAGS -fno-unwind-tables and -fno-asynchronous-unwind-tables. If
debugging is disabled, this will prevent GCC from outputting DWARF2
tables entirely. But since busybox builds with -g by default, the
interesting case is what happens then. I originally thought these
options would break debugging, but they don't; instead, they tell GCC
to output the DWARF2 tables in the .debug_frame section instead of
the newish .eh_frame section (used for exception handling). With these
options added, busybox_unstripped is still fully debuggable, and the
final busybox binary loses the 15% bloat factor from the DWARF2
tables.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
2012-09-04 11:46:44 +02:00

170 lines
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Makefile
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# ==========================================================================
# 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))" -DBB_BT=AUTOCONF_TIMESTAMP
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)
CFLAGS += $(call cc-option,-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,)
# 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,)
# 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
# If arch/$(ARCH)/Makefile did not override it (with, say, -fPIC)...
ARCH_FPIC ?= -fpic
ARCH_FPIE ?= -fpie
ARCH_PIE ?= -pie
ifeq ($(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
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 crypt
else
LDLIBS += m
endif
ifeq ($(CONFIG_PAM),y)
# libpam uses libpthread, so for static builds busybox must be linked to
# libpthread. On some platforms that requires an explicit -lpthread, so
# it should be in LDLIBS. For non-static builds, scripts/trylink will
# take care of removing -lpthread if possible. (Not bothering to check
# CONFIG_STATIC because even in a non-static build it could be that the
# only libpam available is libpam.a, so -lpthread could still be
# needed.)
LDLIBS += pam pam_misc pthread
endif
ifeq ($(CONFIG_SELINUX),y)
LDLIBS += selinux sepol
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),)
EXTRA_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
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