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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>
170 lines
5.9 KiB
Makefile
170 lines
5.9 KiB
Makefile
# ==========================================================================
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# Build system
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# ==========================================================================
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BB_VER = $(VERSION).$(PATCHLEVEL).$(SUBLEVEL)$(EXTRAVERSION)
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export BB_VER
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SKIP_STRIP ?= n
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# -std=gnu99 needed for [U]LLONG_MAX on some systems
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CPPFLAGS += $(call cc-option,-std=gnu99,)
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CPPFLAGS += \
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-Iinclude -Ilibbb \
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$(if $(KBUILD_SRC),-Iinclude2 -I$(srctree)/include -I$(srctree)/libbb) \
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-include include/autoconf.h \
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-D_GNU_SOURCE -DNDEBUG \
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$(if $(CONFIG_LFS),-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64) \
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-D"BB_VER=KBUILD_STR($(BB_VER))" -DBB_BT=AUTOCONF_TIMESTAMP
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CFLAGS += $(call cc-option,-Wall,)
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CFLAGS += $(call cc-option,-Wshadow,)
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CFLAGS += $(call cc-option,-Wwrite-strings,)
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CFLAGS += $(call cc-option,-Wundef,)
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CFLAGS += $(call cc-option,-Wstrict-prototypes,)
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CFLAGS += $(call cc-option,-Wunused -Wunused-parameter,)
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CFLAGS += $(call cc-option,-Wunused-function -Wunused-value,)
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CFLAGS += $(call cc-option,-Wmissing-prototypes -Wmissing-declarations,)
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CFLAGS += $(call cc-option,-Wno-format-security,)
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# warn about C99 declaration after statement
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CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
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# If you want to add more -Wsomething above, make sure that it is
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# still possible to build bbox without warnings.
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ifeq ($(CONFIG_WERROR),y)
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CFLAGS += $(call cc-option,-Werror,)
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## TODO:
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## gcc version 4.4.0 20090506 (Red Hat 4.4.0-4) (GCC) is a PITA:
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## const char *ptr; ... off_t v = *(off_t*)ptr; -> BOOM
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## and no easy way to convince it to shut the hell up.
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## We have a lot of such things all over the place.
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## Classic *(off_t*)(void*)ptr does not work,
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## and I am unwilling to do crazy gcc specific ({ void *ppp = ...; })
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## stuff in macros. This would obfuscate the code too much.
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## Maybe try __attribute__((__may_alias__))?
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#CFLAGS += $(call cc-ifversion, -eq, 0404, -fno-strict-aliasing)
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endif
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# gcc 3.x emits bogus "old style proto" warning on find.c:alloc_action()
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CFLAGS += $(call cc-ifversion, -ge, 0400, -Wold-style-definition)
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CFLAGS += $(call cc-option,-fno-builtin-strlen -finline-limit=0 -fomit-frame-pointer -ffunction-sections -fdata-sections,)
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# -fno-guess-branch-probability: prohibit pseudo-random guessing
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# of branch probabilities (hopefully makes bloatcheck more stable):
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CFLAGS += $(call cc-option,-fno-guess-branch-probability,)
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CFLAGS += $(call cc-option,-funsigned-char -static-libgcc,)
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CFLAGS += $(call cc-option,-falign-functions=1 -falign-jumps=1 -falign-labels=1 -falign-loops=1,)
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# Defeat .eh_frame bloat (gcc 4.6.3 x86-32 defconfig: 20% smaller busybox binary):
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CFLAGS += $(call cc-option,-fno-unwind-tables,)
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CFLAGS += $(call cc-option,-fno-asynchronous-unwind-tables,)
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# FIXME: These warnings are at least partially to be concerned about and should
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# be fixed..
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#CFLAGS += $(call cc-option,-Wconversion,)
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ifneq ($(CONFIG_DEBUG),y)
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CFLAGS += $(call cc-option,-Os,$(call cc-option,-O2,))
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else
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CFLAGS += $(call cc-option,-g,)
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#CFLAGS += "-D_FORTIFY_SOURCE=2"
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ifeq ($(CONFIG_DEBUG_PESSIMIZE),y)
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CFLAGS += $(call cc-option,-O0,)
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else
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CFLAGS += $(call cc-option,-Os,$(call cc-option,-O2,))
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endif
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endif
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# If arch/$(ARCH)/Makefile did not override it (with, say, -fPIC)...
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ARCH_FPIC ?= -fpic
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ARCH_FPIE ?= -fpie
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ARCH_PIE ?= -pie
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ifeq ($(CONFIG_BUILD_LIBBUSYBOX),y)
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# on i386: 14% smaller libbusybox.so
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# (code itself is 9% bigger, we save on relocs/PLT/GOT)
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CFLAGS += $(ARCH_FPIC)
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# and another 4% reduction of libbusybox.so:
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# (external entry points must be marked EXTERNALLY_VISIBLE)
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CFLAGS += $(call cc-option,-fvisibility=hidden)
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endif
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ifeq ($(CONFIG_STATIC),y)
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CFLAGS_busybox += -static
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endif
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ifeq ($(CONFIG_PIE),y)
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CFLAGS_busybox += $(ARCH_PIE)
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CFLAGS += $(ARCH_FPIE)
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endif
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ifneq ($(CONFIG_EXTRA_CFLAGS),)
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CFLAGS += $(strip $(subst ",,$(CONFIG_EXTRA_CFLAGS)))
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#"))
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endif
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# Note: both "" (string consisting of two quote chars) and empty string
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# are possible, and should be skipped below.
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ifneq ($(subst "",,$(CONFIG_SYSROOT)),)
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CFLAGS += --sysroot=$(CONFIG_SYSROOT)
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export SYSROOT=$(CONFIG_SYSROOT)
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endif
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# Android has no separate crypt library
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# gcc-4.2.1 fails if we try to feed C source on stdin:
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# echo 'int main(void){return 0;}' | $(CC) $(CFLAGS) -lcrypt -o /dev/null -xc -
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# fall back to using a temp file:
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CRYPT_AVAILABLE := $(shell echo 'int main(void){return 0;}' >crypttest.c; $(CC) $(CFLAGS) -lcrypt -o /dev/null crypttest.c >/dev/null 2>&1 && echo "y"; rm crypttest.c)
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ifeq ($(CRYPT_AVAILABLE),y)
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LDLIBS += m crypt
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else
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LDLIBS += m
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endif
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ifeq ($(CONFIG_PAM),y)
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# libpam uses libpthread, so for static builds busybox must be linked to
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# libpthread. On some platforms that requires an explicit -lpthread, so
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# it should be in LDLIBS. For non-static builds, scripts/trylink will
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# take care of removing -lpthread if possible. (Not bothering to check
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# CONFIG_STATIC because even in a non-static build it could be that the
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# only libpam available is libpam.a, so -lpthread could still be
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# needed.)
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LDLIBS += pam pam_misc pthread
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endif
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ifeq ($(CONFIG_SELINUX),y)
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LDLIBS += selinux sepol
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endif
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ifeq ($(CONFIG_EFENCE),y)
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LDLIBS += efence
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endif
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ifeq ($(CONFIG_DMALLOC),y)
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LDLIBS += dmalloc
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endif
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# If a flat binary should be built, CFLAGS_busybox="-elf2flt"
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# env var should be set for make invocation.
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# Here we check whether CFLAGS_busybox indeed contains that flag.
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# (For historical reasons, we also check LDFLAGS, which doesn't
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# seem to be entirely correct variable to put "-elf2flt" into).
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W_ELF2FLT = -elf2flt
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ifneq (,$(findstring $(W_ELF2FLT),$(LDFLAGS) $(CFLAGS_busybox)))
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SKIP_STRIP = y
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endif
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ifneq ($(CONFIG_EXTRA_LDFLAGS),)
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EXTRA_LDFLAGS += $(strip $(subst ",,$(CONFIG_EXTRA_LDFLAGS)))
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#"))
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endif
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ifneq ($(CONFIG_EXTRA_LDLIBS),)
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LDLIBS += $(strip $(subst ",,$(CONFIG_EXTRA_LDLIBS)))
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#"))
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endif
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# Busybox is a stack-fatty so make sure we increase default size
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# TODO: use "make stksizes" to find & fix big stack users
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# (we stole scripts/checkstack.pl from the kernel... thanks guys!)
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# Reduced from 20k to 16k in 1.9.0.
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FLTFLAGS += -s 16000
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