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authorDenys Vlasenko <vda.linux@googlemail.com>2012-09-04 09:46:44 (GMT)
committer Denys Vlasenko <vda.linux@googlemail.com>2012-09-04 09:46:44 (GMT)
commit9b80b903c7fd2120a72de287fe6b0920e6d3c8ff (patch)
tree9c6196ae3bfc370f52d9ff59f569f28cf0e0a9b4
parentb7812ce0f7ee230330e18de3ac447b700311ab84 (diff)
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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>
-rw-r--r--Makefile.flags3
1 files changed, 3 insertions, 0 deletions
diff --git a/Makefile.flags b/Makefile.flags
index f5f4465..e77c0e5 100644
--- a/Makefile.flags
+++ b/Makefile.flags
@@ -53,6 +53,9 @@ CFLAGS += $(call cc-option,-fno-builtin-strlen -finline-limit=0 -fomit-frame-poi
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..