On 2014.04.15 at 20:19 +0200, Sam Ravnborg wrote: > On Tue, Apr 15, 2014 at 01:36:02PM +0200, Markus Trippelsdorf wrote: > > On 2014.04.15 at 13:19 +0200, Sam Ravnborg wrote: > > > > > > > > And while the code size reduction is less for MIPS than what others have > > > > reported for their platforms (I'm still investigating) is still is enough > > > > that embedded developers would commit murder for. > > > > > > I have experimented a little with a patch that links all of vmlinux in one step. > > > I compared the text size of vmlinux without and with -ffunction-sections. > > > > > > With a defconfig build on x86 (32 bit) I got following results: > > > > > > size difference > > > singlelink 10266506 > > > function-sections 9487369 779137 7,5% > > > > > > So this is a reduction of ~800 kb by enabling -ffunction-sections which > > > allows the linker to throw away unused sections. > > > > > > I have not boot tested the kernel so chances are that too much was thrown out by the linker. > > > But this is an option that has much smaller cost to use than lto. > > > And seems to benefit nicely in size. > > > > > > I have not tried this wihtout my singlelink patch - but I assume similar results. > > > > No, it wouldn't work, because you cannot mix -r and --gc-sections (or > > gold's --icf (identical code folding)). BTW using --gc-sections during vmlinux link time will not work, because it will "garbage collect" the whole kernel away. > With make allnoconfig I see a 5% decrease in text size by applying -ffunction-sections. > This is with latest mainline and no other than the following applied: > > diff --git a/arch/x86/Makefile b/arch/x86/Makefile > index 602f57e..51bac0a 100644 > --- a/arch/x86/Makefile > +++ b/arch/x86/Makefile > @@ -171,6 +171,8 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > KBUILD_CFLAGS += $(call cc-option,-mno-sse -mno-mmx -mno-sse2 -mno-3dnow,) > KBUILD_CFLAGS += $(call cc-option,-mno-avx,) > > +KBUILD_CFLAGS += -ffunction-sections > + > KBUILD_CFLAGS += $(mflags-y) > KBUILD_AFLAGS += $(mflags-y) > > > What can then explain this size difference? That is a good question. Because one would expect that adding -ffunction-sections should increase the size (and it does with my config). -- Markus -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
