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    SubjectRe: [ANNOUNCE] 2.6.0-tiny1 tree for small systems
    Hi Matt,

    On Wed, Dec 31, 2003 at 07:46:55PM -0600, Matt Mackall wrote:
    > Ok, I added the ability to override the arch-default CFLAGS, but sadly
    > I'm unable to reproduce your space savings here with gcc 3.3.2. The
    > default -march=i586 seems to produce the smallest code for me.

    Same results here. I was a bit stumped at first, but finally found the reason :
    by changing CFLAGS, both you and me have implictly removed '-falign-functions=0',
    which is what grows up the kernel image ! I really don't understand what happens
    in the kernel, because on many other programs, i386 gives me smaller progs than
    i586 for -Os optimization, and -falign-functions=0 is *always* smaller. In the
    kernel, i386, i586 an c3 are identical, but -falign-functions=0 is bigger by
    50 kB :

    -Os -mpreferred-stack-boundary=2 -march=c3 -falign-functions=0 -falign-loops=0 -falign-jumps=0 :

    text data bss dec hex filename
    1306682 111227 50896 1468805 166985 vmlinux

    -Os -mpreferred-stack-boundary=2 -march=c3 -falign-loops=0 -falign-jumps=0 :

    text data bss dec hex filename
    1256604 111227 50896 1418727 15a5e7 vmlinux

    I have tested several values and found that the second compilation above is equivalent
    to the default gcc setting of -falign-functions=1. And using 1 instead of 0 in
    -falign-{loops,jumps,labels} makes not difference at all. So I would suggest
    adding -falign-functions=1 everywhere.

    BTW, I slightly changed your patch to be able to specify several options. I did
    it the dirty way because I don't know how to split the string into several words :

    --- ./arch/i386/Makefile Sat Jan 3 15:10:26 2004
    +++ a./rch/i386/Makefile Sat Jan 3 15:43:12 2004
    @@ -27,7 +27,7 @@
    align := $(subst -functions=0,,$(call check_gcc,-falign-functions=0,-malign-functions=0))

    -cflags-y += $(CONFIG_TINY_CFLAGS_VAL)
    +cflags-y += $(shell echo $(CONFIG_TINY_CFLAGS_VAL))
    cflags-$(CONFIG_M386) += -march=i386
    cflags-$(CONFIG_M486) += -march=i486

    Other than that, I've compiled 2.6.1-rc1-tiny1. It's slightly smaller than 2.6.0-tiny1
    and CONFIG_CPU_SUP_* otherwise it would not link. I can give you the error reports
    and .config in case you're interested.


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