Messages in this thread | | | Date | Sat, 29 Dec 2007 19:22:41 +0100 | From | Sam Ravnborg <> | Subject | Re: [PATCH] x86: unify x86 Makefile(s) |
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On Sat, Dec 29, 2007 at 02:54:13PM +0200, Adrian Bunk wrote: > On Sat, Dec 29, 2007 at 01:16:07PM +0100, Andi Kleen wrote: > > > > If -funit-at-a-time really increases stack size too much on some compiler > > version the right fix would be to check where it does that using make checkstack > > and then add "noinline" attributes there to prevent the compiler from inlining. > > That would prevent them. > > > > Globally disabling it is too big a hammer. > > > > e.g. I know XFS did it in a similar way to prevent this problem. > > > > So I would reenable it for now and if you know it causes problems on specific > > compiler versions, Adrian, you could watch make checkstack there and submit > > noinline patches as needed. > > The main point is that we are _only_ talking about gcc 3.4 on i386 - for > more recent compilers we do not disable unit-at-a-time.
I took a second look and realized that Adrian is right about the disabling. I had overlooked the 'no' part in -fno-unit-at-a-time.
So to try it out I build a gcc with crosstool: gcc --version: i686-unknown-linux-gnu-gcc (GCC) 3.4.5
This is the version that should exhibit the behaviour with increased text size. Build two kernels - one without and one with -funit-at-a-time:
size output: text data bss dec hex filename 4878494 471580 610304 5960378 5af2ba o-i386/vmlinux 4955008 472934 614400 6042342 5c32e6 o-i386-no-funit-at-a-time/vmlinux
[Last line is with unit-at-a-time disabled as per the filename.]
With a i386 defconfig we see an *increase* in text size if we disable -funit-at-a-time. That is we see the opposite of the expected.
Now the bug in gcc may have been fixed between 3.4 and 3.4.5 - I dunno.
So this simple test favour to always enable unit-at-a-time.
Sam
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