Re: [PATCH 4/4] powerpc: Allow LD_DEAD_CODE_DATA_ELIMINATION to be selected

[Nicholas Piggin <npiggin@gmail.com>]

On Wed, 2 May 2018 11:17:52 +0200
Mathieu Malaterre <malat@debian.org> wrote:

> Nick,
> 
> On Sat, Apr 21, 2018 at 4:48 AM, Nicholas Piggin <npiggin@gmail.com> wrote:
> > On Fri, 20 Apr 2018 22:08:27 +0200
> > Mathieu Malaterre <malat@debian.org> wrote:
> >  
> >> On Fri, Apr 20, 2018 at 12:41 PM, Nicholas Piggin <npiggin@gmail.com> wrote:  
> >> > On Fri, 20 Apr 2018 12:00:49 +0200
> >> > Mathieu Malaterre <malat@debian.org> wrote:
> >> >  
> >> >> On Fri, Apr 20, 2018 at 9:34 AM, Nicholas Piggin <npiggin@gmail.com> wrote:  
> >> >> > This requires further changes to linker script to KEEP some tables
> >> >> > and wildcard compiler generated sections into the right place. This
> >> >> > includes pp32 modifications from Christophe Leroy.
> >> >> >
> >> >> > When compiling powernv_defconfig with this option:
> >> >> >
> >> >> > text       data      bss       dec        filename
> >> >> > 11827621   4810490   1341080   17979191   vmlinux
> >> >> > 11752437   4598858   1338776   17690071   vmlinux.dcde
> >> >> >
> >> >> > Resulting kernel is almost 400kB smaller (and still boots).
> >> >> >
> >> >> > [ppc32 numbers here]  
> >> >>
> >> >> ^^^
> >> >>
> >> >> Do you want somebody else to provide those numbers ?  
> >> >
> >> > If you have a booting kernel, yes some more numbers would be good.  
> >>
> >> I've used /boot/config-4.15.0-2-powerpc from my current debian
> >> package. Rebuild master with and without option, boot ok, load/unload
> >> module ok.
> >>
> >> $ size nick/vmlinux.with*
> >>    text    data     bss     dec     hex filename
> >> 7386425 2364370 1425432 11176227 aa8923 nick/vmlinux.with
> >> 7461457 2475122 1428064 11364643 ad6923 nick/vmlinux.without
> >>
> >> This is not clear why with option the size of kernel is slightly bigger:
> >>
> >> $ du -sk nick/vmlinux.with*
> >> 124488 nick/vmlinux.with
> >> 124004 nick/vmlinux.without  
> >
> > Not sure. readelf -S vmlinux may show something.
> >
> > To really get lots of detail, you can add to the top level Makefile:
> >
> > LDFLAGS_vmlinux += -M  
> 
> Here is what I did:
> 
> $ git diff
> diff --git a/Makefile b/Makefile
> index 619a85ad716b..1a2e3d142a59 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -4,6 +4,7 @@ PATCHLEVEL = 17
>  SUBLEVEL = 0
>  EXTRAVERSION = -rc3
>  NAME = Fearless Coyote
> +LDFLAGS_vmlinux += -M

That'll get overwritten further down. Put it down with another line
that starts with LDFLAGS_vmlinux +=

Thanks,
Nick