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

christophe leroy
2018-04-21T07:16:35Z

Le 20/04/2018 à 22:08, Mathieu Malaterre a écrit :
> 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:

The file contains also debug symbols, which might differ.
Only the LOAD part of the file is interesting, that's the part you get
when doing ppc-linux-objcopy vmlinux vmlinux.bin -O binary

You can see it with readelf -l vmlinux

Christophe

>
> $ du -sk nick/vmlinux.with*
> 124488 nick/vmlinux.with
> 124004 nick/vmlinux.without
>
>
>> Thanks,
>> Nick

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