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

[Mathieu Malaterre]

On Wed, May 2, 2018 at 2:24 PM, Nicholas Piggin <npiggin at gmail.com> wrote:
> On Wed, 2 May 2018 11:17:52 +0200
> Mathieu Malaterre <malat at debian.org> wrote:
>
>> Nick,
>>
>> On Sat, Apr 21, 2018 at 4:48 AM, Nicholas Piggin <npiggin at gmail.com> wrote:
>> > On Fri, 20 Apr 2018 22:08:27 +0200
>> > Mathieu Malaterre <malat at debian.org> wrote:
>> >
>> >> On Fri, Apr 20, 2018 at 12:41 PM, Nicholas Piggin <npiggin at gmail.com> wrote:
>> >> > On Fri, 20 Apr 2018 12:00:49 +0200
>> >> > Mathieu Malaterre <malat at debian.org> wrote:
>> >> >
>> >> >> On Fri, Apr 20, 2018 at 9:34 AM, Nicholas Piggin <npiggin at 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 +=

Sorry about that, I was not paying attention :(

Anyway I cannot make sense of the output with -M.

Here is a quick summary if needed (with option / without option).

$ ./scripts/bloat-o-meter nick/vmlinux.without nick/vmlinux.with | head
add/remove: 0/647 grow/shrink: 852/1846 up/down: 11276/-95033 (-83757)
Function                                     old     new   delta
SiSInitPtr                                  2212    2600    +388
xmon_core.isra                              7540    7900    +360
ata_attach_transport                         840    1032    +192
via_pmu_interrupt                           2828    3004    +176
matroxfb_init                               3000    3156    +156
fbcon_scroll                                3092    3248    +156
__do_adjtimex                               1716    1868    +152
fbcon_event_notify                          2044    2184    +140
$ ./scripts/bloat-o-meter nick/vmlinux.without nick/vmlinux.with | tail
aty_set_pll18818                             540       -    -540
sel_ib_pkey_sid                              556       -    -556
pci_dev_acs_enabled                          608       -    -608
aa_label_find_merge                          752       -    -752
drmem_update_dt                              796       -    -796
powerpc_macros                              1176       -   -1176
ima_restore_measurement_list                1224       -   -1224
rtas_os_term_buf                            2048       -   -2048
vle_opcodes                                 8200       -   -8200
Total: Before=9927171, After=9843414, chg -0.84%


> Thanks,
> Nick