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

Mathieu Malaterre
2018-05-14T19:16:59Z

On Wed, May 2, 2018 at 2:24 PM, Nicholas Piggin <npiggin@gmail.com> wrote:
> 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 +=

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