[PATCH 3/3] kallsyms: remove --page-offset command line option

[Maxime Coquelin]

2016-02-03 9:16 GMT+01:00 Ard Biesheuvel <ard.biesheuvel at linaro.org>:
> (+ Uwe, Maxime)
>
> Complete thread here:
> http://thread.gmane.org/gmane.linux.ports.arm.kernel/474400
>
> On 3 February 2016 at 01:05, Russell King - ARM Linux
> <linux at arm.linux.org.uk> wrote:
>> On Tue, Feb 02, 2016 at 02:19:34PM +0100, Ard Biesheuvel wrote:
>>> The --page-offset command line option was only used for ARM, to filter
>>> symbol addresses below CONFIG_PAGE_OFFSET. This is no longer needed, so
>>> remove the functionality altogether.
>>
>> From what I remember, this option has nothing to do with MMU-ful ARM,
>> but noMMU ARM, where the .text segment can be significantly different
>> from the .data segment.
>>
>> I think you need to talk to noMMU people about this patch.
>>
>
> We have
>
> commit f6537f2f0eba4eba3354e48dbe3047db6d8b6254
> Author: Ming Lei <tom.leiming at gmail.com>
> Date:   Sat Nov 2 09:11:33 2013 +1030
>
>     scripts/kallsyms: filter symbols not in kernel address space
>
>     This patch uses CONFIG_PAGE_OFFSET to filter symbols which
>     are not in kernel address space because these symbols are
>     generally for generating code purpose and can't be run at
>     kernel mode, so we needn't keep them in /proc/kallsyms.
>
>     For example, on ARM there are some symbols which may be
>     linked in relocatable code section, then perf can't parse
>     symbols any more from /proc/kallsyms, this patch fixes the
>     problem (introduced b9b32bf70f2fb710b07c94e13afbc729afe221da)
>
> which introduces the --page-offset option to kallsyms, in response to
> your patch that moves .vectors and .stubs to VMA 0x0. Then we have
>
> commit 7122c3e9154b5d9a7422f68f02d8acf050fad2b0
> Author: Ming Lei <tom.leiming at gmail.com>
> Date:   Tue Dec 10 16:46:29 2013 +1030
>
>     scripts/link-vmlinux.sh: only filter kernel symbols for arm
>
>     Actually CONFIG_PAGE_OFFSET isn't same with PAGE_OFFSET, so
>     it isn't easy to figue out PAGE_OFFSET defined in header
>     file from scripts.
>
>     Because CONFIG_PAGE_OFFSET may not be defined in some ARCHs(
>     64bit ARCH), or defined as bogus value in !MMU case, so
>     this patch only applys the filter on ARM when CONFIG_PAGE_OFFSET
>     is defined as the original problem is only on ARM.
>
> which restricts the use of --page-offset to CONFIG_ARM, and
>
> commit cc8475305203ddfd117b81e2e732194b67d8f310
> Author: Maxime Coquelin <mcoquelin.stm32 at gmail.com>
> Date:   Thu May 21 19:17:44 2015 +0800
>
>     scripts: link-vmlinux: Don't pass page offset to kallsyms if XIP Kernel
>
>     When Kernel is executed in place from ROM, the symbol addresses can be
>     lower than the page offset.
>
> which restricts the use of --page-offset to CONFIG_ARM && !CONFIG_XIP_KERNEL
>
> So it looks like the Dec 10 patch fixes some fallout related to !MMU
> that was caused by the Nov 2 patch, but the original patch has nothing
> to do with !MMU. Furthermore, 3 out of 4 !MMU configs we have in the
> tree (efm32, stm32 and vf610m4) are also XIP kernel, for which
> --page-offset isn't even used to begin with after Maxime's patch.
> Hopefully Uwe and/or Maxime can confirm, but removing the PAGE_OFFSET
> lower limit should not affect those platforms at all afaict,
> especially since, after patch 1/3, there are no symbols left to filter
> below that limit in the first place.

I agree with you, removing the PAGE_OFFSET lower limit should not
affect our platforms.

Regards,
Maxime