Re: Build regressions/improvements in v4.17-rc1

Re: Build regressions/improvements in v4.17-rc1

[Geert Uytterhoeven]

CC Dan, Michael, AKPM, powerpc

On Mon, Apr 16, 2018 at 3:10 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> Below is the list of build error/warning regressions/improvements in
> v4.17-rc1[1] compared to v4.16[2].

I'd like to point your attention to:

>   + warning: vmlinux.o(.text+0x376518): Section mismatch in reference from the function .devm_memremap_pages() to the function .meminit.text:.arch_add_memory():  => N/A
>   + warning: vmlinux.o(.text+0x376d64): Section mismatch in reference from the function .devm_memremap_pages_release() to the function .meminit.text:.arch_remove_memory():  => N/A
>   + warning: vmlinux.o(.text+0x37dfd8): Section mismatch in reference from the function .devm_memremap_pages() to the function .meminit.text:.arch_add_memory():  => N/A
>   + warning: vmlinux.o(.text+0x37e824): Section mismatch in reference from the function .devm_memremap_pages_release() to the function .meminit.text:.arch_remove_memory():  => N/A
>   + warning: vmlinux.o(.text+0x3944): Section mismatch in reference from the variable start_here_multiplatform to the function .init.text:early_setup():  => N/A
>   + warning: vmlinux.o(.text+0x3978): Section mismatch in reference from the variable start_here_common to the function .init.text:start_kernel():  => N/A
>   + warning: vmlinux.o(.text+0x3a66c): Section mismatch in reference from the function mips_sc_init() to the function .init.text:mips_sc_probe_cm3():  => N/A
>   + warning: vmlinux.o(.text+0x3e9908): Section mismatch in reference from the function .devm_memremap_pages() to the function .meminit.text:.arch_add_memory():  => N/A
>   + warning: vmlinux.o(.text+0x3ea154): Section mismatch in reference from the function .devm_memremap_pages_release() to the function .meminit.text:.arch_remove_memory():  => N/A
>   + warning: vmlinux.o(.text+0x498dbc): Section mismatch in reference from the function hmm_devmem_release() to the function .meminit.text:arch_remove_memory():  => N/A
>   + warning: vmlinux.o(.text+0x499130): Section mismatch in reference from the function hmm_devmem_pages_create() to the function .meminit.text:arch_add_memory():  => N/A
>   + warning: vmlinux.o(.text+0x4a59ec): Section mismatch in reference from the function .hmm_devmem_release() to the function .meminit.text:.arch_remove_memory():  => N/A
>   + warning: vmlinux.o(.text+0x4a5d08): Section mismatch in reference from the function .hmm_devmem_pages_create() to the function .meminit.text:.arch_add_memory():  => N/A
>   + warning: vmlinux.o(.text+0x4ad8ac): Section mismatch in reference from the function .hmm_devmem_release() to the function .meminit.text:.arch_remove_memory():  => N/A
>   + warning: vmlinux.o(.text+0x4adbc8): Section mismatch in reference from the function .hmm_devmem_pages_create() to the function .meminit.text:.arch_add_memory():  => N/A
>   + warning: vmlinux.o(.text+0x4ca7238): Section mismatch in reference from the function .create_device_attrs() to the function .init.text:.make_sensor_label():  => N/A
>   + warning: vmlinux.o(.text+0x51ffec): Section mismatch in reference from the function .hmm_devmem_release() to the function .meminit.text:.arch_remove_memory():  => N/A
>   + warning: vmlinux.o(.text+0x520308): Section mismatch in reference from the function .hmm_devmem_pages_create() to the function .meminit.text:.arch_add_memory():  => N/A

These are still seen on v4.18-rc8 on various powerpc all{mod,yes}config builds.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: Build regressions/improvements in v4.17-rc1

[Andrew Morton]

On Mon, 6 Aug 2018 12:39:21 +0200 Geert Uytterhoeven <geert@linux-m68k.org> wrote:

> CC Dan, Michael, AKPM, powerpc
> 
> On Mon, Apr 16, 2018 at 3:10 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> > Below is the list of build error/warning regressions/improvements in
> > v4.17-rc1[1] compared to v4.16[2].
> 
> I'd like to point your attention to:
> 
> >   + warning: vmlinux.o(.text+0x376518): Section mismatch in reference from the function .devm_memremap_pages() to the function .meminit.text:.arch_add_memory():  => N/A
> >   + warning: vmlinux.o(.text+0x376d64): Section mismatch in reference from the function .devm_memremap_pages_release() to the function .meminit.text:.arch_remove_memory():  => N/A

hm.  Dan isn't around at present so we're on our own with this one.

x86 doesn't put arch_add_memory and arch_remove_memory into __meminit. 
x86 does

#ifdef CONFIG_MEMORY_HOTPLUG
int arch_add_memory(int nid, u64 start, u64 size, struct vmem_altmap *altmap,
		bool want_memblock)
{
	...


So I guess powerpc should do that as well?

Re: Build regressions/improvements in v4.17-rc1

[Michael Ellerman]

Andrew Morton <akpm@linux-foundation.org> writes:
> On Mon, 6 Aug 2018 12:39:21 +0200 Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
>> CC Dan, Michael, AKPM, powerpc
>> 
>> On Mon, Apr 16, 2018 at 3:10 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>> > Below is the list of build error/warning regressions/improvements in
>> > v4.17-rc1[1] compared to v4.16[2].
>> 
>> I'd like to point your attention to:
>> 
>> >   + warning: vmlinux.o(.text+0x376518): Section mismatch in reference from the function .devm_memremap_pages() to the function .meminit.text:.arch_add_memory():  => N/A
>> >   + warning: vmlinux.o(.text+0x376d64): Section mismatch in reference from the function .devm_memremap_pages_release() to the function .meminit.text:.arch_remove_memory():  => N/A
>
> hm.  Dan isn't around at present so we're on our own with this one.
>
> x86 doesn't put arch_add_memory and arch_remove_memory into __meminit. 
> x86 does
>
> #ifdef CONFIG_MEMORY_HOTPLUG
> int arch_add_memory(int nid, u64 start, u64 size, struct vmem_altmap *altmap,
> 		bool want_memblock)
> {
> 	...
>
>
> So I guess powerpc should do that as well?

But we only recently added it to fix a section mismatch warning:

  WARNING: vmlinux.o(.text+0x6da88): Section mismatch in reference from the function .arch_add_memory() to the function .meminit.text:.create_section_mapping()
  The function .arch_add_memory() references
  the function __meminit .create_section_mapping().
  This is often because .arch_add_memory lacks a __meminit 
  annotation or the annotation of .create_section_mapping is wrong.


I think the problem is that the section mismatch logic isn't able to
cope with __meminit's changing semantics.

When CONFIG_MEMORY_HOTPLUG=y references from .text to .meminit.text
should be allowed, because they're just folded in together in the linker
script.

When CONFIG_MEMORY_HOTPLUG=n references from .text to .meminit.text
should NOT be allowed, because .meminit.text becomes .init.text and will
be freed.

I don't see anything in the section mismatch logic to cope with that
difference.

It looks like __meminit is saving us about 1K on powerpc, so I'm
strongly inclined to just remove it entirely from arch/powerpc.

Also I haven't been seeing this in my local builds because I have:

CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y

So I guess we need to work out why that's interfering with section
mismatch analysis.

cheers

Re: Build regressions/improvements in v4.17-rc1

[Mathieu Malaterre]

On Wed, Aug 8, 2018 at 12:34 PM Michael Ellerman <mpe@ellerman.id.au> wrote:
>
> Andrew Morton <akpm@linux-foundation.org> writes:
> > On Mon, 6 Aug 2018 12:39:21 +0200 Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> >
> >> CC Dan, Michael, AKPM, powerpc
> >>
> >> On Mon, Apr 16, 2018 at 3:10 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> >> > Below is the list of build error/warning regressions/improvements in
> >> > v4.17-rc1[1] compared to v4.16[2].
> >>
> >> I'd like to point your attention to:
> >>
> >> >   + warning: vmlinux.o(.text+0x376518): Section mismatch in reference from the function .devm_memremap_pages() to the function .meminit.text:.arch_add_memory():  => N/A
> >> >   + warning: vmlinux.o(.text+0x376d64): Section mismatch in reference from the function .devm_memremap_pages_release() to the function .meminit.text:.arch_remove_memory():  => N/A
> >
> > hm.  Dan isn't around at present so we're on our own with this one.
> >
> > x86 doesn't put arch_add_memory and arch_remove_memory into __meminit.
> > x86 does
> >
> > #ifdef CONFIG_MEMORY_HOTPLUG
> > int arch_add_memory(int nid, u64 start, u64 size, struct vmem_altmap *altmap,
> >               bool want_memblock)
> > {
> >       ...
> >
> >
> > So I guess powerpc should do that as well?
>
> But we only recently added it to fix a section mismatch warning:
>
>   WARNING: vmlinux.o(.text+0x6da88): Section mismatch in reference from the function .arch_add_memory() to the function .meminit.text:.create_section_mapping()
>   The function .arch_add_memory() references
>   the function __meminit .create_section_mapping().
>   This is often because .arch_add_memory lacks a __meminit
>   annotation or the annotation of .create_section_mapping is wrong.
>
>
> I think the problem is that the section mismatch logic isn't able to
> cope with __meminit's changing semantics.
>
> When CONFIG_MEMORY_HOTPLUG=y references from .text to .meminit.text
> should be allowed, because they're just folded in together in the linker
> script.
>
> When CONFIG_MEMORY_HOTPLUG=n references from .text to .meminit.text
> should NOT be allowed, because .meminit.text becomes .init.text and will
> be freed.
>
> I don't see anything in the section mismatch logic to cope with that
> difference.
>
> It looks like __meminit is saving us about 1K on powerpc, so I'm
> strongly inclined to just remove it entirely from arch/powerpc.
>
> Also I haven't been seeing this in my local builds because I have:
>
> CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y
>
> So I guess we need to work out why that's interfering with section
> mismatch analysis.

...

Well that's a good question actually. Section mismatch
analysis is done on the throwaway vmlinux.o which is not linked
with --gc-sections (and is not a final link), so the via_pmu_driver
symbol should exist and be picked up.

I wonder if something about the  -ffunction-sections is breaking
the reference detection.
...



ref:
https://www.mail-archive.com/linuxppc-dev@lists.ozlabs.org/msg135431.html

>
> cheers

Re: Build regressions/improvements in v4.17-rc1

[Geert Uytterhoeven]

On Wed, Aug 8, 2018 at 12:32 PM Michael Ellerman <mpe@ellerman.id.au> wrote:
> Also I haven't been seeing this in my local builds because I have:
>
> CONFIG_LD_DEAD_CODE_DATA_ELIMINATION=y
>
> So I guess we need to work out why that's interfering with section
> mismatch analysis.

One other common case of missing section mismatch warnings is when some
versions of the compiler inline the called function, while other versions don't.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

Re: Build regressions/improvements in v4.17-rc1

[Michael Ellerman]

Michael Ellerman <mpe@ellerman.id.au> writes:
> Andrew Morton <akpm@linux-foundation.org> writes:
>> On Mon, 6 Aug 2018 12:39:21 +0200 Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>>
>>> CC Dan, Michael, AKPM, powerpc
>>> 
>>> On Mon, Apr 16, 2018 at 3:10 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>>> > Below is the list of build error/warning regressions/improvements in
>>> > v4.17-rc1[1] compared to v4.16[2].
>>> 
>>> I'd like to point your attention to:
>>> 
>>> >   + warning: vmlinux.o(.text+0x376518): Section mismatch in reference from the function .devm_memremap_pages() to the function .meminit.text:.arch_add_memory():  => N/A
>>> >   + warning: vmlinux.o(.text+0x376d64): Section mismatch in reference from the function .devm_memremap_pages_release() to the function .meminit.text:.arch_remove_memory():  => N/A
>>
>> hm.  Dan isn't around at present so we're on our own with this one.
>>
>> x86 doesn't put arch_add_memory and arch_remove_memory into __meminit. 
>> x86 does
>>
>> #ifdef CONFIG_MEMORY_HOTPLUG
>> int arch_add_memory(int nid, u64 start, u64 size, struct vmem_altmap *altmap,
>> 		bool want_memblock)
>> {
>> 	...
>>
>>
>> So I guess powerpc should do that as well?
>
> But we only recently added it to fix a section mismatch warning:
>
>   WARNING: vmlinux.o(.text+0x6da88): Section mismatch in reference from the function .arch_add_memory() to the function .meminit.text:.create_section_mapping()
>   The function .arch_add_memory() references
>   the function __meminit .create_section_mapping().
>   This is often because .arch_add_memory lacks a __meminit 
>   annotation or the annotation of .create_section_mapping is wrong.
>
>
> I think the problem is that the section mismatch logic isn't able to
> cope with __meminit's changing semantics.
>
> When CONFIG_MEMORY_HOTPLUG=y references from .text to .meminit.text
> should be allowed, because they're just folded in together in the linker
> script.
>
> When CONFIG_MEMORY_HOTPLUG=n references from .text to .meminit.text
> should NOT be allowed, because .meminit.text becomes .init.text and will
> be freed.
>
> I don't see anything in the section mismatch logic to cope with that
> difference.
>
> It looks like __meminit is saving us about 1K on powerpc, so I'm
> strongly inclined to just remove it entirely from arch/powerpc.

Gah that doesn't work.

Our arch routines call things in mm/ that are __meminit, so we have to
mark our code __meminit too, otherwise we get a section mismatch
warning.

cheers