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

CC Dan, Michael, AKPM, powerpc

On Mon, Apr 16, 2018 at 3:10 PM Geert Uytterhoeven [off-list ref] 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

On Mon, 6 Aug 2018 12:39:21 +0200 Geert Uytterhoeven [off-list ref] wrote:

CC Dan, Michael, AKPM, powerpc

On Mon, Apr 16, 2018 at 3:10 PM Geert Uytterhoeven [off-list ref] wrote:

quoted

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:

quoted

  + 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?

Andrew Morton [off-list ref] writes:

On Mon, 6 Aug 2018 12:39:21 +0200 Geert Uytterhoeven [off-list ref] wrote:

quoted

CC Dan, Michael, AKPM, powerpc

On Mon, Apr 16, 2018 at 3:10 PM Geert Uytterhoeven [off-list ref] wrote:

quoted

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:

quoted

  + 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

On Wed, Aug 8, 2018 at 12:34 PM Michael Ellerman [off-list ref] wrote:

Andrew Morton [off-list ref] writes:

quoted

On Mon, 6 Aug 2018 12:39:21 +0200 Geert Uytterhoeven [off-list ref] wrote:

quoted

CC Dan, Michael, AKPM, powerpc

On Mon, Apr 16, 2018 at 3:10 PM Geert Uytterhoeven [off-list ref] wrote:

quoted

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:

quoted

  + 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

On Wed, Aug 8, 2018 at 12:32 PM Michael Ellerman [off-list ref] 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

Michael Ellerman [off-list ref] writes:

Andrew Morton [off-list ref] writes:

quoted

On Mon, 6 Aug 2018 12:39:21 +0200 Geert Uytterhoeven [off-list ref] wrote:

quoted

CC Dan, Michael, AKPM, powerpc

On Mon, Apr 16, 2018 at 3:10 PM Geert Uytterhoeven [off-list ref] wrote:

quoted

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:

quoted

  + 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