Build failure in -next due to 'kbuild: allow archs to select link dead code/data elimination'

Build failure in -next due to 'kbuild: allow archs to select link dead code/data elimination'

[Guenter Roeck]

Hi,

your commit 'kbuild: allow archs to select link dead code/data elimination'
is causing the following build failure in -next when building score:defconfig.

arch/score/kernel/built-in.o: In function `work_resched':
arch/score/kernel/entry.o:(.text+0xe84):
	relocation truncated to fit: R_SCORE_PC19 against `schedule'

Reverting the commit fixes the problem.

Please let me know if I can help tracking down the problem.
In case you need a score toochain, you can find the one I use at
http://server.roeck-us.net/toolchains/score.tgz.

Thanks,
Guenter

Re: Build failure in -next due to 'kbuild: allow archs to select link dead code/data elimination'

[Nicholas Piggin]

On Mon, 12 Sep 2016 15:24:43 -0700
Guenter Roeck <linux@roeck-us.net> wrote:

> Hi,
> 
> your commit 'kbuild: allow archs to select link dead code/data elimination'
> is causing the following build failure in -next when building score:defconfig.
> 
> arch/score/kernel/built-in.o: In function `work_resched':
> arch/score/kernel/entry.o:(.text+0xe84):
> 	relocation truncated to fit: R_SCORE_PC19 against `schedule'
> 
> Reverting the commit fixes the problem.
> 
> Please let me know if I can help tracking down the problem.
> In case you need a score toochain, you can find the one I use at
> http://server.roeck-us.net/toolchains/score.tgz.
> 
> Thanks,
> Guenter

It's not supposed to have any real effect unless the
option is selected, but there are a few changes to linker
script which must be causing it.

There are two changes to vmlinux.lds.h. One is to KEEP a
few input sections, that *should* be kept anyway. The other
is to bring in additional sections into their correct output
section.

Could you try reverting those lines of vmlinux.lds.h that
change the latter, i.e.:

-		*(.text.hot .text .text.fixup .text.unlikely)		\
+		*(.text.hot .text .text.fixup .text.unlikely .text.*)	\


-		*(.bss)							\
+		*(.bss .bss.[0-9a-zA-Z_]*)				\

etc?

Thanks,
Nick

Re: Build failure in -next due to 'kbuild: allow archs to select link dead code/data elimination'

[Guenter Roeck]

Hi Nicholas,

On 09/12/2016 07:00 PM, Nicholas Piggin wrote:
> On Mon, 12 Sep 2016 15:24:43 -0700
> Guenter Roeck <linux@roeck-us.net> wrote:
>
>> Hi,
>>
>> your commit 'kbuild: allow archs to select link dead code/data elimination'
>> is causing the following build failure in -next when building score:defconfig.
>>
>> arch/score/kernel/built-in.o: In function `work_resched':
>> arch/score/kernel/entry.o:(.text+0xe84):
>> 	relocation truncated to fit: R_SCORE_PC19 against `schedule'
>>
>> Reverting the commit fixes the problem.
>>
>> Please let me know if I can help tracking down the problem.
>> In case you need a score toochain, you can find the one I use at
>> http://server.roeck-us.net/toolchains/score.tgz.
>>
>> Thanks,
>> Guenter
>
> It's not supposed to have any real effect unless the
> option is selected, but there are a few changes to linker
> script which must be causing it.
>
> There are two changes to vmlinux.lds.h. One is to KEEP a
> few input sections, that *should* be kept anyway. The other
> is to bring in additional sections into their correct output
> section.
>
> Could you try reverting those lines of vmlinux.lds.h that
> change the latter, i.e.:
>
> -		*(.text.hot .text .text.fixup .text.unlikely)		\
> +		*(.text.hot .text .text.fixup .text.unlikely .text.*)	\

This is the culprit. After removing " .text.*" it builds fine.

Guenter

Re: Build failure in -next due to 'kbuild: allow archs to select link dead code/data elimination'

[Nicholas Piggin]

On Mon, 12 Sep 2016 20:17:30 -0700
Guenter Roeck <linux@roeck-us.net> wrote:

> Hi Nicholas,
> 
> On 09/12/2016 07:00 PM, Nicholas Piggin wrote:
> > On Mon, 12 Sep 2016 15:24:43 -0700
> > Guenter Roeck <linux@roeck-us.net> wrote:
> >  
> >> Hi,
> >>
> >> your commit 'kbuild: allow archs to select link dead code/data elimination'
> >> is causing the following build failure in -next when building score:defconfig.
> >>
> >> arch/score/kernel/built-in.o: In function `work_resched':
> >> arch/score/kernel/entry.o:(.text+0xe84):
> >> 	relocation truncated to fit: R_SCORE_PC19 against `schedule'
> >>
> >> Reverting the commit fixes the problem.
> >>
> >> Please let me know if I can help tracking down the problem.
> >> In case you need a score toochain, you can find the one I use at
> >> http://server.roeck-us.net/toolchains/score.tgz.
> >>
> >> Thanks,
> >> Guenter  
> >
> > It's not supposed to have any real effect unless the
> > option is selected, but there are a few changes to linker
> > script which must be causing it.
> >
> > There are two changes to vmlinux.lds.h. One is to KEEP a
> > few input sections, that *should* be kept anyway. The other
> > is to bring in additional sections into their correct output
> > section.
> >
> > Could you try reverting those lines of vmlinux.lds.h that
> > change the latter, i.e.:
> >
> > -		*(.text.hot .text .text.fixup .text.unlikely)		\
> > +		*(.text.hot .text .text.fixup .text.unlikely .text.*)	\  
> 
> This is the culprit. After removing " .text.*" it builds fine.

Thanks for testing it. Some architectures have .text.x sections
not included here, I should have seen that. We should possibly
just revert that line and require implementing archs to do the
right thing.

[ Convention is to use '.' to avoid C identifiers, so we should
use .text..x for these things. But that's not done completely
throughout the kernel, and a little invasive to do with this
series. I'll revisit this and clean things up subsequently after
this round gets merged. ]

Thanks,
Nick

Re: Build failure in -next due to 'kbuild: allow archs to select link dead code/data elimination'

[Guenter Roeck]

On 09/12/2016 08:51 PM, Nicholas Piggin wrote:
> On Mon, 12 Sep 2016 20:17:30 -0700
> Guenter Roeck <linux@roeck-us.net> wrote:
>
>> Hi Nicholas,
>>
>> On 09/12/2016 07:00 PM, Nicholas Piggin wrote:
>>> On Mon, 12 Sep 2016 15:24:43 -0700
>>> Guenter Roeck <linux@roeck-us.net> wrote:
>>>
>>>> Hi,
>>>>
>>>> your commit 'kbuild: allow archs to select link dead code/data elimination'
>>>> is causing the following build failure in -next when building score:defconfig.
>>>>
>>>> arch/score/kernel/built-in.o: In function `work_resched':
>>>> arch/score/kernel/entry.o:(.text+0xe84):
>>>> 	relocation truncated to fit: R_SCORE_PC19 against `schedule'
>>>>
>>>> Reverting the commit fixes the problem.
>>>>
>>>> Please let me know if I can help tracking down the problem.
>>>> In case you need a score toochain, you can find the one I use at
>>>> http://server.roeck-us.net/toolchains/score.tgz.
>>>>
>>>> Thanks,
>>>> Guenter
>>>
>>> It's not supposed to have any real effect unless the
>>> option is selected, but there are a few changes to linker
>>> script which must be causing it.
>>>
>>> There are two changes to vmlinux.lds.h. One is to KEEP a
>>> few input sections, that *should* be kept anyway. The other
>>> is to bring in additional sections into their correct output
>>> section.
>>>
>>> Could you try reverting those lines of vmlinux.lds.h that
>>> change the latter, i.e.:
>>>
>>> -		*(.text.hot .text .text.fixup .text.unlikely)		\
>>> +		*(.text.hot .text .text.fixup .text.unlikely .text.*)	\
>>
>> This is the culprit. After removing " .text.*" it builds fine.
>
> Thanks for testing it. Some architectures have .text.x sections
> not included here, I should have seen that. We should possibly
> just revert that line and require implementing archs to do the
> right thing.
>
I would call the build failure a regression, so it should either be
reverted, or we'll need some other solution to fix the build failure.

Thanks,
Guenter

> [ Convention is to use '.' to avoid C identifiers, so we should
> use .text..x for these things. But that's not done completely
> throughout the kernel, and a little invasive to do with this
> series. I'll revisit this and clean things up subsequently after
> this round gets merged. ]
>
> Thanks,
> Nick
>

Re: Build failure in -next due to 'kbuild: allow archs to select link dead code/data elimination'

[Nicholas Piggin]

On Tue, 13 Sep 2016 13:25:22 -0700
Guenter Roeck <linux@roeck-us.net> wrote:

> On 09/12/2016 08:51 PM, Nicholas Piggin wrote:
> > On Mon, 12 Sep 2016 20:17:30 -0700
> > Guenter Roeck <linux@roeck-us.net> wrote:
> >  
> >> Hi Nicholas,
> >>
> >> On 09/12/2016 07:00 PM, Nicholas Piggin wrote:  
> >>> On Mon, 12 Sep 2016 15:24:43 -0700
> >>> Guenter Roeck <linux@roeck-us.net> wrote:
> >>>  
> >>>> Hi,
> >>>>
> >>>> your commit 'kbuild: allow archs to select link dead code/data elimination'
> >>>> is causing the following build failure in -next when building score:defconfig.
> >>>>
> >>>> arch/score/kernel/built-in.o: In function `work_resched':
> >>>> arch/score/kernel/entry.o:(.text+0xe84):
> >>>> 	relocation truncated to fit: R_SCORE_PC19 against `schedule'
> >>>>
> >>>> Reverting the commit fixes the problem.
> >>>>
> >>>> Please let me know if I can help tracking down the problem.
> >>>> In case you need a score toochain, you can find the one I use at
> >>>> http://server.roeck-us.net/toolchains/score.tgz.
> >>>>
> >>>> Thanks,
> >>>> Guenter  
> >>>
> >>> It's not supposed to have any real effect unless the
> >>> option is selected, but there are a few changes to linker
> >>> script which must be causing it.
> >>>
> >>> There are two changes to vmlinux.lds.h. One is to KEEP a
> >>> few input sections, that *should* be kept anyway. The other
> >>> is to bring in additional sections into their correct output
> >>> section.
> >>>
> >>> Could you try reverting those lines of vmlinux.lds.h that
> >>> change the latter, i.e.:
> >>>
> >>> -		*(.text.hot .text .text.fixup .text.unlikely)		\
> >>> +		*(.text.hot .text .text.fixup .text.unlikely .text.*)	\  
> >>
> >> This is the culprit. After removing " .text.*" it builds fine.  
> >
> > Thanks for testing it. Some architectures have .text.x sections
> > not included here, I should have seen that. We should possibly
> > just revert that line and require implementing archs to do the
> > right thing.
> >  
> I would call the build failure a regression, so it should either be
> reverted, or we'll need some other solution to fix the build failure.

Yes it's definitely a regression and that part should be reverted.
To confirm, the following patch fixes your build?

Thanks,
Nick

commit 0ae28be83b4d6cd03ef5b481487d042f2b91954e
Author: Nicholas Piggin <npiggin@gmail.com>
Date:   Wed Sep 14 12:24:03 2016 +1000

    kbuild: -ffunction-sections fix for archs with conflicting sections
    
    Enabling -ffunction-sections modified the generic linker script to
    pull .text.* sections into regular TEXT_TEXT section, conflicting
    with some architectures. Revert that change and require archs that
    enable the option to ensure they have no conflicting section names,
    and do the appropriate merging.

    Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

diff --git a/arch/Kconfig b/arch/Kconfig
index 6d5b631..8248037 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -487,7 +487,9 @@ config LD_DEAD_CODE_DATA_ELIMINATION
 	  This requires that the arch annotates or otherwise protects
 	  its external entry points from being discarded. Linker scripts
 	  must also merge .text.*, .data.*, and .bss.* correctly into
-	  output sections.
+	  output sections. Care must be taken not to pull in unrelated
+	  sections (e.g., '.text.init'). Typically '.' in section names
+	  is used to distinguish them from label names / C identifiers.
 
 config HAVE_CONTEXT_TRACKING
 	bool
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index ad9d8f9..48dd44f 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -198,9 +198,9 @@
 
 /*
  * .data section
- * -fdata-sections generates .data.identifier which needs to be pulled in
- * with .data, but don't want to pull in .data..stuff which has its own
- * requirements. Same for bss.
+ * LD_DEAD_CODE_DATA_ELIMINATION option enables -fdata-sections generates
+ * .data.identifier which needs to be pulled in with .data, but don't want to
+ * pull in .data..stuff which has its own requirements. Same for bss.
  */
 #define DATA_DATA							\
 	*(.data .data.[0-9a-zA-Z_]*)					\
@@ -434,10 +434,15 @@
 	}
 
 /* .text section. Map to function alignment to avoid address changes
- * during second ld run in second ld pass when generating System.map */
+ * during second ld run in second ld pass when generating System.map
+ * LD_DEAD_CODE_DATA_ELIMINATION option enables -ffunction-sections generates
+ * .text.identifier which needs to be pulled in with .text , but some
+ * architectures define .text.foo which is not intended to be pulled in here.
+ * Those enabling LD_DEAD_CODE_DATA_ELIMINATION must ensure they don't have
+ * conflicting section names, and must pull in .text.[0-9a-zA-Z_]* */
 #define TEXT_TEXT							\
 		ALIGN_FUNCTION();					\
-		*(.text.hot .text .text.fixup .text.unlikely .text.*)	\
+		*(.text.hot .text .text.fixup .text.unlikely)		\
 		*(.ref.text)						\
 	MEM_KEEP(init.text)						\
 	MEM_KEEP(exit.text)						\

Re: Build failure in -next due to 'kbuild: allow archs to select link dead code/data elimination'

[Guenter Roeck]

On Wed, Sep 14, 2016 at 12:30:04PM +1000, Nicholas Piggin wrote:
> On Tue, 13 Sep 2016 13:25:22 -0700
> Guenter Roeck <linux@roeck-us.net> wrote:
> 
> > On 09/12/2016 08:51 PM, Nicholas Piggin wrote:
> > > On Mon, 12 Sep 2016 20:17:30 -0700
> > > Guenter Roeck <linux@roeck-us.net> wrote:
> > >  
> > >> Hi Nicholas,
> > >>
> > >> On 09/12/2016 07:00 PM, Nicholas Piggin wrote:  
> > >>> On Mon, 12 Sep 2016 15:24:43 -0700
> > >>> Guenter Roeck <linux@roeck-us.net> wrote:
> > >>>  
> > >>>> Hi,
> > >>>>
> > >>>> your commit 'kbuild: allow archs to select link dead code/data elimination'
> > >>>> is causing the following build failure in -next when building score:defconfig.
> > >>>>
> > >>>> arch/score/kernel/built-in.o: In function `work_resched':
> > >>>> arch/score/kernel/entry.o:(.text+0xe84):
> > >>>> 	relocation truncated to fit: R_SCORE_PC19 against `schedule'
> > >>>>
> > >>>> Reverting the commit fixes the problem.
> > >>>>
> > >>>> Please let me know if I can help tracking down the problem.
> > >>>> In case you need a score toochain, you can find the one I use at
> > >>>> http://server.roeck-us.net/toolchains/score.tgz.
> > >>>>
> > >>>> Thanks,
> > >>>> Guenter  
> > >>>
> > >>> It's not supposed to have any real effect unless the
> > >>> option is selected, but there are a few changes to linker
> > >>> script which must be causing it.
> > >>>
> > >>> There are two changes to vmlinux.lds.h. One is to KEEP a
> > >>> few input sections, that *should* be kept anyway. The other
> > >>> is to bring in additional sections into their correct output
> > >>> section.
> > >>>
> > >>> Could you try reverting those lines of vmlinux.lds.h that
> > >>> change the latter, i.e.:
> > >>>
> > >>> -		*(.text.hot .text .text.fixup .text.unlikely)		\
> > >>> +		*(.text.hot .text .text.fixup .text.unlikely .text.*)	\  
> > >>
> > >> This is the culprit. After removing " .text.*" it builds fine.  
> > >
> > > Thanks for testing it. Some architectures have .text.x sections
> > > not included here, I should have seen that. We should possibly
> > > just revert that line and require implementing archs to do the
> > > right thing.
> > >  
> > I would call the build failure a regression, so it should either be
> > reverted, or we'll need some other solution to fix the build failure.
> 
> Yes it's definitely a regression and that part should be reverted.
> To confirm, the following patch fixes your build?
> 
> Thanks,
> Nick
> 
> commit 0ae28be83b4d6cd03ef5b481487d042f2b91954e
> Author: Nicholas Piggin <npiggin@gmail.com>
> Date:   Wed Sep 14 12:24:03 2016 +1000
> 
>     kbuild: -ffunction-sections fix for archs with conflicting sections
>     
>     Enabling -ffunction-sections modified the generic linker script to
>     pull .text.* sections into regular TEXT_TEXT section, conflicting
>     with some architectures. Revert that change and require archs that
>     enable the option to ensure they have no conflicting section names,
>     and do the appropriate merging.
> 
>     Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> 
Tested-by: Guenter Roeck <linux@roeck-us.net>

> diff --git a/arch/Kconfig b/arch/Kconfig
> index 6d5b631..8248037 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -487,7 +487,9 @@ config LD_DEAD_CODE_DATA_ELIMINATION
>  	  This requires that the arch annotates or otherwise protects
>  	  its external entry points from being discarded. Linker scripts
>  	  must also merge .text.*, .data.*, and .bss.* correctly into
> -	  output sections.
> +	  output sections. Care must be taken not to pull in unrelated
> +	  sections (e.g., '.text.init'). Typically '.' in section names
> +	  is used to distinguish them from label names / C identifiers.
>  
>  config HAVE_CONTEXT_TRACKING
>  	bool
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index ad9d8f9..48dd44f 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -198,9 +198,9 @@
>  
>  /*
>   * .data section
> - * -fdata-sections generates .data.identifier which needs to be pulled in
> - * with .data, but don't want to pull in .data..stuff which has its own
> - * requirements. Same for bss.
> + * LD_DEAD_CODE_DATA_ELIMINATION option enables -fdata-sections generates
> + * .data.identifier which needs to be pulled in with .data, but don't want to
> + * pull in .data..stuff which has its own requirements. Same for bss.
>   */
>  #define DATA_DATA							\
>  	*(.data .data.[0-9a-zA-Z_]*)					\
> @@ -434,10 +434,15 @@
>  	}
>  
>  /* .text section. Map to function alignment to avoid address changes
> - * during second ld run in second ld pass when generating System.map */
> + * during second ld run in second ld pass when generating System.map
> + * LD_DEAD_CODE_DATA_ELIMINATION option enables -ffunction-sections generates
> + * .text.identifier which needs to be pulled in with .text , but some
> + * architectures define .text.foo which is not intended to be pulled in here.
> + * Those enabling LD_DEAD_CODE_DATA_ELIMINATION must ensure they don't have
> + * conflicting section names, and must pull in .text.[0-9a-zA-Z_]* */
>  #define TEXT_TEXT							\
>  		ALIGN_FUNCTION();					\
> -		*(.text.hot .text .text.fixup .text.unlikely .text.*)	\
> +		*(.text.hot .text .text.fixup .text.unlikely)		\
>  		*(.ref.text)						\
>  	MEM_KEEP(init.text)						\
>  	MEM_KEEP(exit.text)						\

Re: Build failure in -next due to 'kbuild: allow archs to select link dead code/data elimination'

[Michal Marek]

On 2016-09-14 21:48, Guenter Roeck wrote:
> On Wed, Sep 14, 2016 at 12:30:04PM +1000, Nicholas Piggin wrote:
>> commit 0ae28be83b4d6cd03ef5b481487d042f2b91954e
>> Author: Nicholas Piggin <npiggin@gmail.com>
>> Date:   Wed Sep 14 12:24:03 2016 +1000
>>
>>     kbuild: -ffunction-sections fix for archs with conflicting sections
>>     
>>     Enabling -ffunction-sections modified the generic linker script to
>>     pull .text.* sections into regular TEXT_TEXT section, conflicting
>>     with some architectures. Revert that change and require archs that
>>     enable the option to ensure they have no conflicting section names,
>>     and do the appropriate merging.
>>
>>     Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
>>
> Tested-by: Guenter Roeck <linux@roeck-us.net>

Applied to kbuild.git#kbuild.

Thanks,
Michal