[PATCH] powerpc: Handle .text.{hot,unlikely}.* in linker script

[PATCH] powerpc: Handle .text.{hot,unlikely}.* in linker script

[Nathan Chancellor]

Commit eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input
sections") added ".text.unlikely.*" and ".text.hot.*" due to an LLVM
change [1].

After another LLVM change [2], these sections are seen in some PowerPC
builds, where there is a orphan section warning then build failure:

$ make -skj"$(nproc)" \
       ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- LLVM=1 O=out \
       distclean powernv_defconfig zImage.epapr
ld.lld: warning: kernel/built-in.a(panic.o):(.text.unlikely.) is being placed in '.text.unlikely.'
...
ld.lld: warning: address (0xc000000000009314) of section .text is not a multiple of alignment (256)
...
ERROR: start_text address is c000000000009400, should be c000000000008000
ERROR: try to enable LD_HEAD_STUB_CATCH config option
ERROR: see comments in arch/powerpc/tools/head_check.sh
...

Explicitly handle these sections like in the main linker script so
there is no more build failure.

Cc: stable@vger.kernel.org
Fixes: 83a092cf95f2 ("powerpc: Link warning for orphan sections")
Link: https://github.com/ClangBuiltLinux/linux/issues/1218
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 arch/powerpc/kernel/vmlinux.lds.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 0318ba436f34..8e0b1298bf19 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -85,7 +85,7 @@ SECTIONS
 		ALIGN_FUNCTION();
 #endif
 		/* careful! __ftr_alt_* sections need to be close to .text */
-		*(.text.hot TEXT_MAIN .text.fixup .text.unlikely .fixup __ftr_alt_* .ref.text);
+		*(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely .text.unlikely.* .fixup __ftr_alt_* .ref.text);
 #ifdef CONFIG_PPC64
 		*(.tramp.ftrace.text);
 #endif

base-commit: d8a4f20584d5906093a8fc6aa06622102a501095
-- 
2.30.0

Re: [PATCH] powerpc: Handle .text.{hot,unlikely}.* in linker script

[Sedat Dilek]

On Mon, Jan 4, 2021 at 9:49 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> Commit eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input
> sections") added ".text.unlikely.*" and ".text.hot.*" due to an LLVM
> change [1].
>
> After another LLVM change [2], these sections are seen in some PowerPC
> builds, where there is a orphan section warning then build failure:
>

Looks like you forgot to add your references/links to [1] and [2].

Might be good to mention...?

With CONFIG_LD_ORPHAN_WARN=y is enabled

- Sedat

> $ make -skj"$(nproc)" \
>        ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- LLVM=1 O=out \
>        distclean powernv_defconfig zImage.epapr
> ld.lld: warning: kernel/built-in.a(panic.o):(.text.unlikely.) is being placed in '.text.unlikely.'
> ...
> ld.lld: warning: address (0xc000000000009314) of section .text is not a multiple of alignment (256)
> ...
> ERROR: start_text address is c000000000009400, should be c000000000008000
> ERROR: try to enable LD_HEAD_STUB_CATCH config option
> ERROR: see comments in arch/powerpc/tools/head_check.sh
> ...
>
> Explicitly handle these sections like in the main linker script so
> there is no more build failure.
>
> Cc: stable@vger.kernel.org
> Fixes: 83a092cf95f2 ("powerpc: Link warning for orphan sections")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1218
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>  arch/powerpc/kernel/vmlinux.lds.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
> index 0318ba436f34..8e0b1298bf19 100644
> --- a/arch/powerpc/kernel/vmlinux.lds.S
> +++ b/arch/powerpc/kernel/vmlinux.lds.S
> @@ -85,7 +85,7 @@ SECTIONS
>                 ALIGN_FUNCTION();
>  #endif
>                 /* careful! __ftr_alt_* sections need to be close to .text */
> -               *(.text.hot TEXT_MAIN .text.fixup .text.unlikely .fixup __ftr_alt_* .ref.text);
> +               *(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely .text.unlikely.* .fixup __ftr_alt_* .ref.text);
>  #ifdef CONFIG_PPC64
>                 *(.tramp.ftrace.text);
>  #endif
>
> base-commit: d8a4f20584d5906093a8fc6aa06622102a501095
> --
> 2.30.0
>
> --
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Re: [PATCH] powerpc: Handle .text.{hot,unlikely}.* in linker script

[Nathan Chancellor]

On Mon, Jan 04, 2021 at 09:55:20PM +0100, Sedat Dilek wrote:
> On Mon, Jan 4, 2021 at 9:49 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > Commit eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input
> > sections") added ".text.unlikely.*" and ".text.hot.*" due to an LLVM
> > change [1].
> >
> > After another LLVM change [2], these sections are seen in some PowerPC
> > builds, where there is a orphan section warning then build failure:
> >
> 
> Looks like you forgot to add your references/links to [1] and [2].

Indeed, thank you for pointing that out! v2 coming shortly.

> Might be good to mention...?
> 
> With CONFIG_LD_ORPHAN_WARN=y is enabled

Since this symbol is not user selectable, I do not really think it is
worth mentioning, plus PowerPC has had this enabled for a while :)

Cheers,
Nathan

[PATCH v2] powerpc: Handle .text.{hot,unlikely}.* in linker script

[Nathan Chancellor]

Commit eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input
sections") added ".text.unlikely.*" and ".text.hot.*" due to an LLVM
change [1].

After another LLVM change [2], these sections are seen in some PowerPC
builds, where there is a orphan section warning then build failure:

$ make -skj"$(nproc)" \
       ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- LLVM=1 O=out \
       distclean powernv_defconfig zImage.epapr
ld.lld: warning: kernel/built-in.a(panic.o):(.text.unlikely.) is being placed in '.text.unlikely.'
...
ld.lld: warning: address (0xc000000000009314) of section .text is not a multiple of alignment (256)
...
ERROR: start_text address is c000000000009400, should be c000000000008000
ERROR: try to enable LD_HEAD_STUB_CATCH config option
ERROR: see comments in arch/powerpc/tools/head_check.sh
...

Explicitly handle these sections like in the main linker script so
there is no more build failure.

[1]: https://reviews.llvm.org/D79600
[2]: https://reviews.llvm.org/D92493

Cc: stable@vger.kernel.org
Fixes: 83a092cf95f2 ("powerpc: Link warning for orphan sections")
Link: https://github.com/ClangBuiltLinux/linux/issues/1218
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---

v1 -> v2:

* Add missing [1] and [2] references in commit message. Thanks to Sedat
  Dilek for pointing it out!

 arch/powerpc/kernel/vmlinux.lds.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/vmlinux.lds.S b/arch/powerpc/kernel/vmlinux.lds.S
index 0318ba436f34..8e0b1298bf19 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -85,7 +85,7 @@ SECTIONS
 		ALIGN_FUNCTION();
 #endif
 		/* careful! __ftr_alt_* sections need to be close to .text */
-		*(.text.hot TEXT_MAIN .text.fixup .text.unlikely .fixup __ftr_alt_* .ref.text);
+		*(.text.hot .text.hot.* TEXT_MAIN .text.fixup .text.unlikely .text.unlikely.* .fixup __ftr_alt_* .ref.text);
 #ifdef CONFIG_PPC64
 		*(.tramp.ftrace.text);
 #endif

base-commit: d8a4f20584d5906093a8fc6aa06622102a501095
-- 
2.30.0

Re: [PATCH v2] powerpc: Handle .text.{hot, unlikely}.* in linker script

[Michael Ellerman]

On Mon, 4 Jan 2021 13:59:53 -0700, Nathan Chancellor wrote:
> Commit eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input
> sections") added ".text.unlikely.*" and ".text.hot.*" due to an LLVM
> change [1].
> 
> After another LLVM change [2], these sections are seen in some PowerPC
> builds, where there is a orphan section warning then build failure:
> 
> [...]

Applied to powerpc/fixes.

[1/1] powerpc: Handle .text.{hot,unlikely}.* in linker script
      https://git.kernel.org/powerpc/c/3ce47d95b7346dcafd9bed3556a8d072cb2b8571

cheers

Re: [PATCH v2] powerpc: Handle .text.{hot, unlikely}.* in linker script

[Segher Boessenkool]

Hi!

Very late of course, and the patch is fine, but:

On Mon, Jan 04, 2021 at 01:59:53PM -0700, Nathan Chancellor wrote:
> Commit eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input
> sections") added ".text.unlikely.*" and ".text.hot.*" due to an LLVM
> change [1].
> 
> After another LLVM change [2], these sections are seen in some PowerPC
> builds, where there is a orphan section warning then build failure:
> 
> $ make -skj"$(nproc)" \
>        ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- LLVM=1 O=out \
>        distclean powernv_defconfig zImage.epapr
> ld.lld: warning: kernel/built-in.a(panic.o):(.text.unlikely.) is being placed in '.text.unlikely.'

Is the section really called ".text.unlikely.", i.e. the name ending in
a dot?  How very unusual, is there some bug elsewhere?


Segher

Re: [PATCH v2] powerpc: Handle .text.{hot,unlikely}.* in linker script

[Nathan Chancellor]

On Sat, Jan 16, 2021 at 12:44:38PM -0600, Segher Boessenkool wrote:
> Hi!
> 
> Very late of course, and the patch is fine, but:
> 
> On Mon, Jan 04, 2021 at 01:59:53PM -0700, Nathan Chancellor wrote:
> > Commit eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input
> > sections") added ".text.unlikely.*" and ".text.hot.*" due to an LLVM
> > change [1].
> > 
> > After another LLVM change [2], these sections are seen in some PowerPC
> > builds, where there is a orphan section warning then build failure:
> > 
> > $ make -skj"$(nproc)" \
> >        ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- LLVM=1 O=out \
> >        distclean powernv_defconfig zImage.epapr
> > ld.lld: warning: kernel/built-in.a(panic.o):(.text.unlikely.) is being placed in '.text.unlikely.'
> 
> Is the section really called ".text.unlikely.", i.e. the name ending in
> a dot?  How very unusual, is there some bug elsewhere?

No, this was an intention change done by LLVM:
https://reviews.llvm.org/D79600

Cheers,
Nathan