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* [PATCH] arm/build: Always handle .ARM.exidx and .ARM.extab sections
@ 2020-09-28 22:48 Nathan Chancellor
  2020-10-12 21:10 ` Nick Desaulniers
  0 siblings, 1 reply; 6+ messages in thread
From: Nathan Chancellor @ 2020-09-28 22:48 UTC (permalink / raw)
  To: Kees Cook, Ingo Molnar
  Cc: Russell King, linux-arm-kernel, linux-kernel, clang-built-linux,
	Nathan Chancellor, kernel test robot

After turning on warnings for orphan section placement, enabling
CONFIG_UNWINDER_FRAME_POINTER instead of CONFIG_UNWINDER_ARM causes
thousands of warnings when clang + ld.lld are used:

$ scripts/config --file arch/arm/configs/multi_v7_defconfig \
                 -d CONFIG_UNWINDER_ARM \
                 -e CONFIG_UNWINDER_FRAME_POINTER
$ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- LLVM=1 defconfig zImage
ld.lld: warning: init/built-in.a(main.o):(.ARM.extab) is being placed in '.ARM.extab'
ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.ref.text) is being placed in '.ARM.extab.ref.text'
ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab) is being placed in '.ARM.extab'
ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab) is being placed in '.ARM.extab'
ld.lld: warning: init/built-in.a(do_mounts_initrd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab) is being placed in '.ARM.extab'
ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab) is being placed in '.ARM.extab'

These sections are handled by the ARM_UNWIND_SECTIONS define, which is
only added to the list of sections when CONFIG_ARM_UNWIND is set.
CONFIG_ARM_UNWIND is a hidden symbol that is only selected when
CONFIG_UNWINDER_ARM is set so CONFIG_UNWINDER_FRAME_POINTER never
handles these sections. According to the help text of
CONFIG_UNWINDER_ARM, these sections should be discarded so that the
kernel image size is not affected.

Fixes: 5a17850e251a ("arm/build: Warn on orphan section placement")
Link: https://github.com/ClangBuiltLinux/linux/issues/1152
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 arch/arm/kernel/vmlinux.lds.S | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 5f4922e858d0..a2c0d96b0580 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -40,6 +40,10 @@ SECTIONS
 		ARM_DISCARD
 #ifndef CONFIG_SMP_ON_UP
 		*(.alt.smp.init)
+#endif
+#ifndef CONFIG_ARM_UNWIND
+		*(.ARM.exidx*)
+		*(.ARM.extab*)
 #endif
 	}
 

base-commit: 6e0bf0e0e55000742a53c5f3b58f8669e0091a11
-- 
2.28.0


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] arm/build: Always handle .ARM.exidx and .ARM.extab sections
  2020-09-28 22:48 [PATCH] arm/build: Always handle .ARM.exidx and .ARM.extab sections Nathan Chancellor
@ 2020-10-12 21:10 ` Nick Desaulniers
  2020-10-12 21:22   ` Fāng-ruì Sòng
  0 siblings, 1 reply; 6+ messages in thread
From: Nick Desaulniers @ 2020-10-12 21:10 UTC (permalink / raw)
  To: Nathan Chancellor
  Cc: Kees Cook, Ingo Molnar, Russell King, Linux ARM, LKML,
	clang-built-linux, kernel test robot

On Mon, Sep 28, 2020 at 3:49 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> After turning on warnings for orphan section placement, enabling
> CONFIG_UNWINDER_FRAME_POINTER instead of CONFIG_UNWINDER_ARM causes
> thousands of warnings when clang + ld.lld are used:
>
> $ scripts/config --file arch/arm/configs/multi_v7_defconfig \
>                  -d CONFIG_UNWINDER_ARM \
>                  -e CONFIG_UNWINDER_FRAME_POINTER
> $ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- LLVM=1 defconfig zImage
> ld.lld: warning: init/built-in.a(main.o):(.ARM.extab) is being placed in '.ARM.extab'
> ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.ref.text) is being placed in '.ARM.extab.ref.text'
> ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab) is being placed in '.ARM.extab'
> ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab) is being placed in '.ARM.extab'
> ld.lld: warning: init/built-in.a(do_mounts_initrd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab) is being placed in '.ARM.extab'
> ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab) is being placed in '.ARM.extab'
>
> These sections are handled by the ARM_UNWIND_SECTIONS define, which is
> only added to the list of sections when CONFIG_ARM_UNWIND is set.
> CONFIG_ARM_UNWIND is a hidden symbol that is only selected when
> CONFIG_UNWINDER_ARM is set so CONFIG_UNWINDER_FRAME_POINTER never
> handles these sections. According to the help text of
> CONFIG_UNWINDER_ARM, these sections should be discarded so that the
> kernel image size is not affected.

My apologies for taking so long to review this.

I have a suspicion that these come from forcing on configs that
Kconfig/menuconfig would block, and aren't clang or lld specific, yet
are exposed by the new linker warnings for orphan section placement
(good).  That said, we definitely have OEMs in Android land that still
prefer the older unwinder.

From https://developer.arm.com/documentation/ihi0038/b/ (click
download in top left), section 4.4.1 "Sections" has a note:

```
Tables are not required for ABI compliance at the C/Assembler level
but are required for C++.
```

Review-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>

Please submit to:
https://www.arm.linux.org.uk/developer/patches/add.php

>
> Fixes: 5a17850e251a ("arm/build: Warn on orphan section placement")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1152
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> ---
>  arch/arm/kernel/vmlinux.lds.S | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> index 5f4922e858d0..a2c0d96b0580 100644
> --- a/arch/arm/kernel/vmlinux.lds.S
> +++ b/arch/arm/kernel/vmlinux.lds.S
> @@ -40,6 +40,10 @@ SECTIONS
>                 ARM_DISCARD
>  #ifndef CONFIG_SMP_ON_UP
>                 *(.alt.smp.init)
> +#endif
> +#ifndef CONFIG_ARM_UNWIND
> +               *(.ARM.exidx*)

I don't think we need the wildcard, as without this line, I see:

ld.lld: warning: <internal>:(.ARM.exidx) is being placed in '.ARM.exidx'

though I do see binutils linker scripts use precisely what you have.
So I guess that's fine.

I guess we can't reuse `ARM_UNWIND_SECTIONS` since the ALIGN and
linker-script-defined-symbols would be weird in a DISCARD clause?


> +               *(.ARM.extab*)
>  #endif
>         }
>
>
> base-commit: 6e0bf0e0e55000742a53c5f3b58f8669e0091a11
> --


--
Thanks,
~Nick Desaulniers

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] arm/build: Always handle .ARM.exidx and .ARM.extab sections
  2020-10-12 21:10 ` Nick Desaulniers
@ 2020-10-12 21:22   ` Fāng-ruì Sòng
  2020-10-12 21:26     ` Kees Cook
  0 siblings, 1 reply; 6+ messages in thread
From: Fāng-ruì Sòng @ 2020-10-12 21:22 UTC (permalink / raw)
  To: Nick Desaulniers
  Cc: Nathan Chancellor, Kees Cook, Ingo Molnar, Russell King,
	Linux ARM, LKML, clang-built-linux, kernel test robot

On Mon, Oct 12, 2020 at 2:11 PM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@googlegroups.com> wrote:
>
> On Mon, Sep 28, 2020 at 3:49 PM Nathan Chancellor
> <natechancellor@gmail.com> wrote:
> >
> > After turning on warnings for orphan section placement, enabling
> > CONFIG_UNWINDER_FRAME_POINTER instead of CONFIG_UNWINDER_ARM causes
> > thousands of warnings when clang + ld.lld are used:
> >
> > $ scripts/config --file arch/arm/configs/multi_v7_defconfig \
> >                  -d CONFIG_UNWINDER_ARM \
> >                  -e CONFIG_UNWINDER_FRAME_POINTER
> > $ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- LLVM=1 defconfig zImage
> > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab) is being placed in '.ARM.extab'
> > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.ref.text) is being placed in '.ARM.extab.ref.text'
> > ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab) is being placed in '.ARM.extab'
> > ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab) is being placed in '.ARM.extab'
> > ld.lld: warning: init/built-in.a(do_mounts_initrd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab) is being placed in '.ARM.extab'
> > ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab) is being placed in '.ARM.extab'
> >
> > These sections are handled by the ARM_UNWIND_SECTIONS define, which is
> > only added to the list of sections when CONFIG_ARM_UNWIND is set.
> > CONFIG_ARM_UNWIND is a hidden symbol that is only selected when
> > CONFIG_UNWINDER_ARM is set so CONFIG_UNWINDER_FRAME_POINTER never
> > handles these sections. According to the help text of
> > CONFIG_UNWINDER_ARM, these sections should be discarded so that the
> > kernel image size is not affected.
>
> My apologies for taking so long to review this.
>
> I have a suspicion that these come from forcing on configs that
> Kconfig/menuconfig would block, and aren't clang or lld specific, yet
> are exposed by the new linker warnings for orphan section placement
> (good).  That said, we definitely have OEMs in Android land that still
> prefer the older unwinder.
>
> From https://developer.arm.com/documentation/ihi0038/b/ (click
> download in top left), section 4.4.1 "Sections" has a note:
>
> ```
> Tables are not required for ABI compliance at the C/Assembler level
> but are required for C++.
> ```
>
> Review-by: Nick Desaulniers <ndesaulniers@google.com>
> Tested-by: Nick Desaulniers <ndesaulniers@google.com>
>
> Please submit to:
> https://www.arm.linux.org.uk/developer/patches/add.php
>
> >
> > Fixes: 5a17850e251a ("arm/build: Warn on orphan section placement")
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1152
> > Reported-by: kernel test robot <lkp@intel.com>
> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > ---
> >  arch/arm/kernel/vmlinux.lds.S | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> > index 5f4922e858d0..a2c0d96b0580 100644
> > --- a/arch/arm/kernel/vmlinux.lds.S
> > +++ b/arch/arm/kernel/vmlinux.lds.S
> > @@ -40,6 +40,10 @@ SECTIONS
> >                 ARM_DISCARD
> >  #ifndef CONFIG_SMP_ON_UP
> >                 *(.alt.smp.init)
> > +#endif
> > +#ifndef CONFIG_ARM_UNWIND
> > +               *(.ARM.exidx*)
>
> I don't think we need the wildcard, as without this line, I see:
>
> ld.lld: warning: <internal>:(.ARM.exidx) is being placed in '.ARM.exidx'

We may need the wildcard if there are -ffunction-sections builds.
In clang, .ARM.exidx* cannot be removed even with -fno-unwind-tables
-fno-exceptions.

> though I do see binutils linker scripts use precisely what you have.
> So I guess that's fine.
>
> I guess we can't reuse `ARM_UNWIND_SECTIONS` since the ALIGN and
> linker-script-defined-symbols would be weird in a DISCARD clause?
>
>
> > +               *(.ARM.extab*)
> >  #endif
> >         }
> >
> >
> > base-commit: 6e0bf0e0e55000742a53c5f3b58f8669e0091a11
> > --
>
>
> --
> Thanks,
> ~Nick Desaulniers
>
> --
> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/CAKwvOd%3D%2B98r6F4JjrPEoWX88WQ%3DB-KMRP2eWojabLk6it3i5KA%40mail.gmail.com.



-- 
宋方睿

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] arm/build: Always handle .ARM.exidx and .ARM.extab sections
  2020-10-12 21:22   ` Fāng-ruì Sòng
@ 2020-10-12 21:26     ` Kees Cook
  2020-10-13  3:26       ` Nathan Chancellor
  0 siblings, 1 reply; 6+ messages in thread
From: Kees Cook @ 2020-10-12 21:26 UTC (permalink / raw)
  To: Fāng-ruì Sòng
  Cc: Nick Desaulniers, Nathan Chancellor, Ingo Molnar, Russell King,
	Linux ARM, LKML, clang-built-linux, kernel test robot

On Mon, Oct 12, 2020 at 02:22:03PM -0700, Fāng-ruì Sòng wrote:
> On Mon, Oct 12, 2020 at 2:11 PM 'Nick Desaulniers' via Clang Built
> Linux <clang-built-linux@googlegroups.com> wrote:
> >
> > On Mon, Sep 28, 2020 at 3:49 PM Nathan Chancellor
> > <natechancellor@gmail.com> wrote:
> > >
> > > After turning on warnings for orphan section placement, enabling
> > > CONFIG_UNWINDER_FRAME_POINTER instead of CONFIG_UNWINDER_ARM causes
> > > thousands of warnings when clang + ld.lld are used:
> > >
> > > $ scripts/config --file arch/arm/configs/multi_v7_defconfig \
> > >                  -d CONFIG_UNWINDER_ARM \
> > >                  -e CONFIG_UNWINDER_FRAME_POINTER
> > > $ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- LLVM=1 defconfig zImage
> > > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab) is being placed in '.ARM.extab'
> > > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.ref.text) is being placed in '.ARM.extab.ref.text'
> > > ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab) is being placed in '.ARM.extab'
> > > ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab) is being placed in '.ARM.extab'
> > > ld.lld: warning: init/built-in.a(do_mounts_initrd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab) is being placed in '.ARM.extab'
> > > ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab) is being placed in '.ARM.extab'
> > >
> > > These sections are handled by the ARM_UNWIND_SECTIONS define, which is
> > > only added to the list of sections when CONFIG_ARM_UNWIND is set.
> > > CONFIG_ARM_UNWIND is a hidden symbol that is only selected when
> > > CONFIG_UNWINDER_ARM is set so CONFIG_UNWINDER_FRAME_POINTER never
> > > handles these sections. According to the help text of
> > > CONFIG_UNWINDER_ARM, these sections should be discarded so that the
> > > kernel image size is not affected.
> >
> > My apologies for taking so long to review this.
> >
> > I have a suspicion that these come from forcing on configs that
> > Kconfig/menuconfig would block, and aren't clang or lld specific, yet
> > are exposed by the new linker warnings for orphan section placement
> > (good).  That said, we definitely have OEMs in Android land that still
> > prefer the older unwinder.
> >
> > From https://developer.arm.com/documentation/ihi0038/b/ (click
> > download in top left), section 4.4.1 "Sections" has a note:
> >
> > ```
> > Tables are not required for ABI compliance at the C/Assembler level
> > but are required for C++.
> > ```
> >
> > Review-by: Nick Desaulniers <ndesaulniers@google.com>
> > Tested-by: Nick Desaulniers <ndesaulniers@google.com>
> >
> > Please submit to:
> > https://www.arm.linux.org.uk/developer/patches/add.php
> >
> > >
> > > Fixes: 5a17850e251a ("arm/build: Warn on orphan section placement")
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/1152
> > > Reported-by: kernel test robot <lkp@intel.com>
> > > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > > ---
> > >  arch/arm/kernel/vmlinux.lds.S | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> > > index 5f4922e858d0..a2c0d96b0580 100644
> > > --- a/arch/arm/kernel/vmlinux.lds.S
> > > +++ b/arch/arm/kernel/vmlinux.lds.S
> > > @@ -40,6 +40,10 @@ SECTIONS
> > >                 ARM_DISCARD
> > >  #ifndef CONFIG_SMP_ON_UP
> > >                 *(.alt.smp.init)
> > > +#endif
> > > +#ifndef CONFIG_ARM_UNWIND
> > > +               *(.ARM.exidx*)
> >
> > I don't think we need the wildcard, as without this line, I see:
> >
> > ld.lld: warning: <internal>:(.ARM.exidx) is being placed in '.ARM.exidx'
> 
> We may need the wildcard if there are -ffunction-sections builds.
> In clang, .ARM.exidx* cannot be removed even with -fno-unwind-tables
> -fno-exceptions.

Does it need to be:

	*(.ARM.exidx) *(.ARM.exidx.*)
	*(.ARM.extab) *(.ARM.extab.*)

?

> 
> > though I do see binutils linker scripts use precisely what you have.
> > So I guess that's fine.
> >
> > I guess we can't reuse `ARM_UNWIND_SECTIONS` since the ALIGN and
> > linker-script-defined-symbols would be weird in a DISCARD clause?
> >
> >
> > > +               *(.ARM.extab*)
> > >  #endif
> > >         }
> > >
> > >
> > > base-commit: 6e0bf0e0e55000742a53c5f3b58f8669e0091a11
> > > --
> >
> >
> > --
> > Thanks,
> > ~Nick Desaulniers
> >
> > --
> > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com.
> > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/CAKwvOd%3D%2B98r6F4JjrPEoWX88WQ%3DB-KMRP2eWojabLk6it3i5KA%40mail.gmail.com.
> 
> 
> 
> -- 
> 宋方睿

-- 
Kees Cook

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] arm/build: Always handle .ARM.exidx and .ARM.extab sections
  2020-10-12 21:26     ` Kees Cook
@ 2020-10-13  3:26       ` Nathan Chancellor
  2020-10-13 22:56         ` Nick Desaulniers
  0 siblings, 1 reply; 6+ messages in thread
From: Nathan Chancellor @ 2020-10-13  3:26 UTC (permalink / raw)
  To: Kees Cook
  Cc: Fāng-ruì Sòng, Nick Desaulniers, Ingo Molnar,
	Russell King, Linux ARM, LKML, clang-built-linux,
	kernel test robot

On Mon, Oct 12, 2020 at 02:26:52PM -0700, Kees Cook wrote:
> On Mon, Oct 12, 2020 at 02:22:03PM -0700, Fāng-ruì Sòng wrote:
> > On Mon, Oct 12, 2020 at 2:11 PM 'Nick Desaulniers' via Clang Built
> > Linux <clang-built-linux@googlegroups.com> wrote:
> > >
> > > On Mon, Sep 28, 2020 at 3:49 PM Nathan Chancellor
> > > <natechancellor@gmail.com> wrote:
> > > >
> > > > After turning on warnings for orphan section placement, enabling
> > > > CONFIG_UNWINDER_FRAME_POINTER instead of CONFIG_UNWINDER_ARM causes
> > > > thousands of warnings when clang + ld.lld are used:
> > > >
> > > > $ scripts/config --file arch/arm/configs/multi_v7_defconfig \
> > > >                  -d CONFIG_UNWINDER_ARM \
> > > >                  -e CONFIG_UNWINDER_FRAME_POINTER
> > > > $ make -skj"$(nproc)" ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- LLVM=1 defconfig zImage
> > > > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab) is being placed in '.ARM.extab'
> > > > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > > ld.lld: warning: init/built-in.a(main.o):(.ARM.extab.ref.text) is being placed in '.ARM.extab.ref.text'
> > > > ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > > ld.lld: warning: init/built-in.a(do_mounts.o):(.ARM.extab) is being placed in '.ARM.extab'
> > > > ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > > ld.lld: warning: init/built-in.a(do_mounts_rd.o):(.ARM.extab) is being placed in '.ARM.extab'
> > > > ld.lld: warning: init/built-in.a(do_mounts_initrd.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > > ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > > ld.lld: warning: init/built-in.a(initramfs.o):(.ARM.extab) is being placed in '.ARM.extab'
> > > > ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab.init.text) is being placed in '.ARM.extab.init.text'
> > > > ld.lld: warning: init/built-in.a(calibrate.o):(.ARM.extab) is being placed in '.ARM.extab'
> > > >
> > > > These sections are handled by the ARM_UNWIND_SECTIONS define, which is
> > > > only added to the list of sections when CONFIG_ARM_UNWIND is set.
> > > > CONFIG_ARM_UNWIND is a hidden symbol that is only selected when
> > > > CONFIG_UNWINDER_ARM is set so CONFIG_UNWINDER_FRAME_POINTER never
> > > > handles these sections. According to the help text of
> > > > CONFIG_UNWINDER_ARM, these sections should be discarded so that the
> > > > kernel image size is not affected.
> > >
> > > My apologies for taking so long to review this.
> > >
> > > I have a suspicion that these come from forcing on configs that
> > > Kconfig/menuconfig would block, and aren't clang or lld specific, yet
> > > are exposed by the new linker warnings for orphan section placement
> > > (good).  That said, we definitely have OEMs in Android land that still
> > > prefer the older unwinder.
> > >
> > > From https://developer.arm.com/documentation/ihi0038/b/ (click
> > > download in top left), section 4.4.1 "Sections" has a note:
> > >
> > > ```
> > > Tables are not required for ABI compliance at the C/Assembler level
> > > but are required for C++.
> > > ```
> > >
> > > Review-by: Nick Desaulniers <ndesaulniers@google.com>
> > > Tested-by: Nick Desaulniers <ndesaulniers@google.com>
> > >
> > > Please submit to:
> > > https://www.arm.linux.org.uk/developer/patches/add.php

This should go through the tip tree (hence sending it straight to Ingo)
since the patch that this fixes was there. I guess it does not
necessarily matter now that the breakage is in mainline but basing a
set of patches on a non -rc tag is a little taboo I thought so not sure
it is appropriate to go through Russell for now. It is up to the
maintainers though, I will submit it wherever it needs to go.

> > > >
> > > > Fixes: 5a17850e251a ("arm/build: Warn on orphan section placement")
> > > > Link: https://github.com/ClangBuiltLinux/linux/issues/1152
> > > > Reported-by: kernel test robot <lkp@intel.com>
> > > > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > > > ---
> > > >  arch/arm/kernel/vmlinux.lds.S | 4 ++++
> > > >  1 file changed, 4 insertions(+)
> > > >
> > > > diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> > > > index 5f4922e858d0..a2c0d96b0580 100644
> > > > --- a/arch/arm/kernel/vmlinux.lds.S
> > > > +++ b/arch/arm/kernel/vmlinux.lds.S
> > > > @@ -40,6 +40,10 @@ SECTIONS
> > > >                 ARM_DISCARD
> > > >  #ifndef CONFIG_SMP_ON_UP
> > > >                 *(.alt.smp.init)
> > > > +#endif
> > > > +#ifndef CONFIG_ARM_UNWIND
> > > > +               *(.ARM.exidx*)
> > >
> > > I don't think we need the wildcard, as without this line, I see:
> > >
> > > ld.lld: warning: <internal>:(.ARM.exidx) is being placed in '.ARM.exidx'
> > 
> > We may need the wildcard if there are -ffunction-sections builds.
> > In clang, .ARM.exidx* cannot be removed even with -fno-unwind-tables
> > -fno-exceptions.
> 
> Does it need to be:
> 
> 	*(.ARM.exidx) *(.ARM.exidx.*)
> 	*(.ARM.extab) *(.ARM.extab.*)
> 
> ?

I tested the patch and saw no warnings with what I sent. I can change it
to that if it is more proper though!

> > 
> > > though I do see binutils linker scripts use precisely what you have.
> > > So I guess that's fine.
> > >
> > > I guess we can't reuse `ARM_UNWIND_SECTIONS` since the ALIGN and
> > > linker-script-defined-symbols would be weird in a DISCARD clause?
> > >
> > >
> > > > +               *(.ARM.extab*)
> > > >  #endif
> > > >         }
> > > >
> > > >
> > > > base-commit: 6e0bf0e0e55000742a53c5f3b58f8669e0091a11
> > > > --
> > >
> > >
> > > --
> > > Thanks,
> > > ~Nick Desaulniers
> > >
> > > --
> > > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> > > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com.
> > > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/CAKwvOd%3D%2B98r6F4JjrPEoWX88WQ%3DB-KMRP2eWojabLk6it3i5KA%40mail.gmail.com.
> > 
> > 
> > 
> > -- 
> > 宋方睿
> 
> -- 
> Kees Cook

Cheers,
Nathan

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] arm/build: Always handle .ARM.exidx and .ARM.extab sections
  2020-10-13  3:26       ` Nathan Chancellor
@ 2020-10-13 22:56         ` Nick Desaulniers
  0 siblings, 0 replies; 6+ messages in thread
From: Nick Desaulniers @ 2020-10-13 22:56 UTC (permalink / raw)
  To: Nathan Chancellor
  Cc: Kees Cook, Fāng-ruì Sòng, Ingo Molnar,
	Russell King, Linux ARM, LKML, clang-built-linux,
	kernel test robot

On Mon, Oct 12, 2020 at 8:26 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> On Mon, Oct 12, 2020 at 02:26:52PM -0700, Kees Cook wrote:
> > On Mon, Oct 12, 2020 at 02:22:03PM -0700, Fāng-ruì Sòng wrote:
> > > On Mon, Oct 12, 2020 at 2:11 PM 'Nick Desaulniers' via Clang Built
> > > Linux <clang-built-linux@googlegroups.com> wrote:
> > > >
> > > > Please submit to:
> > > > https://www.arm.linux.org.uk/developer/patches/add.php
>
> This should go through the tip tree (hence sending it straight to Ingo)
> since the patch that this fixes was there. I guess it does not
> necessarily matter now that the breakage is in mainline but basing a
> set of patches on a non -rc tag is a little taboo I thought so not sure
> it is appropriate to go through Russell for now. It is up to the
> maintainers though, I will submit it wherever it needs to go.

Ah got it, yeah I don't really care which tree this goes up in.

>
> > > > >
> > > > > Fixes: 5a17850e251a ("arm/build: Warn on orphan section placement")
> > > > > Link: https://github.com/ClangBuiltLinux/linux/issues/1152
> > > > > Reported-by: kernel test robot <lkp@intel.com>
> > > > > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
> > > > > ---
> > > > >  arch/arm/kernel/vmlinux.lds.S | 4 ++++
> > > > >  1 file changed, 4 insertions(+)
> > > > >
> > > > > diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
> > > > > index 5f4922e858d0..a2c0d96b0580 100644
> > > > > --- a/arch/arm/kernel/vmlinux.lds.S
> > > > > +++ b/arch/arm/kernel/vmlinux.lds.S
> > > > > @@ -40,6 +40,10 @@ SECTIONS
> > > > >                 ARM_DISCARD
> > > > >  #ifndef CONFIG_SMP_ON_UP
> > > > >                 *(.alt.smp.init)
> > > > > +#endif
> > > > > +#ifndef CONFIG_ARM_UNWIND
> > > > > +               *(.ARM.exidx*)
> > > >
> > > > I don't think we need the wildcard, as without this line, I see:
> > > >
> > > > ld.lld: warning: <internal>:(.ARM.exidx) is being placed in '.ARM.exidx'
> > >
> > > We may need the wildcard if there are -ffunction-sections builds.
> > > In clang, .ARM.exidx* cannot be removed even with -fno-unwind-tables
> > > -fno-exceptions.
> >
> > Does it need to be:
> >
> >       *(.ARM.exidx) *(.ARM.exidx.*)
> >       *(.ARM.extab) *(.ARM.extab.*)
> >
> > ?
>
> I tested the patch and saw no warnings with what I sent. I can change it
> to that if it is more proper though!

We don't have LTO working on 32b ARM yet, so I'm not worried about
-ffunction-sections for this (yet).  The ld.bfd linker scripts didn't
seem to use the non-wildcard and wildcard suggestion; just the
wildcarded.  (Maybe they have the same "bug?")  I'm happy to revisit
though if we plan to get LTO up and running on 32b ARM.
-- 
Thanks,
~Nick Desaulniers

^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2020-10-14  9:24 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-09-28 22:48 [PATCH] arm/build: Always handle .ARM.exidx and .ARM.extab sections Nathan Chancellor
2020-10-12 21:10 ` Nick Desaulniers
2020-10-12 21:22   ` Fāng-ruì Sòng
2020-10-12 21:26     ` Kees Cook
2020-10-13  3:26       ` Nathan Chancellor
2020-10-13 22:56         ` Nick Desaulniers

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