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[PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and --fix-cortex-a53

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  [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and --fix-cortex-a53 Markus Mayer <code@mmayer.net> - 2016-10-31 20:50 +0100
    Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and --fix-cortex-a53 Markus Mayer <markus.mayer@broadcom.com> - 2016-11-02 22:10 +0100
      Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and  --fix-cortex-a53 Will Deacon <will.deacon@arm.com> - 2016-11-02 22:30 +0100
        Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and --fix-cortex-a53 Markus Mayer <markus.mayer@broadcom.com> - 2016-11-02 22:50 +0100
          Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and  --fix-cortex-a53 Florian Fainelli <f.fainelli@gmail.com> - 2016-11-02 23:00 +0100
            Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and  --fix-cortex-a53 Will Deacon <will.deacon@arm.com> - 2016-11-03 15:20 +0100
              Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and  --fix-cortex-a53 Florian Fainelli <f.fainelli@gmail.com> - 2016-11-03 18:30 +0100
    Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and  --fix-cortex-a53 Will Deacon <will.deacon@arm.com> - 2016-11-02 22:10 +0100

#1512825 — [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and --fix-cortex-a53

From: Markus Mayer <mmayer@broadcom.com>

The new errata check leads to a warning with some older versions of the
linker that do know how to work around the errata, but still use the
original name of the command line option: --fix-cortex-a53. The commit
in question that changed the name of the option can be found at [1].
It looks like only "gold" is affected by this rename. Traditional "ld"
isn't. (There, the argument was always called --fix-cortex-a53-843419.)

To allow older versions of gold to properly handle the erratum if they
can, check whether ld supports the old name of this option in addition
to checking the new one.

[1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=7a2a1c793578a8468604e661dda025ecb8d0bd20;hp=cfbf0e3c5b637d66b2b1aeadecae9c187b825b2f

Signed-off-by: Markus Mayer <mmayer@broadcom.com>
---

Using the change proposed here, things work for me as expected:

$ aarch64-linux-ld -v
GNU ld (GNU Binutils) Linaro 2014.11-2 2.24.0.20141017

$ grep fix-cortex aarch64.log 
  /bin/bash scripts/link-vmlinux.sh aarch64-linux-ld -EL  -p --no-undefined
-X --fix-cortex-a53 --build-id ;  true
+ aarch64-linux-ld -EL -p --no-undefined -X --fix-cortex-a53 --build-id -o
.tmp_vmlinux1 -T ./arch/arm64/kernel/vmlinux.lds arch/arm64/kernel/head.o
init/built-in.o --start-group usr/built-in.o arch/arm64/kernel/built-in.o
arch/arm64/mm/built-in.o arch/arm64/net/built-in.o arch/arm64/kvm/built-in.o
arch/arm64/xen/built-in.o arch/arm64/crypto/built-in.o
./drivers/firmware/efi/libstub/lib.a kernel/built-in.o certs/built-in.o
mm/built-in.o fs/built-in.o ipc/built-in.o security/built-in.o
crypto/built-in.o block/built-in.o arch/arm64/lib/lib.a lib/lib.a
arch/arm64/lib/built-in.o lib/built-in.o drivers/built-in.o sound/built-in.o
firmware/built-in.o net/built-in.o virt/built-in.o --end-group
[...]

 arch/arm64/Makefile | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index ab51aed..231ba69 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -20,7 +20,13 @@ endif
 
 ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
   ifeq ($(call ld-option, --fix-cortex-a53-843419),)
-$(warning ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum)
+    ifeq ($(call ld-option, --fix-cortex-a53),)
+$(warning ld does not support --fix-cortex-a53-843419 or --fix-cortex-a53; kernel may be susceptible to erratum)
+    else
+# When this option was first introduced, it was called --fix-cortex-a53 in gold.
+# So, let's use that as fall-back if the linker understands it.
+LDFLAGS_vmlinux	+= --fix-cortex-a53
+    endif
   else
 LDFLAGS_vmlinux	+= --fix-cortex-a53-843419
   endif
-- 
2.7.4

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#1514123

On 2 November 2016 at 14:03, Will Deacon <will.deacon@arm.com> wrote:
> On Mon, Oct 31, 2016 at 12:44:14PM -0700, Markus Mayer wrote:
>> From: Markus Mayer <mmayer@broadcom.com>
>>
>> The new errata check leads to a warning with some older versions of the
>> linker that do know how to work around the errata, but still use the
>> original name of the command line option: --fix-cortex-a53. The commit
>> in question that changed the name of the option can be found at [1].
>> It looks like only "gold" is affected by this rename. Traditional "ld"
>> isn't. (There, the argument was always called --fix-cortex-a53-843419.)
>>
>> To allow older versions of gold to properly handle the erratum if they
>> can, check whether ld supports the old name of this option in addition
>> to checking the new one.
>>
>> [1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=7a2a1c793578a8468604e661dda025ecb8d0bd20;hp=cfbf0e3c5b637d66b2b1aeadecae9c187b825b2f
>>
>> Signed-off-by: Markus Mayer <mmayer@broadcom.com>
>
> If newer versions of gold accept the correct option name, why do we care?

Because Documentation/Changes states that the minimum requirement for
binutils is 2.12. Right now, that is not really true. And not
everybody can always use the newest toolchain, for various reasons.

The question I am asking is: What do we have to lose by supporting both options?

Thanks,
-Markus

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#1514143 — Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and --fix-cortex-a53

On Wed, Nov 02, 2016 at 02:07:17PM -0700, Markus Mayer wrote:
> On 2 November 2016 at 14:03, Will Deacon <will.deacon@arm.com> wrote:
> > On Mon, Oct 31, 2016 at 12:44:14PM -0700, Markus Mayer wrote:
> >> From: Markus Mayer <mmayer@broadcom.com>
> >>
> >> The new errata check leads to a warning with some older versions of the
> >> linker that do know how to work around the errata, but still use the
> >> original name of the command line option: --fix-cortex-a53. The commit
> >> in question that changed the name of the option can be found at [1].
> >> It looks like only "gold" is affected by this rename. Traditional "ld"
> >> isn't. (There, the argument was always called --fix-cortex-a53-843419.)
> >>
> >> To allow older versions of gold to properly handle the erratum if they
> >> can, check whether ld supports the old name of this option in addition
> >> to checking the new one.
> >>
> >> [1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=7a2a1c793578a8468604e661dda025ecb8d0bd20;hp=cfbf0e3c5b637d66b2b1aeadecae9c187b825b2f
> >>
> >> Signed-off-by: Markus Mayer <mmayer@broadcom.com>
> >
> > If newer versions of gold accept the correct option name, why do we care?
> 
> Because Documentation/Changes states that the minimum requirement for
> binutils is 2.12. Right now, that is not really true. And not
> everybody can always use the newest toolchain, for various reasons.

Well the kernel still builds, right? Can binutils 2.12 even work around
843419? For people who can't use a recent toolchain, then they don't get
erratum workaround and we warn them about it.

> The question I am asking is: What do we have to lose by supporting both options?

We end up passing "--fix-cortex-a53" to the linker, without knowing what it
might do in the future.

Will

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#1514159

On 2 November 2016 at 14:27, Will Deacon <will.deacon@arm.com> wrote:
> On Wed, Nov 02, 2016 at 02:07:17PM -0700, Markus Mayer wrote:
>> On 2 November 2016 at 14:03, Will Deacon <will.deacon@arm.com> wrote:
>> > On Mon, Oct 31, 2016 at 12:44:14PM -0700, Markus Mayer wrote:
>> >> From: Markus Mayer <mmayer@broadcom.com>
>> >>
>> >> The new errata check leads to a warning with some older versions of the
>> >> linker that do know how to work around the errata, but still use the
>> >> original name of the command line option: --fix-cortex-a53. The commit
>> >> in question that changed the name of the option can be found at [1].
>> >> It looks like only "gold" is affected by this rename. Traditional "ld"
>> >> isn't. (There, the argument was always called --fix-cortex-a53-843419.)
>> >>
>> >> To allow older versions of gold to properly handle the erratum if they
>> >> can, check whether ld supports the old name of this option in addition
>> >> to checking the new one.
>> >>
>> >> [1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=7a2a1c793578a8468604e661dda025ecb8d0bd20;hp=cfbf0e3c5b637d66b2b1aeadecae9c187b825b2f
>> >>
>> >> Signed-off-by: Markus Mayer <mmayer@broadcom.com>
>> >
>> > If newer versions of gold accept the correct option name, why do we care?
>>
>> Because Documentation/Changes states that the minimum requirement for
>> binutils is 2.12. Right now, that is not really true. And not
>> everybody can always use the newest toolchain, for various reasons.
>
> Well the kernel still builds, right? Can binutils 2.12 even work around
> 843419? For people who can't use a recent toolchain, then they don't get
> erratum workaround and we warn them about it.

Correct. Linkers as old as 2.12 are not able to work around the
erratum, and the warning is accurate. So, there's no problem there.

But there are newer versions that do know how to work around the
erratum, but use the original name of the option. Right now, you could
be using a linker that knows how to fix the erratum, but instead, the
you get a warning, and the erratum is not fixed.

This one, for instance:

$ arm-linux-ld -v
GNU ld (GNU Binutils) Linaro 2014.11-2 2.24.0.20141017

Without the proposed patch, this linker will produce a kernel without
the workaround, but not because the linker can't do it, but because it
isn't given the command line argument it understands.

>> The question I am asking is: What do we have to lose by supporting both options?
>
> We end up passing "--fix-cortex-a53" to the linker, without knowing what it
> might do in the future.

It seems highly unlikely that such a generic option would be added in
the future, both, because the precedent has been set for topic
specific options, and because they know it has been used in the past,
so they wouldn't add a previously used option to do something
completely different. (And if they really did, then that would be a
huge binutils bug.)

So, we have a trade-off between a real world problem that does
currently exist and avoiding a theoretical issue that may never
materialize.

Regards,
-Markus

> Will

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#1514172 — Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and --fix-cortex-a53

On 11/02/2016 02:41 PM, Markus Mayer wrote:
> On 2 November 2016 at 14:27, Will Deacon <will.deacon@arm.com> wrote:
>> On Wed, Nov 02, 2016 at 02:07:17PM -0700, Markus Mayer wrote:
>>> On 2 November 2016 at 14:03, Will Deacon <will.deacon@arm.com> wrote:
>>>> On Mon, Oct 31, 2016 at 12:44:14PM -0700, Markus Mayer wrote:
>>>>> From: Markus Mayer <mmayer@broadcom.com>
>>>>>
>>>>> The new errata check leads to a warning with some older versions of the
>>>>> linker that do know how to work around the errata, but still use the
>>>>> original name of the command line option: --fix-cortex-a53. The commit
>>>>> in question that changed the name of the option can be found at [1].
>>>>> It looks like only "gold" is affected by this rename. Traditional "ld"
>>>>> isn't. (There, the argument was always called --fix-cortex-a53-843419.)
>>>>>
>>>>> To allow older versions of gold to properly handle the erratum if they
>>>>> can, check whether ld supports the old name of this option in addition
>>>>> to checking the new one.
>>>>>
>>>>> [1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=7a2a1c793578a8468604e661dda025ecb8d0bd20;hp=cfbf0e3c5b637d66b2b1aeadecae9c187b825b2f
>>>>>
>>>>> Signed-off-by: Markus Mayer <mmayer@broadcom.com>
>>>>
>>>> If newer versions of gold accept the correct option name, why do we care?
>>>
>>> Because Documentation/Changes states that the minimum requirement for
>>> binutils is 2.12. Right now, that is not really true. And not
>>> everybody can always use the newest toolchain, for various reasons.
>>
>> Well the kernel still builds, right? Can binutils 2.12 even work around
>> 843419? For people who can't use a recent toolchain, then they don't get
>> erratum workaround and we warn them about it.
> 
> Correct. Linkers as old as 2.12 are not able to work around the
> erratum, and the warning is accurate. So, there's no problem there.
> 
> But there are newer versions that do know how to work around the
> erratum, but use the original name of the option. Right now, you could
> be using a linker that knows how to fix the erratum, but instead, the
> you get a warning, and the erratum is not fixed.
> 
> This one, for instance:
> 
> $ arm-linux-ld -v
> GNU ld (GNU Binutils) Linaro 2014.11-2 2.24.0.20141017
> 
> Without the proposed patch, this linker will produce a kernel without
> the workaround, but not because the linker can't do it, but because it
> isn't given the command line argument it understands.
> 
>>> The question I am asking is: What do we have to lose by supporting both options?
>>
>> We end up passing "--fix-cortex-a53" to the linker, without knowing what it
>> might do in the future.
> 
> It seems highly unlikely that such a generic option would be added in
> the future, both, because the precedent has been set for topic
> specific options, and because they know it has been used in the past,
> so they wouldn't add a previously used option to do something
> completely different. (And if they really did, then that would be a
> huge binutils bug.)
> 
> So, we have a trade-off between a real world problem that does
> currently exist and avoiding a theoretical issue that may never
> materialize.

Agreed, also the way Markus' patch is designed makes it such that we
first try the full and current option name, and if not supported, try
the second (and earlier, now obsolete) option name, so I really don't
see a lot of room for things to go wrong here...
-- 
Florian

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#1514546 — Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and --fix-cortex-a53

On Wed, Nov 02, 2016 at 02:57:26PM -0700, Florian Fainelli wrote:
> On 11/02/2016 02:41 PM, Markus Mayer wrote:
> > On 2 November 2016 at 14:27, Will Deacon <will.deacon@arm.com> wrote:
> >> On Wed, Nov 02, 2016 at 02:07:17PM -0700, Markus Mayer wrote:
> >>> The question I am asking is: What do we have to lose by supporting both options?
> >>
> >> We end up passing "--fix-cortex-a53" to the linker, without knowing what it
> >> might do in the future.
> > 
> > It seems highly unlikely that such a generic option would be added in
> > the future, both, because the precedent has been set for topic
> > specific options, and because they know it has been used in the past,
> > so they wouldn't add a previously used option to do something
> > completely different. (And if they really did, then that would be a
> > huge binutils bug.)
> > 
> > So, we have a trade-off between a real world problem that does
> > currently exist and avoiding a theoretical issue that may never
> > materialize.
> 
> Agreed, also the way Markus' patch is designed makes it such that we
> first try the full and current option name, and if not supported, try
> the second (and earlier, now obsolete) option name, so I really don't
> see a lot of room for things to go wrong here...

It's not beyond the realms of possibility that ld will grow a
"fix-cortex-a53" option in the future, that enables all of the a53
workarounds. Since ld is the linker supported by the kernel and gold isn't,
I don't want to pass this option down.

If you can't change toolchain and you want this worked around, why can't you
either build gold with it enabled by default, or pass the extra flag on the
command line to the kernel build system?

Will

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#1514722 — Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and --fix-cortex-a53

On 11/03/2016 07:16 AM, Will Deacon wrote:
> On Wed, Nov 02, 2016 at 02:57:26PM -0700, Florian Fainelli wrote:
>> On 11/02/2016 02:41 PM, Markus Mayer wrote:
>>> On 2 November 2016 at 14:27, Will Deacon <will.deacon@arm.com> wrote:
>>>> On Wed, Nov 02, 2016 at 02:07:17PM -0700, Markus Mayer wrote:
>>>>> The question I am asking is: What do we have to lose by supporting both options?
>>>>
>>>> We end up passing "--fix-cortex-a53" to the linker, without knowing what it
>>>> might do in the future.
>>>
>>> It seems highly unlikely that such a generic option would be added in
>>> the future, both, because the precedent has been set for topic
>>> specific options, and because they know it has been used in the past,
>>> so they wouldn't add a previously used option to do something
>>> completely different. (And if they really did, then that would be a
>>> huge binutils bug.)
>>>
>>> So, we have a trade-off between a real world problem that does
>>> currently exist and avoiding a theoretical issue that may never
>>> materialize.
>>
>> Agreed, also the way Markus' patch is designed makes it such that we
>> first try the full and current option name, and if not supported, try
>> the second (and earlier, now obsolete) option name, so I really don't
>> see a lot of room for things to go wrong here...
> 
> It's not beyond the realms of possibility that ld will grow a
> "fix-cortex-a53" option in the future, that enables all of the a53
> workarounds. Since ld is the linker supported by the kernel and gold isn't,
> I don't want to pass this option down.

No it's entirely reasonable to think this may happen, although:

- this has not happened yet, so once this happens, you will need to cook
a patch for this anyway, and you will be able to gate this catch all
linker option by an appropriate version check presumably

- you would supposedly want a fine grained set of linker options that
are specific to workarounds you have to have enabled, instead of a catch
all "enable all Cortex A53" workarounds

> 
> If you can't change toolchain and you want this worked around, why can't you
> either build gold with it enabled by default, or pass the extra flag on the
> command line to the kernel build system?

Because that creates a distribution problem and now we have to document
this for people who want to build a kernel on their own, without
necessarily understanding if this is something they might need, or why
this is needed, and why the kernel is not taking care of that on its
own? So yes, this comes down to who is responsible for what, in that
case the kernel's Makefile is the best place where to put such knowledge
as to which workaround needs to be enabled by the linker and it
simplifies things a lot for people.
-- 
Florian

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#1514125 — Re: [PATCH] arm64: errata: Check for --fix-cortex-a53-843419 and --fix-cortex-a53

On Mon, Oct 31, 2016 at 12:44:14PM -0700, Markus Mayer wrote:
> From: Markus Mayer <mmayer@broadcom.com>
> 
> The new errata check leads to a warning with some older versions of the
> linker that do know how to work around the errata, but still use the
> original name of the command line option: --fix-cortex-a53. The commit
> in question that changed the name of the option can be found at [1].
> It looks like only "gold" is affected by this rename. Traditional "ld"
> isn't. (There, the argument was always called --fix-cortex-a53-843419.)
> 
> To allow older versions of gold to properly handle the erratum if they
> can, check whether ld supports the old name of this option in addition
> to checking the new one.
> 
> [1] https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commitdiff;h=7a2a1c793578a8468604e661dda025ecb8d0bd20;hp=cfbf0e3c5b637d66b2b1aeadecae9c187b825b2f
> 
> Signed-off-by: Markus Mayer <mmayer@broadcom.com>

If newer versions of gold accept the correct option name, why do we care?

Will

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