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Re: [PATCH v2] crypto: arm64/sha: Add constant operand modifier to ASM_EXPORT

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  Re: [PATCH v2] crypto: arm64/sha: Add constant operand modifier to ASM_EXPORT Paul Gortmaker <paul.gortmaker@windriver.com> - 2017-04-18 16:50 +0200
    Re: [PATCH v2] crypto: arm64/sha: Add constant operand modifier to ASM_EXPORT Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-04-18 17:40 +0200
      Re: [PATCH v2] crypto: arm64/sha: Add constant operand modifier to  ASM_EXPORT Matthias Kaehlcke <mka@chromium.org> - 2017-04-18 19:40 +0200
        Re: [PATCH v2] crypto: arm64/sha: Add constant operand modifier to  ASM_EXPORT Herbert Xu <herbert@gondor.apana.org.au> - 2017-04-24 10:10 +0200
          Re: [PATCH v2] crypto: arm64/sha: Add constant operand modifier to ASM_EXPORT Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2017-04-24 10:10 +0200
            Re: [PATCH v2] crypto: arm64/sha: Add constant operand modifier to  ASM_EXPORT Herbert Xu <herbert@gondor.apana.org.au> - 2017-04-24 10:20 +0200

#1625374 — Re: [PATCH v2] crypto: arm64/sha: Add constant operand modifier to ASM_EXPORT

On Wed, Apr 5, 2017 at 2:34 PM, Matthias Kaehlcke <mka@chromium.org> wrote:
> The operand is an integer constant, make the constness explicit by
> adding the modifier. This is needed for clang to generate valid code
> and also works with gcc.

Actually it doesn't work with all gcc.  I've got an older arm64 toolchain that I
only use for syntax checking (and hence I don't care if it is the latest and
greatest) and this commit breaks it:

arch/arm64/crypto/sha1-ce-glue.c:21:2: error: invalid 'asm': invalid
operand prefix '%c'
  asm(".globl " #sym "; .set " #sym ", %c0" :: "i"(val));

I'm currently reverting this change locally so I can continue to use the old
toolchain:

$ aarch64-linux-gnu-gcc --version
aarch64-linux-gnu-gcc (crosstool-NG linaro-1.13.1-4.8-2013.12 - Linaro
GCC 2013.11) 4.8.3 20131202 (prerelease)
Copyright (C) 2013 Free Software Foundation, Inc.

$ aarch64-linux-gnu-as --version
GNU assembler (crosstool-NG linaro-1.13.1-4.8-2013.12 - Linaro GCC
2013.11) 2.24.0.20131220
Copyright 2013 Free Software Foundation, Inc.

Maybe it is finally too old and nobody cares, but I thought it worth a mention.

Paul.
--

>
> Also change the constraint of the operand from 'I' ("Integer constant
> that is valid as an immediate operand in an ADD instruction", AArch64)
> to 'i' ("An immediate integer operand").
>
> Based-on-patch-from: Greg Hackmann <ghackmann@google.com>
> Signed-off-by: Greg Hackmann <ghackmann@google.com>
> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
> ---
> Changes in v2:
> - Changed operand constraint from I to i
> - Updated commit message
> - Changed 'From' tag to 'Based-on-patch-from'
>
>  arch/arm64/crypto/sha1-ce-glue.c | 2 +-
>  arch/arm64/crypto/sha2-ce-glue.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/crypto/sha1-ce-glue.c b/arch/arm64/crypto/sha1-ce-glue.c
> index aefda9868627..6b520e3f3ab1 100644
> --- a/arch/arm64/crypto/sha1-ce-glue.c
> +++ b/arch/arm64/crypto/sha1-ce-glue.c
> @@ -18,7 +18,7 @@
>  #include <linux/module.h>
>
>  #define ASM_EXPORT(sym, val) \
> -       asm(".globl " #sym "; .set " #sym ", %0" :: "I"(val));
> +       asm(".globl " #sym "; .set " #sym ", %c0" :: "i"(val));
>
>  MODULE_DESCRIPTION("SHA1 secure hash using ARMv8 Crypto Extensions");
>  MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@linaro.org>");
> diff --git a/arch/arm64/crypto/sha2-ce-glue.c b/arch/arm64/crypto/sha2-ce-glue.c
> index 7cd587564a41..e3abe11de48c 100644
> --- a/arch/arm64/crypto/sha2-ce-glue.c
> +++ b/arch/arm64/crypto/sha2-ce-glue.c
> @@ -18,7 +18,7 @@
>  #include <linux/module.h>
>
>  #define ASM_EXPORT(sym, val) \
> -       asm(".globl " #sym "; .set " #sym ", %0" :: "I"(val));
> +       asm(".globl " #sym "; .set " #sym ", %c0" :: "i"(val));
>
>  MODULE_DESCRIPTION("SHA-224/SHA-256 secure hash using ARMv8 Crypto Extensions");
>  MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@linaro.org>");
> --
> 2.12.2.715.g7642488e1d-goog
>

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#1625403

On 18 April 2017 at 15:47, Paul Gortmaker <paul.gortmaker@windriver.com> wrote:
> On Wed, Apr 5, 2017 at 2:34 PM, Matthias Kaehlcke <mka@chromium.org> wrote:
>> The operand is an integer constant, make the constness explicit by
>> adding the modifier. This is needed for clang to generate valid code
>> and also works with gcc.
>
> Actually it doesn't work with all gcc.  I've got an older arm64 toolchain that I
> only use for syntax checking (and hence I don't care if it is the latest and
> greatest) and this commit breaks it:
>
> arch/arm64/crypto/sha1-ce-glue.c:21:2: error: invalid 'asm': invalid
> operand prefix '%c'
>   asm(".globl " #sym "; .set " #sym ", %c0" :: "i"(val));
>
> I'm currently reverting this change locally so I can continue to use the old
> toolchain:
>
> $ aarch64-linux-gnu-gcc --version
> aarch64-linux-gnu-gcc (crosstool-NG linaro-1.13.1-4.8-2013.12 - Linaro
> GCC 2013.11) 4.8.3 20131202 (prerelease)
> Copyright (C) 2013 Free Software Foundation, Inc.
>
> $ aarch64-linux-gnu-as --version
> GNU assembler (crosstool-NG linaro-1.13.1-4.8-2013.12 - Linaro GCC
> 2013.11) 2.24.0.20131220
> Copyright 2013 Free Software Foundation, Inc.
>
> Maybe it is finally too old and nobody cares, but I thought it worth a mention.
>

Thanks for the report. I think we care more about GCC 4.8 than about
Clang, which argues for reverting this patch.

I understand these issues must be frustrating if you are working on
this stuff, but to me, it is not entirely obvious why we want to
support Clang in the first place (i.e., what does it buy you if your
distro/environment is not already using Clang for userland), and why
the burden is on Linux to make modifications to support Clang,
especially when it comes to GCC extensions such as inline assembly
syntax.

It is ultimately up to the maintainers to decide what to do with this
patch, but my vote would be to revert it, especially given that the %c
placeholder prefix is not documented anywhere, and appears to simply
trigger some GCC internals that happen to do the right thing in this
case.

However, the I -> i change is arguably an improvement, and considering
that the following

asm("foo: .long %0" :: "i"(some value))

doesn't compile with clang either, I suggest you (Matthias) file a bug
against Clang to get this fixed, and we can propose another patch just
for the I->i change.

-- 
Ard.


>>
>> Also change the constraint of the operand from 'I' ("Integer constant
>> that is valid as an immediate operand in an ADD instruction", AArch64)
>> to 'i' ("An immediate integer operand").
>>
>> Based-on-patch-from: Greg Hackmann <ghackmann@google.com>
>> Signed-off-by: Greg Hackmann <ghackmann@google.com>
>> Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
>> ---
>> Changes in v2:
>> - Changed operand constraint from I to i
>> - Updated commit message
>> - Changed 'From' tag to 'Based-on-patch-from'
>>
>>  arch/arm64/crypto/sha1-ce-glue.c | 2 +-
>>  arch/arm64/crypto/sha2-ce-glue.c | 2 +-
>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/crypto/sha1-ce-glue.c b/arch/arm64/crypto/sha1-ce-glue.c
>> index aefda9868627..6b520e3f3ab1 100644
>> --- a/arch/arm64/crypto/sha1-ce-glue.c
>> +++ b/arch/arm64/crypto/sha1-ce-glue.c
>> @@ -18,7 +18,7 @@
>>  #include <linux/module.h>
>>
>>  #define ASM_EXPORT(sym, val) \
>> -       asm(".globl " #sym "; .set " #sym ", %0" :: "I"(val));
>> +       asm(".globl " #sym "; .set " #sym ", %c0" :: "i"(val));
>>
>>  MODULE_DESCRIPTION("SHA1 secure hash using ARMv8 Crypto Extensions");
>>  MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@linaro.org>");
>> diff --git a/arch/arm64/crypto/sha2-ce-glue.c b/arch/arm64/crypto/sha2-ce-glue.c
>> index 7cd587564a41..e3abe11de48c 100644
>> --- a/arch/arm64/crypto/sha2-ce-glue.c
>> +++ b/arch/arm64/crypto/sha2-ce-glue.c
>> @@ -18,7 +18,7 @@
>>  #include <linux/module.h>
>>
>>  #define ASM_EXPORT(sym, val) \
>> -       asm(".globl " #sym "; .set " #sym ", %0" :: "I"(val));
>> +       asm(".globl " #sym "; .set " #sym ", %c0" :: "i"(val));
>>
>>  MODULE_DESCRIPTION("SHA-224/SHA-256 secure hash using ARMv8 Crypto Extensions");
>>  MODULE_AUTHOR("Ard Biesheuvel <ard.biesheuvel@linaro.org>");
>> --
>> 2.12.2.715.g7642488e1d-goog
>>

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#1625497 — Re: [PATCH v2] crypto: arm64/sha: Add constant operand modifier to ASM_EXPORT

El Tue, Apr 18, 2017 at 04:35:02PM +0100 Ard Biesheuvel ha dit:

> On 18 April 2017 at 15:47, Paul Gortmaker <paul.gortmaker@windriver.com> wrote:
> > On Wed, Apr 5, 2017 at 2:34 PM, Matthias Kaehlcke <mka@chromium.org> wrote:
> >> The operand is an integer constant, make the constness explicit by
> >> adding the modifier. This is needed for clang to generate valid code
> >> and also works with gcc.
> >
> > Actually it doesn't work with all gcc.  I've got an older arm64 toolchain that I
> > only use for syntax checking (and hence I don't care if it is the latest and
> > greatest) and this commit breaks it:
> >
> > arch/arm64/crypto/sha1-ce-glue.c:21:2: error: invalid 'asm': invalid
> > operand prefix '%c'
> >   asm(".globl " #sym "; .set " #sym ", %c0" :: "i"(val));

Sorry about that :(

> > I'm currently reverting this change locally so I can continue to use the old
> > toolchain:
> >
> > $ aarch64-linux-gnu-gcc --version
> > aarch64-linux-gnu-gcc (crosstool-NG linaro-1.13.1-4.8-2013.12 - Linaro
> > GCC 2013.11) 4.8.3 20131202 (prerelease)
> > Copyright (C) 2013 Free Software Foundation, Inc.
> >
> > $ aarch64-linux-gnu-as --version
> > GNU assembler (crosstool-NG linaro-1.13.1-4.8-2013.12 - Linaro GCC
> > 2013.11) 2.24.0.20131220
> > Copyright 2013 Free Software Foundation, Inc.
> >
> > Maybe it is finally too old and nobody cares, but I thought it worth a mention.
> >
> 
> Thanks for the report. I think we care more about GCC 4.8 than about
> Clang, which argues for reverting this patch.

I agree, we certainly shouldn't break GCC.

> I understand these issues must be frustrating if you are working on
> this stuff, but to me, it is not entirely obvious why we want to
> support Clang in the first place (i.e., what does it buy you if your
> distro/environment is not already using Clang for userland),

There are environments that use Clang for userland, like Chrome OS or
Android. Debian releases with GCC, but also does Clang builds of most
of its repository: http://clang.debian.net/

I would also argue that Linux directly benefits from additional error
checks provided by Clang.

> and why the burden is on Linux to make modifications to support
> Clang, especially when it comes to GCC extensions such as inline
> assembly syntax.

Personally I'm on the pragmatic side. 99.9x% of the kernel already
builds with Clang (at least for arm64 and x86), only a very tiny
fraction of the code needs adaptation, which should ideally result in
the same code for gcc and clang. And it's not like Clang is just
another proprietary or niche compiler, it's the other big open source
compiler out there, since the effort is relatively small it seems
desirable to support it without out-of-tree patches. In parallel there
is also work ongoing with upstream Clang to improve compatiblity.

> It is ultimately up to the maintainers to decide what to do with this
> patch, but my vote would be to revert it, especially given that the %c
> placeholder prefix is not documented anywhere, and appears to simply
> trigger some GCC internals that happen to do the right thing in this
> case.
> 
> However, the I -> i change is arguably an improvement, and considering
> that the following
> 
> asm("foo: .long %0" :: "i"(some value))
> 
> doesn't compile with clang either, I suggest you (Matthias) file a bug
> against Clang to get this fixed, and we can propose another patch just
> for the I->i change.

Ok, I will see if we can get this fixed in Clang.

Thanks

Matthias

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#1629279 — Re: [PATCH v2] crypto: arm64/sha: Add constant operand modifier to ASM_EXPORT

On Tue, Apr 18, 2017 at 10:34:01AM -0700, Matthias Kaehlcke wrote:
> El Tue, Apr 18, 2017 at 04:35:02PM +0100 Ard Biesheuvel ha dit:
> 
> > On 18 April 2017 at 15:47, Paul Gortmaker <paul.gortmaker@windriver.com> wrote:
> > > On Wed, Apr 5, 2017 at 2:34 PM, Matthias Kaehlcke <mka@chromium.org> wrote:
> > >> The operand is an integer constant, make the constness explicit by
> > >> adding the modifier. This is needed for clang to generate valid code
> > >> and also works with gcc.
> > >
> > > Actually it doesn't work with all gcc.  I've got an older arm64 toolchain that I
> > > only use for syntax checking (and hence I don't care if it is the latest and
> > > greatest) and this commit breaks it:
> > >
> > > arch/arm64/crypto/sha1-ce-glue.c:21:2: error: invalid 'asm': invalid
> > > operand prefix '%c'
> > >   asm(".globl " #sym "; .set " #sym ", %c0" :: "i"(val));
> 
> Sorry about that :(

So what's the consensus? Should I revert this patch?

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

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#1629281

On 24 April 2017 at 09:00, Herbert Xu <herbert@gondor.apana.org.au> wrote:
> On Tue, Apr 18, 2017 at 10:34:01AM -0700, Matthias Kaehlcke wrote:
>> El Tue, Apr 18, 2017 at 04:35:02PM +0100 Ard Biesheuvel ha dit:
>>
>> > On 18 April 2017 at 15:47, Paul Gortmaker <paul.gortmaker@windriver.com> wrote:
>> > > On Wed, Apr 5, 2017 at 2:34 PM, Matthias Kaehlcke <mka@chromium.org> wrote:
>> > >> The operand is an integer constant, make the constness explicit by
>> > >> adding the modifier. This is needed for clang to generate valid code
>> > >> and also works with gcc.
>> > >
>> > > Actually it doesn't work with all gcc.  I've got an older arm64 toolchain that I
>> > > only use for syntax checking (and hence I don't care if it is the latest and
>> > > greatest) and this commit breaks it:
>> > >
>> > > arch/arm64/crypto/sha1-ce-glue.c:21:2: error: invalid 'asm': invalid
>> > > operand prefix '%c'
>> > >   asm(".globl " #sym "; .set " #sym ", %c0" :: "i"(val));
>>
>> Sorry about that :(
>
> So what's the consensus? Should I revert this patch?
>

Yes please.

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#1629288 — Re: [PATCH v2] crypto: arm64/sha: Add constant operand modifier to ASM_EXPORT

On Mon, Apr 24, 2017 at 09:04:19AM +0100, Ard Biesheuvel wrote:
>
> Yes please.

OK, patch reverted.

Thanks,
-- 
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

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