From: Michael Ellerman <mpe@ellerman.id.au>
To: Bill Wendling <morbo@google.com>
Cc: Nick Desaulniers <ndesaulniers@google.com>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v3 3/3] powerpc/64s: feature: Work around inline asm issues
Date: Fri, 27 Nov 2020 12:03:38 +1100 [thread overview]
Message-ID: <87ft4vy5jp.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <CAGG=3QUSF4UwcZQHhFE-PW6As7GVJknsyGkgVMENDXghABzy5A@mail.gmail.com>
Bill Wendling <morbo@google.com> writes:
> On Mon, Nov 23, 2020 at 7:44 PM Michael Ellerman <mpe@ellerman.id.au> wrote:
>> Bill Wendling <morbo@google.com> writes:
>> > On Mon, Nov 23, 2020 at 12:10 PM Segher Boessenkool
>> > <segher@kernel.crashing.org> wrote:
>> >> On Mon, Nov 23, 2020 at 12:01:01PM -0800, Bill Wendling wrote:
>> >> > On Mon, Nov 23, 2020 at 11:58 AM Segher Boessenkool
>> >> > <segher@kernel.crashing.org> wrote:
>> >> > > > On Sun, Nov 22, 2020 at 10:36 PM Segher Boessenkool
>> >> > > > <segher@kernel.crashing.org> wrote:
>> >> > > > > "true" (as a result of a comparison) in as is -1, not 1.
>> >> > >
>> >> > > On Mon, Nov 23, 2020 at 11:43:11AM -0800, Bill Wendling wrote:
>> >> > > > What Segher said. :-) Also, if you reverse the comparison, you'll get
>> >> > > > a build error.
>> >> > >
>> >> > > But that means your patch is the wrong way around?
>> >> > >
>> >> > > - .ifgt (label##4b- label##3b)-(label##2b- label##1b); \
>> >> > > - .error "Feature section else case larger than body"; \
>> >> > > - .endif; \
>> >> > > + .org . - ((label##4b-label##3b) > (label##2b-label##1b)); \
>> >> > >
>> >> > > It should be a + in that last line, not a -.
>> >> >
>> >> > I said so in a follow up email.
>> >>
>> >> Yeah, and that arrived a second after I pressed "send" :-)
>> >>
>> > Michael, I apologize for the churn with these patches. I believe the
>> > policy is to resend the match as "v4", correct?
>> >
>> > I ran tests with the change above. It compiled with no error. If I
>> > switch the labels around to ".org . + ((label##2b-label##1b) >
>> > (label##4b-label##3b))", then it fails as expected.
>>
>> I wanted to retain the nicer error reporting for gcc builds, so I did it
>> like this:
>>
>> diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h
>> index b0af97add751..c4ad33074df5 100644
>> --- a/arch/powerpc/include/asm/feature-fixups.h
>> +++ b/arch/powerpc/include/asm/feature-fixups.h
>> @@ -36,6 +36,24 @@ label##2: \
>> .align 2; \
>> label##3:
>>
>> +
>> +#ifndef CONFIG_CC_IS_CLANG
>> +#define CHECK_ALT_SIZE(else_size, body_size) \
>> + .ifgt (else_size) - (body_size); \
>> + .error "Feature section else case larger than body"; \
>> + .endif;
>> +#else
>> +/*
>> + * If we use the ifgt syntax above, clang's assembler complains about the
>> + * expression being non-absolute when the code appears in an inline assembly
>> + * statement.
>> + * As a workaround use an .org directive that has no effect if the else case
>> + * instructions are smaller than the body, but fails otherwise.
>> + */
>> +#define CHECK_ALT_SIZE(else_size, body_size) \
>> + .org . + ((else_size) > (body_size));
>> +#endif
>> +
>> #define MAKE_FTR_SECTION_ENTRY(msk, val, label, sect) \
>> label##4: \
>> .popsection; \
>> @@ -48,9 +66,7 @@ label##5: \
>> FTR_ENTRY_OFFSET label##2b-label##5b; \
>> FTR_ENTRY_OFFSET label##3b-label##5b; \
>> FTR_ENTRY_OFFSET label##4b-label##5b; \
>> - .ifgt (label##4b- label##3b)-(label##2b- label##1b); \
>> - .error "Feature section else case larger than body"; \
>> - .endif; \
>> + CHECK_ALT_SIZE((label##4b-label##3b), (label##2b-label##1b)); \
>> .popsection;
>>
>>
>>
>> I've pushed a branch with all your patches applied to:
>>
>> https://github.com/linuxppc/linux/commits/next-test
>>
> This works for me. Thanks!
Great.
>> Are you able to give that a quick test? It builds clean with clang for
>> me, but we must be using different versions of clang because my branch
>> already builds clean for me even without your patches.
>>
> You may need to set LLVM_IAS=1 to get the behavior I'm seeing. That
> turns on clang's integrated assembler, which I think is disabled by
> default.
Yep that does it.
But then I get:
clang: error: unsupported argument '-mpower4' to option 'Wa,'
clang: error: unsupported argument '-many' to option 'Wa,'
So I guess I'm still missing something?
> Note that with clang's integrated assembler, arch/powerpc/boot/util.S
> fails to compile. Alan Modra mentioned that he sent you a patch to
> "modernize" the file so that clang can compile it.
Ah you're right he did, it didn't go to patchwork so I missed it. Have
grabbed it now.
cheers
next prev parent reply other threads:[~2020-11-27 1:05 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-17 0:47 [PATCH 0/2] Fixes for clang/lld Bill Wendling
2020-10-17 0:47 ` [PATCH 1/2] powerpc/wrapper: Add "-z notext" flag to disable diagnostic Bill Wendling
2020-10-17 0:47 ` [PATCH 2/2] powerpc/boot: Use clang when CC is clang Bill Wendling
2020-11-18 22:35 ` [PATCH 0/3] PPC: fixes for clang support Bill Wendling
2020-11-20 22:40 ` [PATCH v3 " Bill Wendling
2020-11-20 22:40 ` [PATCH 1/3] powerpc/wrapper: add "-z notext" flag to disable diagnostic Bill Wendling
2020-11-20 22:40 ` [PATCH v3 2/3] powerpc/boot: Use clang when CC is clang Bill Wendling
2020-11-20 22:40 ` [PATCH v3 3/3] powerpc/64s: feature: Work around inline asm issues Bill Wendling
2020-11-23 5:44 ` Michael Ellerman
2020-11-23 6:34 ` Segher Boessenkool
2020-11-23 19:43 ` Bill Wendling
2020-11-23 19:53 ` Bill Wendling
2020-11-23 19:56 ` Segher Boessenkool
2020-11-23 20:01 ` Bill Wendling
2020-11-23 20:08 ` Segher Boessenkool
2020-11-23 20:17 ` Bill Wendling
2020-11-24 3:43 ` Michael Ellerman
2020-11-25 5:13 ` Bill Wendling
2020-11-27 1:03 ` Michael Ellerman [this message]
2020-11-27 1:10 ` Bill Wendling
2020-11-27 1:59 ` Bill Wendling
2020-11-18 22:35 ` [PATCH 1/3] powerpc/wrapper: add "-z notext" flag to disable diagnostic Bill Wendling
2020-11-18 22:35 ` [PATCH 2/3] powerpc/boot: Use clang when CC is clang Bill Wendling
2020-11-18 22:35 ` [PATCH 3/3] powerpc/64s: feature: work around inline asm issues Bill Wendling
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