From: Nicholas Piggin <npiggin@gmail•com>
To: Daniel Axtens <dja@axtens•net>,
Segher Boessenkool <segher@kernel•crashing.org>
Cc: llvmlinux@lists•linuxfoundation.org, linuxppc-dev@lists•ozlabs.org
Subject: Re: [RFC PATCH 4/8] powerpc/ppc_asm: use plain numbers for registers
Date: Fri, 19 Mar 2021 11:39:05 +1000 [thread overview]
Message-ID: <1616117795.mys33l8084.astroid@bobo.none> (raw)
In-Reply-To: <87tupzoffb.fsf@dja-thinkpad.axtens.net>
Excerpts from Daniel Axtens's message of February 26, 2021 10:12 am:
> Segher Boessenkool <segher@kernel•crashing.org> writes:
>
>> On Thu, Feb 25, 2021 at 02:10:02PM +1100, Daniel Axtens wrote:
>>> This is dumb but makes the llvm integrated assembler happy.
>>> https://github.com/ClangBuiltLinux/linux/issues/764
>>
>>> -#define r0 %r0
>>
>>> +#define r0 0
>>
>> This is a big step back (compare 9a13a524ba37).
>>
>> If you use a new enough GAS, you can use the -mregnames option and just
>> say "r0" directly (so not define it at all, or define it to itself).
>>
>> ===
>> addi 3,3,3
>> addi r3,r3,3
>> addi %r3,%r3,3
>>
>> addi 3,3,3
>> addi r3,r3,r3
>> addi %r3,%r3,%r3
>> ===
>>
>> $ as t.s -o t.o -mregnames
>> t.s: Assembler messages:
>> t.s:6: Warning: invalid register expression
>> t.s:7: Warning: invalid register expression
>>
>>
>> Many people do not like bare numbers. It is a bit like not wearing
>> seatbelts (but so is all assembler code really: you just have to pay
>> attention). A better argument is that it is harder to read for people
>> not used to assembler code like this.
>>
>> We used to have "#define r0 0" etc., and that was quite problematic.
>> Like that "addi r3,r3,r3" example, but also, people wrote "r0" where
>> only a plain 0 is allowed (like in "lwzx r3,0,r3": "r0" would be
>> misleading there!)
>
> So an overarching comment on all of these patches is that they're not
> intended to be ready to merge, nor are they necessarily what I think is
> the best solution. I'm just swinging a big hammer to see how far towards
> LLVM_IAS=1 I can get on powerpc, and I accept I'm going to have to come
> back and clean things up.
>
> Anyway, noted, I'll push harder on trying to get llvm to accept %rN:
> there was a patch that went in after llvm-11 that should help.
If you put it under ifdef CONFIG_CC_IS_CLANG in the meantime I think
that would be okay. Then we get error checking with gcc compiles and
llvm at least builds with its assembler which would be nice.
Thanks,
Nick
next prev parent reply other threads:[~2021-03-19 1:39 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-25 3:09 [RFC PATCH 0/8] WIP support for the LLVM integrated assembler Daniel Axtens
2021-02-25 3:09 ` [PATCH 1/8] powerpc/64s/exception: Clean up a missed SRR specifier Daniel Axtens
2021-02-25 3:10 ` [RFC PATCH 2/8] powerpc: check for support for -Wa,-m{power4,any} Daniel Axtens
2021-03-19 1:32 ` [RFC PATCH 2/8] powerpc: check for support for -Wa, -m{power4, any} Nicholas Piggin
2021-03-19 10:53 ` Michael Ellerman
2021-02-25 3:10 ` [RFC PATCH 3/8] powerpc/head-64: do less gas-specific stuff with sections Daniel Axtens
2021-03-19 1:35 ` Nicholas Piggin
2021-02-25 3:10 ` [RFC PATCH 4/8] powerpc/ppc_asm: use plain numbers for registers Daniel Axtens
2021-02-25 15:25 ` Segher Boessenkool
2021-02-26 0:12 ` Daniel Axtens
2021-03-19 1:39 ` Nicholas Piggin [this message]
2021-02-25 3:10 ` [RFC PATCH 5/8] poweprc/lib/quad: Provide macros for lq/stq Daniel Axtens
2021-02-25 15:44 ` Segher Boessenkool
2021-02-26 0:13 ` Daniel Axtens
2021-02-25 3:10 ` [RFC PATCH 6/8] powerpc/mm/book3s64/hash: drop pre 2.06 tlbiel for clang Daniel Axtens
2021-03-19 2:01 ` Nicholas Piggin
2021-03-22 16:49 ` Christophe Leroy
2021-03-22 18:11 ` Nicholas Piggin
2021-03-24 15:51 ` Segher Boessenkool
2021-03-24 21:07 ` Segher Boessenkool
2021-02-25 3:10 ` [RFC PATCH 7/8] powerpc/purgatory: drop .machine specifier Daniel Axtens
2021-02-25 15:58 ` Segher Boessenkool
2021-02-26 0:17 ` Daniel Axtens
2021-03-19 2:05 ` Nicholas Piggin
2021-03-19 10:59 ` Michael Ellerman
2021-02-25 3:10 ` [RFC PATCH 8/8] powerpc/64/asm: don't reassign labels Daniel Axtens
2021-02-25 16:08 ` Segher Boessenkool
2021-02-26 0:28 ` Daniel Axtens
2021-03-19 2:15 ` Nicholas Piggin
2021-03-14 10:01 ` [RFC PATCH 0/8] WIP support for the LLVM integrated assembler Michael Ellerman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1616117795.mys33l8084.astroid@bobo.none \
--to=npiggin@gmail$(echo .)com \
--cc=dja@axtens$(echo .)net \
--cc=linuxppc-dev@lists$(echo .)ozlabs.org \
--cc=llvmlinux@lists$(echo .)linuxfoundation.org \
--cc=segher@kernel$(echo .)crashing.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox