llvm dev - Jun 2011 - [LLVMdev] ARM thumb-2 instruction used for non-thumb2 CPUs

On Jun 22, 2011, at 8:39 AM, Damjan Marion wrote:
> 
> On Jun 22, 2011, at 5:29 PM, Jim Grosbach wrote:
> 
>> 
>> On Jun 22, 2011, at 7:22 AM, Renato Golin wrote:
>> 
>>> On 22 June 2011 14:33, Damjan Marion <damjan.marion at
gmail.com> wrote:
>>>> Problem is that in case when old binutils are used (in my case
freebsd is using old one due to license upgrade to GPLv3) AS doesn't
understand new mnemonics and fails.
>>> 
>>> Indeed, this is new in ARM ARM v7.
>>> 
>>> 
>>>> Can we change to old mnemonic at least when ARMv4 and ARMv5
code is generated?
>>> 
>>> We definitely should. Feel free to send a patch if you already
have,
>>> or create a bug in bugzilla. Shouldn't be too hard to add it.
>> 
>> LLVM always uses unified syntax, including updated mnemonics for older
instructions. Older binutils aren't supported. This is unlikely to change.
>> 
> 
> This sounds like a dead end as newer binutils are GPLv3.
Yeah, that's definitely a very real concern and a big motivation to get the
MC based asm parser whipped into usable shape. We're much more in control of
our own destiny then.
> What is the status of integrated-as for arm, is it stable?

The encoding information in the back end is generally in pretty decent shape for
direct object file emission. Some of the folks working on the ELF emitter would
be better able to tell you how that part of the things is working. The asm
parser, on the other hand, is still in pretty rough shape.

That said, I'm hoping to get back to that stuff near future, so it's
still under active development.

-Jim

On 22 June 2011 16:50, Jim Grosbach <grosbach at apple.com>
wrote:
>> This sounds like a dead end as newer binutils are GPLv3.
>
> Yeah, that's definitely a very real concern and a big motivation to get
the MC based asm parser whipped into usable shape. We're much more in
control of our own destiny then.
So, how do we solve the problem until then?

cheers,
--renato

On Jun 22, 2011, at 9:00 AM, Renato Golin wrote:
> On 22 June 2011 16:50, Jim Grosbach <grosbach at apple.com> wrote:
>>> This sounds like a dead end as newer binutils are GPLv3.
>> 
>> Yeah, that's definitely a very real concern and a big motivation to
get the MC based asm parser whipped into usable shape. We're much more in
control of our own destiny then.
> 
> So, how do we solve the problem until then?
In general, it's a tricky thing. If it were only a few instructions, we
could just switch to the older mnemonic as a special case w/ a FIXME saying that
we should change it when newer assemblers become available on FreeBSD.
That's unfortunately not really the case, though. For example, all of the
VFP instructions use newer mnemonics, and the predicated condition code setting
arithmetic instructions have changed the order of the 's' and
'cc' suffices (e.g., addseq vs. addeqs).

I suspect we'll care about all of them, as we're wanting to handle
userspace apps, not just kernel code, here, right? This is the system assembler
that's too old.

If so, the best answer is to teach the assembler the new mnemonics. To help with
that, the majority of the work for v7 was released under GPLv2, even though it
didn't make it into an official binutils release until post-v3 changeover.
There are GPLv2 CodeSourcery drops which contain v7 support, for example,
including binutils support for unified syntax. While there are some bugs (Anton
can probably give more details), they do generally work and would likely provide
a good starting point so that the support wouldn't have to be done from
scratch.

-Jim