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Re: [PATCHv2, MIPS] Add support for O32 FPXX and program header based ABI information
- From: Richard Sandiford <rdsandiford at googlemail dot com>
- To: "Joseph S. Myers" <joseph at codesourcery dot com>
- Cc: Matthew Fortune <Matthew dot Fortune at imgtec dot com>, Will Newton <will dot newton at linaro dot org>, Andrew Pinski <pinskia at gmail dot com>, Rich Fuhler <Rich dot Fuhler at imgtec dot com>, "macro\ at codesourcery dot com" <macro at codesourcery dot com>, "libc-alpha\ at sourceware dot org" <libc-alpha at sourceware dot org>
- Date: Mon, 02 Jun 2014 18:43:49 +0100
- Subject: Re: [PATCHv2, MIPS] Add support for O32 FPXX and program header based ABI information
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"Joseph S. Myers" <joseph@codesourcery.com> writes:
> On Sun, 25 May 2014, Richard Sandiford wrote:
>
>> "Joseph S. Myers" <joseph@codesourcery.com> writes:
>> > On Fri, 16 May 2014, Matthew Fortune wrote:
>> >
>> >> I don't understand the use-case that would want a whole module (and/or
>> >> subset of modules within one library) to freely deploy an ISA extension
>> >> but have no overall marking to that extent. Such global enablement must be
>> >
>> > It's the most basic, obvious, longstanding way of using an ISA feature
>> > conditionally: compile different source files with different options and
>> > then use "if" conditionals to choose between them.
>>
>> The MIPS toolchain has never worked like that AFAIK. Command-line options
>> decide the ABI of the TU and only compatible TUs can be linked together.
>> The ABI of the output reflects all requirements of the input TUs.
>> I think that's the natural behaviour for an architecture with as many
>> variations as MIPS.
>
> Linking objects built -mdsp and -mno-dsp, or -march=mips32r2 and
> -march=mips64r2, works for me. The result does get marked as having the
> appropriate superset instruction set
Right, that's I was trying to say.
> - are you saying there is some existing Solaris-style check somewhere
> (where?) that disallows such a combination from executing on hardware
> lacking the features for all of the objects, even if the relevant
> instructions are only executed conditionally? Or that some other
> combinations get disallowed at static link time?
No, I was arguing that taking the superset was the right behaviour.
You seemed to be saying that we should allow -mmsa to be used for
individual objects without marking the linked output as -mmsa
(because the functions in the -mmsa input object might all be
protected by a runtime check for MSA).
In other words, I was saying -mmsa and -mno-msa should work in the
same way as -mdsp and -mno-dsp: the output is marked as MSA if one
input was compiled with -mmsa.
Thanks,
Richard