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Re: [WWWDocs] Deprecate support for non-thumb ARM devices
- From: "Richard Earnshaw (lists)" <Richard dot Earnshaw at arm dot com>
- To: Stefan Ring <stefanrin at gmail dot com>
- Cc: Joseph Myers <joseph at codesourcery dot com>, gcc-patches <gcc-patches at gcc dot gnu dot org>, gcc at gcc dot gnu dot org, Ramana Radhakrishnan <Ramana dot Radhakrishnan at arm dot com>, Kyrylo Tkachov <Kyrylo dot Tkachov at arm dot com>, "nickc at redhat dot com" <nickc at redhat dot com>
- Date: Thu, 25 Feb 2016 14:06:29 +0000
- Subject: Re: [WWWDocs] Deprecate support for non-thumb ARM devices
- Authentication-results: sourceware.org; auth=none
- References: <56CDB728 dot 1050300 at arm dot com> <alpine dot DEB dot 2 dot 10 dot 1602241734510 dot 27089 at digraph dot polyomino dot org dot uk> <56CEC761 dot 3060204 at arm dot com> <CAAxjCEyoF+bs2njh_oi7oNHkkddN9AVSPecgQVsKygbeNmrBPw at mail dot gmail dot com>
On 25/02/16 13:32, Stefan Ring wrote:
> On Thu, Feb 25, 2016 at 10:20 AM, Richard Earnshaw (lists)
> <Richard.Earnshaw@arm.com> wrote:
>> The point is to permit the compiler to use interworking compatible
>> sequences of code when generating ARM code, not to force users to use
>> Thumb code. The necessary instruction (BX) is available in armv5 and
>> armv5e, even though Thumb is not supported in those architecture variants.
>> It might be worth deprecating v5 and v5e at some point in the future: to
>> the best of my knowledge no v5 class device without Thumb has ever
>> existed - but it's not a decision that needs to be related to this proposal.
> Slightly off topic, but related: What does the "e" stand for? Also,
> what does "l" stand for in armv5tel, which is what I usually get --
> little endian?
The 'e' represented some extensions to the original v5 ISA (you can make
your own mind up as to what the 'e' stands for).
The 'l' isn't anything to do with the architecture per-se. It simply
means in the Linux context a little-endian device, as opposed to a
'b'ig-endian device. Most ARM based systems are little-endian so you'll
see that far more often than 'b'.
> I have no idea if there is an authoritative source for these host
> specifications and cannot find any. config.guess seems to just rely on
> uname -m.
For the AArch32 it's extremely ad-hoc. There's a bit more sanity in the
AArch64 world, but it relies on people following some conventions and
not just creating anarchy.