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Add support for ARMv5TE architecture #37615

Merged
merged 2 commits into from
Nov 12, 2016
Merged

Add support for ARMv5TE architecture #37615

merged 2 commits into from
Nov 12, 2016

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atilag
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@atilag atilag commented Nov 6, 2016

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Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nrc (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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japaric commented Nov 6, 2016

r? @alexcrichton

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japaric reviewed Nov 6, 2016
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src/librustc_back/target/armv5te_unknown_linux_gnueabi.rs

options: TargetOptions {
features: "+soft-float".to_string(),
max_atomic_width: Some(64),
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LLVM can't lower atomic stuff to actual ARMv5 instructions because there are no instructions in the instruction set to implement atomics. This is going to require something like rust-lang/compiler-builtins#115

cc @Amanieu

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Even with my PR the maximum atomic width would be 32 bits, not 64 bits.

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cc @rust-lang/tools, thoughts on adding a new target?

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Thanks for the PR @atilag! Could you also expand a bit on your use case for this target and why you'd like to see it in the compiler itself? (as opposed to using custom target specs)

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Amanieu commented Nov 7, 2016

Another question is, should we also add support for ARMv4T as a target? This is the minimum architecture that Debian armel requires.

@atilag
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atilag commented Nov 7, 2016 •
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Hi guys!
Well, me and me colleagues were trying to build a project around a hardware that, despite of being a little oldish, seems to be still very common in IoT based products. We could use other technologies, like C/C++ of course, but our experience in Rust is being very positive and we would love to keep using it and prove that Rust is a valid option even for these elderly platforms. We don't have special desires to include it as part of the compiler, so maybe using a custom target would work for us, but, is there any strong reason to not include it?
Thanks guys!
Keep up the good work!

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japaric commented Nov 7, 2016

@alexcrichton

Not the OP but if they are building std programs then having the target in-tree + binary releases of std is the most ergonomic option until we get std-aware Cargo. Or, IOW, compiling std for custom targets is a pain in the neck.

@Amanieu

Do you know for how long does Debian intent to provide ARMv4+ support?

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Indeed we are building std programs (the OS is Linux), so having an in-tree target helps.

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Amanieu commented Nov 7, 2016

@japaric I don't think Debian has any intention of dropping armel any time soon. Debian currently supports only two ARM variants: armel (ARMv4t+, soft float) and armhf (ARMv7+, hard float).

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atilag commented Nov 7, 2016

@japaric @Amanieu @Amanieu so I have updated the max_atomic_width to 32 bits. I guess that we need to merge rust-lang/compiler-builtins#115 before merging this one, right?

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japaric commented Nov 7, 2016

@atilag #36992 would have to land as well.

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Amanieu commented Nov 7, 2016

We also need to decide whether we want to support ARMv4T, ARMv5TE, or both.

@atilag
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atilag commented Nov 8, 2016

@Amanieu I guess that in case we need to support ARMv4T, this could be done in another PR.
My understanding is that supporting ARMv5TE would only increase the added value of the language, so the question would be whether there's any drawback that outperforms this support. If we don't want to deal with a potential instability because of the atomic support, is there any way to mark this support as "unstable" or "experimental" ?

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Thanks for the explanation @atilag! I think we should hold off on armv4 here and perhaps add that in a future PR (if at all).

If ARMv5 doesn't have atomic instructions, though, then the current stance of the libs team is to set the max_atomic_width field to Some(0) as we can't actually create any instructions there. The fallbacks in compiler-builtins are intended to be optional for other use cases, if needed. We haven't figured out a great story yet, unfortunately, for pulling in those intrinsics on demand.

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@bors: r+

Thanks @atilag! cc @rust-lang/tools, a new target, but not necessarily libstd support just yet

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bors commented Nov 10, 2016

📌 Commit 365ea80 has been approved by alexcrichton

@brson brson added the relnotes Marks issues that should be documented in the release notes of the next release. label Nov 11, 2016
eddyb added a commit to eddyb/rust that referenced this pull request Nov 11, 2016
@eddyb
Rollup merge of rust-lang#37615 - atilag:armv5te-support, r=alexcrichton
df060c4 
Add support for ARMv5TE architecture
@eddyb eddyb mentioned this pull request Nov 11, 2016
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eddyb added a commit to eddyb/rust that referenced this pull request Nov 12, 2016
@eddyb
Rollup merge of rust-lang#37615 - atilag:armv5te-support, r=alexcrichton
8d2da2b 
Add support for ARMv5TE architecture
@eddyb eddyb mentioned this pull request Nov 12, 2016
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bors added a commit that referenced this pull request Nov 12, 2016
@bors
Auto merge of #37730 - eddyb:rollup, r=eddyb
f3af8c8 
Rollup of 30 pull requests

- Successful merges: #37190, #37368, #37481, #37503, #37527, #37535, #37551, #37584, #37600, #37613, #37615, #37659, #37662, #37669, #37682, #37688, #37690, #37692, #37693, #37694, #37695, #37696, #37698, #37699, #37705, #37708, #37709, #37716, #37724, #37727
- Failed merges: #37640, #37689, #37717
@bors bors merged commit 365ea80 into rust-lang:master Nov 12, 2016
@malbarbo malbarbo mentioned this pull request Dec 26, 2017
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bors added a commit that referenced this pull request Dec 28, 2017
@bors
Auto merge of #47018 - malbarbo:armv4t, r=alexcrichton
9a8c753 
Add armv4t-unknown-linux-gnueabi target

armv4t was left out of #37615 (armv5te addition) to be included in a [future PR](#37615 (comment)).  So this PR adds armv4t target.

armv4t target is useful because the [armel](https://wiki.debian.org/ArmEabiPort) port of Debian targets armv4t
@davidtwco davidtwco mentioned this pull request Sep 20, 2023
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@atilag @rust-highfive @japaric @alexcrichton @Amanieu @fabricedesre @bors @brson @nrc