doc asm feature - Added new 'Label' section with example and explanations

[tdelabro]

Fixes #76704

[rust-highfive]

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[tdelabro]

@Amanieu

https://github.com/rust-lang/rust/pull/84015/checks?check_run_id=2305123299

It seems to me that the asm! block are converted to the AT&T asm syntax, while we are using the intel one all along the documentation, making it unable to recognise the used symbols.

[Amanieu]

Ouch, I thought that bug was fixed in LLVM 10. It seems that it is only fixed in 10.0.1, which our CI doesn't have. So we may have to add allow_fail back to make CI pass.

[Amanieu]

Can you run the examples manually on the playground to ensure they work with the nightly compiler?

[Amanieu]

Note that the issue here is that LLVM is incorrectly adding % to register names even though we have told it to use Intel syntax. This is fixed in LLVM 10.0.1.

[tdelabro]

So, I built the doc locally, opened it in my browser and ran each example by clicking on the play arrow. They all worked fine.

I have added the allow_fail flags back. It should pass the CI now.

[Amanieu]

@bors r+ rollup

[bors]

📌 Commit 1f7de3f has been approved by Amanieu

[tdelabro]

This is my first PR to the rust repo so I'm unsure: is there something I'm expected to do before we merge this PR ?

[bors]

⌛ Testing commit 1f7de3f with merge dbcf345...

[bors]

☀️ Test successful - checks-actions
Approved by: Amanieu
Pushing dbcf345 to master...

[Amanieu]

This is my first PR to the rust repo so I'm unsure: is there something I'm expected to do before we merge this PR ?

Nope! Once the pull request is approved with r+, bors will automatically merge it after running tests.

[tdelabro]

Nice ! Thanks for you help and review !