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inline assembly register limits aren't correct when using instruction_set attribute #92378

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Lokathor opened this issue Dec 28, 2021 · 1 comment · Fixed by #94169
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inline assembly register limits aren't correct when using instruction_set attribute #92378

Lokathor opened this issue Dec 28, 2021 · 1 comment · Fixed by #94169
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A-inline-assembly Area: inline asm!(..) C-bug Category: This is a bug. F-asm `#![feature(asm)]` (not `llvm_asm`) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@Lokathor
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First discussed on zulip.

Quick summary: the set of what registers are available for inline assembly is related to the current target arch. However, the instruction_set attribute lets a function be compiled for what's effectively an alternate arch. This should allow the other arch's registers to be used, but currently that's not the case.

  • Specifically for ARM a32/t32, the thumb-mode target attribute is either not present (a32) or present (t32) in the target, and using the instruction_set attribute lets you have the opposite mode.
  • Note: The actual assembly code is already compiled correctly on LLVM's side, it's just that rustc gives you the incorrect register class limits.

Quoting Amanieu's Zulip post on the probable fix for this:

You'd need to somehow remove the thumb-mode target feature from the list passed to the asm handling code in ast_lowering and intrinsicck when the containing function uses the a32 ISA.
@Lokathor Lokathor added the C-bug Category: This is a bug. label Dec 28, 2021
@BGR360
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BGR360 commented Dec 29, 2021

@rustbot label +A-inline-assembly +F-asm +T-compiler

@rustbot rustbot added A-inline-assembly Area: inline asm!(..) F-asm `#![feature(asm)]` (not `llvm_asm`) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Dec 29, 2021
@Amanieu Amanieu mentioned this issue Feb 19, 2022
Merged
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Feb 20, 2022
@matthiaskrgr
Rollup merge of rust-lang#94169 - Amanieu:asm_stuff, r=nagisa
fd448d5 
Fix several asm! related issues

This is a combination of several fixes, each split into a separate commit. Splitting these into PRs is not practical since they conflict with each other.

Fixes rust-lang#92378
Fixes rust-lang#85247

r? `@nagisa`
Manishearth added a commit to Manishearth/rust that referenced this issue Feb 20, 2022
@Manishearth
Rollup merge of rust-lang#94169 - Amanieu:asm_stuff, r=nagisa
97abac2 
Fix several asm! related issues

This is a combination of several fixes, each split into a separate commit. Splitting these into PRs is not practical since they conflict with each other.

Fixes rust-lang#92378
Fixes rust-lang#85247

r? ``@nagisa``
matthiaskrgr added a commit to matthiaskrgr/rust that referenced this issue Feb 22, 2022
@matthiaskrgr
Rollup merge of rust-lang#94169 - Amanieu:asm_stuff, r=nagisa
fa60d8d 
Fix several asm! related issues

This is a combination of several fixes, each split into a separate commit. Splitting these into PRs is not practical since they conflict with each other.

Fixes rust-lang#92378
Fixes rust-lang#85247

r? `@nagisa`
@bors bors closed this as completed in 1cf2e69 Feb 22, 2022
bjorn3 pushed a commit to bjorn3/rust that referenced this issue Feb 23, 2022
@matthiaskrgr
Rollup merge of rust-lang#94169 - Amanieu:asm_stuff, r=nagisa
a063e13 
Fix several asm! related issues

This is a combination of several fixes, each split into a separate commit. Splitting these into PRs is not practical since they conflict with each other.

Fixes rust-lang#92378
Fixes rust-lang#85247

r? ``@nagisa``
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A-inline-assembly Area: inline asm!(..) C-bug Category: This is a bug. F-asm `#![feature(asm)]` (not `llvm_asm`) T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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Fix several asm! related issues Amanieu/rust
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@Lokathor @BGR360 @rustbot