Add reference for asm-goto #1693
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89 tasks
ehuss
added
S-waiting-on-stabilization
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@Amanieu: What do you think? |
Amanieu
reviewed
Dec 12, 2024
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@rustbot author |
rustbot
added
S-waiting-on-author
40 tasks
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We reviewed this in the lang call today. Everyone read through it. It looked right. Nobody had any notes. |
The asm-goto-with-outputs is still unstable, so in the reference it's still mentioned as forbidden by a check rule.
traviscross
reviewed
Dec 23, 2024
| @@ -180,6 +180,13 @@ r[asm.operand-type.supported-operands.sym] | |||
| - The type of the expression may be any integer type, but defaults to `i32` just like integer literals. | |||
| - The value of the expression is formatted as a string and substituted directly into the asm template string. | |||
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| r[asm.operand-type.supported-operands.label] | |||
| * `label <block>` | |||
| - The address of the block is substituted into the asm template string. The assembly block may jump to the substituted addresses. | |||
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Suggested change
| - The address of the block is substituted into the asm template string. The assembly block may jump to the substituted addresses. | |
| - The address of the block is substituted into the asm template string. The assembly block may jump to the substituted address. |
| - The address of the block is substituted into the asm template string. The assembly block may jump to the substituted addresses. | ||
| - After execution of the block, the `asm!` expression returns. | ||
| - The type of the block must be unit or `!` (never). | ||
| - The block starts new safety context; despite the outer `unsafe` needed for `asm!`, you need an extra `unsafe` to perform unsafe operations inside the block. |
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Suggested change
| - The block starts new safety context; despite the outer `unsafe` needed for `asm!`, you need an extra `unsafe` to perform unsafe operations inside the block. | |
| - The block starts a new safety context; despite the outer `unsafe` block needed for `asm!`, unsafe operations within the `label` block must be wrapped in an inner `unsafe` block. |
| @@ -553,6 +560,8 @@ r[asm.options.supported-options.noreturn] | |||
| - `noreturn`: The `asm!` block never returns, and its return type is defined as `!` (never). | |||
| Behavior is undefined if execution falls through past the end of the asm code. | |||
| A `noreturn` asm block behaves just like a function which doesn't return; notably, local variables in scope are not dropped before it is invoked. | |||
| - When labels are present, `noreturn` means the execution of the `asm!` block never falls through; the asm block may only exit by jumping to one of the specified blocks. | |||
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Suggested change
| - When labels are present, `noreturn` means the execution of the `asm!` block never falls through; the asm block may only exit by jumping to one of the specified blocks. | |
| - When one or more `label` blocks are present, `noreturn` means the execution of the `asm!` block never falls through; the asm block may only exit by jumping to one of the specified blocks. |
| @@ -553,6 +560,8 @@ r[asm.options.supported-options.noreturn] | |||
| - `noreturn`: The `asm!` block never returns, and its return type is defined as `!` (never). | |||
| Behavior is undefined if execution falls through past the end of the asm code. | |||
| A `noreturn` asm block behaves just like a function which doesn't return; notably, local variables in scope are not dropped before it is invoked. | |||
| - When labels are present, `noreturn` means the execution of the `asm!` block never falls through; the asm block may only exit by jumping to one of the specified blocks. | |||
| The entire `asm!` block will have unit type in this case, unless all label blocks diverge, in which case the return type is `!`. | |||
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Suggested change
| The entire `asm!` block will have unit type in this case, unless all label blocks diverge, in which case the return type is `!`. | |
| The entire `asm!` block will have unit type in this case, unless all `label` blocks diverge, in which case the return type is `!`. |
| @@ -576,7 +585,10 @@ r[asm.options.checks.pure] | |||
| - It is a compile-time error to specify `pure` on an asm block with no outputs or only discarded outputs (`_`). | |||
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| r[asm.options.checks.noreturn] | |||
| - It is a compile-time error to specify `noreturn` on an asm block with outputs. | |||
| - It is a compile-time error to specify `noreturn` on an asm block with outputs and without labels. | |||
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Suggested change
| - It is a compile-time error to specify `noreturn` on an asm block with outputs and without labels. | |
| - It is a compile-time error to specify `noreturn` on an asm block with outputs. |
If it's a compile-time error to have a label block on an asm block with outputs (as below), then whether it's a compile-time error to specify noreturn on an asm block with outputs is invariant to whether there are labels, no?
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This change is to make r[asm.options.checks.label-with-outputs] be the only thing that blocks the asm-goto-with-outputs feature.
| - It is a compile-time error to specify `noreturn` on an asm block with outputs and without labels. | ||
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| r[asm.options.checks.label-with-outputs] | ||
| - It is a compile-time error to specify label on an asm block with outputs. |
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Suggested change
| - It is a compile-time error to specify label on an asm block with outputs. | |
| - It is a compile-time error to have a `label` block on an asm block with outputs. |
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The asm-goto-with-outputs is still unstable, so in the reference it's still mentioned as forbidden by a check rule.
Stabilization PR: rust-lang/rust#133870