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update for more ABIs supporting c-variadics #1936

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Sep 17, 2025
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update for more ABIs supporting c-variadics #1936

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679dabc
update for more ABIs supporting c-variadics
RalfJung Jul 17, 2025
596cfde
Revise c-variadics changes editorially
traviscross Sep 17, 2025
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10 changes: 10 additions & 0 deletions src/items/external-blocks.md
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Expand Up @@ -189,6 +189,16 @@ unsafe extern "C" {
> [!WARNING]
> The `safe` qualifier should not be used on a function in an `extern` block unless that function guarantees that it will not access the variadic arguments at all. Passing an unexpected number of arguments or arguments of unexpected type to a variadic function may lead to [undefined behavior][undefined].

r[items.extern.variadic.conventions]
Variadic parameters can only be specified within `extern` blocks with the following ABI strings or their corresponding [`-unwind` variants][items.fn.extern.unwind]:

- `"aapcs"`
- `"C"`
- `"cdecl"`
- `"efiapi"`
- `"sysv64"`
- `"win64"`

r[items.extern.attributes]
## Attributes on extern blocks

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5 changes: 1 addition & 4 deletions src/types/function-pointer.md
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Expand Up @@ -50,10 +50,7 @@ The `unsafe` qualifier indicates that the type's value is an [unsafe
function], and the `extern` qualifier indicates it is an [extern function].

r[type.fn-pointer.constraint-variadic]
Variadic parameters can only be specified with [`extern`] function types with
the `"C"` or `"cdecl"` calling convention.

This also includes the corresponding [`-unwind` variants][items.fn.extern.unwind].
For the function to be variadic, its `extern` ABI must be one of those listed in [items.extern.variadic.conventions].

r[type.fn-pointer.attributes]
## Attributes on function pointer parameters
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