diff --git a/src/items/external-blocks.md b/src/items/external-blocks.md index b60cb4505..d153fae4b 100644 --- a/src/items/external-blocks.md +++ b/src/items/external-blocks.md @@ -197,199 +197,256 @@ r[items.extern.attributes.link] ### The `link` attribute r[items.extern.attributes.link.intro] -The *`link` attribute* specifies the name of a native library that the -compiler should link with for the items within an `extern` block. +The *`link` [attribute][attributes]* specifies the name of a native library that the compiler should link with for the items within an `extern` block. + +> [!EXAMPLE] +> +> ```rust,ignore +> #[link(name = "crypto")] +> unsafe extern "C" { +> // … +> } +> +> #[link(name = "CoreFoundation", kind = "framework")] +> unsafe extern "C" { +> // … +> } +> +> #[link(wasm_import_module = "foo")] +> unsafe extern "C" { +> // … +> } +> ``` r[items.extern.attributes.link.syntax] -It uses the [MetaListNameValueStr] syntax to specify its inputs. The `name` key is the -name of the native library to link. The `kind` key is an optional value which -specifies the kind of library with the following possible values: +The `link` attribute uses the [MetaListNameValueStr] syntax to specify its inputs. It accepts the following keys: -r[items.extern.attributes.link.dylib] -- `dylib` --- Indicates a dynamic library. This is the default if `kind` is not - specified. +- [`name`][items.extern.attributes.link.name] --- the name of the native library to link. +- [`kind`][items.extern.attributes.link.kind] --- the kind of library. +- [`modifiers`][items.extern.attributes.link.modifiers] --- modifiers that change the behavior of how the library is linked. +- [`wasm_import_module`][items.extern.attributes.link.wasm_import_module] --- specifies the WebAssembly module name. +- [`import_name_type`][items.extern.attributes.link.import_name_type] --- on x86 Windows, this changes how functions are named. -r[items.extern.attributes.link.static] -- `static` --- Indicates a static library. +None of the keys may be specified more than once. -r[items.extern.attributes.link.framework] -- `framework` --- Indicates a macOS framework. This is only valid for macOS - targets. +r[items.extern.attributes.link.allowed-positions] +The `link` attribute may be applied to [`extern` blocks]. -r[items.extern.attributes.link.raw-dylib] -- `raw-dylib` --- Indicates a dynamic library where the compiler will generate - an import library to link against (see [`dylib` versus `raw-dylib`] below - for details). This is only valid for Windows targets. +> [!NOTE] +> `rustc` currently warns in other positions, but this may be rejected in the future. -r[items.extern.attributes.link.name-requirement] -The `name` key must be included if `kind` is specified. +r[items.extern.attributes.link.duplicates] +The `link` attribute may be specified multiple times, and the corresponding linking instructions for each attribute will be passed to the linker. -r[items.extern.attributes.link.modifiers] -The optional `modifiers` argument is a way to specify linking modifiers for the -library to link. +r[items.extern.attributes.link.empty-block] +It is valid to add the `link` attribute on an empty extern block. You can use this to satisfy the linking requirements of extern blocks elsewhere in your code (including upstream crates) instead of adding the attribute to each extern block. -r[items.extern.attributes.link.modifiers.syntax] -Modifiers are specified as a comma-delimited string with each modifier prefixed -with either a `+` or `-` to indicate that the modifier is enabled or disabled, -respectively. +r[items.extern.attributes.link.name] +#### The `name` key -r[items.extern.attributes.link.modifiers.multiple] -Specifying multiple `modifiers` arguments in a single `link` attribute, -or multiple identical modifiers in the same `modifiers` argument is not currently supported. \ -Example: `#[link(name = "mylib", kind = "static", modifiers = "+whole-archive")]`. +r[items.extern.attributes.link.name.intro] +The `name` key specifies the name of the library to link. -r[items.extern.attributes.link.wasm_import_module] -The `wasm_import_module` key may be used to specify the [WebAssembly module] -name for the items within an `extern` block when importing symbols from the -host environment. The default module name is `env` if `wasm_import_module` is -not specified. - - -```rust,ignore -#[link(name = "crypto")] -unsafe extern { - // … -} + -#[link(name = "CoreFoundation", kind = "framework")] -unsafe extern { - // … -} + -#[link(wasm_import_module = "foo")] -unsafe extern { - // … -} -``` +r[items.extern.attributes.link.name.requirement] +The `name` key must be included unless `wasm_import_module` is used. -r[items.extern.attributes.link.empty-block] -It is valid to add the `link` attribute on an empty extern block. You can use -this to satisfy the linking requirements of extern blocks elsewhere in your -code (including upstream crates) instead of adding the attribute to each extern -block. +r[items.extern.attributes.link.kind] +#### The `kind` key + +r[items.extern.attributes.link.kind.intro] +The `kind` key specifies the kind of the library. + +r[items.extern.attributes.link.kind.dylib] +The `dylib` kind indicates a dynamic library. This is the default if `kind` is not specified. + +> [!EXAMPLE] +> +> ```rust,ignore +> #[link(name = "example", kind = "dylib")] +> unsafe extern "C" {} +> ``` + +r[items.extern.attributes.link.kind.static] +The `static` kind indicates a static library. + +> [!EXAMPLE] +> +> ```rust,ignore +> #[link(name = "example", kind = "static")] +> unsafe extern "C" {} +> ``` + +r[items.extern.attributes.link.kind.framework] +The `framework` kind indicates a macOS framework. This is only valid for macOS targets. + +> [!EXAMPLE] +> +> ```rust,ignore +> #[link(name = "CoreFoundation", kind = "framework")] +> unsafe extern "C" {} +> ``` + +r[items.extern.attributes.link.kind.raw-dylib] +The `raw-dylib` kind indicates a dynamic library where the compiler will generate an import library to link against (see [`dylib` versus `raw-dylib`] below for details). This is only valid for Windows targets. + +> [!EXAMPLE] +> +> ```rust,ignore +> #[link(name = "example", kind = "raw-dylib")] +> unsafe extern "C" {} +> ``` + +> [!NOTE] +> ##### `dylib` versus `raw-dylib` +> +> On Windows, linking against a dynamic library requires that an import library is provided to the linker. This is a special static library that declares all of the symbols exported by the dynamic library in such a way that the linker knows that they have to be dynamically loaded at runtime. +> +> Specifying `kind = "dylib"` links an import library based on the `name` key. The linker will then use its normal library resolution logic to find that import library. Alternatively, specifying `kind = "raw-dylib"` generates an import library during compilation and provide that to the linker instead. + +r[items.extern.attributes.link.modifiers] +#### The `modifiers` key + +r[items.extern.attributes.link.modifiers.intro] +The optional `modifiers` argument is a way to specify linking modifiers for the library to link. + +> [!EXAMPLE] +> +> ```rust,ignore +> #[link(name = "mylib", kind = "static", modifiers = "+whole-archive")] +> unsafe extern "C" {} +> ``` + +r[items.extern.attributes.link.modifiers.syntax] +Modifiers are specified as a comma-delimited string with each modifier prefixed with either a `+` or `-` to indicate that the modifier is enabled or disabled, respectively. + +r[items.extern.attributes.link.modifiers.once] +The `modifiers` argument may only be specified once. + +r[items.extern.attributes.link.modifiers.duplicates] +Duplicate modifiers are not allowed within a `modifiers` argument. r[items.extern.attributes.link.modifiers.bundle] #### Linking modifiers: `bundle` +> [!EXAMPLE] +> +> ```rust,ignore +> #[link(name = "mylib", kind = "static", modifiers = "+bundle")] +> unsafe extern "C" {} +> ``` + r[items.extern.attributes.link.modifiers.bundle.allowed-kinds] -This modifier is only compatible with the `static` linking kind. -Using any other kind will result in a compiler error. +The `bundle` modifier may only be used with [`static` linking]. r[items.extern.attributes.link.modifiers.bundle.behavior] -When building a rlib or staticlib `+bundle` means that the native static library -will be packed into the rlib or staticlib archive, and then retrieved from there -during linking of the final binary. +When building a rlib or staticlib, `+bundle` means that the native static library will be packed into the rlib or staticlib archive, and then retrieved from there during linking of the final binary. r[items.extern.attributes.link.modifiers.bundle.behavior-negative] -When building a rlib `-bundle` means that the native static library is registered as a dependency -of that rlib "by name", and object files from it are included only during linking of the final -binary, the file search by that name is also performed during final linking. \ -When building a staticlib `-bundle` means that the native static library is simply not included -into the archive and some higher level build system will need to add it later during linking of -the final binary. +When building a rlib, `-bundle` means that the native static library is registered as a dependency of that rlib "by name", and object files from it are included only during linking of the final binary, the file search by that name is also performed during final linking. + +When building a staticlib, `-bundle` means that the native static library is simply not included into the archive and some higher level build system will need to add it later during linking of the final binary. r[items.extern.attributes.link.modifiers.bundle.no-effect] -This modifier has no effect when building other targets like executables or dynamic libraries. +The `bundle` modifier has no effect when building other targets like executables or dynamic libraries. r[items.extern.attributes.link.modifiers.bundle.default] The default for this modifier is `+bundle`. -More implementation details about this modifier can be found in -[`bundle` documentation for rustc]. +> [!NOTE] +> More implementation details about this modifier can be found in [`bundle` documentation for rustc]. r[items.extern.attributes.link.modifiers.whole-archive] #### Linking modifiers: `whole-archive` +> [!EXAMPLE] +> +> ```rust,ignore +> #[link(name = "mylib", kind = "static", modifiers = "+whole-archive")] +> unsafe extern "C" {} +> ``` + r[items.extern.attributes.link.modifiers.whole-archive.allowed-kinds] -This modifier is only compatible with the `static` linking kind. -Using any other kind will result in a compiler error. +The `whole-archive` modifier may only be used with [`static` linking]. r[items.extern.attributes.link.modifiers.whole-archive.behavior] -`+whole-archive` means that the static library is linked as a whole archive -without throwing any object files away. +`+whole-archive` means that the static library is linked as a whole archive without throwing any object files away. r[items.extern.attributes.link.modifiers.whole-archive.default] The default for this modifier is `-whole-archive`. -More implementation details about this modifier can be found in -[`whole-archive` documentation for rustc]. +> [!NOTE] +> More implementation details about this modifier can be found in [`whole-archive` documentation for rustc]. r[items.extern.attributes.link.modifiers.verbatim] -### Linking modifiers: `verbatim` +#### Linking modifiers: `verbatim` + +> [!EXAMPLE] +> +> ```rust,ignore +> #[link(name = "mylib", kind = "static", modifiers = "+verbatim")] +> unsafe extern "C" {} +> ``` r[items.extern.attributes.link.modifiers.verbatim.allowed-kinds] This modifier is compatible with all linking kinds. r[items.extern.attributes.link.modifiers.verbatim.behavior] -`+verbatim` means that rustc itself won't add any target-specified library prefixes or suffixes -(like `lib` or `.a`) to the library name, and will try its best to ask for the same thing from the -linker. +`+verbatim` means that the compiler won't add any target-specified library prefixes or suffixes (like `lib` or `.a`) to the library name, and will try its best to ask for the same thing from the linker. r[items.extern.attributes.link.modifiers.verbatim.behavior-negative] -`-verbatim` means that rustc will either add a target-specific prefix and suffix to the library -name before passing it to linker, or won't prevent linker from implicitly adding it. +`-verbatim` means that the compiler will either add a target-specific prefix and suffix to the library name before passing it to linker, or won't prevent linker from implicitly adding it. r[items.extern.attributes.link.modifiers.verbatim.default] The default for this modifier is `-verbatim`. -More implementation details about this modifier can be found in -[`verbatim` documentation for rustc]. - -r[items.extern.attributes.link.kind-raw-dylib] -#### `dylib` versus `raw-dylib` +> [!NOTE] +> More implementation details about this modifier can be found in [`verbatim` documentation for rustc]. -r[items.extern.attributes.link.kind-raw-dylib.intro] -On Windows, linking against a dynamic library requires that an import library -is provided to the linker: this is a special static library that declares all -of the symbols exported by the dynamic library in such a way that the linker -knows that they have to be dynamically loaded at runtime. +r[items.extern.attributes.link.wasm_import_module] +#### The `wasm_import_module` key -r[items.extern.attributes.link.kind-raw-dylib.import] -Specifying `kind = "dylib"` instructs the Rust compiler to link an import -library based on the `name` key. The linker will then use its normal library -resolution logic to find that import library. Alternatively, specifying -`kind = "raw-dylib"` instructs the compiler to generate an import library -during compilation and provide that to the linker instead. +r[items.extern.attributes.link.wasm_import_module.behavior] +The `wasm_import_module` key may be used to specify the [WebAssembly module] name for the items within an `extern` block when importing symbols from the host environment. The default module name is `env` if `wasm_import_module` is not specified. -r[items.extern.attributes.link.kind-raw-dylib.platform-specific] -`raw-dylib` is only supported on Windows. Using it when targeting other -platforms will result in a compiler error. +> [!EXAMPLE] +> +> ```rust,ignore +> #[link(wasm_import_module = "foo")] +> unsafe extern "C" {} +> ``` r[items.extern.attributes.link.import_name_type] #### The `import_name_type` key +> [!EXAMPLE] +> +> ```rust,ignore +> #[link(name = "mylib", kind = "raw-dylib", import_name_type = "undecorated")] +> unsafe extern "C" {} +> ``` + r[items.extern.attributes.link.import_name_type.intro] -On x86 Windows, names of functions are "decorated" (i.e., have a specific prefix -and/or suffix added) to indicate their calling convention. For example, a -`stdcall` calling convention function with the name `fn1` that has no arguments -would be decorated as `_fn1@0`. However, the [PE Format] does also permit names -to have no prefix or be undecorated. Additionally, the MSVC and GNU toolchains -use different decorations for the same calling conventions which means, by -default, some Win32 functions cannot be called using the `raw-dylib` link kind -via the GNU toolchain. +On x86 Windows, names of functions are "decorated" (i.e., have a specific prefix and/or suffix added) to indicate their calling convention. For example, a `stdcall` calling convention function with the name `fn1` that has no arguments would be decorated as `_fn1@0`. However, the [PE Format] does also permit names to have no prefix or be undecorated. Additionally, the MSVC and GNU toolchains use different decorations for the same calling conventions which means, by default, some Win32 functions cannot be called using the `raw-dylib` link kind via the GNU toolchain. r[items.extern.attributes.link.import_name_type.values] -To allow for these differences, when using the `raw-dylib` link kind you may -also specify the `import_name_type` key with one of the following values to -change how functions are named in the generated import library: - -* `decorated`: The function name will be fully-decorated using the MSVC - toolchain format. -* `noprefix`: The function name will be decorated using the MSVC toolchain - format, but skipping the leading `?`, `@`, or optionally `_`. +To allow for these differences, when using the `raw-dylib` link kind you may also specify the `import_name_type` key with one of the following values to change how functions are named in the generated import library: + +* `decorated`: The function name will be fully-decorated using the MSVC toolchain format. +* `noprefix`: The function name will be decorated using the MSVC toolchain format, but skipping the leading `?`, `@`, or optionally `_`. * `undecorated`: The function name will not be decorated. r[items.extern.attributes.link.import_name_type.default] -If the `import_name_type` key is not specified, then the function name will be -fully-decorated using the target toolchain's format. +If the `import_name_type` key is not specified, then the function name will be fully-decorated using the target toolchain's format. r[items.extern.attributes.link.import_name_type.variables] -Variables are never decorated and so the `import_name_type` key has no effect on -how they are named in the generated import library. +Variables are never decorated and so the `import_name_type` key has no effect on how they are named in the generated import library. r[items.extern.attributes.link.import_name_type.platform-specific] -The `import_name_type` key is only supported on x86 Windows. Using it when -targeting other platforms will result in a compiler error. +The `import_name_type` key is only supported on x86 Windows. Using it when targeting other platforms will result in a compiler error. r[items.extern.attributes.link_name] ### The `link_name` attribute @@ -461,3 +518,5 @@ restrictions as [regular function parameters]. [statics]: static-items.md [unwind-behavior]: functions.md#unwinding [value namespace]: ../names/namespaces.md +[`extern` blocks]: external-blocks.md +[`static` linking]: link.staticlib