Document asm_cfg inline assembly attributes

src/changelog.rst

@@ -35,6 +35,16 @@ Language changes in Rust 1.93.0
   - No change: this bug was not documented in FLS
 
 - `Stabilize asm_cfg <https://github.com/rust-lang/rust/pull/147736>`_
+
+  - Changed syntax: :s:`AssemblyCodeBlock`, :s:`AsmArguments`, :s:`GlobalAsmArguments`
+  - New syntax: :s:`AssemblyTemplate`, :s:`AssemblyAttributeRegisterArgument`, :s:`AssemblyAttributeAbiClobber`, :s:`AssemblyAttributeAssemblyOption`
+
+  - New paragraphs:
+
+    - :p:`fls_nLBhw2w6uznH`
+    - :p:`fls_xzDPz2zfRfoI`
+    - :p:`fls_cTEiqjf6haEg`
+
 - `During const-evaluation, support copying pointers byte-by-byte <https://github.com/rust-lang/rust/pull/148259>`_
 
   * No change: Already covered by the classification of :t:`[constant expression]s`.

src/inline-assembly.rst

@@ -963,7 +963,10 @@ Assembly Instructions
 .. syntax::
 
    AssemblyCodeBlock ::=
-       AssemblyInstruction ($$,$$ AssemblyInstruction)*
+       AssemblyTemplate ($$,$$ AssemblyTemplate)*
+
+   AssemblyTemplate ::=
+       OuterAttribute* AssemblyInstruction
 
    AssemblyInstruction ::=
        StringLiteral
@@ -1625,10 +1628,19 @@ Macros: asm, global_asm, and naked_asm
 .. syntax::
 
    AsmArguments ::=
-       $$($$ AssemblyCodeBlock ($$,$$ LabelBlock)? ($$,$$ RegisterArgument)* ($$,$$ AbiClobber)* ($$,$$ AssemblyOption)* $$,$$? $$)$$
+       $$($$ AssemblyCodeBlock ($$,$$ LabelBlock)? ($$,$$ AssemblyAttributeRegisterArgument)* ($$,$$ AssemblyAttributeAbiClobber)* ($$,$$ AssemblyAttributeAssemblyOption)* $$,$$? $$)$$
 
    GlobalAsmArguments ::=
-       $$($$ AssemblyCodeBlock ($$,$$ RegisterArgument)* ($$,$$ AssemblyOption)* $$,$$? $$)$$
+       $$($$ AssemblyCodeBlock ($$,$$ AssemblyAttributeRegisterArgument)* ($$,$$ AssemblyAttributeAssemblyOption)* $$,$$? $$)$$
+
+   AssemblyAttributeRegisterArgument ::=
+       OuterAttribute* RegisterArgument
+
+   AssemblyAttributeAbiClobber ::=
+       OuterAttribute* AbiClobber
+
+   AssemblyAttributeAssemblyOption ::=
+       OuterAttribute* AssemblyOption
 
    LabelBlock ::=
        $$block$$ $${$$ StatementList $$}$$
@@ -1641,6 +1653,15 @@ Macros: asm, global_asm, and naked_asm
 :std:`core::arch::global_asm`, and
 :std:`core::arch::naked_asm`.
 
+:dp:`fls_nLBhw2w6uznH`
+Only :t:`attribute` :c:`cfg` and :t:`attribute` :c:`cfg_attr` shall decorate :t:`[assembly instruction]s`, :t:`[register argument]s`, :t:`[ABI clobber]s`, and :t:`[assembly option]s` in :s:`AsmArguments` and :s:`GlobalAsmArguments`; all other :t:`[attribute]s` shall be rejected.
+
+:dp:`fls_xzDPz2zfRfoI`
+If a :t:`assembly instruction`, :t:`register argument`, :t:`ABI clobber`, or :t:`assembly option` in :s:`AsmArguments` or :s:`GlobalAsmArguments` is subject to :t:`attribute` :c:`cfg` or :t:`attribute` :c:`cfg_attr` where the related :t:`configuration predicate` evaluates to ``false``, then that construct is not considered part of the related :s:`AsmArguments` or :s:`GlobalAsmArguments`, consistent with :t:`conditional compilation`.
+
+:dp:`fls_cTEiqjf6haEg`
+It is a static error for a :t:`register argument`, :t:`ABI clobber`, or :t:`assembly option` to appear before the first :t:`assembly instruction`, including when that construct is subject to :t:`attribute` :c:`cfg` or :t:`attribute` :c:`cfg_attr` where the related :t:`configuration predicate` evaluates to ``false``.
+
 :dp:`fls_1ikzov7cxic1`
 When invoking :t:`macro` :std:`core::arch::asm`, the :s:`DelimitedTokenTree` of
 the related :t:`macro invocation` shall follow the syntax of :s:`AsmArguments`.
@@ -1698,6 +1719,20 @@ The :t:`execution` of an :t:`assembly code block` produced by
 
 .. rubric:: Examples
 
+.. code-block:: rust
+
+   unsafe {
+       core::arch::asm!(
+           "nop",
+           #[cfg(target_feature = "sse2")]
+           "nop",
+           #[cfg(target_feature = "sse2")]
+           in(reg) 0_u32,
+           #[cfg(target_feature = "sse2")]
+           options(nomem, nostack),
+       );
+   }
+
 .. code-block:: rust
 
    fn asm_example() -> u32 {