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[clang][doc] Document and prefer __asm as mangled name attribute #167226

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Nov 10, 2025
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[clang][doc] Document and prefer __asm as mangled name attribute #167226

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2 changes: 1 addition & 1 deletion clang/include/clang/Basic/Attr.td
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Original file line number Diff line number Diff line change
Expand Up @@ -1069,7 +1069,7 @@ def AVRSignal : InheritableAttr, TargetSpecificAttr<TargetAVR> {
}

def AsmLabel : InheritableAttr {
let Spellings = [CustomKeyword<"asm">, CustomKeyword<"__asm__">];
let Spellings = [CustomKeyword<"asm">, CustomKeyword<"__asm">, CustomKeyword<"__asm__">];
let Args = [
// Label specifies the mangled name for the decl.
StringArgument<"Label">, ];
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8 changes: 4 additions & 4 deletions clang/include/clang/Basic/AttrDocs.td
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Expand Up @@ -4295,17 +4295,17 @@ used by other languages. (This prefix is also added to the standard Itanium
C++ ABI prefix on "mangled" symbol names, so that e.g. on such targets the true
symbol name for a C++ variable declared as ``int cppvar;`` would be
``__Z6cppvar``; note the two underscores.) This prefix is *not* added to the
symbol names specified by the ``asm`` attribute; programmers wishing to match a
C symbol name must compensate for this.
symbol names specified by the ``__asm`` attribute; programmers wishing to match
a C symbol name must compensate for this.

For example, consider the following C code:

.. code-block:: c

int var1 asm("altvar") = 1; // "altvar" in symbol table.
int var1 __asm("altvar") = 1; // "altvar" in symbol table.
int var2 = 1; // "_var2" in symbol table.

void func1(void) asm("altfunc");
void func1(void) __asm("altfunc");
void func1(void) {} // "altfunc" in symbol table.
void func2(void) {} // "_func2" in symbol table.

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