https://sourceware.org/bugzilla/show_bug.cgi?id=33336
Bug ID: 33336
Summary: gas: Clarify whitespace between a label’s symbol and
its colon
Product: binutils
Version: unspecified
Status: NEW
Severity: normal
Priority: P2
Component: gas
Assignee: unassigned at sourceware dot org
Reporter: i at maskray dot me
Target Milestone: ---
https://sourceware.org/binutils/docs/as/Statements.html specifies
> A label is a symbol immediately followed by a colon (:). Whitespace before a
> label or after a colon is permitted, **but you may not have whitespace
> between a label’s symbol and its colon**. See Labels.
According to this description, the following assembly should not be permitted:
f :op:nop
However, this is identical to `f: op: nop` and will be assembled as two labels
with a nop instruction (in at least x86, aarch64, powerpc64; I believe this
likely applies to most targets). LLVM integrated assembler interprets this the
same way.
If we are not going to change the implementation regarding labels, I think we
should clarify the documentation.
---
Context:
AArch32 and AArch64 adopt this colon-framed prefix notation, avoiding the
confusion that parentheses might introduce.
// AArch32
movw r0, :lower16:x
// AArch64
add x8, x8, :lo12:sym
Applying this syntax to the first operand, however, could create parsing
ambiguity. In
https://maskray.me/blog/2025-03-16-relocation-generation-in-assemblers ,
I am suggesting that data directives switch to %specifier(expr).
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