RFC: AArch64 Disassembler: Annotate undefined instructions

[Michael Matz]

Hey,

On Tue, 28 Apr 2026, Nick Clifton wrote:

> >>>        41fdd8:	00400764 	.inst	0x00400764 ; undefined
> >>>        41fddc:	00000000 	udf	#0
> >>>
> >>>    Whereas with the option enabled this changes to:
> >>>    
> >>>      000000000041fdd8 <__frame_dummy_init_array_entry>:
> >>>        41fdd8:	00400764 	.inst	0x00400764 ; [frame_dummy]
> >>>        41fddc:	00000000 	udf	#0
> 
> >> This is what mapping symbols are supposed to address.  If the user writes
> >> '.word' in a code section then the value will be tagged with $d and the
> >> output should then disassemble as data.  '.inst' means 'this is an
> >> instruction'.
...
> >   objdump -d test.o
> > 
> > Maybe .word should be annotated with a suitable label, but I don't think
> > .inst should.
> 
> OK, that makes sense.  So the disassembler should check to see if closest
> previous mapping symbol is $d and only proceed with the annotation in this
> case, yes ?

But we're talking about doing the annotations for a final-linked file, not 
for relocatable files.  Are the $d symbols even part of them?

(And it's an annotation only, I think it'd be acceptable to say "[foobar]" 
even when an undefined instruction really was meant as undefined 
instruction, not as .data, but just so happens to match the address of 
foobar.  It certainly would be a very interesting coincidence, and also 
certainly much more interesting than "; undefined". )


Ciao,
Michael.