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[Bug gas/5457] INTOUCH instruction incorrectly disassembled.

From: shap at eros-os dot com
Subject: [Bug gas/5457] INTOUCH instruction incorrectly disassembled.
Date: 8 Dec 2007 02:27:21 -0000

------- Additional Comments From shap at eros-os dot com  2007-12-08 02:27 
Hmm. Thank you for pointing that out.

Actually, M68000PRM specifies that if that field is 0 then the operation is a
no-op. While the encoding is hypothetically legal, the definition of the
assembly language syntax for caches on page 3-3 does not define any syntax for
legally specifying that the no-op was the intended cache.

On the whole, I'm inclined to think that any instruction actually specifying
this field as zero is a bug, and doing something clever in the disassembler here
may not be called for. The worst that will happen is that an instruction that
shouldn't have been specifiable in legal assembly input will decode as INTOUCH
in the disassembler.

In all honesty I prefer your approach, but I'm not clear how to express it
within the mechanisms of the current opcode tables. Also, I'm not clear (that
is: I do not know) whether the object file format provides sufficient
information to know what the target CPU was at dissassembly time. If it does
not, then I think it's better to allow the syntactically invalid M68000
instruction to decode as INTOUCH.




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