<html><head><base href="x-msg://8188/"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hi James,<br><div><div>On Aug 12, 2011, at 1:02 AM, James Molloy wrote:</div><br><blockquote type="cite"><span class="Apple-style-span" style="border-collapse: separate; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div lang="EN-GB" link="blue" vlink="purple" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div class="WordSection1" style="page: WordSection1; "><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125); ">I’ve got a load of examples for this, but I’ll pick one.<o:p></o:p></span></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125); "><o:p> </o:p></span></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 11pt; font-family: Consolas; color: rgb(31, 73, 125); ">echo '0xB0 0x00 0x00 0x00' |/work/llvm-cmake2/build/bin/llvm-mc -arch arm --disassemble –<o:p></o:p></span></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 11pt; font-family: Consolas; color: rgb(31, 73, 125); "> strheq r0, [r0], -r0<o:p></o:p></span></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125); "><o:p> </o:p></span></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125); ">This instruction encoding is marked UNPREDICTABLE. The question is: does a disassembly of it have value? One use case put to me was in a debugger, where one needs to know if an instruction was ARM-mode or Thumb-mode so it can correctly guess the mode of the previous instruction in the stream and disassemble that correctly.<o:p></o:p></span></div><div style="margin-top: 0cm; margin-right: 0cm; margin-left: 0cm; margin-bottom: 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 11pt; font-family: Calibri, sans-serif; color: rgb(31, 73, 125); "></span></div></div></div></span></blockquote><div><br></div><div>OK, I think I was misunderstanding what you wrote initially. I thought you meant there were ambiguous decodings where special UNPREDICTABLE handling was necessary for disambiguation, and was going to be very disturbed if that were true!</div><div><br></div><div>The initial new disassembler implementation, as you've noticed, does very little UNPREDICTABLE checking. I'm adding more checking to it as I have time/inclination, but I'm more concerned with getting it to decode more <i>correct</i> instructions than with getting it to reject more invalid ones. </div><div><br></div><div>That said, I do think it would be useful to a) have more UNPREDICTABLE checking, mostly in the form of greater operand validation, and b) to have a means of conveying that to the user. I'm not sure that adding a bit to MCInst is necessary, however. Perhaps we could just promote the return value of getInstruction() from bool to a trinary value that can indicate success, failure, or soft failure. Then it can be up to the client to handle that in some useful fashion.</div><div><br></div><div>I'm not going to have the bandwidth to work on a structural change like that in the immediate future, but if you're interested it would be a great addition!</div><div><br></div><div>--Owen</div></div><br></body></html>