[LLVMdev] Mips's MicroMips ??

[Jun Koi]

On Mon, Nov 3, 2014 at 10:44 PM, Zoran Jovanovic <Zoran.Jovanovic at imgtec.com
> wrote:

>  Hello Daniel,
> At the moment we are preparing the patch for disassembling microMIPS 16
> bit instructions and it will be on Phabricator tomorrow or on Wednesday.
> Functionality is implemented in MipsDisassembler::getInstruction where
> first two bytes are read and decodeInstruction is called
> with DecoderTableMicroMips16 and only if it fails we read 4 bytes and call
> decodeInstruction  with DecoderTableMicroMips32.
>
>
awesome! looking forward to it.

thanks,
Jun



 ------------------------------
*From:* Daniel Sanders
*Sent:* Sunday, November 02, 2014 5:49 PM
*To:* Jun Koi; Vladimir Medic; Sasa Stankovic; Jozef Kolek; Zoran Jovanovic
*Cc:* llvmdev at cs.uiuc.edu
*Subject:* RE: Mips's MicroMips ??

  Hi,

I've had a quick look through MipsDisassembler.cpp and it seems that the
disassembler doesn't know anything about 16-bit instructions at the moment.
The two main problems are that DecoderTableMicroMips16 (which contains
ADDU16_MM) is never used, and the disassembler always reads the opcode as a
4-byte value.

Vladimir/Sasa/Jozef/Zoran: I don't know much about the microMIPS encodings
at the moment. Do you have the details on distinguishing 16-bit from 32-bit
instructions?
 ------------------------------
*From:* Jun Koi [junkoi2004 at gmail.com]
*Sent:* 29 October 2014 14:46
*To:* Daniel Sanders
*Cc:* llvmdev at cs.uiuc.edu
*Subject:* Mips's MicroMips ??

  Hi,

 We have this line in micromips-16-bit-instructions.s

    # CHECK-EB: addu16  $6, $17, $4     # encoding: [0x07,0x42]

However, when I check this with llvm-mc, like below, I dont get back the
assembly.
This is against the latest LLVM code. What is wrong here?

Thanks,
Jun


$ echo "0x07,0x42"|./Release+Asserts/bin/llvm-mc -disassemble -triple=mips
-show-encoding -mattr=micromips
    .text
<stdin>:1:1: warning: invalid instruction encoding
0x07,0x42
^
<stdin>:1:6: warning: invalid instruction encoding
0x07,0x42
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