[LLVMdev] Mips's MicroMips ??

[Jozef Kolek]

Hi all,
the patch is on Phabricator (http://reviews.llvm.org/D6149). With the help of new method readInstruction16() two bytes are read and decodeInstruction() is called with DecoderTableMicroMips16, if this fails another two bytes are read and decodeInstruction() is called with DecoderTableMicroMips32.

Regards,
Jozef

________________________________
From: Jun Koi [junkoi2004 at gmail.com]
Sent: Tuesday, November 04, 2014 3:18 AM
To: Zoran Jovanovic
Cc: Daniel Sanders; Vladimir Medic; Sasa Stankovic; Jozef Kolek; llvmdev at cs.uiuc.edu
Subject: Re: Mips's MicroMips ??



On Mon, Nov 3, 2014 at 10:44 PM, Zoran Jovanovic <Zoran.Jovanovic at imgtec.com<mailto: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<mailto: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<mailto:junkoi2004 at gmail.com>]
Sent: 29 October 2014 14:46
To: Daniel Sanders
Cc: llvmdev at cs.uiuc.edu<mailto: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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