Fwd: RE: Fwd: Question wrt ppc.ad (for 64b PPC)

Tue May 13 16:39:53 UTC 2014

Hi Ruchika,

> As per "64-bit PowerPC ELF Application Binary Interface Supplement 1.7" register r2 holds the "TOC base" so why not use r2 instead of using using another register r29.
Because |r2 - r29| >> 2^32 is possible, and we introduced our toc in r29 to reach the constants with a small offset < 2^32.
> You say we don't need a coop on 32b machines because the oop pointer is <= 32 bits anyways since the memory span is 32GB, yes ?
Yes.
> Now deviating some from the original question a little:
> Now for the 32b port of the code base referring to the e500 ABI doc, r2 holds the TOC and r13 the small data area and I need to use those 2 together instead of the r2 toc on the 64b.  If that information is handy, do you know which files would need change in the openjdk ?
The file ppc.ad specifies the nodes of the low IR of the C2 compiler, as well as rules for register allocation, matching etc.. The compiled code will not read the abi content of the registers.  r13 is just left alone, r2 is saved and used for allocation, so it basically does not matter what they contain.  On 32-bit I would just load constants directly, as only two instructions are needed, so you don't need a toc there at all.  But freeing r29 and r30 and using them for register allocation in the C2 compiler is one of the last things you should address because it's only an optimization.
I can't enumber all files you need to edit, but a lot of code issued by the compiler is implemented in macroAssembler_ppc.*. The biggest effort will probably be to identify all loads of pointers and replace 64-bit loads with 32-bit loads there.
> Secondly, the 64 b 1.7 eabi has register r13 dedicated to the system thread id, there isn't one dedicated in the e500 abi doc, any recommendation on how that would need to get handled ?
I don't remember that we use the system thread, we just don't touch the register.
How do you plan to do the port?  Will you do the template interpreter right away?  Or will you start with the cpp interpreter? I would first port a 'core' build that only contains one of interpreters without any compiler, because that will get you to a running VM much faster.  There is a build target 'debugcore' in hotspot.  The abi relevant stuff needed for the interpreter is specified in the frame_ppc.* files.
Best regards, Goetz.

Thank you
Regards,
Ruchika
On 5/13/2014 7:05 AM, Monica Beckwith wrote:
Thanks Goetz. As requested, I am forwarding to the alias so this gets documented. :)

Regards,
-Monica

-------- Original Message --------
Subject:

RE: Fwd: Question wrt ppc.ad (for 64b PPC)

Date:

Tue, 13 May 2014 07:34:50 +0000

From:

Lindenmaier, Goetz <goetz.lindenmaier at sap.com><mailto:goetz.lindenmaier at sap.com>

To:

Monica Beckwith <monica.b at servergy.com><mailto:monica.b at servergy.com>, "Simonis, Volker" <volker.simonis at sap.com><mailto:volker.simonis at sap.com>

CC:

Ruchika <ruchika.k at servergy.com><mailto:ruchika.k at servergy.com>

Hi Ruchika,

these are values needed for the runtime functionality of the VM, so they are not
found in an official ppc document.

R16 points to a thread of class Thread from runtime/thread.hpp.
R29 is the global TOC we use to compute the tocs for methods with
few instructions.  Loading a 64-bit address requires 5 instructions,
so it's cheaper to have some address nearby in a register and compute
the address by an offset to that.
(toc: pointer to the constant section of a method)
R30 is used for compressed oops.  This is a feature only needed on 64-bit
machines.  If the Java heap is < 32GB, oop pointers are compressed to 32-bit
by  cOop = (oop - heap_base) >> 3.  heap_base is held in R30 (cOop: compressed oop)

Best regards,
  Goetz.

Question:

While reading the ppc.ad file for ppc (./hotspot/src/cpu/ppc/vm/ppc.ad) I came across these lines
wrt the register definitions (line 434 in file)
/*R13*/             // system thread id  <-- THis is as per "64-bit PowerPC ELF Application Binary
Interface Supplement 1.7" so it is ok
  R14,
  R15,
/*R16*/             // R16_thread <--- Where does this convention arise from ? Which document/supplement?
  R17,
  R18,
  R19,
  R20,
  R21,
  R22,
  R23,
  R24,
  R25,
  R26,
  R27,
  R28,
/*R29*/             // global TOC <--- Where does this convention arise from ? Which document/supplement?
/*R30*/             // Narrow Oop Base<--- Where does this convention arise from ? Which document/supplement?

Thank you
Regards
Ruchika

--

Ruchika Kharwar

Senior Validation Engineer

Servergy, Inc.

Mobile:(469) 919-5635

Fax:(972) 542-5633

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--

Ruchika Kharwar

Senior Validation Engineer

Servergy, Inc.

Mobile:(469) 919-5635

Fax:(972) 542-5633

Email:ruchika.k at servergy.com<mailto:Email:ruchika.k at servergy.com>

Website:Servergy.com

Twitter:Twitter.com/Servergy

Servergy Makes # 4 on the EE Times 2013 Global Top 10 List of Most Disruptive Tech Start-up Plays!

O Energy-efficiency is #1 reason data centers look to expand.  -- Digital Realty Trust

O Green Data Centers spending to increase 300% worldwide by 2016.  -- Pike Research

O Data Centers have become as vital to the functioning of society as power stations.  -- The Economist

O By 2015, 30% of investments in $150B+ data center market will be in energy-efficiency plays  [like Servergy].  -- Pike Research

O By 2015 there will be 2B+ more people online and 10X more servers in the world.  -- IDC Research

CONFIDENTIALITY NOTICE: Copyright (c) 2014 by Servergy, Inc. All Rights Reserved. This communication contains privileged and/or confidential information to be maintained with the strictest confidence. It is intended solely for the use of the person or entity in which it is addressed. If you are not the intended recipient, you are STRICTLY PROHIBITED from disclosing, copying, distributing or using any of this information. If you received this communication in error, please contact the sender immediately and destroy the material in its entirety, whether electronic or hard copy.

--

Ruchika Kharwar

Senior Validation Engineer

Servergy, Inc.

Mobile:(469) 919-5635

Fax:(972) 542-5633

Email:ruchika.k at servergy.com<mailto:Email:ruchika.k at servergy.com>

Website:Servergy.com

Twitter:Twitter.com/Servergy

Servergy Makes # 4 on the EE Times 2013 Global Top 10 List of Most Disruptive Tech Start-up Plays!

O Energy-efficiency is #1 reason data centers look to expand.  -- Digital Realty Trust

O Green Data Centers spending to increase 300% worldwide by 2016.  -- Pike Research

O Data Centers have become as vital to the functioning of society as power stations.  -- The Economist

O By 2015, 30% of investments in $150B+ data center market will be in energy-efficiency plays  [like Servergy].  -- Pike Research

O By 2015 there will be 2B+ more people online and 10X more servers in the world.  -- IDC Research

CONFIDENTIALITY NOTICE: Copyright (c) 2014 by Servergy, Inc. All Rights Reserved. This communication contains privileged and/or confidential information to be maintained with the strictest confidence. It is intended solely for the use of the person or entity in which it is addressed. If you are not the intended recipient, you are STRICTLY PROHIBITED from disclosing, copying, distributing or using any of this information. If you received this communication in error, please contact the sender immediately and destroy the material in its entirety, whether electronic or hard copy.

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