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

[Monica Beckwith]

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

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

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