Porting Kaffe to a new platform

Edouard G. Parmelan

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".


Table of Contents
Preface
1. Overview
2. Port Kaffe intrp engine to a new platform
2.1. Configuration files
2.2. Alignment of various types
2.3. Threads subsystem
2.4. Locks subsystem
2.5. Function sysdepCallMethod()
2.5.1. The callMethodInfo structure
2.5.2. libffi
2.6. GNU Libtool
3. Port Kaffe JIT engine to a new platform
4. Write JIT back-end for a new processor family
4.1. Overview of JIT back-end functions.
4.1.1. Register spills and reloads
4.1.2. Prologues and epilogues
4.1.3. Conditional monitor management
4.1.4. Moves
4.1.5. Arithmetic operators
4.1.6. Logical operators
4.1.7. pushing parameters
4.2. Registers description.
4.3. Slots usage.
5. Tips
A. GNU Free Documentation License
0. PREAMBLE
1. APPLICABILITY AND DEFINITIONS
2. VERBATIM COPYING
3. COPYING IN QUANTITY
4. MODIFICATIONS
5. COMBINING DOCUMENTS
6. COLLECTIONS OF DOCUMENTS
7. AGGREGATION WITH INDEPENDENT WORKS
8. TRANSLATION
9. TERMINATION
10. FUTURE REVISIONS OF THIS LICENSE
How to use this License for your documents

Preface

I had port JIT engine to Alpha Tru64 and GNU/Linux Alpha in the past and I know how it's difficult to understand correctly intrp and JIT engines with only sources as documentation. I had write this document latter while I was porting intrp engine to Darwin (Mac OS X) operating system. In the same time I was writing JIT back-end for PowerPC.

This document is written in SGML DocBook with GNU Emacs and PSGML major mode. Source of this document may be found in Kaffe CVS Tree or in my Kaffe repository.

If you find some bullets in this document, send an email to . All comments are welcome. If you want to fix typo or grammar use SGML sources only and send me "diff -u" result. Never fill-paragraph NOR reformat them.

Preview current working draft here: http://egp.free.fr/port-kaffe/port-kaffe.html.

Others persons have already written documents on this subject. I some time peek phrases, sections or inspiration from them.


Chapter 1. Overview

The first step to port Kaffe to a new platform or new processor family is to port intrp engine. Then As soon as intrp engine works, you can port JIT engine (see Chapter 3). The biggest task will be to write JIT back-end for your processor family (see Chapter 4).

I will try to covers all these tasks in this document.


Chapter 2. Port Kaffe intrp engine to a new platform


2.1. Configuration files

config/config.alias

This shell script maps configure's variables $host_cpu and $host_os to Kaffe cananical forms $Khost_os and $Khost_os. These variables define access paths to cpu family and platform configuration files.

config/$Khost_cpu/Make.frag

Optional Makefile fragments required for this cpu family.

config/$Khost_cpu/common.h

Common definitions for all platforms of this cpu family.

config/$Khost_cpu/thread.h

Common thread definitions for all platforms of this cpu family.

config/$Khost_cpu/$Khost_os/config.frag

configure's fragment for this platform.

It may holds specials $CFLAGS add-ons and cross-compile definitions.

config/$Khost_cpu/$Khost_os/md.h, config/$Khost_cpu/$Khost_os/md.c

Platform dependent header and functions.

File md.h typically includes $Khost_cpu/common.h and $Khost_cpu/thread.h and defines SP_OFFSET macro.

config/$Khost_cpu/jit.h, config/$Khost_cpu/jit-$Khost_cpu.def, config/$Khost_cpu/jit-icode.h, config/$Khost_cpu/jit3-$Khost_cpu.def, config/$Khost_cpu/jit3-icode.h

JIT/JIT3 definitions for this cpu family.

config/$Khost_cpu/$Khost_os/jit-md.h, config/$Khost_cpu/$Khost_os/jit3-md.h

Platform JIT/JIT3 dependent header.

It includes $Khost_cpu/jit.h and defines EXCEPTIONPROTO and EXCEPTIONFRAME macros.


2.2. Alignment of various types

Fields inside classe objects must follow the alignment constraints of the C calling conventions. If alignment of type TYPE is not sizeof(TYPE) you must define macro ALIGNMENT_OF_SIZE(SIZE) in file config/$Khost_cpu/common.h.

The small C program developers/alignment_of_size.c may helps you to discover correct alignment. Simply compiles it and runs it.


2.3. Threads subsystem

Sources of threads subsystems are located into directory kaffe/kaffevm/systems/.

The common threads subsystem is unix-jthread. It uses setjmp() and longjmp() functions. In order to use it you must provide stack pointer offset into jmp_env.

The small C program developers/sp_offset.c may helps you to discover SP_OFFSET. Simply compiles it and runs it. It may leaves core file in you current directory.

Some platforms need to setup Frame-Pointer register when creating a new thread stack. In this case you must provide his offset FP_OFFSET into jmp_env.

Macros SP_OFFSET and FP_OFFSET should be defined in file config/$Khost_cpu/$Kost_os/md.h.

Define the macro THREADSTACKSIZE in file config/$Khost_cpu/thread.h to the size in bytes of each thread's stack. This size may depends on INTERPRETER defined as intrp engine will need greater stack size than JIT engine. Commun values are 64K for intrp engine and 32K for JIT engine.

You may want to use another threads subsystem specific to your platform. It is possible but it's not cover by this document. Read files FAQ/FAQ.jsignal and FAQ/FAQ.locks.

To select another threads subsystem, configure with option --with-threads=thread-subsystem.


2.4. Locks subsystem

Kaffe Fast Locking scheme (read FAQ/FAQ.locks) need a macro to atomic compare and exchange a lock address. This macro COMPARE_AND_EXCHANGE() must be implemented in assembler.

Macro COMPARE_AND_EXCHANGE() should be define in file config/$Khost_cpu/common.h. It is only used into file kaffe/kaffevm/locks.c.

If you can't implement it but have an atomic exchange instruction, defines macro ATOMIC_EXCHANGE() as in Sparc port.

Otherwise, fall back to plain C implementations as in MIPS I port. You should note that it will fail on a multi-processors machine.


2.5. Function sysdepCallMethod()

Function sysdepCallMethod() setups standard registers and stack parameters for your ABI. It obeys to the C calling conventions of your platform.

It makes a call to a native or Java (JIT) method. This assembly code should build a standard C call using the passed call information. By its nature this is highly processor specific. This function is mandatory for both JIT and Interpreter (since stubs have now been deprecated).

It should be implemented in file config/$Khost_cpu/sysdepCallMethod.h.

The sysdepCallMethod() macro takes a single argument of type callMethodInfo* that describes where the parameters are, where the return value should go and what the signature of the method is.

The function sysdepCallMethod() is only used by functions callMethodA() and callMethodV() in file kaffe/kaffevm/support.c.

The followings macros control the construction of callMethodInfo structure. Define or not define some of them may help you to implements function sysdepCallMethod().

NO_HOLES

This define causes all types to occupy only one slot in callargs, but not affecting their callsizes, that can still be used to distinguish among types. It avoids introducing unused slots after jlongs and jdoubles.

NO_HOLES is incompatible with ALIGN_AT_64bits.

PROMOTE_TO_64bits

It causes all integer arguments to be promoted to jlong, and all jfloats to be promoted to jdouble, unless explicitly overridden. It implies NO_HOLES, unless explicitly defined otherwise.

PROMOTE_jint2jlong

If PROMOTE_jint2jlong is enabled, all integer values are to be passed as jlongs. It is only set by PROMOTE_TO_64bits.

PROMOTE_jfloat2jdouble

If PROMOTE_jfloat2jdouble is enabled, jfloats are to be passed as jdoubles. Note that, when a jfloat is promoted, its calltype will be marked as 'D'. No known port uses this. In fact, alpha must explicitly set it to 0, to prevent PROMOTE_TO_64bits from enabling it.

ALIGN_AT_64bits

This causes all 64bit arguments to be aligned at even arguments. If a jlong or jdouble appears as on odd argument, a place-holder will be introduced.

ALIGN_AT_64bits is incompatible with NO_HOLES.


2.5.1. The callMethodInfo structure

The callMethodInfo structure describes the information necessary to invoke a native or just-in-time compiled method.

jvalue is a union defined in include/jtypes.h. It corresponds to an entry on the Java stack. The suffixes i, j, b, c, s, l, f, d access the corresponding element of (Java) type int, long, boolean, char, short, ref, float, and double.

args is an array containing the arguments passed to the function. It corresponds to the Java stack and has nrargs valid entries with the following property:

  • If two adjacent slots on the Java stack are combined to a 64bit value, it will also use two array entries, and not one. However, the first entry will contain the 64bit value (in j or d, depending on the type), and the second entry will be undefined. This allows for easier access, while preserving indexing. Thus, some array entries will have 0, some 32 and some 64 bits of valid data in them. The callsize array says which one it is.

  • callsize[i] may be 0, 1, or 2, depending on the number of valid bits in args[i]. Similarly, calltype[i] contains the signature type of the argument in args[i] ('J', 'F', etc.)

  • To simplify 32 bit assembly code, we copy the last 32 bits of a 64 bit arg into the next slot. This allows you to treat args as an array of 32 bit values. This simplification also makes a C version of sysdepCallMethod() more viable.

  • Note that "callsize[i] == 2 iff callsize[i+1] == 0" -- this property can also be exploited by function sysdepCallMethod().

function is a pointer to the method to be invoked.

retsize and rettype have the same value ranges as callsize[i] and calltype[i], except they correspond to the return value. The function sysdepCallMethod() must store the return value in the proper type at *ret.


2.5.2. libffi

If libffi handle your platform, you can use it to implements function sysdepCallMethod(). But it's better to implement it as described bellow.

Configure Kaffe with option --with-libffi explicitly in order to use libffi.


2.6. GNU Libtool

Kaffe use GNU libtool to build dynamic libraries and modules. If it is not able to create them, configure Kaffe with options --with-staticlib and --with-staticvm.


Chapter 3. Port Kaffe JIT engine to a new platform

In order to port JIT engine, you must understand some parts of JIT engine.

If your platform use another C calling convensions (ABI) than those handled by JIT back-end of your cpu family you must change it to handle your ABI (see Chapter 4).

WRITE-ME: NullPointerException, ArithmeticException and signals.

WRITE-ME: buildStackTrace() and stack inspection.

WRITE-ME: retreiving lock object in a given stack frame.

WRITE-ME: method trampoline.


Chapter 4. Write JIT back-end for a new processor family

Before write new JIT back-end, Kaffe intrp engine must work on your platform (see Chapter 2).

To write new JIT back-end, you must implements the following files:

config/$Khost_cpu/jit.h

This file contains definitions for: exception handling, method dispatching, register management, opcode generation and slots management.

config/$Khost_cpu/jit3-$Khost_cpu.def

This file is the main implementation of the JIT back-end. It contains all back-end functions with special marker define_inst(function_name, internal_name).

config/$Khost_cpu/jit3-icode.h

This file contains definition of all JIT back-end functions. There are in fact macro HAVE_function_name define to back-end internal-name.


4.1. Overview of JIT back-end functions.

4.1.1. Register spills and reloads

4.1.1.1. spill_TYPE()

Function spill_TYPE() spills TYPE register seq_slot(0) into its assigned frame location offset seq_slot(1).

r = sreg_TYPE(0);
o = const_int(1);

$fp[o] = $r;
	  

List of functions: spill_int(), spill_ref(), spill_long(), spill_float(), spill_double()


4.1.1.2. reload_TYPE()

Function reload_TYPE() reloads TYPE register seq_slot(0) from given frame location offset seq_slot(1).

r = lreg_TYPE(0);
o = const_int(1);

$r = $fp[o];
	  

List of functions: reload_int() reload_ref() reload_long() reload_float() reload_double()


4.1.4. Moves

4.1.4.1. move_TYPE_const()

Optional

Require macro HAVE_move_TYPE_const_rangecheck()

TODO

move_int_const() move_ref_const() move_long_const() move_float_const() move_double_const()


4.1.4.2. load_constpool_TYPE()

Optional

If not present, define functions move_label_const() and load_TYPE().

TODO

load_constpool_int() load_constpool_ref() load_constpool_long() load_constpool_double() load_constpool_float()


4.1.4.3. move_TYPE()

Optional

TODO

move_int() move_ref() move_long() move_float() move_double()


4.1.5. Arithmetic operators

4.1.5.1. add_TYPE_const()

Optional

Require macro add_TYPE_const_rangecheck()

TODO

add_int_const() add_ref_const() add_long_const()


4.1.5.2. add_TYPE()

Optional

TODO

add_int() add_ref() add_long() add_float() add_double()


4.1.5.3. adc_int()

Optional

TODO


4.1.5.4. sub_TYPE_const()

Optional

Require macro sub_TYPE_const_rangecheck()

TODO

sub_int_const() sub_ref_const() sub_long_const()


4.1.5.5. sub_TYPE()

Optional

TODO

sub_int() sub_ref() sub_long() sub_float() sub_double()


4.1.5.6. sbc_int()

Optional

Required if sub_long() and set_lt_int() are not implemented.

TODO


4.1.5.7. set_lt_int()/set_lt_int_const()

Optional

Required if sub_long() and sbc_int() are not implemented.

TODO


4.1.5.8. mul_TYPE_const()

Optional

Require macro mul_TYPE_const_rangecheck()

TODO

mul_int_const() mul_long_const()


4.1.5.9. mul_TYPE()

Optional

TODO

mul_int() mul_long() mul_float() mul_double()


4.1.5.10. div_TYPE_const()

Optional

Require macro div_TYPE_const_rangecheck()

TODO

div_int_const()


4.1.5.11. div_TYPE()

Optional

TODO

div_int() div_long() div_float() div_double()


4.1.5.12. rem_TYPE_const()

Optional

Require macro rem_TYPE_const_rangecheck()

TODO

rem_int_const()


4.1.5.13. rem_TYPE()

Optional

TODO

rem_int() rem_long() rem_float() rem_double()


4.1.5.14. neg_TYPE()

Optional

TODO

neg_int() neg_long() neg_float() neg_double()


4.1.7. pushing parameters

pusharg_TYPE() WRITE-ME: PUSHARG_FORWARDS kaffe/kaffevm/jni.c kaffe/kaffevm/jit3/icode.c


Chapter 5. Tips


Appendix A. GNU Free Documentation License

Version 1.1, March 2000

Copyright (C) 2000 Free Software Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.


0. PREAMBLE

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1. APPLICABILITY AND DEFINITIONS

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