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Following an entry into the
Jazelle state mode, bytecodes can be processed in one of three ways: decoded and executed natively in hardware, handled in software (with optimised ARM/ThumbEE JVM code), or treated as an invalid/illegal opcode. The third case will cause a branch to an ARM exception mode,
104:
and other JVM accelerating techniques. JVM instructions that are not implemented in
Jazelle hardware cause appropriate routines in the Jazelle-aware JVM implementation to be invoked. Details are not published, since all JVM innards are transparent (except for performance) if correctly interpreted.
136:
Employees of ARM have in the past published several white papers that do give some good pointers about the processor extension. Versions of the ARM Architecture reference Manual available from 2008 have included pseudocode for the "BXJ" (Branch and eXchange to Java) instruction, but with the finer
108:
Jazelle mode is entered via the BXJ instructions. A hardware implementation of
Jazelle will only cover a subset of JVM bytecodes. For unhandled bytecodes—or if overridden by the operating system—the hardware will invoke the software JVM. The system is designed so that the software JVM does not
283:
ThumbEE was a variant of the Thumb2 16/32-bit instruction set. It integrated null pointer checking; defined some new fault mechanisms; and repurposed the 16-bit LDM and STM opcode space to support a few instructions such as range checking, a new handler invocation scheme, and more. Accordingly,
74:
code that can support a JVM that uses
Jazelle. The declared intent is that only the JVM software needs to (or is allowed to) depend on the hardware interface details. This tight binding facilitates the hardware and JVM evolving together without affecting other software. In effect, this gives
194:
For entry to
Jazelle hardware state to succeed, the JE (Jazelle Enable) bit in the CP14:C0(C2) register must be set; clearing of the JE bit by a operating system provides a high-level override to prevent application programs from using the hardware Jazelle acceleration. Additionally, the CV
160:
The entire VM state is held within normal ARM registers, allowing compatibility with existing operating systems and interrupt handlers unmodified. Restarting a bytecode (such as following a return from interrupt) will re-execute the complete sequence of related ARM instructions.
67:(JVM) will attempt to run Java bytecode in hardware, while returning to the software for more complicated, or lesser-used bytecode operations. ARM claims that approximately 95% of bytecode in typical program usage ends up being directly processed in the hardware.
132:
goes as far as to state: "For the avoidance of doubt, distribution of products containing software code to exercise the BXJ instruction and enable the use of the ARM Jazelle architecture extension without agreement from ARM is expressly forbidden."
221:
Execution will continue in hardware until an unhandled bytecode is encountered, or an exception occurs. Between 134 and 149 bytecodes (out of 203 bytecodes specified in the JVM specification) are translated and executed directly in the hardware.
230:
Low-level configuration registers, for the hardware virtual machine, are held in the ARM Co-processor "CP14 register c0". The registers allow detecting, enabling or disabling the hardware accelerator (if it is available).
79:
considerable control over which JVMs are able to exploit
Jazelle. It also prevents open source JVMs from using Jazelle. These issues do not apply to the ARMv7 ThumbEE environment, the nominal successor to Jazelle DBX.
211:(PC) pointing to the next instructions must be placed in the Link Register (R14) before executing the BXJ branch request, as regardless of hardware or software processing, the system must know where to begin decoding.
99:
The
Jazelle mode moves JVM interpretation into hardware for the most common simple JVM instructions. This is intended to significantly reduce the cost of interpretation. Among other things, this reduces the need for
190:
Bytecodes are decoded by the hardware in two stages (versus a single stage for Thumb and ARM code) and switching between hardware and software decoding (Jazelle mode and ARM mode) takes ~4 clock cycles.
261:
of JVM bytecodes. In implementation terms, only trivial hardware support for
Jazelle is now required: support for entering and exiting Jazelle mode, but not for executing any Java bytecodes.
164:
Specific registers are designated to hold the most important parts of the JVM state: registers R0–R3 hold an alias of the top of the Java stack, R4 holds Java local operand zero (pointer to
187:
Java bytecode is indicated as the current instruction set by a combination of two bits in the ARM CPSR (Current
Program Status Register). The "T"-bit must be cleared and the "J"-bit set.
276:
Support for ThumbEE was mandatory in ARMv7-A processors (such as the Cortex-A8 and Cortex-A9), and optional in ARMv7-R processors. ThumbEE targeted compiled environments, perhaps using
249:
emulator) is only required to support the BXJ opcode itself (treating BXJ as a normal BX instruction) and to return RAZ (Read-As-Zero) for all of the CP14:c0 Jazelle-related registers.
322:
214:
Because the current state is held in the CPSR, the bytecode instruction set is automatically reselected after task-switching and processing of the current Java bytecode is restarted.
203:
The BXJ instruction attempts to switch to
Jazelle state, and if allowed and successful, sets the "J" bit in the CPSR; otherwise, it "falls through" and acts as a standard BX (
445:
207:) instruction. The only time when an operating system or debugger must be fully aware of the Jazelle mode is when decoding a faulted or trapped instruction. The Java
42:. Jazelle is denoted by a "J" appended to the CPU name, except for post-v5 cores where it is required (albeit only in trivial form) for architecture conformance.
640:
280:
technologies. It was not at all specific to Java, and was fully documented; much broader adoption was anticipated than Jazelle was able to achieve.
560:
480:
109:
need to know which bytecodes are implemented in hardware and a software fallback is provided by the software JVM for the full set of bytecodes.
336:
195:(Configuration Valid) bit found in CP14:c0(c1) must be set to show that there is a consistent Jazelle state setup for the hardware to use.
238:
The Jazelle OS Control Register at CP14:c0(c1) is only accessible in kernel mode and will cause an exception when accessed in user mode.
507:
420:
38:
modes. Jazelle functionality was specified in the ARMv5TEJ architecture and the first processor with Jazelle technology was the
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406:
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125:. However, ARM has not released details on the exact execution environment details; the documentation provided with Sun's
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269:
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363:
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compilers that produced Thumb or Thumb2 code could be modified to work with ThumbEE-based runtime environments.
241:
The Jazelle Main Configuration Register at CP14:C0(C2) is write-only in user mode and read-write in kernel mode.
967:
691:
59:
The most prominent use of Jazelle DBX is by manufacturers of mobile phones to increase the execution speed of
1125:
1037:
947:
932:
463:
421:"CPM Design Online - Using ARM DBX hardware extensions to accelerate Java in space-constrained embedded apps"
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150:
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957:
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49:
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bytecode goes in R14, so the use of the PC is not generally user-visible except during debugging.
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96:. Recognised bytecodes are converted into a string of one or more native ARM instructions.
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663:
235:
The Jazelle Identity Register in register CP14:C0(C0) is read-only accessible in all modes.
154:
129:
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48:(Runtime Compilation Target) is a different technology based on ThumbEE mode; it supports
8:
35:
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146:
89:
457:
378:
92:, implemented as an extra stage between the fetch and decode stages in the processor
31:
521:"Re: [RFC][PATCH] Add ARM Jazelle state info in show_regs tombstone"
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70:
The published specifications are very incomplete, being only sufficient for writing
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as will a Java bytecode of 0xff, which is used for setting JVM breakpoints.
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details being shown as "SUB-ARCHITECTURE DEFINED" and documented elsewhere.
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76:
762:
45:
952:
680:
600:
ARM reference Manual, Understanding ARM11 Processor Power Saving Modes
922:
686:
481:"ARM Whitepaper, Accelerating to meet the challenge of embedded Java"
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992:
927:
868:
843:
792:
731:
696:
60:
245:
A "trivial" hardware implementation of Jazelle (as found in the
997:
942:
772:
741:
446:"Release Notes - CLDC HotSpotTM Implementation - Version 1.1.3"
508:
Intel, ARM Architecture introduction. Dead link, February 2020
56:(JIT) compilation with Java and other execution environments.
937:
22:(direct bytecode execution) is an extension that allows some
246:
39:
399:"Shanghai Jade Licenses ARM Prime Starter Kit for DCP SoC"
34:
as a third execution state alongside the existing ARM and
546:
ARM Whitepaper, High performance Java on embedded devices
452:. 2007-10-26. Archived from the original on 2008-06-02.
149:
between the JVM and the Jazelle hardware state. This
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The ARMv7 architecture has de-emphasized Jazelle and
140:
291:
611:
ARM reference, Cortex-A8 Technical reference Manual
175:PC or its synonym register R15. A pointer to the
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475:
473:
153:is not published by ARM, rendering Jazelle an
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648:
563:[ARM Architecture Reference Manual]
337:"Artificial Intelligence Enhanced Computing"
589:ARM, ARM1026EJ-S Technical reference Manual
582:
555:
553:
470:
373:. Archived from the original on 2007-01-26.
641:
627:
320:, "Program instruction interpretation"
168:) and R6 contains the Java stack pointer.
604:
571:(in Japanese). 2008-09-10. Archived from
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63:games and applications. A Jazelle-aware
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157:for most users and Free Software JVMs.
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225:
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145:The Jazelle state relies on an agreed
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88:The Jazelle extension uses low-level
16:Hardware extension for ARM processors
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364:"ARM Architecture reference Manual"
13:
413:
141:Application binary interface (ABI)
112:
14:
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83:
1095:
1084:
1083:
705:
519:Marinas, Catalin (4 June 2007).
409:from the original on 2004-02-06.
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1102:Computer programming portal
274:has since also been deprecated.
807:Major third-party technologies
1:
1038:Sun Microsystems Laboratories
287:
490:. 2004-04-14. Archived from
171:Jazelle reuses the existing
151:application binary interface
7:
302:Computer programming portal
272:) was to be preferred, but
266:Thumb Execution Environment
10:
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1014:Apache Software Foundation
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1006:
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908:
900:Free Java implementations
877:
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561:"ARM アーキテクチャ リファレンスマニュアル"
462:: CS1 maint: unfit URL (
383:: CS1 maint: unfit URL (
259:Direct Bytecode Execution
1131:Interpreters (computing)
650:Java (software platform)
102:Just-in-time compilation
1024:Java Community Process
890:Java Community Process
121:is well documented as
26:processors to execute
756:Platform technologies
183:CPSR: Mode indication
1126:Java virtual machine
885:Java version history
737:Java virtual machine
727:Java Development Kit
155:undocumented feature
130:Java Virtual Machine
94:instruction pipeline
65:Java virtual machine
715:Oracle technologies
226:Low-level registers
199:BXJ: Branch to Java
1029:Oracle Corporation
1019:Eclipse Foundation
253:Successor: ThumbEE
147:calling convention
90:binary translation
1108:
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1034:Sun Microsystems
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578:on 2008-09-10.
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527:(Mailing list)
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405:. 2004-01-12.
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28:Java bytecode
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683:(Enterprise)
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573:the original
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541:
529:. Retrieved
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492:the original
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450:java.sun.com
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54:just-in-time
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985:Conferences
692:Android SDK
46:Jazelle RCT
20:Jazelle DBX
1115:Categories
1064:Urs Hölzle
953:Processing
681:Jakarta EE
677:(Standard)
569:jp.arm.com
488:jp.arm.com
431:2009-02-25
318:US 7089539
288:References
52:(AOT) and
40:ARM926EJ-S
977:Community
923:BeanShell
839:Hibernate
814:Blackdown
747:Maxine VM
687:Java Card
657:Platforms
1090:Category
768:Servlets
458:cite web
407:Archived
379:cite web
32:hardware
1093:
993:JavaOne
968:Oxygene
928:Clojure
878:History
869:WildFly
864:TopLink
849:Jazelle
844:IcedTea
834:Harmony
819:Eclipse
798:Modules
793:Pack200
773:MIDlets
763:Applets
732:OpenJDK
697:GraalVM
675:Java SE
671:(Micro)
669:Java ME
371:arm.com
270:ThumbEE
127:HotSpot
61:Java ME
1047:People
998:Devoxx
948:Kotlin
943:Jython
933:Groovy
859:Struts
854:Spring
742:JavaFX
722:Squawk
531:5 June
324:
205:Branch
963:Scala
958:Rhino
938:JRuby
576:(PDF)
565:(PDF)
495:(PDF)
484:(PDF)
367:(PDF)
166:*this
36:Thumb
918:Java
533:2020
464:link
385:link
247:QEMU
177:next
829:GWT
783:JSF
778:JSP
664:JVM
278:JIT
30:in
24:ARM
1117::
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456:{{
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377:{{
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349:^
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268:(
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