zafena development

October 6, 2009

picture of the day!

The picture that made my day!

Ok.. so what happened?

xerxes@babbage-karmic:/wd/icedtea6/openjdk/build/linux-arm/bin$ ./java -version
java version "1.6.0_0"
OpenJDK Runtime Environment (IcedTea6 1.7pre-r2a3725ce72d4) (build 1.6.0_0-b16)
OpenJDK Shark VM (build 14.0-b16-product, mixed mode)

xerxes@babbage-karmic:/wd/icedtea6/openjdk/build/linux-arm/bin$ cat /proc/cpuinfo
Processor    : ARMv7 Processor rev 1 (v7l)
BogoMIPS    : 799.53
Features    : swp half thumb fastmult vfp edsp
CPU implementer    : 0x41
CPU architecture: 7
CPU variant    : 0x2
CPU part    : 0xc08
CPU revision    : 1
Hardware    : Freescale MX51 Babbage Board
Revision    : 51011
Serial        : 0000000000000000

xerxes@babbage-karmic:/wd/llvm$ svn info
Repository Root:
Repository UUID: 91177308-0d34-0410-b5e6-96231b3b80d8
Revision: 82896
Node Kind: directory
Schedule: normal
Last Changed Author: edwin
Last Changed Rev: 82896
Last Changed Date: 2009-09-27 11:08:03 +0000 (Sun, 27 Sep 2009)

xerxes@babbage-karmic:/wd/llvm$ quilt diff
Index: llvm/lib/Target/ARM/
--- llvm.orig/lib/Target/ARM/    2009-10-06 12:35:26.000000000 +0000
+++ llvm/lib/Target/ARM/    2009-10-06 12:36:03.000000000 +0000
@@ -645,7 +645,7 @@
 IIC_Br, "mov lr, pc\n\tbx $func",
 [(ARMcall_nolink GPR:$func)]>,
 Requires<[IsARM, IsNotDarwin]> {
-    let Inst{7-4}   = 0b0001;
+    let Inst{7-4}   = 0b0011;
 let Inst{19-8}  = 0b111111111111;
 let Inst{27-20} = 0b00010010;

The last patch on LLVM are currently a hack. basically it makes LLVM emit ARM BLX instructions instead of BX instructions for ARM::CALL_NOLINK. So why did this little hack make it work?

In order to understand that, one have to find out what made Shark on ARM crash before...

Lets rewind time to some days ago... 

Hi, i have been enjoying myself inside gdb for some days, and I have now at least found the reason why the cpu
ends up in garbage memory when running shark on arm.

The problem can be illustrated like this:

frame manager invokes jited code
entry_zero.hpp:57 invokes jit code at 0x67c9e990

jited code runs
0x67c9e990:    push    {r4, r5, r6, r7, r8, r9, r10, r11, lr}
0x67c9e994:    sub    sp, sp, #12    ; 0xc
0x67c9e998:    ldr    r12, [r3, #756]
0x67c9e99c:    ldr    lr, [r3, #764]
0x67c9e9a0:    sub    r4, lr, #56    ; 0x38
0x67c9e9a4:    cmp    r4, r12
0x67c9e9a8:    bcc    0x67c9ebd0
0x67c9e9ac:    mov    r5, r3
0x67c9e9b0:    str    r2, [sp, #4]
0x67c9e9b4:    mov    r6, r0
0x67c9e9b8:    str    r4, [r5, #764]
0x67c9e9bc:    str    r4, [r4, #20]
0x67c9e9c0:    ldr    r0, [pc, #640]    ; 0x67c9ec48
0x67c9e9c4:    str    r0, [r4, #28]
0x67c9e9c8:    ldr    r0, [r5, #768]
0x67c9e9cc:    str    r0, [r4, #32]
0x67c9e9d0:    add    r0, r4, #32    ; 0x20
0x67c9e9d4:    str    r0, [r5, #768]
0x67c9e9d8:    str    r6, [r4, #16]
0x67c9e9dc:    ldr    r7, [r1]
0x67c9e9e0:    ldr    r0, [r1, #4]
0x67c9e9e4:    str    r0, [sp]
0x67c9e9e8:    ldr    r8, [r1, #8]
0x67c9e9ec:    ldr    r9, [r1, #12]
0x67c9e9f0:    ldr    r0, [r1, #16]
0x67c9e9f4:    str    r0, [sp, #8]
0x67c9e9f8:    ldr    r10, [r1, #20]
0x67c9e9fc:    ldr    r2, [pc, #584]    ; 0x67c9ec4c   <------ jit code calls a jvm function stored in this address
0x67c9ea00:    mov    r0, r1
0x67c9ea04:    bx    r2 <---------------------------   problem!  should have been blx!

(gdb) x 0x67c9ec4c
0x67c9ec4c:    0x40836d9c
(gdb) x 0x40836d9c
0x40836d9c <_ZN13SharedRuntime17OSR_migration_endEPi>:    0xe92d41f0

so lets check out _ZN13SharedRuntime17OSR_migration_endEPi

0x40836d9c <_ZN13SharedRuntime17OSR_migration_endEPi+0>:    push    {r4, r5, r6, r7, r8, lr}    <------  lr are backed up..  but bx did not update lr..
0x40836da0 <_ZN13SharedRuntime17OSR_migration_endEPi+4>:    ldr    r4, [pc, #284]    ; 0x40836ec4 <_ZN13SharedRuntime17OSR_migration_endEPi+296>
0x40836da4 <_ZN13SharedRuntime17OSR_migration_endEPi+8>:    ldr    r7, [pc, #284]    ; 0x40836ec8 <_ZN13SharedRuntime17OSR_migration_endEPi+300>
0x40836da8 <_ZN13SharedRuntime17OSR_migration_endEPi+12>:    ldr    r6, [pc, #284]    ; 0x40836ecc <_ZN13SharedRuntime17OSR_migration_endEPi+304>
0x40836dac <_ZN13SharedRuntime17OSR_migration_endEPi+16>:    add    r4, pc, r4
0x40836db0 <_ZN13SharedRuntime17OSR_migration_endEPi+20>:    ldr    r12, [r4, r7]
0x40836db4 <_ZN13SharedRuntime17OSR_migration_endEPi+24>:    ldr    r1, [r4, r6]
0x40836db8 <_ZN13SharedRuntime17OSR_migration_endEPi+28>:    ldr    r5, [r12]
0x40836dbc <_ZN13SharedRuntime17OSR_migration_endEPi+32>:    ldrb    r2, [r1]
0x40836dc0 <_ZN13SharedRuntime17OSR_migration_endEPi+36>:    add    r3, r5, #1    ; 0x1
0x40836dc4 <_ZN13SharedRuntime17OSR_migration_endEPi+40>:    cmp    r2, #0    ; 0x0
0x40836dc8 <_ZN13SharedRuntime17OSR_migration_endEPi+44>:    sub    sp, sp, #24    ; 0x18
0x40836dcc <_ZN13SharedRuntime17OSR_migration_endEPi+48>:    str    r3, [r12]
0x40836dd0 <_ZN13SharedRuntime17OSR_migration_endEPi+52>:    mov    r7, r0
0x40836dd4 <_ZN13SharedRuntime17OSR_migration_endEPi+56>:    bne 0x40836e74 <_ZN13SharedRuntime17OSR_migration_endEPi+216>
0x40836dd8 <_ZN13SharedRuntime17OSR_migration_endEPi+60>:    ldr    r2, [pc, #240]    ; 0x40836ed0 <_ZN13SharedRuntime17OSR_migration_endEPi+308>
0x40836ddc <_ZN13SharedRuntime17OSR_migration_endEPi+64>:    ldr    r12, [r4, r2]
0x40836de0 <_ZN13SharedRuntime17OSR_migration_endEPi+68>:    ldrb    r3, [r12]
0x40836de4 <_ZN13SharedRuntime17OSR_migration_endEPi+72>:    cmp    r3, #0    ; 0x0
0x40836de8 <_ZN13SharedRuntime17OSR_migration_endEPi+76>:    beq 0x40836e20 <_ZN13SharedRuntime17OSR_migration_endEPi+132>
0x40836dec <_ZN13SharedRuntime17OSR_migration_endEPi+80>:    ldr    r6, [pc, #224]    ; 0x40836ed4 <_ZN13SharedRuntime17OSR_migration_endEPi+312>
0x40836df0 <_ZN13SharedRuntime17OSR_migration_endEPi+84>:    ldr    r5, [r4, r6]
0x40836df4 <_ZN13SharedRuntime17OSR_migration_endEPi+88>:    add    r0, r4, r6
0x40836df8 <_ZN13SharedRuntime17OSR_migration_endEPi+92>:    tst    r5, #1    ; 0x1
0x40836dfc <_ZN13SharedRuntime17OSR_migration_endEPi+96>:    beq 0x40836e8c <_ZN13SharedRuntime17OSR_migration_endEPi+240>
0x40836e00 <_ZN13SharedRuntime17OSR_migration_endEPi+100>:    ldr    r5, [pc, #208]    ; 0x40836ed8 <_ZN13SharedRuntime17OSR_migration_endEPi+316>
0x40836e04 <_ZN13SharedRuntime17OSR_migration_endEPi+104>:    ldr    r3, [r4, r5]
0x40836e08 <_ZN13SharedRuntime17OSR_migration_endEPi+108>:    cmp    r3, #0    ; 0x0
0x40836e0c <_ZN13SharedRuntime17OSR_migration_endEPi+112>:    movne r0, r3
0x40836e10 <_ZN13SharedRuntime17OSR_migration_endEPi+116>:    ldrne r6, [r3]
0x40836e14 <_ZN13SharedRuntime17OSR_migration_endEPi+120>:    ldrne r12, [r6, #16]
0x40836e18 <_ZN13SharedRuntime17OSR_migration_endEPi+124>:    movne lr, pc
0x40836e1c <_ZN13SharedRuntime17OSR_migration_endEPi+128>:    bxne    r12
0x40836e20 <_ZN13SharedRuntime17OSR_migration_endEPi+132>:    add    r6, sp, #20    ; 0x14
0x40836e24 <_ZN13SharedRuntime17OSR_migration_endEPi+136>:    mov    r0, r6
0x40836e28 <_ZN13SharedRuntime17OSR_migration_endEPi+140>:    bl 0x40596c84 <NoHandleMark>
0x40836e2c <_ZN13SharedRuntime17OSR_migration_endEPi+144>:    mov    r0, sp
0x40836e30 <_ZN13SharedRuntime17OSR_migration_endEPi+148>:    bl 0x4057909c <JRT_Leaf_Verifier>
0x40836e34 <_ZN13SharedRuntime17OSR_migration_endEPi+152>:    ldr    r3, [pc, #160]    ; 0x40836edc <_ZN13SharedRuntime17OSR_migration_endEPi+320>
0x40836e38 <_ZN13SharedRuntime17OSR_migration_endEPi+156>:    mov    r5, sp
0x40836e3c <_ZN13SharedRuntime17OSR_migration_endEPi+160>:    ldr r12, [r4, r3]
0x40836e40 <_ZN13SharedRuntime17OSR_migration_endEPi+164>:    ldrb r0, [r12]
0x40836e44 <_ZN13SharedRuntime17OSR_migration_endEPi+168>:    cmp    r0, #0    ; 0x0
0x40836e48 <_ZN13SharedRuntime17OSR_migration_endEPi+172>:    movne r0, r7
0x40836e4c <_ZN13SharedRuntime17OSR_migration_endEPi+176>:    blne 0x4039b20c <_Z15trace_heap_freePv>
0x40836e50 <_ZN13SharedRuntime17OSR_migration_endEPi+180>:    mov    r0, r7
0x40836e54 <_ZN13SharedRuntime17OSR_migration_endEPi+184>:    bl 0x407b6a94 <_ZN2os4freeEPv>
0x40836e58 <_ZN13SharedRuntime17OSR_migration_endEPi+188>:    mov    r0, sp
0x40836e5c <_ZN13SharedRuntime17OSR_migration_endEPi+192>:    bl 0x40578c5c <~JRT_Leaf_Verifier>
0x40836e60 <_ZN13SharedRuntime17OSR_migration_endEPi+196>:    mov    r0, r6
0x40836e64 <_ZN13SharedRuntime17OSR_migration_endEPi+200>:    bl 0x40596b04 <~NoHandleMark>
0x40836e68 <_ZN13SharedRuntime17OSR_migration_endEPi+204>:    add    sp, sp, #24    ; 0x18
0x40836e6c <_ZN13SharedRuntime17OSR_migration_endEPi+208>:    pop {r4, r5, r6, r7, r8, lr}
0x40836e70 <_ZN13SharedRuntime17OSR_migration_endEPi+212>:    bx    lr <------  and woho. lets enjoy a trip to garbage memory!

So when the function that the jit calls returns we find ourself eating
garbage memory.

So the small hack fixed this issue quite well but broke armv4t compatibility for the moment.

My next task would be to fix this properly in LLVM.


  1. Congrats Xerxes!

    This is great day for Java-enabled ARM + GNU/Linux netbooks and other gadgets.

    Comment by Robert Schuster — October 6, 2009 @ 16:55

  2. Xerxes, that's awesome! Following your shark trailblazing with great interest.

    Comment by Ken Gilmer — October 6, 2009 @ 17:45

  3. Congrats! Really cool!
    Looking foreward to run shark on my armv5tje based 770 soon :)

    Comment by Clemens Eisserer — October 6, 2009 @ 23:12

  4. Yep, I'm looking forward to jumping (on the) Shark!

    Good work.



    Comment by Damon Hart-Davis — October 7, 2009 @ 18:29

  5. Thank you all for your parts as well!
    Robert and Ken:, the initial work you two made to enable quick cross-compile builds of OpenJDK have helped me enormously to make me able to quickly test and generate debug builds of Shark.

    Clemens: Thank you for your work as well on the XRender backends to speeding up the Swing GUI operations, you work really makes a difference for Client GUI performance on ARM!
    For you who dont know about Clemens XRender work check out: and try run your favourite application with java -Dsun.java2d.xrender=True my.fancy.gui.HelloWorld its cool!

    Damon: Hey, your work with running a green power efficient server running tomcat on a Sheevaplug are a true green computing future gem!
    Checkout Damons notes on how to make a 1-5w main internet facing server running on ARM:

    Clemens and Damon: The Jalimo cross compile work that I also have recently been involved in together with Ken and Robert will surely produce some cool binarys for you to use on your armv5tel maemo phone and sheeva plug. I plan to publish some binarys for testing somewhere during next week.
    The Jalimo project can be checked out at:

    Comment by xerxes — October 9, 2009 @ 13:51

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