[kaffe] mipsel and jit3

Mikolaj Habryn dichro at rcpt.to
Fri Oct 8 23:06:59 PDT 2004

On Sat, 2004-10-09 at 12:54, Mikolaj Habryn wrote:
> And, and... how exactly did that method get JITted in 0 ms? Something
> very, very fishy here.

Well, it's a null method, that's how. I'm about puzzled out for one day.
Turning on various bits of debug and sprinkling in some dprintfs yields
this output just before crashing:

  Method Constant Pool:
  10093da8: (ref) 0x1006baf4      0x1006baf4
  10093db0: (ref) 0x2ab51f28      0x2ab51f28
  10093db8: (ref) 0x2ab51e40      0x2ab51e40
  10093dc0: (ref) 0x1005e2b8      0x1005e2b8
  set jitted for method 0x1006baf4 to 0x10093dc8
  Translating java/lang/String$ICComp.<init>()V (normal) 0x10093dc8
  <JIT: java/lang/String$ICComp.<init>()V time 44ms (220ms) @ 0x10093dc8 (0x1006baf4)>
  soft_fixup_trampoline(): return 0x10093dc8
  soft_fixup_trampoline(): meth 0x1005e2a4, where 0x1005e2b8, native code 0x1005e2b8
  callinfo = 0x7fff7590
  null call?? 0x1005e2a4 going to soft_null_call 0x2ab50a50
  called soft_null_call (0x2ab50a50), seemed to work
  set native for method 0x1005e2a4 to 0x2ab50a50
  Translating java/lang/Object.<init>()V (normal) 0x2ab50a50
  <JIT: java/lang/Object.<init>()V time 15ms (235ms) @ 0x2ab50a50 (0x1005e2a4)>
  soft_fixup_trampoline(): return 0x2ab50a50
  Illegal instruction (core dumped)
  root at OpenWrt:~#

The crash is an illegal instruction at 0x1005e2b0. Disassembling the
region shows:

0x1005e2a4:     beq     zero,v0,0x1006a708
0x1005e2a8:     b       0x1007afac
0x1005e2ac:     0xc801
0x1005e2b0:     sdc3    $31,-1(ra)
0x1005e2b4:     sll     zero,at,0x0
0x1005e2b8:     slti    s5,s5,2640

Which makes me suspect that it's actually dying at 0x1005e2ac but
advancing the PC nonetheless. Or something. Anyway. From the first
snippet, you can see that there's something from some previous method's
constant pool right after that point, at 0x1005e2b8, and the previous
method block itself (?) just before it, at 0x1005e2a4.

So, how did we wind up jumping to that address? Broken trampoline?


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