[B2-devel] SheepShaver SIGBUS handler

[Gwenole B. <gb...@di...>]

Hi,

I finally found out why SheepShaver no longer worked for me on earlier 
systems. It turns out kernel is finally generating bus errors on 
unaligned accesses (e.g. through stmw instructionts). Indeed, I got 
this while booting MacOS 8.1:

SIGSEGV
    pc 40a4f9dc     lr 40a4a0cc    ctr 40a4a078    msr 0000d032
   xer 00000000     cr 44000441
    r0 00000000     r1 20bf7eb0     r2 20186a68     r3 202d6c4e
    r4 20000a98     r5 40a4a0cc     r6 44000441     r7 201862e8
    r8 201869a8     r9 202d6970    r10 20186828    r11 20186c60
   r12 201868e8    r13 1008e380    r14 2000042c    r15 0000004b
   r16 2000042c    r17 20187570    r18 73637269    r19 408187ce
   r20 000007d2    r21 00000000    r22 00000816    r23 000007d2
   r24 202c7a60    r25 00000000    r26 20000428    r27 201fa5e0
   r28 202d69b8    r29 00000001    r30 202d6a3c    r31 202d6970
Welcome to the sheep factory.
40a4f9c4: 7ca802a6      mflr    r5
40a4f9c8: 7cc00026      mfcr    r6
40a4f9cc: 90a30000      stw     r5,$0000(r3)
40a4f9d0: 90c30004      stw     r6,$0004(r3)
40a4f9d4: 90230008      stw     r1,$0008(r3)
40a4f9d8: 9043000c      stw     r2,$000c(r3)
40a4f9dc: bda30014      stmw    r13,$0014(r3)
40a4f9e0: fc00048e      mffs    fr0
40a4f9e4: d9c30060      stfd    fr14,$0060(r3)
40a4f9e8: d9e30068      stfd    fr15,$0068(r3)
40a4f9ec: da030070      stfd    fr16,$0070(r3)
40a4f9f0: da230078      stfd    fr17,$0078(r3)
40a4f9f4: da430080      stfd    fr18,$0080(r3)
40a4f9f8: da630088      stfd    fr19,$0088(r3)
40a4f9fc: da830090      stfd    fr20,$0090(r3)

And EA is not aligned on 4-byte boundaries as stmw requests. I don't 
know why it's so "recently". The workaround is to hook the 
sigsegv_handler to SIGBUS and set ignoresegv to true in the prefs file. 
Is it OK with you? The same error probably prevented from running MacOS 
8.6 too.

Does someone know why r3 contents is unaligned?

Bye,
Gwenole.