Wimp invalid error pointer during initialisation

In RISC OS 5.27, the WindowManager can fail to initialise, and return an invalid error pointer from the module initialisation.

A trace of the error:

Initialise module: #  7 WindowManager            flags &00000001
Module instantiate: <Module(WindowManager @ &fc110890 + &20808)>
Instantiate module WindowManager: class=<class 'riscos.modules.Instance'>
Calling module init for <Instance(WindowManager%Base, pw=&00000000)>
Init dispatch for module WindowManager%Base (instance 0) to &fc1116b4 (arguments='')
fc1116b4: {DA 'Extension ROM', module 'WindowManager': Entry Initialise}
...
==== Begin RISC OS error pointer ====
Error pointer &0fffffff is not valid memory
Registers:
  r0  = &0fffffff, r1  = &00000000, r2  = &00000000, r3  = &00000000
  r4  = &00000000, r5  = &00000000, r6  = &00000000, r7  = &00000000
  r8  = &00000000, r9  = &00000000, r10 = &00000000, r11 = &00000000
  r12 = &00000000, sp  = &04108000, lr  = &00000000, pc  = &00000000
  CPSR= &70000013 : SVC-32 ARM fi ae qVCZn
  SPSR= &00000000 : USR-26 ARM fi ae qvczn
Locations:
  pc is DA 'Zero Page'
  lr is DA 'Zero Page'
Recently executed code:
  ---- Block &fc12f46c, 1 instructions ----
  fc12f46c: {DA 'Extension ROM', module 'WindowManager'}
  fc12f46c: POP     {r0, r1, pc}
  ---- Block &fc12f3a8, 2 instructions ----
  fc12f3a8: MOV     r0, #0
  fc12f3ac: BL      &FC12F6F0
  ---- Block &fc12f6f0, 5 instructions ----
  fc12f6f0: PUSH    {r1, r2, lr}
  fc12f6f4: LDR     r1, [r12, #&1a0]
  fc12f6f8: ADD     r1, r1, #&3ac
  fc12f6fc: TEQ     r0, #0
  fc12f700: BEQ     &FC12F720
  ---- Block &fc12f720, 2 instructions ----
  fc12f720: ADD     r0, r1, #8
  fc12f724: POP     {r1, r2, pc}
  ---- Block &fc12f3b0, 15 instructions ----
  fc12f3b0: MOV     r9, r0
  fc12f3b4: MOV     r0, #&110                 ; #272
  fc12f3b8: MOV     r1, r9
  fc12f3bc: ADR     r2, &FC12F2C4             ; -> "ipboard Workspace"
  fc12f3c0: SUB     r2, r2, #8
  fc12f3c4: MOV     r3, #0
  fc12f3c8: LDR     lr, [r12, #&24]
  fc12f3cc: SUB     r5, r5, #1
  fc12f3d0: MOV     r7, r5, LSL lr
  fc12f3d4: LDR     lr, [r12, #&20]
  fc12f3d8: SUB     r4, r4, #1
  fc12f3dc: MOV     r6, r4, LSL lr
  fc12f3e0: MOV     r5, #0
  fc12f3e4: MOV     r4, #0
  fc12f3e8: SWI     XOS_SpriteOp
  ---- Block &fc12f3ec, 1 instructions ----
  fc12f3ec: BVS     &FC12F40C
  ---- Block &fc12f40c, 4 instructions ----
  fc12f40c: MOVVS   lr, #0
  fc12f410: STR     lr, [r8]
  fc12f414: STRVS   r0, [sp]
  fc12f418: POP     {r0, r1, r2, r3, r4, r5, r6, r7, r8, r9, pc}
  ---- Block &fc1121d0, 2 instructions ----
  fc1121d0: POP     {r0}
  fc1121d4: POP     {pc}
  ---- Block &fc111c10, 2 instructions ----
  fc111c10: STRVS   r0, [sp]
  fc111c14: POP     {r0, r1, r2, r3, r4, r5, r6, r7, r8, r9, r10, r11, r12, pc}
  ---- Block &04107fac, 1 instructions ----
   4107fac: {DA 'SVC Stack'}
   4107fac: SWI     &FEED05
==== End RISC OS error pointer ====
Instantiate failed: RISCOSSyntheticError('[Synthetic] Invalid error pointer &0fffffff',)
  Error: [Synthetic] Invalid error pointer &0fffffff

Implies to me that the error from XOS_SpriteOp is identified and leaves the V flag set. This is preserved in the stack at &fc12f414, but then corrupted by the POP at &fc1121d0, which is then preserved on to the return registers by the STRVS at &fc111c10.

Testing with the latest RC of 5.31, this bug remains.

The error report from RISC OS Pyromaniac is near identical, implying that no change has been made, and the same problem persists.

Initialise module: #  7 WindowManager            flags &00000001
==== Begin RISC OS error pointer ====
Error pointer &0fffffff is not valid memory
Registers:
  r0  = &0fffffff, r1  = &00000000, r2  = &00000000, r3  = &00000000
  r4  = &00000000, r5  = &00000000, r6  = &00000000, r7  = &00000000
  r8  = &00000000, r9  = &00000000, r10 = &00000000, r11 = &00000000
  r12 = &00000000, sp  = &04108000, lr  = &00000000, pc  = &00000000
  CPSR= &70000013 : SVC-32 ARM fi ae qVCZn
  SPSR= &00000000 : USR-26 ARM fi ae qvczn
Locations:
  pc is DA 'Zero Page'
  lr is DA 'Zero Page'
Recently executed code:
  ---- Block &fc1307cc, 3 instructions ----
  fc1307cc: {DA 'Extension ROM', module 'WindowManager'}
  fc1307cc: MOV     r0, #&228                 ; #552
  fc1307d0: ADD     r2, r9, #&10
  fc1307d4: SWI     XOS_SpriteOp
  ---- Block &fc1307d8, 1 instructions ----
  fc1307d8: BVS     &FC1307E8
  ---- Block &fc1307dc, 2 instructions ----
  fc1307dc: STR     r6, [r8, #4]
  fc1307e0: BL      &FC1307F8
  ---- Block &fc1307f8, 2 instructions ----
  fc1307f8: PUSH    {r0, r1, r2, r3, lr}
  fc1307fc: LDR     r0, &FC130B3C             ; = &0000023e
  ---- Block &fc130800, 4 instructions ----
  fc130800: MOV     r1, r9
  fc130804: LDR     r2, [r1, #8]
  fc130808: ADD     r2, r2, r9
  fc13080c: SWI     XOS_SpriteOp
  ---- Block &fc130810, 1 instructions ----
  fc130810: POPVS   {r0, r1, r2, r3, pc}
  ---- Block &fc1307e4, 5 instructions ----
  fc1307e4: MOVVC   lr, #1
  fc1307e8: MOVVS   lr, #0
  fc1307ec: STR     lr, [r8]
  fc1307f0: STRVS   r0, [sp]
  fc1307f4: POP     {r0, r1, r2, r3, r4, r5, r6, r7, r8, r9, pc}
  ---- Block &fc11333c, 2 instructions ----
  fc11333c: POP     {r0}
  fc113340: POP     {pc}
  ---- Block &fc112d70, 2 instructions ----
  fc112d70: STRVS   r0, [sp]
  fc112d74: POP     {r0, r1, r2, r3, r4, r5, r6, r7, r8, r9, r10, r11, r12, pc}
  ---- Block &04107fac, 1 instructions ----
   4107fac: {DA 'SVC Stack'}
   4107fac: SWI     &FEED05
==== End RISC OS error pointer ====
  Error: [Synthetic] Invalid error pointer &0fffffff

The same description of the fault as the original error report remains true.