LDMIA/STMIA a register to itself?

Hi,

I wanted to take a look at !FYEO2 to see why JPEG decoding failed. I think it is using half-word accesses.

That’s when I came across this:

|my_thread_enter|

                LDR     ip,=CallerCtx
                STMIA   ip!,{a1-lr}
                STMIA   ip!,{lr}

                LDR     ip,=CallerCtx
                LDMIA   ip,{a1-pc}

The second instruction is writing the ip to the address pointed to by ip. What exactly is supposed to be written? The original value of ip? The updated (writeback) value? Some work-in-progress-as-the-instruction-is-executing value?

According to this ‘it can’t be relied upon’

On the Xscale, stacking the stack pointer results in it being corrupted and set to (IIRC) &80F0