Re: [PATCH RFC 2/2] m68k: Make allowance for signal delivery following an address error

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On Wed, 3 May 2023, Michael Schmitz wrote:

So the case that you are concerned about here is where the instruction 
in execution is e.g. a moveml using USP as one of the data addresses 
(making USP unreliable) and the instruction faulting is one of the next 
ones being decoded. [...]

Right. The instruction in execution may be an incomplete stack operation 
like MOVEM. If the signal handler fixes up the address error, that stack 
operation might be resumed after sys_sigreturn(), like the bus error case.
The kernel allows the exception frame to fixed up by the user program.

(You mentioned cpBcc or cpDBcc instructions in another mail - where did 
you find that? It's not mentioned in my copy of the 030 UM...)


It's in the 3rd edition (1990), section 10.5.2.8.
https://www.nxp.com/files-static/32bit/doc/ref_manual/MC68030UM-P1.pdf
https://www.nxp.com/files-static/32bit/doc/ref_manual/MC68030UM-P2.pdf

I'm not trying to say this all isn't necessary for address errors. I'm 
just trying to understand why it is.


I haven't yet tried to write code to demonstrate the theoretical address 
error issue but I can attempt that if need be. However, such code would be 
moot if this patch is going to be required anyway, just to fix the bus 
error case...



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