Re: [PATCH v2 1/7] aarch64: Use br instead of ret for eh_return

[Szabolcs Nagy <szabolcs.nagy@arm.com>]

The 11/13/2023 01:27, Hans-Peter Nilsson wrote:
> > From: Szabolcs Nagy <szabolcs.nagy@arm.com>
> > Date: Fri, 3 Nov 2023 15:36:08 +0000
> 
> I don't see others commenting on this patch, and you're not
> mentioning this aspect, so I wonder:
> 
> > 	* config/aarch64/aarch64.h (EH_RETURN_TAKEN_RTX): Define.
> > 	(EH_RETURN_STACKADJ_RTX): Change to R5.
> > 	(EH_RETURN_HANDLER_RTX): Change to R6.
> 
> Isn't this an ABI change?

not really: this is interface between the function body
and the epilogue, so all within the code of a single
function doing eh return, not a public abi boundary.

(e.g. R0..R3 are preserved from the function throwing
the exception to the exception handler, so that's abi.
R4..R6 are just an internal detail of the function doing
the eh return in the unwinder.)

> 
> (I've forgotten relevant bits of the exception machinery; if
> throw and catch are always in the same object and everything
> in between register-number-agnostic then the only flaw would
> be not mentioning that in the commit message.)
> 
> brgds, H-P