[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

Re: Help needed for small assembler script for the iraf package

On Mon, 2018-01-01 at 15:20 +0100, Ole Streicher wrote:
> However, I have no idea how to write the same for the 64-bit platform
> arm64 (the code in the repo does not work). Maybe someone could help
> me here? Preferably under the IRAF license [3], so that it can be
> included upstream later.

My arm ASM is a bit rusty but doesn't this first instruction:
	stp     x29, x30, [sp, -32]!
cause sp to be updated (due to the "!")? That leaves the current stack
frame unbalanced since nothing undoes the push before the branch to
__sigsetjmp which cannot itself know to undo that change, so presumably
when __sigsetjmp (or whatever comes next) tries to return over this
stack frame explodes.

It looks like the intention is to preserve x29 in order to use it as a
scratch register, perhaps just use one of the caller saved registers
instead? (infocentre.arm.com seems to be down so I can't refresh my
memory which registers that would be).

Compared to the armhf version it seems to be making a lot of use of
spilling things to the stack slots created by moving sp, and seems to
do awful lot of pointless looking shuffling (although I've not fully
traced through to try and figure out what it thinks it is doing). Does
a more direct translation of the armhf code work, something like

	str	xzr, [x1]      @ *status = 0
	str	x1, [x0]       @ buf[0] = status
	add	x0, x0, #8     @ &buf[1] --> 1st arg for sigsetjmp
	mov	x1, xzr        @ 0       --> 2nd arg for sigsetjmp
	b	__sigsetjmp    @ call sigsetjmp

Apart from changing the register names the main difference from armhf
is the use of xzr instead of loading 0 into r2 and the array step being
8 instead of 4. I also dropped the explicit 0 offsets on the stores,
not sure if that might be possible on the armhf side too -- perhaps the
eventual instruction encoding is the same either way.

I hardly feel like it deserves my copyright, but for formalities sake
please feel free to take the above snippet under an IRAF license.


Reply to: