ARMv8 illegal instruction

Asked Aug 21 '17 at 09:39

Active Aug 21 '17 at 09:39

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I have written the following assembly for ARMv8:

        .text
        .align  4
        .global permute
        .type   permute, %function
permute:
        ld2 {v0.2d - v1.2d}, [x0], #32
        ld2 {v2.2d - v3.2d}, [x0], #32
        ld2 {v4.2d - v5.2d}, [x0], #32
        ld2 {v6.2d - v7.2d}, [x0]  
        zip1 v8.2d, v0.2d, v4.2d
        st1 {v0.2d - v3.2d}, [x1], #64
        st1 {v4.2d - v7.2d}, [x1]

The function permute is called from a regular C program with two byte pointers of length 128 as inputs. This compiles fine, but when I run it I get Illegal instruction. If I comment out the zip1 instruction, it also runs fine.

Any tips on what might be wrong, and how to debug Illegal instruction in general?

asked Aug 21 '17 at 09:39

Martin Lauridsen

1

Does any ARM documentation say anything about a `zip1` instruction? – klutt Aug 21 '17 at 09:51
@klutt. http://115.28.165.193/down/arm/arch/ARM_v8_Instruction_Set_Architecture_%28Overview%29.pdf – Sir Jo Black Aug 21 '17 at 10:01
why do not you use C with vector intrinsics? They are well defined in the CMSIS – 0___________ Aug 21 '17 at 10:09
See page 1636 of this document: http://infocenter.arm.com/help/topic/com.arm.doc.dui0801g/DUI0801G_armasm_user_guide.pdf. – Sir Jo Black Aug 21 '17 at 10:10
@SergioFormiggini I've read the documentation, but I still don't understand why it gives `Illegal instruction`. – Martin Lauridsen Aug 21 '17 at 10:41
3

Okay, it seems that adding `ret` in the end of the function fixes things – Martin Lauridsen Aug 21 '17 at 11:01
:) really you forgot to return from the routine? – 0___________ Aug 21 '17 at 11:39
@MartinLauridsen Why did it work without the `zip1`, then? – unwind Aug 21 '17 at 12:26
I think it worked 'cause you were "lucky" ... ;) Honestly, I thought it was obvious the ret in the end ... – Sir Jo Black Aug 21 '17 at 12:39

ARMv8 illegal instruction

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