On Tue, Sep 01, 2020 at 02:57:14PM +0530, Amit Daniel Kachhap wrote: > diff --git a/tools/testing/selftests/arm64/mte/mte_helper.S b/tools/testing/selftests/arm64/mte/mte_helper.S > new file mode 100644 > index 000000000000..91af6d1293f8 > --- /dev/null > +++ b/tools/testing/selftests/arm64/mte/mte_helper.S > @@ -0,0 +1,116 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* Copyright (C) 2020 ARM Limited */ > + > +#include "mte_def.h" > + > +#define ENTRY(name) \ > + .globl name ;\ > + .p2align 2;\ > + .type name, @function ;\ > +name: > + > +#define ENDPROC(name) \ > + .size name, .-name ; > + > + .text > +/* > + * mte_insert_random_tag: Insert random tag and different from > + * the orginal tag if source pointer has it. > + * Input: > + * x0 - source pointer with a tag/no-tag > + * Return: > + * x0 - pointer with random tag > + */ > +ENTRY(mte_insert_random_tag) > + mov x1, #0x0 > + gmi x1, x0, x1 > + irg x0, x0, x1 > + ret > +ENDPROC(mte_insert_random_tag) What was the reason for gmi here? The test fails when you have an include mask of 0x8000 (exclude mask 0x7fff) and x0 has tag 0xf. In this case we exclude the only allowed tag here, so the CPU falls back to the default tag 0. You can (a) stop the check_multiple_included_tags() earlier to have two allowed tags here, (b) clear the pointer old tag so that you don't end up in this scenario or (c) simply remove the gmi. My preference is the latter, we don't test the hardware here, we only want to check whether the kernel sets the GCR_EL1 correctly. BTW, you also remove mov x1, #0, just: irg x0, x0, xzr -- Catalin
