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Date: Tue, 10 Oct 2017 10:56:19 +0100 From: Mark Rutland <mark.rutland@....com> To: Dmitry Vyukov <dvyukov@...gle.com> Cc: Alexander Potapenko <glider@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, Alexander Popov <alex.popov@...ux.com>, Andrey Ryabinin <aryabinin@...tuozzo.com>, Quentin Casasnovas <quentin.casasnovas@...cle.com>, andreyknvl <andreyknvl@...gle.com>, Kees Cook <keescook@...omium.org>, Vegard Nossum <vegard.nossum@...cle.com>, syzkaller <syzkaller@...glegroups.com>, "linux-mm@...ck.org" <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2 1/3] kcov: support comparison operands collection On Mon, Oct 09, 2017 at 08:46:18PM +0200, 'Dmitry Vyukov' via syzkaller wrote: > On Mon, Oct 9, 2017 at 8:37 PM, Mark Rutland <mark.rutland@....com> wrote: > > On Mon, Oct 09, 2017 at 08:15:10PM +0200, 'Dmitry Vyukov' via syzkaller wrote: > >> On Mon, Oct 9, 2017 at 5:46 PM, Mark Rutland <mark.rutland@....com> wrote: > >> > On Mon, Oct 09, 2017 at 05:05:19PM +0200, Alexander Potapenko wrote: > > > >> > ... I note that a few places in the kernel use a 128-bit type. Are > >> > 128-bit comparisons not instrumented? > >> > >> Yes, they are not instrumented. > >> How many are there? Can you give some examples? > > > > From a quick scan, it doesn't looks like there are currently any > > comparisons. > > > > It's used as a data type in a few places under arm64: > > > > arch/arm64/include/asm/checksum.h: __uint128_t tmp; > > arch/arm64/include/asm/checksum.h: tmp = *(const __uint128_t *)iph; > > arch/arm64/include/asm/fpsimd.h: __uint128_t vregs[32]; > > arch/arm64/include/uapi/asm/ptrace.h: __uint128_t vregs[32]; > > arch/arm64/include/uapi/asm/sigcontext.h: __uint128_t vregs[32]; > > arch/arm64/kernel/signal32.c: __uint128_t raw; > > arch/arm64/kvm/guest.c: __uint128_t tmp; > > Then I think we just continue ignoring them for now :) > In the future we can extend kcov to trace 128-bits values. We will > need to add a special flag and write 2 consecutive entries for them. > Or something along these lines. Just wanted to make sure that we weren't backing ourselves into a corner w.r.t. ABI; that sounds fine to me. Thanks, Mark.
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