linux-kernel - RE: [PATCH 3/3] Fix insn.c misaligned address error

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Date:   Thu, 25 Jul 2019 13:06:32 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Numfor Mbiziwo-Tiapo' <nums@...gle.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "jolsa@...hat.com" <jolsa@...hat.com>,
        "namhyung@...nel.org" <namhyung@...nel.org>,
        "songliubraving@...com" <songliubraving@...com>,
        "mbd@...com" <mbd@...com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "irogers@...gle.com" <irogers@...gle.com>,
        "eranian@...gle.com" <eranian@...gle.com>
Subject: RE: [PATCH 3/3] Fix insn.c misaligned address error

From: Numfor Mbiziwo-Tiapo
> Sent: 24 July 2019 19:45
> 
> The ubsan (undefined behavior sanitizer) version of perf throws an
> error on the 'x86 instruction decoder - new instructions' function
> of perf test.
> 
> To reproduce this run:
> make -C tools/perf USE_CLANG=1 EXTRA_CFLAGS="-fsanitize=undefined"
> 
> then run: tools/perf/perf test 62 -v
> 
> The error occurs in the __get_next macro (line 34) where an int is
> read from a potentially unaligned address. Using memcpy instead of
> assignment from an unaligned pointer.
...
>  #define __get_next(t, insn)	\
> -	({ t r = *(t*)insn->next_byte; insn->next_byte += sizeof(t); r; })
> +	({ t r; memcpy(&r, insn->next_byte, sizeof(t)); \
> +		insn->next_byte += sizeof(t); r; })

Isn't there a get_unaligned_u32() (or similar) that can be used?

	David

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