linux-kernel - Re: [PATCH tip 1/2] signal, perf: Fix siginfo_t by avoiding u64 on 32-bit architectures

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Date:   Thu, 22 Apr 2021 09:15:30 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Marco Elver <elver@...gle.com>, <peterz@...radead.org>,
        <mingo@...hat.com>, <tglx@...utronix.de>
CC:     <m.szyprowski@...sung.com>, <dvyukov@...gle.com>,
        <glider@...gle.com>, <arnd@...db.de>, <christian@...uner.io>,
        <axboe@...nel.dk>, <pcc@...gle.com>, <oleg@...hat.com>,
        <kasan-dev@...glegroups.com>, <linux-arch@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH tip 1/2] signal, perf: Fix siginfo_t by avoiding u64 on
 32-bit architectures


On 22/04/2021 07:44, Marco Elver wrote:
> On some architectures, like Arm, the alignment of a structure is that of
> its largest member.
> 
> This means that there is no portable way to add 64-bit integers to
> siginfo_t on 32-bit architectures, because siginfo_t does not contain
> any 64-bit integers on 32-bit architectures.
> 
> In the case of the si_perf field, word size is sufficient since there is
> no exact requirement on size, given the data it contains is user-defined
> via perf_event_attr::sig_data. On 32-bit architectures, any excess bits
> of perf_event_attr::sig_data will therefore be truncated when copying
> into si_perf.
> 
> Since this field is intended to disambiguate events (e.g. encoding
> relevant information if there are more events of the same type), 32 bits
> should provide enough entropy to do so on 32-bit architectures.
> 
> For 64-bit architectures, no change is intended.
> 
> Fixes: fb6cc127e0b6 ("signal: Introduce TRAP_PERF si_code and si_perf to siginfo")
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Reported-by: Jon Hunter <jonathanh@...dia.com>
> Signed-off-by: Marco Elver <elver@...gle.com>


Thanks for fixing!

Tested-by: Jon Hunter <jonathanh@...dia.com>

Cheers
Jon

-- 
nvpublic