Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Marco Elver <elver@google.com>, Arnd Bergmann <arnd@arndb.de>,
        Florian Weimer <fweimer@redhat.com>,
        "David S. Miller" <davem@davemloft.net>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Collingbourne <pcc@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        sparclinux <sparclinux@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>
References: <YIpkvGrBFGlB5vNj@elver.google.com>
        <m11rat9f85.fsf@fess.ebiederm.org>
        <CAK8P3a0+uKYwL1NhY6Hvtieghba2hKYGD6hcKx5n8=4Gtt+pHA@mail.gmail.com>
        <m15z031z0a.fsf@fess.ebiederm.org> <YIxVWkT03TqcJLY3@elver.google.com>
        <m1zgxfs7zq.fsf_-_@fess.ebiederm.org>
        <m11rarqqx2.fsf_-_@fess.ebiederm.org>
        <CANpmjNNJ_MnNyD4R2+9i24E=9xPHKnwTh6zwWtBYkuAq1Xo6-w@mail.gmail.com>
        <m1wnshm14b.fsf@fess.ebiederm.org>
        <YI/wJSwQitisM8Xf@hirez.programming.kicks-ass.net>
Date:   Mon, 03 May 2021 14:38:39 -0500
In-Reply-To: <YI/wJSwQitisM8Xf@hirez.programming.kicks-ass.net> (Peter
        Zijlstra's message of "Mon, 3 May 2021 14:44:21 +0200")
Message-ID: <m1sg33ip4w.fsf@fess.ebiederm.org>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
MIME-Version: 1.0
Content-Type: text/plain
Subject: Re: [PATCH 7/3] signal: Deliver all of the perf_data in si_perf
Precedence: bulk

Peter Zijlstra <peterz@infradead.org> writes:

> On Sun, May 02, 2021 at 01:39:16PM -0500, Eric W. Biederman wrote:
>
>> The one thing that this doesn't do is give you a 64bit field
>> on 32bit architectures.
>> 
>> On 32bit builds the layout is:
>> 
>> 	int si_signo;
>> 	int si_errno;
>> 	int si_code;
>> 	void __user *_addr;
>>         
>> So I believe if the first 3 fields were moved into the _sifields union
>> si_perf could define a 64bit field as it's first member and it would not
>> break anything else.
>> 
>> Given that the data field is 64bit that seems desirable.
>
> The data field is fundamentally an address, it is internally a u64
> because the perf ring buffer has u64 alignment and it saves on compat
> crap etc.
>
> So for the 32bit/compat case the high bits will always be 0 and
> truncating into an unsigned long is fine.

I see why it is fine to truncate the data field into an unsigned long.

Other than technical difficulties in extending siginfo_t is there any
reason not to define data as a __u64?

Eric