From: Marek Szyprowski <m.szyprowski@samsung.com>
To: Marco Elver <elver@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Jiri Olsa <jolsa@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Namhyung Kim <namhyung@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Alexander Potapenko <glider@google.com>,
Al Viro <viro@zeniv.linux.org.uk>, Arnd Bergmann <arnd@arndb.de>,
Christian Brauner <christian@brauner.io>,
Dmitry Vyukov <dvyukov@google.com>, Jann Horn <jannh@google.com>,
Jens Axboe <axboe@kernel.dk>, Matt Morehouse <mascasa@google.com>,
Peter Collingbourne <pcc@google.com>,
Ian Rogers <irogers@google.com>, Oleg Nesterov <oleg@redhat.com>,
kasan-dev <kasan-dev@googlegroups.com>,
linux-arch <linux-arch@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
linux-tegra@vger.kernel.org, jonathanh@nvidia.com
Subject: Re: [PATCH v4 05/10] signal: Introduce TRAP_PERF si_code and si_perf to siginfo
Date: Thu, 22 Apr 2021 08:12:54 +0200 [thread overview]
Message-ID: <dd99b921-3d79-a21f-8942-40fa5bf53190@samsung.com> (raw)
In-Reply-To: <YIBtr2w/8KhOoiUA@elver.google.com>
Hi Marco,
On 21.04.2021 20:23, Marco Elver wrote:
> On Wed, Apr 21, 2021 at 06:27PM +0200, Marco Elver wrote:
>> On Wed, Apr 21, 2021 at 05:11PM +0200, Marco Elver wrote:
>>> +Cc linux-arm-kernel
>>>
>> [...]
>>>> I've managed to reproduce this issue with a public Raspberry Pi OS Lite
>>>> rootfs image, even without deploying kernel modules:
>>>>
>>>> https://downloads.raspberrypi.org/raspios_lite_armhf/images/raspios_lite_armhf-2021-03-25/2021-03-04-raspios-buster-armhf-lite.zip
>>>>
>>>> # qemu-system-arm -M virt -smp 2 -m 512 -kernel zImage -append "earlycon
>>>> console=ttyAMA0 root=/dev/vda2 rw rootwait" -serial stdio -display none
>>>> -monitor null -device virtio-blk-device,drive=virtio-blk -drive
>>>> file=/tmp/2021-03-04-raspios-buster-armhf-lite.img,id=virtio-blk,if=none,format=raw
>>>> -netdev user,id=user -device virtio-net-device,netdev=user
>>>>
>>>> The above one doesn't boot if zImage z compiled from commit fb6cc127e0b6
>>>> and boots if compiled from 2e498d0a74e5. In both cases I've used default
>>>> arm/multi_v7_defconfig and
>>>> gcc-linaro-6.4.1-2017.11-x86_64_arm-linux-gnueabi toolchain.
>>> Yup, I've narrowed it down to the addition of "__u64 _perf" to
>>> siginfo_t. My guess is the __u64 causes a different alignment for a
>>> bunch of adjacent fields. It seems that x86 and m68k are the only ones
>>> that have compile-time tests for the offsets. Arm should probably add
>>> those -- I have added a bucket of static_assert() in
>>> arch/arm/kernel/signal.c and see that something's off.
>>>
>>> I'll hopefully have a fix in a day or so.
>> Arm and compiler folks: are there some special alignment requirement for
>> __u64 on arm 32-bit? (And if there is for arm64, please shout as well.)
>>
>> With the static-asserts below, the only thing that I can do to fix it is
>> to completely remove the __u64. Padding it before or after with __u32
>> just does not work. It seems that the use of __u64 shifts everything
>> in __sifields by 4 bytes.
>>
>> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
>> index d0bb9125c853..b02a4ac55938 100644
>> --- a/include/uapi/asm-generic/siginfo.h
>> +++ b/include/uapi/asm-generic/siginfo.h
>> @@ -92,7 +92,10 @@ union __sifields {
>> __u32 _pkey;
>> } _addr_pkey;
>> /* used when si_code=TRAP_PERF */
>> - __u64 _perf;
>> + struct {
>> + __u32 _perf1;
>> + __u32 _perf2;
>> + } _perf;
>> };
>> } _sigfault;
>>
>> ^^ works, but I'd hate to have to split this into 2 __u32 because it
>> makes the whole design worse.
>>
>> What alignment trick do we have to do here to fix it for __u64?
> So I think we just have to settle on 'unsigned long' here. On many
> architectures, like 32-bit 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.
>
> In the case of the si_perf field, word size is sufficient since the data
> it contains is user-defined. On 32-bit architectures, any excess bits of
> perf_event_attr::sig_data will therefore be truncated when copying into
> si_perf.
>
> Feel free to test the below if you have time, but the below lets me boot
> 32-bit arm which previously timed out. It also passes all the
> static_asserts() I added (will send those as separate patches).
>
> Once I'm convinced this passes all others tests too, I'll send a patch.
This fixes the issue I've observed on my test systems. Feel free to add:
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Thanks,
> -- Marco
>
>
> diff --git a/include/linux/compat.h b/include/linux/compat.h
> index c8821d966812..f0d2dd35d408 100644
> --- a/include/linux/compat.h
> +++ b/include/linux/compat.h
> @@ -237,7 +237,7 @@ typedef struct compat_siginfo {
> u32 _pkey;
> } _addr_pkey;
> /* used when si_code=TRAP_PERF */
> - compat_u64 _perf;
> + compat_ulong_t _perf;
> };
> } _sigfault;
>
> diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h
> index d0bb9125c853..03d6f6d2c1fe 100644
> --- a/include/uapi/asm-generic/siginfo.h
> +++ b/include/uapi/asm-generic/siginfo.h
> @@ -92,7 +92,7 @@ union __sifields {
> __u32 _pkey;
> } _addr_pkey;
> /* used when si_code=TRAP_PERF */
> - __u64 _perf;
> + unsigned long _perf;
> };
> } _sigfault;
>
>
Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland
next prev parent reply other threads:[~2021-04-22 6:13 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-08 10:35 [PATCH v4 00/10] Add support for synchronous signals on perf events Marco Elver
2021-04-08 10:35 ` [PATCH v4 01/10] perf: Rework perf_event_exit_event() Marco Elver
2021-04-08 10:35 ` [PATCH v4 02/10] perf: Apply PERF_EVENT_IOC_MODIFY_ATTRIBUTES to children Marco Elver
2021-04-08 10:35 ` [PATCH v4 03/10] perf: Support only inheriting events if cloned with CLONE_THREAD Marco Elver
2021-04-08 10:35 ` [PATCH v4 04/10] perf: Add support for event removal on exec Marco Elver
2021-04-08 10:36 ` [PATCH v4 05/10] signal: Introduce TRAP_PERF si_code and si_perf to siginfo Marco Elver
[not found] ` <CGME20210420212618eucas1p102b427d1af9c682217dfe093f3eac3e8@eucas1p1.samsung.com>
2021-04-20 21:26 ` Marek Szyprowski
2021-04-20 22:42 ` Marco Elver
2021-04-21 6:21 ` Marek Szyprowski
2021-04-21 7:35 ` Marek Szyprowski
2021-04-21 8:11 ` Marco Elver
2021-04-21 9:35 ` Marek Szyprowski
2021-04-21 10:57 ` Marek Szyprowski
2021-04-21 11:03 ` Marco Elver
2021-04-21 13:19 ` Marek Szyprowski
2021-04-21 15:11 ` Marco Elver
2021-04-21 16:27 ` Marco Elver
2021-04-21 18:23 ` Marco Elver
2021-04-22 6:12 ` Marek Szyprowski [this message]
2021-04-22 6:47 ` Marco Elver
2021-04-22 8:16 ` Jon Hunter
2021-04-26 7:35 ` Alexander Egorenkov
2021-04-21 15:07 ` Jon Hunter
2021-04-08 10:36 ` [PATCH v4 06/10] perf: Add support for SIGTRAP on perf events Marco Elver
2021-04-08 10:36 ` [PATCH v4 07/10] selftests/perf_events: Add kselftest for process-wide sigtrap handling Marco Elver
2021-04-08 10:36 ` [PATCH v4 08/10] selftests/perf_events: Add kselftest for remove_on_exec Marco Elver
2021-04-08 10:36 ` [PATCH v4 09/10] tools headers uapi: Sync tools/include/uapi/linux/perf_event.h Marco Elver
2021-04-08 10:36 ` [PATCH v4 10/10] perf test: Add basic stress test for sigtrap handling Marco Elver
2021-04-14 8:37 ` [PATCH v4 00/10] Add support for synchronous signals on perf events Peter Zijlstra
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