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Message-Id: <69EFB859-ED05-4C47-AC69-76CBBEC7C2DE@goldelico.com>
Date: Sat, 23 Nov 2019 08:29:30 +0100
From: "H. Nikolaus Schaller" <hns@...delico.com>
To: Vincenzo Frascino <vincenzo.frascino@....com>,
Paul Burton <paul.burton@...s.com>,
Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...r.kernel.org,
MIPS Creator CI20 Development
<mips-creator-ci20-dev@...glegroups.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Discussions about the Letux Kernel
<letux-kernel@...nphoenux.org>
Subject: Re:MIPS: bug: gettimeofday syscall broken on CI20 board
Nobody with an idea?
> Am 17.11.2019 um 14:14 schrieb H. Nikolaus Schaller <hns@...delico.com>:
>
> Hi Vincenzo,
>
>> Am 07.11.2019 um 17:21 schrieb H. Nikolaus Schaller <hns@...delico.com>:
>>
>> Hi,
>> I am trying to run v5.4-rc6 on the CI20 board (jz4780) and it
>> is almost ok. Except one strange thing.
>>
>> If I install a v4.19.81 kernel I can initialize the
>> ethernet interface and dhclient works.
>>
>> If I install a v5.4-rc6 kernel on exactly the same
>> rootfs dhclient fails with
>>
>> root@...ux:~# dhclient
>> ../../../../lib/isc/unix/time.c:200: Operation not permitted
>> root@...ux:~#
>>
>> I have done some strace and the first significant difference
>> is that with v5.4-rc6 there is no gettimeofday syscall.
>>
>> Another symptom pointing in the same direction is that
>> after manually assigning an IP address I can run ping
>> but get strange time values.
>>
>> So it may be that
>>
>> 24640f233b46 mips: Add support for generic vDSO
>>
>> did break gettimeofday when used with latest Debian Stretch
>> libraries. I tried to git revert but there are conflicts.
>>
>> Just a side-note: both kernels work with Debian Jessie,
>> which likely has an older gettimeofday wrapper that
>> is not influenced by some subtle change.
>
> I finally found time to do a bisect and it confirms:
>
> 24640f233b466051ad3a5d2786d2951e43026c9d is the first bad commit
> commit 24640f233b466051ad3a5d2786d2951e43026c9d
> Author: Vincenzo Frascino <vincenzo.frascino@....com>
> Date: Fri Jun 21 10:52:46 2019 +0100
>
> mips: Add support for generic vDSO
>
> The mips vDSO library requires some adaptations to take advantage of the
> newly introduced generic vDSO library.
>
> Introduce the following changes:
> - Modification of vdso.c to be compliant with the common vdso datapage
> - Use of lib/vdso for gettimeofday
>
> Cc: Ralf Baechle <ralf@...ux-mips.org>
> Cc: Paul Burton <paul.burton@...s.com>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@....com>
> [paul.burton@...s.com: Prepend $(src) to config-n32-o32-env.c path.]
> Signed-off-by: Paul Burton <paul.burton@...s.com>
>
> arch/mips/Kconfig | 2 +
> arch/mips/include/asm/vdso.h | 78 +--------------
> arch/mips/include/asm/vdso/gettimeofday.h | 151 ++++++++++++++++++++++++++++++
> arch/mips/include/asm/vdso/vdso.h | 85 +++++++++++++++++
> arch/mips/include/asm/vdso/vsyscall.h | 43 +++++++++
> arch/mips/kernel/vdso.c | 37 ++------
> arch/mips/vdso/Makefile | 33 ++++++-
> arch/mips/vdso/config-n32-o32-env.c | 17 ++++
> arch/mips/vdso/elf.S | 2 +-
> arch/mips/vdso/sigreturn.S | 2 +-
> arch/mips/vdso/vdso.h | 85 -----------------
> arch/mips/vdso/vgettimeofday.c | 40 ++++++++
> 12 files changed, 378 insertions(+), 197 deletions(-)
> create mode 100644 arch/mips/include/asm/vdso/gettimeofday.h
> create mode 100644 arch/mips/include/asm/vdso/vdso.h
> create mode 100644 arch/mips/include/asm/vdso/vsyscall.h
> create mode 100644 arch/mips/vdso/config-n32-o32-env.c
> delete mode 100644 arch/mips/vdso/vdso.h
> create mode 100644 arch/mips/vdso/vgettimeofday.c
>
> So this patch intoruced in v5.4-rc1 breaks compatibility with Debian 9.9
> user space assumptions.
>
> One thing seems strange to me:
>
> -/**
> - * union mips_vdso_data - Data provided by the kernel for the VDSO.
> - * @xtime_sec: Current real time (seconds part).
> - * @xtime_nsec: Current real time (nanoseconds part, shifted).
> - * @wall_to_mono_sec: Wall-to-monotonic offset (seconds part).
> - * @wall_to_mono_nsec: Wall-to-monotonic offset (nanoseconds part).
> - * @seq_count: Counter to synchronise updates (odd = updating).
> - * @cs_shift: Clocksource shift value.
> - * @clock_mode: Clocksource to use for time functions.
> - * @cs_mult: Clocksource multiplier value.
> - * @cs_cycle_last: Clock cycle value at last update.
> - * @cs_mask: Clocksource mask value.
> - * @tz_minuteswest: Minutes west of Greenwich (from timezone).
> - * @tz_dsttime: Type of DST correction (from timezone).
> - *
> - * This structure contains data needed by functions within the VDSO. It is
> - * populated by the kernel and mapped read-only into user memory. The time
> - * fields are mirrors of internal data from the timekeeping infrastructure.
> - *
> - * Note: Care should be taken when modifying as the layout must remain the same
> - * for both 64- and 32-bit (for 32-bit userland on 64-bit kernel).
> - */
> union mips_vdso_data {
> - struct {
> - u64 xtime_sec;
> - u64 xtime_nsec;
> - u64 wall_to_mono_sec;
> - u64 wall_to_mono_nsec;
> - u32 seq_count;
> - u32 cs_shift;
> - u8 clock_mode;
> - u32 cs_mult;
> - u64 cs_cycle_last;
> - u64 cs_mask;
> - s32 tz_minuteswest;
> - s32 tz_dsttime;
> - };
> -
> + struct vdso_data data[CS_BASES];
> u8 page[PAGE_SIZE];
> };
>
> If I look at the definition of vdso_data it *is* significantly differen
> from mips_vdso_data.
>
> What I would assume is that the struct mips_vdso_data is embossed in user
> space code and therefore using vdso_data instead is breaking API.
>
> Please advise what I should try or check to narrow down further.
>
> BR and thanks,
> Nikolaus Schaller
>
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