[RFC PATCH 0/8] arm64: Add a compat vDSO

[Kevin Brodsky]

On 27/10/16 16:23, Dmitry Safonov wrote:
> 2016-09-08 17:00 GMT+03:00 Kevin Brodsky <kevin.brodsky at arm.com>:
>> Hi,
>>
>> This series adds support for a compat (AArch32) vDSO, providing two
>> userspace functionalities to compat processes:
>>
>> * "Virtual" time syscalls (gettimeofday and clock_gettime). The
>>   implementation is an adaptation of the arm vDSO (vgettimeofday.c),
>>   sharing the data page with the 64-bit vDSO.
>>
>> * sigreturn trampolines, following the example of the 64-bit vDSO
>>   (sigreturn.S), but slightly more complicated because we provide A32
>>   and T32 variants for both sigreturn and rt_sigreturn.
>>
>> The first point brings the performance improvement expected of a vDSO,
>> by implementing time syscalls directly in userspace. The second point
>> allows us to get rid of the compat vector page, at the expense of the
>> kuser helpers (this is one reason for not enabling the compat vDSO by
>> default).
>>
>> Unfortunately, this time we cannot escape using a 32-bit toolchain. To
>> build the compat VDSO, CONFIG_COMPAT_VDSO must be set *and*
>> CROSS_COMPILE_ARM32 must be defined to the prefix of a 32-bit compiler.
>> Failure to do so will not prevent building the kernel, but a warning
>> will be printed and the compat vDSO will not be built.
>>
>> I have only tested the series with a 64-bit userspace (+ 32-bit glibc).
>> Testing it with a 32-bit userspace would be very welcome.
>
> Hi, what's up with these patches, are you gonna resend them or prepare
> a new version?

Absolutely, actually I was working on it just now, sending v2 very soon :-)

Kevin

>> Thanks,
>> Kevin
>>
>> Kevin Brodsky (8):
>>   arm64: Refactor vDSO setup
>>   arm64: compat: Add time-related syscall numbers
>>   arm64: compat: Expose offset to registers in sigframes
>>   arm64: compat: Add a 32-bit vDSO
>>   arm64: compat: 32-bit vDSO setup
>>   arm64: elf: Set AT_SYSINFO_EHDR in compat processes
>>   arm64: compat: Use vDSO sigreturn trampolines if available
>>   arm64: Wire up and expose the new compat vDSO
>>
>>  arch/arm64/Kconfig                       |  20 +++
>>  arch/arm64/Makefile                      |  20 ++-
>>  arch/arm64/include/asm/elf.h             |  15 +-
>>  arch/arm64/include/asm/signal32.h        |  46 +++++
>>  arch/arm64/include/asm/unistd.h          |   2 +
>>  arch/arm64/include/asm/vdso.h            |   3 +
>>  arch/arm64/kernel/Makefile               |   8 +-
>>  arch/arm64/kernel/asm-offsets.c          |  13 ++
>>  arch/arm64/kernel/signal32.c             |  61 ++-----
>>  arch/arm64/kernel/vdso.c                 | 198 ++++++++++++---------
>>  arch/arm64/kernel/vdso32/Makefile        | 121 +++++++++++++
>>  arch/arm64/kernel/vdso32/sigreturn.S     |  86 +++++++++
>>  arch/arm64/kernel/vdso32/vdso.S          |  32 ++++
>>  arch/arm64/kernel/vdso32/vdso.lds.S      |  98 +++++++++++
>>  arch/arm64/kernel/vdso32/vgettimeofday.c | 294 +++++++++++++++++++++++++++++++
>>  15 files changed, 883 insertions(+), 134 deletions(-)
>>  create mode 100644 arch/arm64/kernel/vdso32/Makefile
>>  create mode 100644 arch/arm64/kernel/vdso32/sigreturn.S
>>  create mode 100644 arch/arm64/kernel/vdso32/vdso.S
>>  create mode 100644 arch/arm64/kernel/vdso32/vdso.lds.S
>>  create mode 100644 arch/arm64/kernel/vdso32/vgettimeofday.c
>