On June 21, 2018 6:58:51 PM PDT, Ingo Molnar <mi...@kernel.org> wrote:
>
>* H. Peter Anvin, Intel <h.peter.an...@intel.com> wrote:
>
>> From: "H. Peter Anvin" <h...@linux.intel.com>
>>
>> Give a debugger access to the visible part of the GDT and LDT. This
>> allows a debugger to find out what a particular segment descriptor
>> corresponds to; e.g. if %cs is 16, 32, or 64 bits.
>>
>> v3:
>> Requalify LDT segments for selectors that have actually changed.
>>
>> v2:
>> Add missing change to elf.h for the very last patch.
>>
>> Cc: Ingo Molnar <mi...@kernel.org>
>> Cc: Thomas Gleixner <t...@linutronix.de>
>> Cc: Andy Lutomirski <l...@kernel.org>
>> Cc: Chang S. Bae <chang.seok....@intel.com>
>> Cc: Markus T. Metzger <markus.t.metz...@intel.com>
>> Cc: H. Peter Anvin <h...@zytor.com>
>>
>> arch/x86/Kconfig | 4 +
>> arch/x86/include/asm/desc.h | 24 +++-
>> arch/x86/include/asm/ldt.h | 16 +++
>> arch/x86/include/asm/segment.h | 10 ++
>> arch/x86/kernel/Makefile | 3 +-
>> arch/x86/kernel/ldt.c | 283
>++++++++++++++++++++++++++++++++---------
>> arch/x86/kernel/ptrace.c | 103 ++++++++++++++-
>> arch/x86/kernel/tls.c | 102 +++++----------
>> arch/x86/kernel/tls.h | 8 +-
>> include/uapi/linux/elf.h | 2 +
>> 10 files changed, 413 insertions(+), 142 deletions(-)
>
>Ok, this looks mostly good to me at a quick glance, but could you
>please do one
>more iteration and more explicitly describe where you change/extend
>existing ABIs?
>
>I.e. instead of a terse and somewhat vague summary:
>
>> x86/tls,ptrace: provide regset access to the GDT
>>
>> Give a debugger access to the visible part of the GDT and LDT. This
>> allows a debugger to find out what a particular segment descriptor
>> corresponds to; e.g. if %cs is 16, 32, or 64 bits.
>
>Please make it really explicit how the ABI is affected, both in the
>title and in
>the description, and also _explain_ how this helps us over what we had
>before,
>plus also list limitations of the new ABI.
>
>I.e. something like:
>
> x86/tls, ptrace: Extend the ptrace ABI with the new REGSET_GDT method
>
> Add the new REGSET_GDT ptrace variant to PTRACE_{GET|SET}REGSET,
> to give read and write access to the GDT:
>
>- Previously only certain parts of the GDT were visible, and only via
>random
>ABIs and instructions - there was no architectured access to all of it.
>
>- The SETREGSET variant is only allowed to change the TLS area of the
>GDT.
>
>(or so.)
>
>This is important not just for documentation and library support
>purposes, but
>also to be able to review it properly, to match 'intent' to
>'implementation'.
>
>(It might also help later on in finding bugs/quirks, if any.)
>
>Please do this for all patches in the series that change the ABI.
>
>Thanks,
>
> Ingo
ACK.
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