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Re: V2: [PATCH 01/24] x86: Rename __glibc_reserved1 to feature_1 in tcbhead_t [BZ #22563]

On 07/13/2018 02:55 PM, Jeff Law wrote:
> On 07/13/2018 12:51 PM, Carlos O'Donell wrote:
>> On 07/13/2018 09:19 AM, H.J. Lu wrote:
>>> On Wed, Jun 13, 2018 at 08:31:44AM -0700, H.J. Lu wrote:
>>>> This will be used by CET run-time control.
>>>> 	[BZ #22563]
>>>> 	* nptl/pthread_create.c (__pthread_create_2_1): Use
>>>> 	THREAD_COPY_ADDITONAL_INFO to copy additonal info if defined.
>>>> 	* sysdeps/i386/nptl/tcb-offsets.sym (FEATURE_1_OFFSET): New.
>>>> 	* sysdeps/x86_64/nptl/tcb-offsets.sym (FEATURE_1_OFFSET):
>>>> 	Likewise.
>>>> 	* sysdeps/i386/nptl/tls.h (tcbhead_t): Rename __glibc_reserved1
>>>> 	to feature_1.
>>>> 	* sysdeps/x86_64/nptl/tls.h (tcbhead_t): Likewise.
>>>> 	* sysdeps/unix/sysv/linux/x86/pthreaddef.h: New file.
>>> Here is the updated patch to add feature_1 to tcbhead_t and
>>> introduce macros for CET enabling.  OK for master?
>> Fix the typo-prone macro API and post a v3 please.
>> Thank you.
> Umm, has this been tested with the sanitizers?  I thought they used that
> field.

The size of tcbhead_t has not changed, which is something that might impact
the santiziers.

But now that you mention it, why do I vaguely remember a conversation about
the santizers using the reserved bytes as storage for themselves?

Is that what you are talking about?

HJ, could you look into this please?

I think the sanitizers are not within their rights to use any bytes in the
tcbhead_t structure, particularly reserved bytes. We should coordinate with
them, but that should not stop the acceptance of this patch in 2.28.


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