From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: "H.J. Lu" <hjl.tools@gmail.com>
Cc: GNU C Library <libc-alpha@sourceware.org>
Subject: Re: Compatibility issues around <sys/platform/x86.h>
Date: Tue, 22 Dec 2020 09:43:27 -0300 [thread overview]
Message-ID: <c2c669cb-3e9e-47e7-d1ee-e410c8b85c24@linaro.org> (raw)
In-Reply-To: <CAMe9rOoZhm=5+vKQO=3pD9xtcoaAmNtMT-Q5wk0mnJ4meC_69A@mail.gmail.com>
On 22/12/2020 08:42, H.J. Lu wrote:
> On Mon, Dec 21, 2020 at 9:16 AM Adhemerval Zanella via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
>>
>>
>>
>> On 21/12/2020 14:05, H.J. Lu via Libc-alpha wrote:
>>> On Mon, Dec 21, 2020 at 5:00 AM Florian Weimer <fweimer@redhat.com> wrote:
>>>>
>>>> I finally had some time to review the <sys/platform/x86.h> interface.
>>>>
>>>> I have two major concerns:
>>>>
>>>> (a) Placement of struct cpu_features in _rtld_global_ro
>>>>
>>>> This means that backporting new feature support changes the internal
>>>> GLIBC_PRIVATE ABI. Consequently, there's a race condition during
>>>> in-place updates where loading binaries can fail in obscure ways, due to
>>>> the change in _rtld_global_ro offsets. We should really avoid this.
>>>
>>> This applies to all members in _rtld_global_ro.
>>
>> Couldn't it be mitigated by adding member solely at the end of the struct
>> and making sure the backport uses the same offset?
>
> What if we need to extend a member in the middle?
>
My question also extends if we would need to do so. Do we plan to extend
the cpu_features indefinitely or can we pre-allocate a large space now
for future extensions?
next prev parent reply other threads:[~2020-12-22 12:43 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-21 13:00 Florian Weimer
2020-12-21 17:05 ` H.J. Lu
2020-12-21 17:15 ` Adhemerval Zanella
2020-12-22 11:42 ` H.J. Lu
2020-12-22 12:43 ` Adhemerval Zanella [this message]
2020-12-22 12:57 ` H.J. Lu
2020-12-22 11:42 ` H.J. Lu
2020-12-22 13:32 ` Florian Weimer
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