From: Laurent Dufour <ldufour@linux.ibm.com>
To: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: linuxppc-dev@lists.ozlabs.org
Subject: Re: VDSO ELF header
Date: Thu, 25 Mar 2021 20:02:20 +0100 [thread overview]
Message-ID: <30c51951-332b-7aa8-13ba-44a0b6ae3498@linux.ibm.com> (raw)
In-Reply-To: <5b03e966-2cfd-5f0c-c48d-dea5e0001833@linux.ibm.com>
Le 25/03/2021 à 17:56, Laurent Dufour a écrit :
> Le 25/03/2021 à 17:46, Christophe Leroy a écrit :
>> Hi Laurent
>>
>> Le 25/03/2021 à 17:11, Laurent Dufour a écrit :
>>> Hi Christophe,
>>>
>>> Since v5.11 and the changes you made to the VDSO code, it no more exposing
>>> the ELF header at the beginning of the VDSO mapping in user space.
>>>
>>> This is confusing CRIU which is checking for this ELF header cookie
>>> (https://github.com/checkpoint-restore/criu/issues/1417).
>>
>> How does it do on other architectures ?
>
> Good question, I'll double check the CRIU code.
On x86, there are 2 VDSO entries:
7ffff7fcb000-7ffff7fce000 r--p 00000000 00:00 0 [vvar]
7ffff7fce000-7ffff7fcf000 r-xp 00000000 00:00 0 [vdso]
And the VDSO is starting with the ELF header.
>
>>
>>>
>>> I'm not an expert in loading and ELF part and reading the change you made, I
>>> can't identify how this could work now as I'm expecting the loader to need
>>> that ELF header to do the relocation.
>>
>> I think the loader is able to find it at the expected place.
>
> Actually, it seems the loader relies on the AUX vector AT_SYSINFO_EHDR. I guess
> CRIU should do the same.
>
>>>
>>> From my investigation it seems that the first bytes of the VDSO area are now
>>> the vdso_arch_data.
>>>
>>> Is the ELF header put somewhere else?
>>> How could the loader process the VDSO without that ELF header?
>>>
>>
>> Like most other architectures, we now have the data section as first page and
>> the text section follows. So you will likely find the elf header on the second
>> page.
I'm wondering if the data section you're refering to is the vvar section I can
see on x86.
>>
>> Done in this commit:
>> https://github.com/linuxppc/linux/commit/511157ab641eb6bedd00d62673388e78a4f871cf
>
> I'll double check on x86, but anyway, I think CRIU should rely on
> AT_SYSINFO_EHDR and not assume that the ELF header is at the beginning of VDSO
> mapping.
>
> Thanks for your help.
> Laurent.
>
next prev parent reply other threads:[~2021-03-25 19:03 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <c45ae4f8-1cbc-c687-b6a2-9a431fafc85c@linux.ibm.com>
2021-03-25 16:46 ` VDSO ELF header Christophe Leroy
2021-03-25 16:56 ` Laurent Dufour
2021-03-25 19:02 ` Laurent Dufour [this message]
2021-03-26 10:46 ` Michael Ellerman
2021-03-26 10:50 ` Christophe Leroy
2021-03-26 15:13 ` Dmitry Safonov
2021-03-26 16:11 ` Christophe Leroy
2021-03-26 16:32 ` Dmitry Safonov
2021-03-26 17:07 ` Christophe Leroy
2021-03-26 17:11 ` Dmitry Safonov
2021-03-26 18:40 ` Christophe Leroy
2021-03-26 18:54 ` Dmitry Safonov
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