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From: ebiederm@xmission.com (Eric W. Biederman)
To: Baoquan He <bhe@redhat.com>
Cc: Dave Young <dyoung@redhat.com>,
	kexec@lists.infradead.org, Michael Ellerman <mpe@ellerman.id.au>,
	Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>,
	linuxppc-dev@lists.ozlabs.org, Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [RFC]  kexec_file: Add support for purgatory built as PIE
Date: Fri, 04 Nov 2016 10:13:39 -0500	[thread overview]
Message-ID: <871syrcm70.fsf@xmission.com> (raw)
In-Reply-To: <20161104073840.GD4314@x1> (Baoquan He's message of "Fri, 4 Nov 2016 15:38:40 +0800")

Baoquan He <bhe@redhat.com> writes:

> On 11/02/16 at 04:00am, Thiago Jung Bauermann wrote:
>> Hello,
>> 
>> The kexec_file code currently builds the purgatory as a partially linked object 
>> (using ld -r). Is there a particular reason to use that instead of a position 
>> independent executable (PIE)?
>
> It's taken as "-r", relocatable in user space kexec-tools too originally.
> I think Vivek just keeps it the same when moving into kernel.

At least on x86 using just -r removed the need for a GOT and all of the
other nasty dynamic relocatable bits, that are not needed when the you
don't want to share your text bits with the page cache.

I can see reaons for refactoring code but I expect PIE expecutables need
a GOT and all of that pain in the neck stuff that can just be avoided by
building the code to run at an absolute address.

So far I have not seen ELF relocations that are difficult to process.

Eric

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WARNING: multiple messages have this Message-ID (diff)
From: ebiederm@xmission.com (Eric W. Biederman)
To: Baoquan He <bhe@redhat.com>
Cc: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>,
	kexec@lists.infradead.org, linuxppc-dev@lists.ozlabs.org,
	Michael Ellerman <mpe@ellerman.id.au>,
	Dave Young <dyoung@redhat.com>, Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [RFC]  kexec_file: Add support for purgatory built as PIE
Date: Fri, 04 Nov 2016 10:13:39 -0500	[thread overview]
Message-ID: <871syrcm70.fsf@xmission.com> (raw)
In-Reply-To: <20161104073840.GD4314@x1> (Baoquan He's message of "Fri, 4 Nov 2016 15:38:40 +0800")

Baoquan He <bhe@redhat.com> writes:

> On 11/02/16 at 04:00am, Thiago Jung Bauermann wrote:
>> Hello,
>> 
>> The kexec_file code currently builds the purgatory as a partially linked object 
>> (using ld -r). Is there a particular reason to use that instead of a position 
>> independent executable (PIE)?
>
> It's taken as "-r", relocatable in user space kexec-tools too originally.
> I think Vivek just keeps it the same when moving into kernel.

At least on x86 using just -r removed the need for a GOT and all of the
other nasty dynamic relocatable bits, that are not needed when the you
don't want to share your text bits with the page cache.

I can see reaons for refactoring code but I expect PIE expecutables need
a GOT and all of that pain in the neck stuff that can just be avoided by
building the code to run at an absolute address.

So far I have not seen ELF relocations that are difficult to process.

Eric

  reply	other threads:[~2016-11-04 15:16 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-02  6:00 [RFC] kexec_file: Add support for purgatory built as PIE Thiago Jung Bauermann
2016-11-02  6:00 ` Thiago Jung Bauermann
2016-11-04  7:38 ` Baoquan He
2016-11-04  7:38   ` Baoquan He
2016-11-04 15:13   ` Eric W. Biederman [this message]
2016-11-04 15:13     ` Eric W. Biederman
2016-11-04 19:19     ` Thiago Jung Bauermann
2016-11-04 19:19       ` Thiago Jung Bauermann
2016-11-04 15:43   ` Thiago Jung Bauermann
2016-11-04 15:43     ` Thiago Jung Bauermann

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