linux-kernel - Re: [PATCH 2/2] x86,vdso: Fix vdso

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Date:	Wed, 11 Jun 2014 13:45:40 -0400
From:	Josh Boyer <jwboyer@...oraproject.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	"linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] x86,vdso: Fix vdso_install

On Wed, Jun 11, 2014 at 1:42 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Wed, Jun 11, 2014 at 10:33 AM, Josh Boyer <jwboyer@...oraproject.org> wrote:
>> On Wed, Jun 11, 2014 at 1:27 PM, H. Peter Anvin <hpa@...or.com> wrote:
>>> On 06/11/2014 10:23 AM, Josh Boyer wrote:
>>>>
>>>> So this does fix the invocation of 'make vdso_install' and the
>>>> resulting files look to be accurate to me, with the glaring exception
>>>> that now we get e.g. vdso64.so on x86_64 as the installed file instead
>>>> of vdso.so.  How much that actually matters, I have no idea.
>>>> Plausibly fixed with a symlink if we really need to perhaps.
>>>>
>>>
>>> You have that problem anyway, no?  After all, there are three different
>>> vdso images for 32 bits, and you can run 32-bit apps on 64-bit systems, too.
>>
>> Yeah, true.
>>
>>> Is there realistically any way for the debugger to pick up the correct one?
>>
>> Probably not.
>
> Sure there is: build ids.  See /usr/lib/debug/.build-id.

Oh, duh.

> It would be great if we could teach the various debugging tools
> (libdw?  gdb?  I don't know what's responsible for the search path) to
> search both /usr/lib/debug/.build-id and /lib/modules/`uname
> -r`/build-id or something like that.
>
>>
>> I'm planning on pushing out our first 3.16 build with
>> these two patches with no symlink.  I very much doubt anyone is going
>> to complain.  It was just something I noticed.
>
> Does the Fedora RPM magic debuginfo script notice these files and
> symlink them into the .build-id directory?
>
> Of course, we don't seem to be generating build ids right now.  I
> thought we were.  I'll see if I can fix it.

My builds have it:

[jwboyer@sb ~]$ file /lib/modules/3.16.0-0.rc0.git1.1.fc21.x86_64/vdso/vdso64.so
/lib/modules/3.16.0-0.rc0.git1.1.fc21.x86_64/vdso/vdso64.so: ELF
64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically
linked, BuildID[sha1]=0x85ab0014891b5be97871e5e1183b761b9d2e8d9d,
stripped
[jwboyer@sb ~]$

I forget if we're doing something special to get that or not.

josh
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