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

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Date:	Wed, 11 Jun 2014 10:42:50 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Josh Boyer <jwboyer@...oraproject.org>
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 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.

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.

--Andy

>
> josh



-- 
Andy Lutomirski
AMA Capital Management, LLC
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