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

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Message-ID: <CALCETrXC2ihRWhcAPRGchuRrO3ZPmfrEzS9CemxsM_TeWfTqZA@mail.gmail.com>
Date:	Wed, 11 Jun 2014 11:45:05 -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 10:45 AM, Josh Boyer <jwboyer@...oraproject.org> wrote:
> 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.

Apparently not.  file can see it, but apparently objdump can't.  go figure.

>
> josh



-- 
Andy Lutomirski
AMA Capital Management, LLC
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