From: Doug Goldstein <cardoe@cardoe.com>
To: Wei Liu <wei.liu2@citrix.com>
Cc: euan.harris@citrix.com,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>,
xen-devel@lists.xen.org
Subject: Re: [PATCH 2/2] tools: detect appropriate debug optimization level
Date: Mon, 28 Mar 2016 10:01:16 -0500 [thread overview]
Message-ID: <56F9473C.9090508@cardoe.com> (raw)
In-Reply-To: <56E9B09A.3020808@cardoe.com>
[-- Attachment #1.1.1: Type: text/plain, Size: 3378 bytes --]
On 3/16/16 2:14 PM, Doug Goldstein wrote:
> On 3/8/16 10:50 AM, Wei Liu wrote:
>> On Tue, Mar 08, 2016 at 10:34:42AM -0600, Doug Goldstein wrote:
>>> On 3/8/16 9:38 AM, Wei Liu wrote:
>>>> On Mon, Mar 07, 2016 at 08:23:40PM -0600, Doug Goldstein wrote:
>>>>> The build should not use -O0 as that results in miscompilations. There
>>>>
>>>> This needs some (concrete) references. Is that a known issue in gcc? If
>>>> so can you reference the bug number?
>>>
>>> So its not really a bug in GCC but just the complete lack of
>>> optimizations in play. inlines aren't inlined. dead code elimination
>>> isn't run so things are much bigger. structures aren't padded the same way.
>>>
>>
>> Urgh...
>>
>>> This came about from reading reports on the -devel and -user's ML that
>>> were solved by building Xen with debug=n. I was also striving to reduce
>>> the duplication of CFLAGS that are passed on the command line of builds.
>>>
>>
>> I agree this is a good idea.
>>
>>>>
>>>>> have been a few instances on the ML where users were told to switch
>>>>> from -O0 to -O1 or -O2 or to set debug=n and their issue went away. The
>>>>> preferred route should be to use -Og if its available, otherwise use
>>>>> -O1 which is the default. This change undoes the change from -O1 to -O0
>>>>
>>>> gcc manual says -O0 is the default.
>>>
>>> I wasn't clear about where the 'the default' came from. That's the
>>> default in the Xen tree (see: config/StdGNU.mk for example but every
>>> platform has -O1 set).
>>>
>>
>> OK. I thought you're talking about something in the manual.
>>
>>>>
>>>> Not that I disagree with this patch in general, but the commit message
>>>> seems a bit misleading.
>>>
>>> I can rewrite it. I'd also be willing to change the patch to prefer -Og
>>> if its available and use -O0 if its not.
>>>
>>
>> No need to do it now because ...
>>
>>>>
>>>>> in 1166ecf781b1016eaa61f8d5ba4fb1fde9d599b6.
>>>>>
>>>>
>>>> And I have no idea why -O1 confuses the debugger so I've CC'ed Euan for
>>>> more input.
>>>
>>> -O1 can optimize things out when you look at them with gdb but -Og is
>>> suppose to do the right thing.
>>>
>>
>> .. I don't know much about gcc so I would like to wait for Ian to give
>> some input.
>>
>> Wei.
>>
>>>>
>>>>> Signed-off-by: Doug Goldstein <cardoe@cardoe.com>
>>>>> ---
>>>>> CC: Ian Jackson <ian.jackson@eu.citrix.com>
>>>>> CC: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
>>>>> CC: Wei Liu <wei.liu2@citrix.com>
>>>>> ---
>>>>> tools/Rules.mk | 3 ++-
>>>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/tools/Rules.mk b/tools/Rules.mk
>>>>> index 9ef0b47..ae6b01f 100644
>>>>> --- a/tools/Rules.mk
>>>>> +++ b/tools/Rules.mk
>>>>> @@ -137,7 +137,8 @@ SHLIB_libxenvchan = $(SHDEPS_libxenvchan) -Wl,-rpath-link=$(XEN_LIBVCHAN)
>>>>>
>>>>> ifeq ($(debug),y)
>>>>> # Disable optimizations and enable debugging information for macros
>>>>> -CFLAGS += -O0 -g3
>>>>> +$(call cc-option-add,CFLAGS,CC,-Og)
>>>>> +CFLAGS += -g3
>>>>> # But allow an override to -O0 in case Python enforces -D_FORTIFY_SOURCE=<n>.
>>>>> PY_CFLAGS += $(PY_NOOPT_CFLAGS)
>>>>> endif
>>>>> --
>>>>> 2.4.10
>>>>>
>>>
>>>
>>> --
>>> Doug Goldstein
>>>
>>
>>
>>
>
> ping?
>
>
ping the ping?
--
Doug Goldstein
[-- Attachment #1.2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 959 bytes --]
[-- Attachment #2: Type: text/plain, Size: 126 bytes --]
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xen.org
http://lists.xen.org/xen-devel
next prev parent reply other threads:[~2016-03-28 15:01 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-08 2:23 [PATCH 1/2] libxl: ensure var is inited in libxl__domain_firmware Doug Goldstein
2016-03-08 2:23 ` [PATCH 2/2] tools: detect appropriate debug optimization level Doug Goldstein
2016-03-08 15:38 ` Wei Liu
2016-03-08 16:34 ` Doug Goldstein
2016-03-08 16:50 ` Wei Liu
2016-03-16 19:14 ` Doug Goldstein
2016-03-28 15:01 ` Doug Goldstein [this message]
2016-03-29 11:44 ` George Dunlap
2016-03-29 17:21 ` Doug Goldstein
2016-03-30 9:52 ` George Dunlap
2016-03-30 16:00 ` Ian Jackson
2016-03-30 16:11 ` Ian Jackson
2016-03-30 16:20 ` Doug Goldstein
2016-03-31 8:24 ` George Dunlap
2016-04-06 14:07 ` Ian Jackson
2016-04-06 14:34 ` George Dunlap
2016-04-06 14:57 ` Ian Jackson
2016-03-08 15:38 ` [PATCH 1/2] libxl: ensure var is inited in libxl__domain_firmware Wei Liu
2016-03-10 15:13 ` Doug Goldstein
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=56F9473C.9090508@cardoe.com \
--to=cardoe@cardoe.com \
--cc=euan.harris@citrix.com \
--cc=ian.jackson@eu.citrix.com \
--cc=stefano.stabellini@eu.citrix.com \
--cc=wei.liu2@citrix.com \
--cc=xen-devel@lists.xen.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).