[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 2/2] tools: detect appropriate debug optimization level
On Mon, Mar 28, 2016 at 4:01 PM, Doug Goldstein <cardoe@xxxxxxxxxx> wrote: > 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@xxxxxxxxxx> >>>>>> --- >>>>>> CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx> >>>>>> CC: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> >>>>>> CC: Wei Liu <wei.liu2@xxxxxxxxxx> >>>>>> --- >>>>>> 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? So just reading through the history -- I'm a bit confused why, if -Og is supposed to "do the right thing", why you didn't add that in this patch? In any case, having debug=y *functioning* should take priority over having gdb working, so I'm inclined to say that we should take a patch like this. -George _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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