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 >>>> --- >>>> CC: Ian Jackson >>>> CC: Stefano Stabellini >>>> CC: Wei Liu >>>> --- >>>> 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=. >>>> PY_CFLAGS += $(PY_NOOPT_CFLAGS) >>>> endif >>>> -- >>>> 2.4.10 >>>> >> >> >> -- >> Doug Goldstein >> > > > ping? -- Doug Goldstein