On Thu, Feb 22, 2018 at 01:02:05PM +0100, Peter Lieven wrote: > Am 22.02.2018 um 13:00 schrieb Daniel P. Berrangé: > > On Thu, Feb 22, 2018 at 12:51:58PM +0100, Peter Lieven wrote: > >> Am 22.02.2018 um 12:40 schrieb Daniel P. Berrangé: > >>> On Thu, Feb 22, 2018 at 12:32:04PM +0100, Kevin Wolf wrote: > >>>> Am 22.02.2018 um 12:01 hat Peter Lieven geschrieben: > >>>>> Am 22.02.2018 um 11:57 schrieb Kevin Wolf: > >>>>>> Am 20.02.2018 um 22:54 hat Paolo Bonzini geschrieben: > >>>>>>> On 20/02/2018 18:04, Peter Lieven wrote: > >>>>>>>> Hi, > >>>>>>>> > >>>>>>>> I remember we discussed a long time ago to limit the stack usage of > >>>>>>>> all > >>>>>>>> functions that are executed in a coroutine > >>>>>>>> context to a very low value to be able to safely limit the coroutine > >>>>>>>> stack size as well. > >>>>>>> IIRC the only issue was that hw/ide/atapi.c has mutual recursion > >>>>>>> between > >>>>>>> ide_atapi_cmd_reply_end -> ide_transfer_start -> ahci_start_transfer > >>>>>>> -> > >>>>>>> ide_atapi_cmd_reply_end. > >>>>>>> > >>>>>>> But perhaps it's not an issue, somebody needs to audit the code. > >>>>>> I think John intended to get rid of the recursion sometime, but I doubt > >>>>>> he has had the time so far. > >>>>> Apart from this is is possible to define special cflags in the > >>>>> Makefile.objs just for a subdirectory? I have patches ready to make > >>>>> the block layer files and other coroutine users compile with > >>>>> -Wstack-size=2048. But I do not want to specify each file separately. > >>>> Our Makefiles have lines like this: > >>>> > >>>> iscsi.o-cflags := $(LIBISCSI_CFLAGS) > >>>> > >>>> I don't think there is a direct mechanism to apply cflags to a whole > >>>> directory or just to block-obj-y/block-obj-m, but just looping over them > >>>> could work. I'm not a Makefile expert at all, but after some toying with > >>>> a simple example, something like this might work: > >>>> > >>>> $(foreach x,$(block-obj-y),$(eval $x-cflags += -Wstack-size=2048)) > >>> You'll need it for anything block layer depends on too - so that's much > >>> of util/, crypto/ and io/ directories at least. > >>> > >>> So perhaps it would be shorter if we do the opposite - set > >>> -Wstack-size=2048 > >>> globally for everything in QEMU, and then override -Wstack-size=$BIGGER > >>> for the (hopefully) few sources that have a larger stack need ? > >> I tried that already. 2048 is a strong limit for many functions. > >> It breaks already as soon as some buffer has a size of PATH_MAX, but > >> thats handleable. But there are some structs around that are very large. > > There are surprisingly few "char [PATH_MAX]" variables left in QEMU - we > > should have a final push to eliminate them regardless. > > > >> Generally, it would be a good idea to have a global limit, of course. > > We could at least put a limit on that matches the current worst case to > > prevent it getting worse than it already is. > > That would be a good idea, yes. > > How would you handle the override for a smaller -Wstack-usage ?
If you have multiple -Wstack-size=$XXX flags to GCC, I expect the last one wins. So just need to double check that the per-object file CFLAGS occur after the global CFLAS in the compiler args Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|