Am 22.02.2018 um 13:06 hat Peter Lieven geschrieben: > Am 22.02.2018 um 13:03 schrieb Daniel P. Berrangé: > > 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 > > I will check that, thanks. > > When I am at it, what would be the proper replacement for char[PATH_MAX] ?
g_malloc() with the exact size? Kevin