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 ? > > Regards, > Daniel
