Date: Thu, 18 Aug 2011 11:24:35 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-current@freebsd.org Cc: Jason Harmening <jason.harmening@gmail.com> Subject: Re: device_probe_and_attach() fails in kernel built w/ clang Message-ID: <201108181124.35122.jhb@freebsd.org> In-Reply-To: <CAM=8qan9D45ovCMD46yQFRxv8VZJKTg0MWi_BS_vSpPBtb6RKg@mail.gmail.com> References: <CAM=8qan9D45ovCMD46yQFRxv8VZJKTg0MWi_BS_vSpPBtb6RKg@mail.gmail.com>
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On Thursday, August 18, 2011 2:03:14 am Jason Harmening wrote: > Hi everyone, > > I have a driver for PCI devices that have onboard I2C buses, so my > driver needs to create an iicbus child for the PCI device. So in my > driver I use DRIVER_MODULE(iicbus, <my_pci_driver>, iicbus_driver, > iicbus_devclass, NULL, NULL). This works because iicbus_driver and > iicbus_devclass are declared extern in iicbus.h. > > Then during device attachment I create the iicbus child using: > > device_add_child(parent, "iicbus", -1); > ... > device_probe_and_attach(iicbus_dev); > > This all works fine for a kernel built w/ gcc. But if I build the > same kernel w/ clang, the device_probe_and_attach() call returns > ENXIO. I was able to debug this far enough to determine that > device_probe_child() in subr_bus.c wasn't finding any matching > drivers, so first_matching_driver() returned NULL and the matching > loops fell through. > > Interestingly enough, I have another driver for a similar class of > devices that also uses iicbus, and if I load that driver after loading > the first one, the *first* driver will be re-probed, and this time it > will successfully create its iicbus devices and attach to the PCI > devices. The *second* driver, though, will still fail to create its > iicbuses. > > I'm not sure if this is some weird problem w/ the iicbus driver, with > the kernel's probing routines, or with the module data structures and > init calls generated by DRIVER_MODULE(). Whatever it is seems to be > clang-related; removing optimization and march= from CFLAGS had no > effect. I'm using r224899/amd64. > > Any help would be really appreciated. Hmm, I would add some tracing to see if the iicbus/<my_pci_driver> is being registered at all. You might also just use kldstat -v to check for it without needing any extra tracing as a first step. However, if you dig into DRIVER_MODULE() you will see it creates a structure that is passed to a MOD_EVENT handler in sys/kern/subr_bus.c that registers new drivers. That is where I would add instrumentation to make sure the new iicbus driver is being registered correctly. -- John Baldwin
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