COMPAT_32BIT libusb ABI problem

[Hans Petter Selasky]

Hi,

LibUSB 32-bit is compiled using -m32 in a 64-bit environment. What happens when you pass -m32 to the compiler?

Thank you for your report.

Another alternative is to use __packed attribute, but that has some implications too.

--HPS
 
-----Original message-----
> From:Damjan Jovanovic <damjan.jov at gmail.com <mailto:damjan.jov at gmail.com> >
> Sent: Thursday 25th July 2013 20:55
> To: Hans Petter Selasky <hans.petter.selasky at bitfrost.no <mailto:hans.petter.selasky at bitfrost.no> >
> Cc: freebsd-usb at freebsd.org <mailto:freebsd-usb at freebsd.org> 
> Subject: Re: COMPAT_32BIT libusb ABI problem
> 
> On Thu, Jul 25, 2013 at 6:11 AM, Hans Petter Selasky <hps at bitfrost.no <mailto:hps at bitfrost.no> > wrote:
> > On 07/24/13 22:09, Damjan Jovanovic wrote:
> >>
> >> Hi
> >>
> >> The ioctl:
> >> #define USB_FS_INIT             _IOW ('U', 195, struct usb_fs_init)
> >> when used by a COMPAT_32BIT libusb on amd64, fails (causing
> >> libusb_open() to fail) due to:
> >>
> >> freebsd32_ioctl(0x6,0x800c55c3,0xffffc710,0x0,0x0,0x0) ERR#25
> >> 'Inappropriate ioctl for device'
> >> but when hacked a bit:
> >> freebsd32_ioctl(0x6,0x801055c3,0xffffc710,0x0,0x0,0x0) = 0 (0x0)
> >>
> >> because sizeof(struct usb_fs_init) is 12 bytes on i386, and 16 bytes on
> >> amd64.
> >>
> >> But the failure of even libusb_open() - a fundamental libusb function
> >> - must mean that the COMPAT_32BIT libusb never worked. Can we please
> >> take this opportunity to kill it and do a real 32 bit compatibility
> >> layer in the kernel that will work from 32 bit chroots and statically
> >> linked 32 bit binaries? I'll help.
> >
> >
> > Hi,
> >
> > How did you compile it? Is the structure the same size, compiled with GCC
> > and LLVM?
> 
> GCC 4.2.1
> "gcc file.c -o file -lusb" in a 32 bit chroot = 12 bytes
> "gcc file.c -o file -lusb" 64 bit = 16 bytes
> 
> Clang 3.1
> "clang file.c -o file -lusb" in a 32 bit chroot = 12 bytes
> "clang file.c -o file -lusb" 64 bit = 16 bytes
> 
> The "uint8_t ep_index_max" field at the end of struct usb_fs_init must
> be getting padded to a 4 byte boundary on 32 bit, and 8 byte boundary
> on 64 bit.
> 
> > The LIB32 for USB has been tested. I did a quick test and found on 9-stable:
> >
> > cc -m32 -I . -L /usr/lib32 -lusb usbconfig.c dump.c
> > env LD_PRELOAD=/usr/lib32/libusb.so ./a.out
> > ugen0.1: <UHCI root HUB Intel> at usbus0, cfg=0 md=HOST spd=FULL (12Mbps)
> > pwr=SAVE (0mA)
> > ugen1.1: <UHCI root HUB Intel> at usbus1, cfg=0 md=HOST spd=FULL (12Mbps)
> > pwr=SAVE (0mA)
> >
> > ...
> 
> But usbconfig uses the libusb20 API and never seems to get to that broken ioctl.
> 
> > Your approach requires much more code. It is not just about some structures,
> > but also about code accessing those structures. Feel free to submit a patch
> > however.
> 
> I'll see what I can do.
> 
> > I would rather fix this by adding the proper __aligned() to the structures
> > in question.
> 
> Do that in the meanwhile?
> 
> > --HPS
> >
> 
> Damjan
>