Date: Mon, 29 Dec 2008 11:25:28 +0100 From: Hans Petter Selasky <hselasky@c2i.net> To: Dag-Erling =?utf-8?q?Sm=C3=B8rgrav?= <des@des.no> Cc: freebsd-current@freebsd.org, current@freebsd.org, Alfred Perlstein <alfred@freebsd.org> Subject: Re: HEADSUP usb2 (usb4bsd) to become default in 2 weeks. Message-ID: <200812291125.30222.hselasky@c2i.net> In-Reply-To: <86d4fb72se.fsf@ds4.des.no> References: <20081222214010.GA18389@elvis.mu.org> <200812231736.29198.hselasky@c2i.net> <86d4fb72se.fsf@ds4.des.no>
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On Monday 29 December 2008, Dag-Erling Sm=C3=B8rgrav wrote:
> Hans Petter Selasky <hselasky@c2i.net> writes:
> > LIBUSB20_ADD_BYTES() is a hack to circumvent things like un-constifying
> > and making a byte increment to any pointer type. USB descriptors are
> > byte-packed. I have tested the macro with several kinds of compilers and
> > none have complained yet.
>
> 1) if you need to de-constify, your API is broken.
The following function is a candidate for de-constifying. You have a data=20
pointer there which is read or write, and to be able to transfer constant=20
data you need to do a deconst before passing the pointer to this function.
usb2_do_request_flags(struct usb2_device *udev, struct mtx *mtx,
struct usb2_device_request *req, void *data, uint32_t flags,
uint16_t *actlen, uint32_t timeout)
Deconstifying is not illegal in C using standard pointer arithmetics.
(void *)((const uint8_t *)(ptr) - (const uint8_t *)0)
>
> 2) just because the compiler doesn't know it's wrong doesn't mean it
> isn't.
>
> 3) the pointer magic you do in (for instance) libusb20_me_encode() and
> libusb20_me_decode() won't work on strict-alignment platforms.
>
Yes, it will, because all addresses are aligned before they get casted.
=2D-HPS
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