Date: Fri, 9 Mar 2012 22:36:48 +0100 From: Robert Millan <rmh@freebsd.org> To: freebsd-arch@freebsd.org Subject: [PATCH] Add compatibility <sys/io.h> Message-ID: <CAOfDtXPGPP0reN9NTBw_5%2BNwXZ56Yy0oyx_fH%2BDOvmpc1O%2BQdQ@mail.gmail.com>
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This patch adds a compatibility <sys/io.h> that would make it easier
to build on FreeBSD software that has been written for glibc (see
example1.c).
The functionality in <sys/io.h> is more or less equivalent to
<machine/cpufunc.h> but provides some declarations which are
incompatible with those in <machine/cpufunc.h>. One of these cases is
very unfortunate because it alters I/O semantics, it applies to
outb(), outw() and outl():
FreeBSD code: outw(port, data);
Glibc code: outw(data, port);
The undefined I/O behaviour that could potentially result from this is
very scary. Because of this I've written a few checks to prevent both
headers from being used at the same time. Overall, aside from the
portability benefit, my proposed addition has some less obvious
side-effects:
Desireable side-effect: Adding <sys/io.h> would break
buildability of code that attempts to use both headers at the same
time _WITHOUT_ changing the outw() call semantics (see example2.c).
Undesireable side-effect: Adding <sys/io.h> would break
buildability of code that attempts to use both headers at the same
time, and was otherwise fine due to conditionalized outw() calls (see
example3.c [1]).
[1] I found a real case where this happens, in
sane-backends-1.0.22/backend/umax_pp_low.c. In case my patch is
accepted, I commit to provide a fix for sane-backends and also to
adjust Debian GNU/kFreeBSD headers to follow the same route [2].
[2] This means: reenable outb(), outw() and outl() in
<machine/cpufunc.h>. Currently we provide both headers, but outb(),
outw() and outl() are entirely disabled. I think it's better for both
projects to provide <sys/io.h> since the majority of code out there is
written with GNU/Linux in mind.
Attached patch is tested against HEAD with "make universe".
--
Robert Millan
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