On Thu, Jan 12, 2023 at 12:37:46PM -0500, Michael S. Tsirkin wrote:
> On Thu, Jan 12, 2023 at 03:47:19PM +0100, Markus Armbruster wrote:
> > "Michael S. Tsirkin" <m...@redhat.com> writes:
> >
> > > On Thu, Jan 12, 2023 at 08:51:32AM -0500, Michael S. Tsirkin wrote:
> > >> On Thu, Jan 12, 2023 at 12:50:05PM +0100, Markus Armbruster wrote:
> > >> > docs/devel/style.rst mandates:
> > >> >
> > >> > The "qemu/osdep.h" header contains preprocessor macros that affect
> > >> > the behavior of core system headers like <stdint.h>. It must be
> > >> > the first include so that core system headers included by external
> > >> > libraries get the preprocessor macros that QEMU depends on.
> > >> >
> > >> > Do not include "qemu/osdep.h" from header files since the .c file
> > >> > will have already included it.
> > >> >
> > >> > A few violations have crept in. Fix them.
> > >> >
> > >> > Signed-off-by: Markus Armbruster <arm...@redhat.com>
> > >> > Reviewed-by: Philippe Mathieu-Daudé <phi...@linaro.org>
> > >> > Reviewed-by: Bin Meng <bmeng...@gmail.com>
> > >> > Reviewed-by: Taylor Simpson <tsimp...@quicinc.com>
> > >> > Reviewed-by: Alistair Francis <alistair.fran...@wdc.com>
> > >>
> > >> With my awesome grep skillz I found one more:
> > >> $ grep -r --include='*.h' qemu/osdep.h
> > >> include/block/graph-lock.h:#include "qemu/osdep.h"
> >
> > Crept in after I prepared my v1. I neglected to re-check.
> >
> > > Also:
> > > $ grep -r --include='*.inc' qemu/osdep.h
> > > ui/vnc-enc-zrle.c.inc:#include "qemu/osdep.h"
> > > crypto/akcipher-nettle.c.inc:#include "qemu/osdep.h"
> > > crypto/akcipher-gcrypt.c.inc:#include "qemu/osdep.h"
> > > crypto/rsakey-nettle.c.inc:#include "qemu/osdep.h"
> > > crypto/cipher-gnutls.c.inc:#include "qemu/osdep.h"
> > > target/xtensa/core-dc233c/xtensa-modules.c.inc:#include "qemu/osdep.h"
> > > target/xtensa/core-sample_controller/xtensa-modules.c.inc:#include
> > > "qemu/osdep.h"
> > > target/xtensa/core-de212/xtensa-modules.c.inc:#include "qemu/osdep.h"
> > > target/xtensa/core-dc232b/xtensa-modules.c.inc:#include "qemu/osdep.h"
> > > target/xtensa/core-fsf/xtensa-modules.c.inc:#include "qemu/osdep.h"
> > > target/cris/translate_v10.c.inc:#include "qemu/osdep.h"
> >
> > Good point. Looks like I successfully supressed all memory of .inc.
> >
> > >> Looks like all C files must include qemu/osdep.h, no?
> >
> > I remember there are a few exceptions, but I don't remember which .c
> > they are. Hmm... see commit 4bd802b209cff612d1a99674a91895b735be8630.
> >
> > >> How about
> > >>
> > >> 1- add -include qemu/osdep.h on compile command line
> > >> drop #include "qemu/osdep.h" from C files
> >
> > Then you need to encode the exceptions in the build system. Which might
> > not be a bad thing.
> >
> > >> 2- drop double include guards, replace with a warning.
> > >>
> > >> following patch implements part 2:
> > >>
> > >>
> > >> qemu/osdep: don't include it from headers
> > >>
> > >> doing so will lead to trouble eventually - instead of
> > >> working around such cases make it more likely it will fail.
> > >>
> > >> Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
> > >>
> > >> ---
> > >>
> > >> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> > >> index 7d059ad526..e4a60f911c 100644
> > >> --- a/include/qemu/osdep.h
> > >> +++ b/include/qemu/osdep.h
> > >> @@ -24,7 +24,12 @@
> > >> * This work is licensed under the terms of the GNU GPL, version 2 or
> > >> later.
> > >> * See the COPYING file in the top-level directory.
> > >> */
> > >> -#ifndef QEMU_OSDEP_H
> > >> +#ifdef QEMU_OSDEP_H
> > >> +#warning "Never include qemu/osdep.h from a header!"
> > >> +#endif
> > >> +
> > >> +static inline void qemu_osdep_never_include_from_header(void) {}
> > >> +
> >
> > Why do you need the function, too?
>
> This seems to give a bit more info if header does get included
> twice: instead of just a warning on the second include compiler says
> definition is duplicated and then shows where the first definition was.
> OTOH first one was almost for sure from the proper first include so
> maybe we don't care. Let me drop this.
FWIW, if we want to simplify our header guards, we could replace the
#ifndef FOO_H
#define FOO_H
....
#endif /* FOO_H */
with merely
#pragma once
at the top of each header.
With regards,
Daniel
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