Date: Wed, 19 Sep 2012 07:18:11 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Attilio Rao <attilio@FreeBSD.org> Cc: Davide Italiano <davide@FreeBSD.org>, src-committers@FreeBSD.org, John Baldwin <jhb@FreeBSD.org>, Jeff Roberson <jeff@FreeBSD.org>, Dimitry Andric <dim@FreeBSD.org>, svn-src-projects@FreeBSD.org Subject: Re: svn commit: r238907 - projects/calloutng/sys/kern Message-ID: <20120919041811.GM37286@deviant.kiev.zoral.com.ua> In-Reply-To: <CAJ-FndCmg-GdTf9FWQGZPYB-iGuEt-JH8HrCL%2BwaOqJ%2B8ZUbHQ@mail.gmail.com> References: <201207301350.q6UDobCI099069@svn.freebsd.org> <CAJ-FndBj8tpC_BJXs_RH8sG2TBG8yA=Lxu3-GTVT9Ap_zOCuVQ@mail.gmail.com> <CAJ-FndDnO7wjnWPV0tTu%2BUGHjsxa3YDarMxmyei3ZmjLAFvRkQ@mail.gmail.com> <201207301732.33474.jhb@freebsd.org> <CAJ-FndD5EO12xsWOAe6u0EvX00q33wxO4OivnGjzj0=T2Oe8uA@mail.gmail.com> <CAJ-FndCRg0UCThFkatp=tw7rUWWCvhsApLE=iztLpxpGBC1F9w@mail.gmail.com> <20120918083324.GX37286@deviant.kiev.zoral.com.ua> <CAJ-FndAXw6zjXr=zB3gAVQDKUV_K4=SF39iYQQOV23NkfJ=MPw@mail.gmail.com> <CAJ-FndCmg-GdTf9FWQGZPYB-iGuEt-JH8HrCL%2BwaOqJ%2B8ZUbHQ@mail.gmail.com>
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On Tue, Sep 18, 2012 at 08:00:48PM +0100, Attilio Rao wrote:
> On Tue, Sep 18, 2012 at 4:30 PM, Attilio Rao <attilio@freebsd.org> wrote:
> > On 9/18/12, Konstantin Belousov <kostikbel@gmail.com> wrote:
> >> Traditionally, we do provide the fallback for non-GNUC compilers, by
> >> defining extern function with the compatible signature. In this case,
> >> the empty function just works for the purpose, although with higher
> >> overhead than the GNUC case.
> >
> > I agree, we need a fallback here. Unfortunately I'm buried with job
> > stuff but I will provide an errata patch ASAP.
>=20
> Here is the patch. I didn't use a real extern function body for it,
> but just went with an empty macro.
>=20
> Attilio
> +/*
> + * Compiler memory barriers, specific to gcc and clang.
> + */
> +#if defined(__GNUC__)
> +#define __compiler_membar() __asm __volatile(" " : : : "memor=
y")
> +#else
> +#define __compiler_membar() struct __hack
> +#endif
I would not call this an empty macro. If this works at all, it requires
c99 compiler. Why not just do
extern void __compiler_membar(void);
for !GNUC. Note that we never supplied actual implementation for the
placeholders, as evidenced e.g. by cpufunc.h or fpu.c.
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