Re: [PATCH 2/4] Add NR_syscalls for x86_64

From: Mathieu Desnoyers
Date: Tue Aug 25 2009 - 19:28:49 EST


* Jason Baron (jbaron@xxxxxxxxxx) wrote:
> On Tue, Aug 25, 2009 at 03:04:15PM -0400, Mathieu Desnoyers wrote:
> > * Jason Baron (jbaron@xxxxxxxxxx) wrote:
> > > On Tue, Aug 25, 2009 at 09:40:05AM -0400, Jason Baron wrote:
> > > > > > On Mon, Aug 24, 2009 at 05:40:18PM -0400, Jason Baron wrote:
> > > > > > > Add a dynamic definition of NR_syscalls for x86_64. This is used in the
> > > > > > > syscall events tracing code.
> > > > > > >
> > > > > > > Signed-off-by: Jason Baron <jbaron@xxxxxxxxxx>
> > > > > > >
> > > > > > > ---
> > > > > > > include/linux/ftrace.h | 5 +++++
> > > > > > > 1 files changed, 5 insertions(+), 0 deletions(-)
> > > > > > >
> > > > > > > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> > > > > > > index dc3b132..3bd94ee 100644
> > > > > > > --- a/include/linux/ftrace.h
> > > > > > > +++ b/include/linux/ftrace.h
> > > > > > > @@ -14,6 +14,11 @@
> > > > > > >
> > > > > > > #include <asm/ftrace.h>
> > > > > > >
> > > > > > > +#ifdef CONFIG_X86_64
> > > > > > > +#include <asm/asm-offsets.h>
> > > > > > > +#define NR_syscalls (__NR_syscall_max + 1)
> > > > > > > +#endif
> > > > > > > +
> > > > > >
> > > > > >
> > > > > > I'd rather see this in arch/x86/include/unistd_64.h, since
> > > > > > NR_syscalls seems to be the defined in unistd.h in all archs.
> > > > > >
> > > > > > That also makes a unified way to retrieve this number for
> > > > > > other users.
> > > > > >
> > > > >
> > > > > Yes, NR_syscalls should be included there.
> > > > >
> > > > > -- Steve
> > > >
> > > > right, for x86_64, unistd.h is included to generate __NR_syscall_max
> > > > which is then used for NR_syscalls. So I did initially try it there, but
> > > > there were dependency problems. I'll see what I can come up with...
> > > >
> > > > thanks,
> > > >
> > > > -Jason
> > >
> > > ok, since unistd_64.h is used to generate offsets.c, which eventually
> > > generates, asm/asm-offsets.h, which defines, __NR_syscall_max, we can't
> > > just put #define of NR_syscalls in unistd_64.h. However, it seems the
> > > only point in time that unistd_64.h can not depend upon __NR_syscall_max,
> > > is before asm/asm-offsets.h is defined. Thus, the patch below passes in
> > > a '-DCREATE_OFFSETS' during the creation of asm/asm-offsets.h, so that
> > > we do not include it before it exists. The patch is hacky but works.
> > > thoughts?
> >
> > Ugh! My eyes hurt!
> >
>
> sorry :)
>
> > What you are doing here is to basically put back the hardcoded
> > NR_syscalls rather that using the build infrastructure already in place.
> >
>
> no. NR_syscalls is not hardcoded by this patch. Its defined in terms of
> __NR_syscall_max which is dynamically generated by the kernel build.
>
> > If my memory serves me well, unistd_64.h generates __NR_syscall_max
> > automatically by being included multiples times. Can we generalize this
> > and make the information generated available in an automaticaly
> > generated header instead ? It is saved in ams-offsets.h currently as
> > "__NR_syscall_max". We could also save it somewhere else meant to be
> > included by C code.
> >
> > Mathieu
> >
>
> The request was to define NR_syscalls in unistd.h, since that is the
> historical Linux location for it. Adding another automatically generated
> header does not accomplish that. Even if I include that new file in
> unistd.h, I'm still going to have a circular dependency, and require a
> solution similar to what I've proposed.
>

OK, it may not be pretty, but it makes sense. :)

Thanks,

Mathieu

> thanks,
>
> -Jason
>

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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