On Tue, 26 Jun 2007 16:03:58 +1000 Michael Ellerman <[email protected]> wrote:
> On Tue, 2007-06-26 at 07:53 +0200, Christoph Hellwig wrote:
> > On Tue, Jun 26, 2007 at 11:48:51AM +1000, Michael Ellerman wrote:
> > > I realise jprobes are a razor-blades-included type of interface, but
> > > that doesn't mean we can't try and make them safer to use. This guy I
> > > know once wrote code like this:
> > >
> > > struct jprobe jp = { .kp.symbol_name = "foo", .entry = "jprobe_foo" };
> > >
> > > And then his kernel exploded. Oops.
> > >
> > > This patch adds an arch hook, arch_deref_entry_point() (I don't like it either)
> > > which takes the void * in a struct jprobe, and gives back the text address
> > > that it represents.
> > >
> > > We can then use that in register_jprobe() to check that the entry point
> > > we're passed is actually in the kernel text, rather than just some random
> > > value.
> >
> > Please don't add more weak functions, they're utterly horrible for
> > anyone trying to understand the code. Otherwise this looks fine to me.
>
> What do you recommend instead? #define ARCH_HAS_FOO_BAR ?
o lord, save us, no.
> I don't see what's utterly horrible about them.
Me either.
> The fact that they're
> weak is fairly reasonable documentation that they're overridden
> somewhere else. And grep/cscope/ctags will find both the weak and
> non-weak versions for you?
yup.
In this case we could just require that each jprobes-supporting
architecture implement arch_deref_entry_point().
Or one could do the Linus trick. In each architecture which implements
arch_deref_entry_point() do:
#define arch_deref_entry_point arch_deref_entry_point
in the per-arch header file then, in non-arch code, do
#ifndef arch_deref_entry_point
static unsigned long arch_deref_entry_point(...)
{
<generic implementation>
}
#endif
That's just the ARCH_HAS_FOO_BAR thing, only less fugly.
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