Re: [PATCH] ARM: Convert BUG() to use unreachable()

[David Daney]

Joe Buck wrote:
> On Thu, Dec 17, 2009 at 11:06:13AM -0800, Russell King - ARM Linux wrote:
> > On Thu, Dec 17, 2009 at 10:35:17AM -0800, Joe Buck wrote:
> > > Besides, didn't I see a whole bunch of kernel security patches related
> > > to null pointer dereferences lately?  If page 0 can be mapped, you
> > > suddenly won't get your trap.
> > Page 0 can not be mapped on ARM kernels since the late 1990s, and this
> > protection is independent of the generic kernel.
> >
> > Milage may vary on other architectures, but that's not a concern here.
>
> I don't understand, though, why you would want to implement a generally
> useful facility (make the kernel trap so you can do a post-mortem
> analysis) in a way that's only safe for the ARM port.

Each Linux kernel architecture has in its architecture specific bug.h an 
implementation that is deemed by the architecture maintainers to work. 
As far as I know, few if any of these use __builtin_trap().

Some could be converted to __builtin_trap(), others cannot (x86 for 
example).  If we enhanced __builtin_trap() to take an argument for the 
trap code, MIPS could be converted.  But as it stands now 
__builtin_trap() is not very useful.

As more architectures start adding funky tables that get generated by 
the inline asm (as in x86), __builtin_trap() becomes less useful.

David Daney
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