[llvm-commits] [PATCH] improve ARM halt encoding

[Jim Grosbach]

Hi JF,

There is a lot of extant code that uses the current values and has for quite a long time. Changing has pretty extreme ripple effects, to put it mildly.

Given the circumstances for when the compiler will use a TRAP instruction, I'm pretty skeptical of any real-world security benefits to this. Can you elaborate?

-Jim

On Jan 16, 2013, at 12:46 PM, JF Bastien <jfb at chromium.org> wrote:

> I've attached a patch from PNaCl with changes the ARM halt encoding so that it also looks like a halt in Thumb. This can catch bugs when executing ARM code as Thumb, whether it be in the context of compiler/JIT bugs, or an attacker trying to get validated ARM code to execute as Thumb (which is a concern for PNaCl).
> 
> Note that the instruction itself isn't changing (it's still UDF), only the immediate.
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