Re: [PATCH] arm: mm: Poison freed init memory

From: Russell King - ARM Linux
Date: Wed Jan 05 2011 - 15:27:04 EST

On Wed, Jan 05, 2011 at 11:47:25AM -0800, Stephen Boyd wrote:
> Poisoning __init marked memory can be useful when tracking down
> obscure memory corruption bugs. When a pointer is 0xCCCCCCCC in an

That's a bad idea for a value. With a 3GB page offset and 256MB or
more memory, accesses to such an address will always succeed.

There's two things to be considered when selecting a possible poison

1. what value is guaranteed to provoke an undefined instruction exception?
2. what value when used as an address and dereferenced is mostly always
going to abort?

1 for ARM mode implies an 0xe7fXXXfX value. For Thumb mode 0xdeXX. We
use this space for breakpoints.

2 unfortunately depends on the platform.
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