On 4/19/2011 5:21 PM, Nicolas Pitre wrote:
Are you saying that your user space libc was reading at 0xffff0ff0
directly? I hope not, because if you did so, you clearly abused the
interface and the contract between user space and the kernel. Here's
what I wrote in the comment right above the related code:
* These are segment of kernel provided user code reachable from user space
* at a fixed address in kernel memory. This is used to provide user space
* with some operations which require kernel help because of unimplemented
* native feature and/or instructions in many ARM CPUs. The idea is for
* this code to be executed directly in user mode for best efficiency but
* which is too intimate with the kernel counter part to be left to user
* libraries. In fact this code might even differ from one CPU to another
* depending on the available instruction set and restrictions like on
* SMP systems. In other words, the kernel reserves the right to change
* this code as needed without warning. Only the entry points and their
* results are guaranteed to be stable.
This has been there since April 29th 2005 i.e. 6 years ago.
Yes, unfortunately Android appears to do this as an 'optimization' in
the case of dynamically linked execs. That is, it skips the helper code
all together.
Mike
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