icache coherency

[Anton Blanchard]

> 1. The segment with the blrl is not always marked executable.
>
> 2. The PLT was not always marked executable. More bad news.

3. PLTs are in mmap(/dev/zero) memory, so I cant even optimise
icache syncing in anonymous memory regions.

Milton suggested adding something in the ELF header to say the
executable is compiled correctly, this might be worth pursuing.

Dave Gibson tried enabling per page execute permission a while ago
(the 4XX supports it). Of course nothing worked :) We should
look towards fixing this mess.

Anton

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