[PATCH] D14571: [ELF2] - Implemented PT_GNU_STACK support, -z execstack option.

[Rafael Espíndola via llvm-commits]

> What do you mean by legacy? An old loader will just ignore this
> program header, no?

Sorry, just read that that was not the case.

OK, I think we are all in agreement on the objective: non executable
stacks by default.

The problem them is that how to do it is dependent on the dynamic
linker, and we don't have a reliable way saying which dynamic linker
will be used.

How about

* -z execstack: add the program header marking the stack exectuable.
* -z noexecstack: add the program header marking the stack non exectuable.
* If neither, mark the stack non executable if we ever see
.note.GNU-stack. I.E., use it as an indication that the dynamic linker
uses that segment.

Cheers,
Rafael