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Re: [PATCH, RFC] MIPS: Implement the getcontext API


Daniel Jacobowitz wrote:
On Wed, Mar 04, 2009 at 09:19:28AM +0100, Brian Foster wrote:
 moving the signal trampoline to a vdso (which
 is(? was?) called, maybe misleadingly, âvsyscallâ,
 on other architectures) is the obvious solution to
 that part of the puzzle.  and yes, it is possible
 to maintain the ABI; the signal trampoline is still
 also put on the stack, and modulo XI, would work if
 used â the trampoline-on-stack is simply not used
 if there is a vdso with the signal trampoline.

That won't quite retain the ABI: you need to make sure everyone locates it by using the stack pointer instead of the return pc. Fortunately, GCC uses the return PC only for instruction matching today. I have a vague memory it used to use the stack pointer but this was more reliable.

That is correct. Due to various errata the trampoline cannot always be at a fixed offset to the signal context bits. So we had to use the return PC as you indicate.


David Daney


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