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-----Original Message-----
From: linux-mips-bounce@linux-mips.org [mailto:linux-mips-bounce@linux-mips.org] On Behalf Of Ralf Baechle
Sent: Wednesday, March 04, 2009 7:44 AM
To: Brian Foster
Cc: David Daney; Maciej W. Rozycki; linux-mips@linux-mips.org; libc-ports@sourceware.org; Maciej W. Rozycki
Subject: Re: [PATCH, RFC] MIPS: Implement the getcontext API
On Wed, Mar 04, 2009 at 09:19:28AM +0100, Brian Foster wrote:
On Tuesday 03 March 2009 17:56:25 David Daney wrote:we should be[ ... ]
When (and if) we move the sigreturn trampoline to a vdsoWe generally want to get rid of stack trampolines. Trampolines requireable to maintain the ABI.it's more a matter of "when" rather than "if". there is still an intention here to use XI (we have SmartMIPS), which requires not using the signal (or FP) trampoline on the stack.
moving the signal trampoline to a vdso (which is(? was?) called, maybe misleadingly, 'vsyscall', 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 - the trampoline-on-stack is simply not used if there is a vdso with the signal trampoline.
cacheflushing which especially on SMP systems can be a rather expensive
operation.
If I understand this correctly, using a vdso would allow a stack without execute permission on those processors that differentiate between read and execute permission. This defeats attaches that use buffer overrun to write code to be executed onto the stack, a nice thing for more secure systems.
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