> -----Original Message----- > From: linux-mips-bounce@xxxxxxxxxxxxxx > [mailto:linux-mips-bounce@xxxxxxxxxxxxxx] On Behalf Of Ralf Baechle > Sent: Wednesday, March 04, 2009 7:44 AM > To: Brian Foster > Cc: David Daney; Maciej W. Rozycki; > linux-mips@xxxxxxxxxxxxxx; libc-ports@xxxxxxxxxxxxxx; 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: > > >[ ... ] > > > When (and if) we move the sigreturn trampoline to a vdso > we should be > > > able 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. > > We generally want to get rid of stack trampolines. > Trampolines require > 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.
