On Oct 7, 2014 1:03 PM, "David Daney" <ddaney.cavm@xxxxxxxxx> wrote: > > On 10/07/2014 12:28 PM, Andy Lutomirski wrote: >> >> On Tue, Oct 7, 2014 at 12:21 PM, Rich Felker <dalias@xxxxxxxx> wrote: >>> >>> On Tue, Oct 07, 2014 at 12:16:59PM -0700, Leonid Yegoshin wrote: >>>> >>>> On 10/07/2014 12:09 PM, Rich Felker wrote: >>>>> >>>>> I agree completely here. We should not break things (or, as it >>>>> seems, leave them broken) for common usage cases that affect >>>>> everyone just to coddle proprietary vendor-specific instructions. >>>>> The latter just should not be used in delay slots unless the chip >>>>> vendor also promises to provide fpu branch in hardware. Rich >>>> >>>> And what do you propose - remove a current in-stack emulation and >>>> you still think it doesn't break a status-quo? >>> >>> >>> The in-stack trampoline support could be left but used only for >>> emulating instructions the kernel doesn't know. This would make all >>> normal binaries immediately usable with non-executable stack, and >>> would avoid the only potential source of regressions. Ultimately I >>> think the "xol" stuff should be removed, but that could be a long term >>> goal. >> >> >> Does anything break if the xol stuff is disabled for PT_GNU_STACK tasks? >> > > The instructions must be executed, if you turn on a non-executable stack, you cannot execute them on the stack, so they must be handled in another way, which is the subject of this thread. > > Options: > > 1a) XOL kernel manages the memory > 1b) XOL userspace manages the menory > 2) Emulate the instructions. > 3) I don't think there is a 3rd. option. 4) SIGILL 5) single-step or use an HW breakpoint if available But, yes, 3 seems reasonable. --Andy
