Hi Will, On Tue, Aug 11, 2015 at 01:52:42AM +0100, David Long wrote: > From: William Cohen <wco...@redhat.com> > > The trampoline code is used by kretprobes to capture a return from a probed > function. This is done by saving the registers, calling the handler, and > restoring the registers. The code then returns to the original saved caller > return address. It is necessary to do this directly instead of using a > software breakpoint because the code used in processing that breakpoint > could itself be kprobe'd and cause a problematic reentry into the debug > exception handler. > > Signed-off-by: William Cohen <wco...@redhat.com> > Signed-off-by: David A. Long <dave.l...@linaro.org>
[...] > diff --git a/arch/arm64/kernel/kprobes_trampoline.S > b/arch/arm64/kernel/kprobes_trampoline.S > new file mode 100644 > index 0000000..dd0172b > --- /dev/null > +++ b/arch/arm64/kernel/kprobes_trampoline.S > @@ -0,0 +1,61 @@ > +/* > + * trampoline entry and return code for kretprobes. > + */ > + > +#include <linux/linkage.h> > +#include <generated/asm-offsets.h> > + > + .text > + > +ENTRY(kretprobe_trampoline) > + > + sub sp, sp, #S_FRAME_SIZE > + > + stp x0, x1, [sp, #S_X0] > + stp x2, x3, [sp, #S_X2] > + stp x4, x5, [sp, #S_X4] > + stp x6, x7, [sp, #S_X6] > + stp x8, x9, [sp, #S_X8] > + stp x10, x11, [sp, #S_X10] > + stp x12, x13, [sp, #S_X12] > + stp x14, x15, [sp, #S_X14] > + stp x16, x17, [sp, #S_X16] > + stp x18, x19, [sp, #S_X18] > + stp x20, x21, [sp, #S_X20] > + stp x22, x23, [sp, #S_X22] > + stp x24, x25, [sp, #S_X24] > + stp x26, x27, [sp, #S_X26] > + stp x28, x29, [sp, #S_X28] > + str x30, [sp, #S_LR] > + mrs x0, nzcv > + str x0, [sp, #S_PSTATE] I'm slightly wary of this, as it means user_mode(regs) will return true for the pt_regs passed into the handler. Do we need to force the mode? What about things like the I bit? Similarly, why don't you save the stack pointer? > + > + mov x0, sp > + bl trampoline_probe_handler > + /* Replace trampoline address in lr with actual > + orig_ret_addr return address. */ > + str x0, [sp, #S_LR] Why can't the trampoline_probe_handler update the pt_regs directly? Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
