On Wed, May 28, 2014 at 08:35:51PM +0100, Larry Bassel wrote: > On 28 May 14 12:27, Will Deacon wrote: > > On Mon, May 26, 2014 at 07:56:12PM +0100, Larry Bassel wrote: > > > To implement the context tracker properly on arm64, > > > a function call needs to be made after debugging and > > > interrupts are turned on, but before the lr is changed > > > to point to ret_to_user(). If the function call > > > is made after the lr is changed the function will not > > > return to the correct place. > > > > > > For similar reasons, defer the setting of x0 so that > > > it doesn't need to be saved around the function call > > > (save far_el1 in x26 temporarily instead). > > > > > > Signed-off-by: Larry Bassel <larry.bas...@linaro.org> > > > > [...] > > > > > > Why have you added this mov instruction? > > I believe (please correct me if I'm wrong) that it is necessary. > Here is why: > > > > @@ -476,23 +481,27 @@ el0_undef: > > > // enable interrupts before calling the main handler > > > enable_dbg_and_irq > > > mov x0, sp > > > + adr lr, ret_to_user > > > b do_undefinstr > > > el0_dbg: > > > /* > > > * Debug exception handling > > > */ > > > tbnz x24, #0, el0_inv // EL0 only > > > - mrs x0, far_el1 > > > + mrs x26, far_el1 > > needed because do_debug_exception may clobber x0, so save far_el1 > in x26 (as other parts of this patch do)
Actually, do_debug_exception consumes the FAR as its first parameter, so you don't need to put this in x26 afaict. > > > + mov x0, x26 > > needed because far_el1 is expected to be in x0 here > > > > mov x1, x25 > > > mov x2, sp > > > bl do_debug_exception > > > enable_dbg > > [call to ct_user_exit will go here in the next patch, this may re-clobber x0] > > > > + mov x0, x26 > > needed because far_el1 is expected to be in x0 here Is it? ret_to_user doesn't care. Does ct_user_exit use the FAR? I don't think it does... 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/
