On Fri, May 23, 2014 at 01:11:38AM +0100, Kevin Hilman wrote: > Christopher Covington <c...@codeaurora.org> writes: > > On 05/22/2014 03:27 PM, Larry Bassel wrote: > >> Make calls to ct_user_enter when the kernel is exited > >> and ct_user_exit when the kernel is entered (in el0_da, > >> el0_ia, el0_svc, el0_irq and all of the "error" paths). > >> > >> These macros expand to function calls which will only work > >> properly if el0_sync and related code has been rearranged > >> (in a previous patch of this series). > >> > >> The calls to ct_user_exit are made after hw debugging has been > >> enabled (enable_dbg_and_irq). > >> > >> The call to ct_user_enter is made at the beginning of the > >> kernel_exit macro. > >> > >> This patch is based on earlier work by Kevin Hilman. > >> Save/restore optimizations were also done by Kevin. > > > >> --- a/arch/arm64/kernel/entry.S > >> +++ b/arch/arm64/kernel/entry.S > >> @@ -30,6 +30,44 @@ > >> #include <asm/unistd32.h> > >> > >> /* > >> + * Context tracking subsystem. Used to instrument transitions > >> + * between user and kernel mode. > >> + */ > >> + .macro ct_user_exit, restore = 0 > >> +#ifdef CONFIG_CONTEXT_TRACKING > >> + bl context_tracking_user_exit > >> + .if \restore == 1 > >> + /* > >> + * Save/restore needed during syscalls. Restore syscall arguments from > >> + * the values already saved on stack during kernel_entry. > >> + */ > >> + ldp x0, x1, [sp] > >> + ldp x2, x3, [sp, #S_X2] > >> + ldp x4, x5, [sp, #S_X4] > >> + ldp x6, x7, [sp, #S_X6] > >> + .endif > >> +#endif > >> + .endm > >> + > >> + .macro ct_user_enter, save = 0 > >> +#ifdef CONFIG_CONTEXT_TRACKING > >> + .if \save == 1 > >> + /* > >> + * Save/restore only needed on syscall fastpath, which uses > >> + * x0-x2. > >> + */ > >> + push x2, x3 > > > > Why is x3 saved? > > I'll respond here since I worked with Larry on the context save/restore > part. > > [insert rather embarassing disclamer of ignorance of arm64 assembly] > > Based on my reading of the code, I figured only x0-x2 needed to be > saved. However, based on some experiments with intentionally clobbering > the registers[1] (as suggested by Mark Rutland) in order to make sure > we're saving/restoring the right things, I discovered x3 was needed too > (I missed updating the comment to mention x0-x3.) > > Maybe Will/Catalin/Mark R. can shed some light here?
I haven't checked all the code paths but at least for pushing onto the stack we must keep it 16-bytes aligned (architecture requirement). -- Catalin -- 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/
