On Fri, May 23, 2014 at 01:11:38AM +0100, Kevin Hilman wrote:
Christopher Covington cov@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).