+Mark Rutland
Christopher Covington cov@codeaurora.org writes:
Hi Larry,
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?
Kevin
[1]
From 8a8702b4d597d08def22221368beae5db2f4a8aa Mon Sep 17 00:00:00 2001
From: Kevin Hilman khilman@linaro.org Date: Fri, 9 May 2014 13:37:43 -0700 Subject: [PATCH] KJH: test: clobber regs
--- arch/arm64/kernel/entry.S | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+)
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 520da4c02ece..232f0200e88d 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -36,6 +36,25 @@ .macro ct_user_exit, restore = 0 #ifdef CONFIG_CONTEXT_TRACKING bl context_tracking_user_exit + movz x0, #0xff, lsl #48 + movz x1, #0xff, lsl #48 + movz x2, #0xff, lsl #48 + movz x3, #0xff, lsl #48 + movz x4, #0xff, lsl #48 + movz x5, #0xff, lsl #48 + movz x6, #0xff, lsl #48 + movz x7, #0xff, lsl #48 + movz x8, #0xff, lsl #48 + movz x9, #0xff, lsl #48 + movz x10, #0xff, lsl #48 + movz x11, #0xff, lsl #48 + movz x12, #0xff, lsl #48 + movz x13, #0xff, lsl #48 + movz x14, #0xff, lsl #48 + movz x15, #0xff, lsl #48 + movz x16, #0xff, lsl #48 + movz x17, #0xff, lsl #48 + movz x18, #0xff, lsl #48 .if \restore == 1 /* * Save/restore needed during syscalls. Restore syscall arguments from @@ -60,6 +79,25 @@ push x0, x1 .endif bl context_tracking_user_enter + movz x0, #0xff, lsl #48 + movz x1, #0xff, lsl #48 + movz x2, #0xff, lsl #48 + movz x3, #0xff, lsl #48 + movz x4, #0xff, lsl #48 + movz x5, #0xff, lsl #48 + movz x6, #0xff, lsl #48 + movz x7, #0xff, lsl #48 + movz x8, #0xff, lsl #48 + movz x9, #0xff, lsl #48 + movz x10, #0xff, lsl #48 + movz x11, #0xff, lsl #48 + movz x12, #0xff, lsl #48 + movz x13, #0xff, lsl #48 + movz x14, #0xff, lsl #48 + movz x15, #0xff, lsl #48 + movz x16, #0xff, lsl #48 + movz x17, #0xff, lsl #48 + movz x18, #0xff, lsl #48 .if \save == 1 pop x0, x1 pop x2, x3