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Subject[PATCH 2/5] arm64: entry: introduce restore_syscall_args macro
Date
Syscall arguments are passed in registers x0..x7. If assembler
code has to call C functions before passing control to syscall
handler, it should restore original state of that registers
after the call.

Currently, syscall arguments restoring is opencoded in el0_svc_naked
and __sys_trace. This patch introduces restore_syscall_args macro to
use it there.

Also, parameter 'syscall = 0' is removed from ct_user_exit to make
el0_svc_naked call restore_syscall_args explicitly. This is needed
because the following patch of the series adds another call to C
function in el0_svc_naked, and restoring of syscall args becomes not
only a matter of ct_user_exit.

Signed-off-by: Yury Norov <ynorov@caviumnetworks.com>
---
arch/arm64/kernel/entry.S | 37 +++++++++++++++++++++----------------
1 file changed, 21 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 9c06b4b80060..c8d9ec363ddd 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -37,22 +37,29 @@
#include <asm/unistd.h>

/*
- * Context tracking subsystem. Used to instrument transitions
- * between user and kernel mode.
+ * Save/restore needed during syscalls. Restore syscall arguments from
+ * the values already saved on stack during kernel_entry.
*/
- .macro ct_user_exit, syscall = 0
-#ifdef CONFIG_CONTEXT_TRACKING
- bl context_tracking_user_exit
- .if \syscall == 1
- /*
- * Save/restore needed during syscalls. Restore syscall arguments from
- * the values already saved on stack during kernel_entry.
- */
+ .macro restore_syscall_args
ldp x0, x1, [sp]
ldp x2, x3, [sp, #S_X2]
ldp x4, x5, [sp, #S_X4]
ldp x6, x7, [sp, #S_X6]
- .endif
+ .endm
+
+ .macro el0_svc_restore_syscall_args
+#if defined(CONFIG_CONTEXT_TRACKING)
+ restore_syscall_args
+#endif
+ .endm
+
+/*
+ * Context tracking subsystem. Used to instrument transitions
+ * between user and kernel mode.
+ */
+ .macro ct_user_exit
+#ifdef CONFIG_CONTEXT_TRACKING
+ bl context_tracking_user_exit
#endif
.endm

@@ -943,7 +950,8 @@ alternative_else_nop_endif
el0_svc_naked: // compat entry point
stp x0, xscno, [sp, #S_ORIG_X0] // save the original x0 and syscall number
enable_daif
- ct_user_exit 1
+ ct_user_exit
+ el0_svc_restore_syscall_args

tst x16, #_TIF_SYSCALL_WORK // check for syscall hooks
b.ne __sys_trace
@@ -976,10 +984,7 @@ __sys_trace:
mov x1, sp // pointer to regs
cmp wscno, wsc_nr // check upper syscall limit
b.hs __ni_sys_trace
- ldp x0, x1, [sp] // restore the syscall args
- ldp x2, x3, [sp, #S_X2]
- ldp x4, x5, [sp, #S_X4]
- ldp x6, x7, [sp, #S_X6]
+ restore_syscall_args
ldr x16, [stbl, xscno, lsl #3] // address in the syscall table
blr x16 // call sys_* routine

--
2.14.1
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