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Subject[RFC PATCH v2 2/2] LoongArch: No need to call RESTORE_ALL_AND_RET for all syscalls
Date
In handle_syscall, it is unnecessary to call RESTORE_ALL_AND_RET
for all syscalls.

(1) If syscall number is __NR_clone and __NR_clone3,
call RESTORE_STATIC_SOME_SP_AND_RET.
(2) If syscall number is __NR_rt_sigreturn and __NR_rt_sigsuspend,
call RESTORE_TEMP_SOME_SP_AND_RET.
(3) The other syscalls call RESTORE_SOME_SP_AND_RET.

With this patch, it can reduce many load instructions.

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
---
arch/loongarch/include/asm/stackframe.h | 17 +++++++++++++++++
arch/loongarch/kernel/entry.S | 24 +++++++++++++++++++++++-
2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/include/asm/stackframe.h b/arch/loongarch/include/asm/stackframe.h
index 4ca9530..52649a5f 100644
--- a/arch/loongarch/include/asm/stackframe.h
+++ b/arch/loongarch/include/asm/stackframe.h
@@ -216,4 +216,21 @@
RESTORE_SP_AND_RET \docfi
.endm

+ .macro RESTORE_SOME_SP_AND_RET docfi=0
+ RESTORE_SOME \docfi
+ RESTORE_SP_AND_RET \docfi
+ .endm
+
+ .macro RESTORE_STATIC_SOME_SP_AND_RET docfi=0
+ RESTORE_STATIC \docfi
+ RESTORE_SOME \docfi
+ RESTORE_SP_AND_RET \docfi
+ .endm
+
+ .macro RESTORE_TEMP_SOME_SP_AND_RET docfi=0
+ RESTORE_TEMP \docfi
+ RESTORE_SOME \docfi
+ RESTORE_SP_AND_RET \docfi
+ .endm
+
#endif /* _ASM_STACKFRAME_H */
diff --git a/arch/loongarch/kernel/entry.S b/arch/loongarch/kernel/entry.S
index 53ce2cb..58fe507 100644
--- a/arch/loongarch/kernel/entry.S
+++ b/arch/loongarch/kernel/entry.S
@@ -79,7 +79,29 @@ SYM_FUNC_START(handle_syscall)
move a0, sp
bl do_syscall

- RESTORE_ALL_AND_RET
+ /*
+ * Syscall number held in a7 which is stored in PT_R11.
+ * If syscall number is __NR_clone and __NR_clone3,
+ * call RESTORE_STATIC_SOME_SP_AND_RET.
+ * If syscall number is __NR_rt_sigreturn and __NR_rt_sigsuspend,
+ * call RESTORE_TEMP_SOME_SP_AND_RET.
+ * The other syscalls call RESTORE_SOME_SP_AND_RET.
+ */
+ cfi_ld t3, PT_R11
+ li.w t4, __NR_clone
+ beq t3, t4, 3f
+ li.w t4, __NR_clone3
+ beq t3, t4, 3f
+ li.w t4, __NR_rt_sigreturn
+ beq t3, t4, 4f
+ li.w t4, __NR_rt_sigsuspend
+ beq t3, t4, 4f
+
+ RESTORE_SOME_SP_AND_RET
+3:
+ RESTORE_STATIC_SOME_SP_AND_RET
+4:
+ RESTORE_TEMP_SOME_SP_AND_RET
SYM_FUNC_END(handle_syscall)

SYM_CODE_START(ret_from_fork)
--
2.1.0
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