[PATCH 4/8] riscv: ftrace: always preserve s0 in dynamic ftrace register frame

[Wang Han]

The dynamic ftrace entry/exit only saved s0 (the architectural frame
pointer) when HAVE_FUNCTION_GRAPH_FP_TEST was selected. The upcoming
reliable frame-pointer unwinder needs s0 to be present in
ftrace_regs unconditionally so it can use the frame pointer as the
function-graph return-address cookie regardless of FP_TEST.

Save and restore s0 unconditionally in the dynamic ftrace ABI register
frame. The cost is one extra REG_S/REG_L pair per traced call, which is
negligible compared to the overall ftrace cost; the benefit is a
consistent ftrace_regs layout for the unwinder.

Signed-off-by: Wang Han <wanghan@xxxxxxxxxxxxxxxxx>
---
 arch/riscv/kernel/mcount-dyn.S | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index 082fe0b0e3c0..26c55fba8fec 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -85,9 +85,7 @@
 	addi	sp, sp, -FREGS_SIZE_ON_STACK
 	REG_S	t0,  FREGS_EPC(sp)
 	REG_S	x1,  FREGS_RA(sp)
-#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
 	REG_S	x8,  FREGS_S0(sp)
-#endif
 	REG_S	x6,  FREGS_T1(sp)
 #ifdef CONFIG_CC_IS_CLANG
 	REG_S	x7,  FREGS_T2(sp)
@@ -113,9 +111,7 @@
 	.macro RESTORE_ABI_REGS
 	REG_L	t0, FREGS_EPC(sp)
 	REG_L	x1, FREGS_RA(sp)
-#ifdef HAVE_FUNCTION_GRAPH_FP_TEST
 	REG_L	x8, FREGS_S0(sp)
-#endif
 	REG_L	x6,  FREGS_T1(sp)
 #ifdef CONFIG_CC_IS_CLANG
 	REG_L	x7,  FREGS_T2(sp)
-- 
2.43.0