[RFC PATCH -next v2 2/4] arm64/ftrace: introduce ftrace dynamic trampoline entrances

[Wang ShaoBo]

From: Cheng Jian <cj.chengjian@xxxxxxxxxx>

We introduce two function entrances ftrace_(regs)_caller_tramp
for dynamic trampoline use, which are put into Read-Only section
and should be entirely copied to the space allocated for trampoline.

Signed-off-by: Cheng Jian <cj.chengjian@xxxxxxxxxx>
Signed-off-by: Wang ShaoBo <bobo.shaobowang@xxxxxxxxxx>
---
 arch/arm64/kernel/entry-ftrace.S | 80 +++++++++++++++++++++++++-------
 1 file changed, 64 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
index e535480a4069..88462d925446 100644
--- a/arch/arm64/kernel/entry-ftrace.S
+++ b/arch/arm64/kernel/entry-ftrace.S
@@ -76,6 +76,23 @@
 	add	x29, sp, #S_STACKFRAME
 	.endm
 
+	.macro ftrace_regs_restore
+	/* Restore function arguments */
+	ldp	x0, x1, [sp]
+	ldp	x2, x3, [sp, #S_X2]
+	ldp	x4, x5, [sp, #S_X4]
+	ldp	x6, x7, [sp, #S_X6]
+	ldr	x8, [sp, #S_X8]
+
+	/* Restore the callsite's FP, LR, PC */
+	ldr	x29, [sp, #S_FP]
+	ldr	x30, [sp, #S_LR]
+	ldr	x9, [sp, #S_PC]
+
+	/* Restore the callsite's SP */
+	add	sp, sp, #PT_REGS_SIZE + 16
+	.endm
+
 SYM_CODE_START(ftrace_regs_caller)
 	bti	c
 	ftrace_regs_entry	1
@@ -108,22 +125,8 @@ SYM_INNER_LABEL(ftrace_graph_call, SYM_L_GLOBAL) // ftrace_graph_caller();
  * x19-x29 per the AAPCS, and we created frame records upon entry, so we need
  * to restore x0-x8, x29, and x30.
  */
-ftrace_common_return:
-	/* Restore function arguments */
-	ldp	x0, x1, [sp]
-	ldp	x2, x3, [sp, #S_X2]
-	ldp	x4, x5, [sp, #S_X4]
-	ldp	x6, x7, [sp, #S_X6]
-	ldr	x8, [sp, #S_X8]
-
-	/* Restore the callsite's FP, LR, PC */
-	ldr	x29, [sp, #S_FP]
-	ldr	x30, [sp, #S_LR]
-	ldr	x9, [sp, #S_PC]
-
-	/* Restore the callsite's SP */
-	add	sp, sp, #PT_REGS_SIZE + 16
-
+SYM_INNER_LABEL(ftrace_common_return, SYM_L_GLOBAL)
+	ftrace_regs_restore
 	ret	x9
 SYM_CODE_END(ftrace_common)
 
@@ -138,6 +141,51 @@ SYM_CODE_START(ftrace_graph_caller)
 SYM_CODE_END(ftrace_graph_caller)
 #endif
 
+.pushsection ".rodata", "a"
+// ftrace trampoline for ftrace_regs_caller
+SYM_CODE_START(ftrace_regs_caller_tramp)
+	bti	c
+	ftrace_regs_entry	1		// save all regs
+
+	sub	x0, x30, #AARCH64_INSN_SIZE	// ip (callsite's BL insn)
+	mov	x1, x9				// parent_ip (callsite's LR)
+SYM_INNER_LABEL(ftrace_regs_caller_tramp_ops, SYM_L_GLOBAL)
+	ldr	x2, 0				// ops
+	mov	x3, sp				// regs
+SYM_INNER_LABEL(ftrace_regs_caller_tramp_call, SYM_L_GLOBAL)
+	nop
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+SYM_INNER_LABEL(ftrace_regs_caller_tramp_graph_call, SYM_L_GLOBAL)
+	nop					// ftrace_graph_caller()
+#endif
+	ftrace_regs_restore
+SYM_INNER_LABEL(ftrace_regs_caller_tramp_end, SYM_L_GLOBAL)
+	ret	x9
+SYM_CODE_END(ftrace_regs_caller_tramp)
+
+// ftrace trampoline for ftrace_caller
+SYM_CODE_START(ftrace_caller_tramp)
+	bti	c
+	ftrace_regs_entry	0		// save all regs
+
+	sub	x0, x30, #AARCH64_INSN_SIZE	// ip (callsite's BL insn)
+	mov	x1, x9				// parent_ip (callsite's LR)
+SYM_INNER_LABEL(ftrace_caller_tramp_ops, SYM_L_GLOBAL)
+	ldr	x2, 0				// ops
+	mov	x3, sp				// regs
+SYM_INNER_LABEL(ftrace_caller_tramp_call, SYM_L_GLOBAL)
+	nop
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+SYM_INNER_LABEL(ftrace_caller_tramp_graph_call, SYM_L_GLOBAL)
+	nop					// ftrace_graph_caller()
+#endif
+	ftrace_regs_restore
+SYM_INNER_LABEL(ftrace_caller_tramp_end, SYM_L_GLOBAL)
+	ret	x9
+SYM_CODE_END(ftrace_caller_tramp)
+.popsection		// .rodata
+
+
 #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
 
 /*
-- 
2.25.1