[PATCH 4/9] Loongarch/ftrace: Add dynamic function graph tracer support

[Qing Zhang]

Once the function_graph tracer is enabled, a filtered function has the
following call sequence:

1) ftracer_caller        ==> on/off by ftrace_make_call/ftrace_make_nop
2) ftrace_graph_caller
3) ftrace_graph_call     ==> on/off by ftrace_en/disable_ftrace_graph_caller
4) prepare_ftrace_return

Considering the following DYNAMIC_FTRACE_WITH_REGS feature, it would be
more extendable to have a ftrace_graph_caller function, instead of
calling prepare_ftrace_return directly in ftrace_caller.

Co-developed-by: Jinyang He <hejinyang@xxxxxxxxxxx>
Signed-off-by: Jinyang He <hejinyang@xxxxxxxxxxx>
Signed-off-by: Qing Zhang <zhangqing@xxxxxxxxxxx>
---
 arch/loongarch/kernel/entry_dyn.S  | 33 ++++++++++++++++++++++
 arch/loongarch/kernel/ftrace_dyn.c | 45 ++++++++++++++++++++++++++++++
 arch/loongarch/kernel/inst.c       | 24 ++++++++++++++++
 3 files changed, 102 insertions(+)

diff --git a/arch/loongarch/kernel/entry_dyn.S b/arch/loongarch/kernel/entry_dyn.S
index e4686e67f049..4e3fb0c9a48f 100644
--- a/arch/loongarch/kernel/entry_dyn.S
+++ b/arch/loongarch/kernel/entry_dyn.S
@@ -62,6 +62,11 @@ SYM_CODE_START(ftrace_common)
 	.globl ftrace_call
 ftrace_call:
 	bl		ftrace_stub
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	.globl ftrace_graph_call
+ftrace_graph_call:
+	nop				/* b ftrace_graph_caller */
+#endif
 /*
  * As we didn't use S series regs in this assmembly code and all calls
  * are C function which will save S series regs by themselves, there is
@@ -84,6 +89,34 @@ ftrace_common_return:
 	jirl	zero, t0, 0
 SYM_CODE_END(ftrace_common)
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+SYM_CODE_START(ftrace_graph_caller)
+	PTR_L		a0, sp, PT_ERA
+	PTR_ADDI	a0, a0, -8	/* arg0: self_addr */
+	PTR_ADDI	a1, sp, PT_R1	/* arg1: parent */
+	bl		prepare_ftrace_return
+	b		ftrace_common_return
+SYM_CODE_END(ftrace_graph_caller)
+
+SYM_CODE_START(return_to_handler)
+	/* save return value regs */
+	PTR_ADDI 	sp, sp, -2 * SZREG
+	PTR_S		a0, sp, 0
+	PTR_S		a1, sp, SZREG
+
+	move		a0, zero	/* Has no check FP now. */
+	bl		ftrace_return_to_handler
+	move		ra, a0		/* parent ra */
+
+	/* restore return value regs */
+	PTR_L		a0, sp, 0
+	PTR_L		a1, sp, SZREG
+	PTR_ADDI 	sp, sp, 2 * SZREG
+
+	jirl		zero, ra, 0
+SYM_CODE_END(return_to_handler)
+#endif
+
 SYM_FUNC_START(ftrace_stub)
 	jirl	zero, ra, 0
 SYM_FUNC_END(ftrace_stub)
diff --git a/arch/loongarch/kernel/ftrace_dyn.c b/arch/loongarch/kernel/ftrace_dyn.c
index 1f8955be8b64..3fe791b6783e 100644
--- a/arch/loongarch/kernel/ftrace_dyn.c
+++ b/arch/loongarch/kernel/ftrace_dyn.c
@@ -109,3 +109,48 @@ int __init ftrace_dyn_arch_init(void)
 {
 	return 0;
 }
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+extern void ftrace_graph_call(void);
+
+void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent)
+{
+	unsigned long return_hooker = (unsigned long)&return_to_handler;
+	unsigned long old;
+
+	if (unlikely(atomic_read(&current->tracing_graph_pause)))
+		return;
+
+	old = *parent;
+
+	if (!function_graph_enter(old, self_addr, 0, NULL))
+		*parent = return_hooker;
+}
+
+static int ftrace_modify_graph_caller(bool enable)
+{
+	unsigned long pc, func;
+	u32 branch, nop;
+
+	pc = (unsigned long)&ftrace_graph_call;
+	func = (unsigned long)&ftrace_graph_caller;
+
+	branch = larch_insn_gen_b(pc, func);
+	nop = larch_insn_gen_nop();
+
+	if (enable)
+		return ftrace_modify_code(pc, nop, branch, true);
+	else
+		return ftrace_modify_code(pc, branch, nop, true);
+}
+
+int ftrace_enable_ftrace_graph_caller(void)
+{
+	return ftrace_modify_graph_caller(true);
+}
+
+int ftrace_disable_ftrace_graph_caller(void)
+{
+	return ftrace_modify_graph_caller(false);
+}
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
diff --git a/arch/loongarch/kernel/inst.c b/arch/loongarch/kernel/inst.c
index f2759ae9a8bd..4f7a62ddf210 100644
--- a/arch/loongarch/kernel/inst.c
+++ b/arch/loongarch/kernel/inst.c
@@ -55,6 +55,30 @@ u32 larch_insn_gen_nop(void)
 	return INSN_NOP;
 }
 
+u32 larch_insn_gen_b(unsigned long pc, unsigned long dest)
+{
+	unsigned int immediate_l, immediate_h;
+	union loongarch_instruction insn;
+	long offset = dest - pc;
+
+	if ((offset & 3) || offset < -SZ_128M || offset >= SZ_128M) {
+		pr_warn("The generated b instruction is out of range.\n");
+		return INSN_BREAK;
+	}
+
+	offset >>= 2;
+
+	immediate_l = offset & 0xffff;
+	offset >>= 16;
+	immediate_h = offset & 0x3ff;
+
+	insn.reg0i26_format.opcode = b_op;
+	insn.reg0i26_format.immediate_l = immediate_l;
+	insn.reg0i26_format.immediate_h = immediate_h;
+
+	return insn.word;
+}
+
 u32 larch_insn_gen_bl(unsigned long pc, unsigned long dest)
 {
 	unsigned int immediate_l, immediate_h;
-- 
2.36.1