LoongArch/ftrace: Add dynamic function tracer support

The compiler has inserted 2 NOPs before the regular function prologue.
T series registers are available and safe because of LoongArch's psABI.

At runtime, we can replace nop with bl to enable ftrace call and replace
bl with nop to disable ftrace call. The bl instruction requires us to
save the original RA value, so it saves RA at t0 here.

Details are:

| Compiled   |       Disabled         |        Enabled         |
+------------+------------------------+------------------------+
| nop        | move     t0, ra        | move    t0, ra         |
| nop        | nop                    | bl      ftrace_caller  |
| func_body  | func_body              | func_body              |

The RA value will be recovered by ftrace_regs_entry, and restored into
RA before returning to the regular function prologue. When a function is
not being traced, the "move t0, ra" is not harmful.

1) ftrace_make_call, ftrace_make_nop (in kernel/ftrace.c)
   The two functions turn each recorded call site of filtered functions
   into a call to ftrace_caller or nops.

2) ftracce_update_ftrace_func (in kernel/ftrace.c)
   turns the nops at ftrace_call into a call to a generic entry for
   function tracers.

3) ftrace_caller (in kernel/mcount_dyn.S)
   The entry where each _mcount call sites calls to once they are
   filtered to be traced.

Co-developed-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

3 files changed, 33 insertions, 1 deletions

diff --git a/arch/loongarch/include/asm/ftrace.h b/arch/loongarch/include/asm/ftrace.h
index c3f5cde40464..09ff0f84663d 100644
--- a/arch/loongarch/include/asm/ftrace.h
+++ b/arch/loongarch/include/asm/ftrace.h
@@ -11,9 +11,30 @@
 #define MCOUNT_INSN_SIZE 4		/* sizeof mcount call */
 
 #ifndef __ASSEMBLY__
+
+#ifndef CONFIG_DYNAMIC_FTRACE
+
 #define mcount _mcount
 extern void _mcount(void);
 extern void prepare_ftrace_return(unsigned long self_addr, unsigned long callsite_sp, unsigned long old);
+
+#else
+
+struct dyn_ftrace;
+struct dyn_arch_ftrace { };
+
+#define ftrace_init_nop ftrace_init_nop
+int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
+
+static inline unsigned long ftrace_call_adjust(unsigned long addr)
+{
+	return addr;
+}
+
+void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent);
+
+#endif /* CONFIG_DYNAMIC_FTRACE */
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* CONFIG_FUNCTION_TRACER */
diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
index 67215af47b3d..88e1673524e1 100644
--- a/arch/loongarch/include/asm/inst.h
+++ b/arch/loongarch/include/asm/inst.h
@@ -349,6 +349,17 @@ static inline bool is_stack_alloc_ins(union loongarch_instruction *ip)
 		is_imm12_negative(ip->reg2i12_format.immediate);
 }
 
+int larch_insn_read(void *addr, u32 *insnp);
+int larch_insn_write(void *addr, u32 insn);
+int larch_insn_patch_text(void *addr, u32 insn);
+
+u32 larch_insn_gen_nop(void);
+u32 larch_insn_gen_b(unsigned long pc, unsigned long dest);
+u32 larch_insn_gen_bl(unsigned long pc, unsigned long dest);
+
+u32 larch_insn_gen_or(enum loongarch_gpr rd, enum loongarch_gpr rj, enum loongarch_gpr rk);
+u32 larch_insn_gen_move(enum loongarch_gpr rd, enum loongarch_gpr rj);
+
 u32 larch_insn_gen_lu32id(enum loongarch_gpr rd, int imm);
 u32 larch_insn_gen_lu52id(enum loongarch_gpr rd, enum loongarch_gpr rj, int imm);
 u32 larch_insn_gen_jirl(enum loongarch_gpr rd, enum loongarch_gpr rj, unsigned long pc, unsigned long dest);
diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h
index 6af4718bdf01..a51eec00efb8 100644
--- a/arch/loongarch/include/asm/unwind.h
+++ b/arch/loongarch/include/asm/unwind.h
@@ -20,7 +20,7 @@ struct unwind_state {
 	char type; /* UNWINDER_XXX */
 	struct stack_info stack_info;
 	struct task_struct *task;
-	bool first, error;
+	bool first, error, is_ftrace;
 	unsigned long sp, pc, ra;
 };