[PATCH 1/2] riscv/ftrace: add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

[Song Shuai <suagrfillet@gmail.com>]

This patch adds DYNAMIC_FTRACE_WITH_DIRECT_CALLS support for RISC-V.

select the DYNAMIC_FTRACE_WITH_DIRECT_CALLS to provide the
register_ftrace_direct[_multi] interfaces allowing users to register
the customed trampoline (direct_caller) as the mcount for one or
more target functions. And modify_ftrace_direct[_multi] are also
provided for modifying direct_caller.

To make the direct_caller and the other ftrace hooks (eg. function/fgraph
tracer, k[ret]probes) co-exist, a temporary register is nominated to
store the address of direct_caller in ftrace_regs_caller. After the
setting of the address direct_caller by direct_ops->func and the
RESTORE_REGS in ftrace_regs_caller, direct_caller will be jumped to
by the `jr` inst.

Signed-off-by: Song Shuai <suagrfillet@gmail.com>
---
 arch/riscv/Kconfig              | 1 +
 arch/riscv/include/asm/ftrace.h | 6 ++++++
 arch/riscv/kernel/mcount-dyn.S  | 4 ++++
 3 files changed, 11 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 39ec8d628cf6..d083ec08d0b6 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -278,6 +278,7 @@ config ARCH_RV64I
 	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
 	select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && $(cc-option,-fpatchable-function-entry=8)
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
+	select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 01bebb28eabe..be4d57566139 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -114,6 +114,12 @@ struct ftrace_regs;
 void ftrace_graph_func(unsigned long ip, unsigned long parent_ip,
 		       struct ftrace_ops *op, struct ftrace_regs *fregs);
 #define ftrace_graph_func ftrace_graph_func
+
+static inline void arch_ftrace_set_direct_caller(struct pt_regs *regs, unsigned long addr)
+{
+		regs->t1 = addr;
+}
+
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
 
 #endif /* __ASSEMBLY__ */
diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index 466c6ef217b1..b89c85a58569 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -233,6 +233,7 @@ ENDPROC(ftrace_caller)
 #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
 ENTRY(ftrace_regs_caller)
 	SAVE_ABI_REGS 1
+	REG_S	x0, PT_T1(sp)
 	PREPARE_ARGS
 
 ftrace_regs_call:
@@ -241,7 +242,10 @@ ftrace_regs_call:
 
 
 	RESTORE_ABI_REGS 1
+	bnez	t1,.Ldirect
 	jr t0
+.Ldirect:
+	jr t1
 ENDPROC(ftrace_regs_caller)
 
 ENTRY(ftrace_caller)
-- 
2.20.1