[PATCH -next V5 6/7] riscv: ftrace: Add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

From: guoren@kernel.org
To: anup@brainfault.org, paul.walmsley@sifive.com,
	palmer@dabbelt.com, conor.dooley@microchip.com, heiko@sntech.de,
	rostedt@goodmis.org, mhiramat@kernel.org, jolsa@redhat.com,
	bp@suse.de, jpoimboe@kernel.org, suagrfillet@gmail.com,
	andy.chiu@sifive.com
Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	Guo Ren <guoren@kernel.org>
Subject: [PATCH -next V5 6/7] riscv: ftrace: Add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support
Date: Thu,  8 Dec 2022 04:12:43 -0500	[thread overview]
Message-ID: <20221208091244.203407-7-guoren@kernel.org> (raw)
In-Reply-To: <20221208091244.203407-1-guoren@kernel.org>

From: 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>
Tested-by: Guo Ren <guoren@kernel.org>
Signed-off-by: Guo Ren <guoren@kernel.org>
---
 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 da59182cb5f1..27c2bc613ecd 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -133,6 +133,7 @@ config RISCV
 	select UACCESS_MEMCPY if !MMU
 	select ZONE_DMA32 if 64BIT
 	select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && $(cc-option,-fpatchable-function-entry=8)
+	select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE
 	select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
 	select HAVE_FUNCTION_GRAPH_TRACER
diff --git a/arch/riscv/include/asm/ftrace.h b/arch/riscv/include/asm/ftrace.h
index 84f856a3286e..4539f10fea56 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..fef7c460f991 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -232,6 +232,7 @@ ENDPROC(ftrace_caller)
 
 #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
 ENTRY(ftrace_regs_caller)
+	move	t1, zero
 	SAVE_ABI_REGS 1
 	PREPARE_ARGS
 
@@ -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)
-- 
2.36.1

