[V10,3/4] riscv: ftrace: Add DYNAMIC_FTRACE_WITH_DIRECT_CALLS support

Commit Message

Song Shuai May 11, 2023, 9:32 a.m. UTC

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 <[e-mail]>
Tested-by: Guo Ren <[e-mail]>
Signed-off-by: Guo Ren <[e-mail]>
---
 arch/riscv/Kconfig              |  1 +
 arch/riscv/include/asm/ftrace.h |  8 ++++++++
 arch/riscv/kernel/mcount-dyn.S  | 10 ++++++++++
 3 files changed, 19 insertions(+)

Comments

Björn Töpel May 11, 2023, 7:42 p.m. UTC | #1

Song Shuai <[e-mail]> writes:

> 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 <[e-mail]>
> Tested-by: Guo Ren <[e-mail]>
> Signed-off-by: Guo Ren <[e-mail]>

Thank you for addressing my comments, and for your work on
WITH_DIRECT_CALLS!

Acked-by: Björn Töpel <[e-mail]>

Patch

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index e0632493482f..fdf0b219a02c 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -144,6 +144,7 @@  config RISCV
 	select UACCESS_MEMCPY if !MMU
 	select ZONE_DMA32 if 64BIT
 	select HAVE_DYNAMIC_FTRACE if !XIP_KERNEL && MMU && (CLANG_SUPPORTS_DYNAMIC_FTRACE || GCC_SUPPORTS_DYNAMIC_FTRACE)
+	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..84904c1e4369 100644
--- a/arch/riscv/include/asm/ftrace.h
+++ b/arch/riscv/include/asm/ftrace.h
@@ -114,6 +114,14 @@  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;
+}
+#define arch_ftrace_set_direct_caller(fregs, addr) \
+	__arch_ftrace_set_direct_caller(&(fregs)->regs, 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 fb8286b80cfc..b6f4e1847d61 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -231,6 +231,7 @@  ENDPROC(ftrace_caller)
 
 #else /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
 ENTRY(ftrace_regs_caller)
+	mv	t1, zero
 	SAVE_ABI_REGS 1
 	PREPARE_ARGS
 
@@ -239,7 +240,10 @@  ftrace_regs_call:
 	call	ftrace_stub
 
 	RESTORE_ABI_REGS 1
+	bnez	t1,.Ldirect
 	jr	t0
+.Ldirect:
+	jr	t1
 ENDPROC(ftrace_regs_caller)
 
 ENTRY(ftrace_caller)
@@ -254,3 +258,9 @@  ftrace_call:
 	jr	t0
 ENDPROC(ftrace_caller)
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_REGS */
+
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+SYM_CODE_START(ftrace_stub_direct_tramp)
+	jr	t0
+SYM_CODE_END(ftrace_stub_direct_tramp)
+#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */