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* [PATCH] riscv: ftrace: Fix the logic issue in DYNAMIC_FTRACE selection
@ 2025-07-03  8:48 ChenMiao
  2025-07-04  2:22 ` kernel test robot
  2025-07-06  2:12 ` kernel test robot
  0 siblings, 2 replies; 10+ messages in thread
From: ChenMiao @ 2025-07-03  8:48 UTC (permalink / raw)
  To: Linux RISCV
  Cc: chenmiao, Paul Walmsley, Palmer Dabbelt, Albert Ou,
	Alexandre Ghiti, linux-kernel

From: chenmiao <chenmiao.ku@gmail.com>

When I was reading the source code of ftrace, I learned that
ftrace has two types: static and dynamic. Initially, I planned
to prioritize reading the static source code, so I disabled
the enable dynamic option in RISCV.

[*]   Kernel Function Tracer
[ ]   Kernel Function Graph Tracer
[ ]   enable/disable function tracing dynamically (NEW)

However, when I tried to compile it, the build failed.

./include/linux/ftrace.h:190:16: error: implicit declaration of
function ‘arch_ftrace_get_regs’; did you mean ‘arch_ftrace_regs’?
[-Wimplicit-function-declaration]
  190 |         return arch_ftrace_get_regs(fregs);
      |                ^~~~~~~~~~~~~~~~~~~~
      |                arch_ftrace_regs

After comparing it with the ARM64 architecture, I found that
ARM64 automatically enables DYNAMIC_FTRACE by default once
FUNCTION_TRACER is turned on, and this cannot be set to "no".
Therefore, I believe the optional DYNAMIC_FTRACE setting in
RISC-V has a logic flaw—if FUNCTION_TRACER is enabled,
DYNAMIC_FTRACE should also be enabled, and vice versa. Moreover,
it's clear that RISC-V lacks the necessary support to successfully
compile the kernel when DYNAMIC_FTRACE is disabled.

[*]   Kernel Function Tracer
[ ]   Kernel Function Graph Tracer
-*-   enable/disable function tracing dynamically

Signed-off-by: chenmiao <chenmiao.ku@gmail.com>
---
 arch/riscv/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 36061f473..f7fc8b460 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -97,6 +97,7 @@ config RISCV
 	select CLONE_BACKWARDS
 	select COMMON_CLK
 	select CPU_PM if CPU_IDLE || HIBERNATION || SUSPEND
+	select DYNAMIC_FTRACE if FUNCTION_TRACER
 	select EDAC_SUPPORT
 	select FRAME_POINTER if PERF_EVENTS || (FUNCTION_TRACER && !DYNAMIC_FTRACE)
 	select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY if DYNAMIC_FTRACE
-- 
2.45.2


^ permalink raw reply related	[flat|nested] 10+ messages in thread
* [PATCH] riscv: ftrace: Fix the logic issue in DYNAMIC_FTRACE selection
@ 2025-07-03  8:45 ChenMiao
  2025-07-03 13:00 ` Alexandre Ghiti
  0 siblings, 1 reply; 10+ messages in thread
From: ChenMiao @ 2025-07-03  8:45 UTC (permalink / raw)
  To: Linux RISCV
  Cc: chenmiao, Paul Walmsley, Palmer Dabbelt, Albert Ou,
	Alexandre Ghiti, linux-riscv, linux-kernel

From: chenmiao <chenmiao.ku@gmail.com>

When I was reading the source code of ftrace, I learned that
ftrace has two types: static and dynamic. Initially, I planned
to prioritize reading the static source code, so I disabled
the enable dynamic option in RISCV.

[*]   Kernel Function Tracer
[ ]   Kernel Function Graph Tracer
[ ]   enable/disable function tracing dynamically (NEW)

However, when I tried to compile it, the build failed.

./include/linux/ftrace.h:190:16: error: implicit declaration of
function ‘arch_ftrace_get_regs’; did you mean ‘arch_ftrace_regs’?
[-Wimplicit-function-declaration]
  190 |         return arch_ftrace_get_regs(fregs);
      |                ^~~~~~~~~~~~~~~~~~~~
      |                arch_ftrace_regs

After comparing it with the ARM64 architecture, I found that
ARM64 automatically enables DYNAMIC_FTRACE by default once
FUNCTION_TRACER is turned on, and this cannot be set to "no".
Therefore, I believe the optional DYNAMIC_FTRACE setting in
RISC-V has a logic flaw—if FUNCTION_TRACER is enabled,
DYNAMIC_FTRACE should also be enabled, and vice versa. Moreover,
it's clear that RISC-V lacks the necessary support to successfully
compile the kernel when DYNAMIC_FTRACE is disabled.

[*]   Kernel Function Tracer
[ ]   Kernel Function Graph Tracer
-*-   enable/disable function tracing dynamically

Signed-off-by: chenmiao <chenmiao.ku@gmail.com>
---
 arch/riscv/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 36061f473..f7fc8b460 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -97,6 +97,7 @@ config RISCV
 	select CLONE_BACKWARDS
 	select COMMON_CLK
 	select CPU_PM if CPU_IDLE || HIBERNATION || SUSPEND
+	select DYNAMIC_FTRACE if FUNCTION_TRACER
 	select EDAC_SUPPORT
 	select FRAME_POINTER if PERF_EVENTS || (FUNCTION_TRACER && !DYNAMIC_FTRACE)
 	select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY if DYNAMIC_FTRACE
-- 
2.45.2


^ permalink raw reply related	[flat|nested] 10+ messages in thread
end of thread, other threads:[~2025-07-06  2:13 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2025-07-03  8:48 [PATCH] riscv: ftrace: Fix the logic issue in DYNAMIC_FTRACE selection ChenMiao
2025-07-04  2:22 ` kernel test robot
2025-07-06  2:12 ` kernel test robot
  -- strict thread matches above, loose matches on Subject: below --
2025-07-03  8:45 ChenMiao
2025-07-03 13:00 ` Alexandre Ghiti
2025-07-03 15:40   ` Steven Rostedt
2025-07-03 16:06     ` Alexandre Ghiti
     [not found]       ` <CAKxVwgeDcqo83ZV+xBcHwNuMk6yeU+yp7RYo22OARAVOBgrsJQ@mail.gmail.com>
2025-07-04 12:28         ` Alexandre Ghiti
2025-07-04 12:41           ` Steven Rostedt
2025-07-04 15:42           ` Miao Chen

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