[PATCH 1/2] powerpc/ftrace: support CONFIG_FUNCTION_GRAPH_RETVAL

[PATCH 1/2] powerpc/ftrace: support CONFIG_FUNCTION_GRAPH_RETVAL

[Aditya Bodkhe]

From: Aditya Bodkhe <aditya.b1@linux.ibm.com>

commit a1be9ccc57f0 ("function_graph: Support recording and printing the
return value of function") introduced support for function graph return
value tracing.

Additionally, commit a3ed4157b7d8 ("fgraph: Replace fgraph_ret_regs with
ftrace_regs") further refactored and optimized the implementation,
making `struct fgraph_ret_regs` unnecessary.

This patch enables the above modifications for powerpc64, ensuring that
function graph return value tracing is available on this architecture.

After this patch, v6.14+ kernel can also be built with FPROBE on powerpc
but there are a few other build and runtime dependencies for FPROBE to
work properly. The next patch addresses them.

Signed-off-by: Aditya Bodkhe <aditya.b1@linux.ibm.com>
---
 arch/powerpc/Kconfig                     |  1 +
 arch/powerpc/include/asm/ftrace.h        | 15 +++++++++
 arch/powerpc/kernel/trace/ftrace_entry.S | 41 ++++++++++++++----------
 3 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index c3e0cc83f120..9163521bc4b9 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -250,6 +250,7 @@ config PPC
 	select HAVE_FUNCTION_ARG_ACCESS_API
 	select HAVE_FUNCTION_DESCRIPTORS	if PPC64_ELF_ABI_V1
 	select HAVE_FUNCTION_ERROR_INJECTION
+	select HAVE_FUNCTION_GRAPH_FREGS
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER		if !COMPILE_TEST && (PPC64 || (PPC32 && CC_IS_GCC))
 	select HAVE_GCC_PLUGINS			if GCC_VERSION >= 50200   # plugin support on gcc <= 5.1 is buggy on PPC
diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
index 82da7c7a1d12..6ffc9c9cf4e3 100644
--- a/arch/powerpc/include/asm/ftrace.h
+++ b/arch/powerpc/include/asm/ftrace.h
@@ -50,6 +50,21 @@ static __always_inline struct pt_regs *arch_ftrace_get_regs(struct ftrace_regs *
 		asm volatile("mfmsr %0" : "=r" ((_regs)->msr));	\
 	} while (0)
 
+#undef ftrace_regs_get_return_value
+static __always_inline unsigned long
+ftrace_regs_get_return_value(const struct ftrace_regs *fregs)
+{
+	return arch_ftrace_regs(fregs)->regs.gpr[3];
+}
+#define ftrace_regs_get_return_value ftrace_regs_get_return_value
+
+#undef ftrace_regs_get_frame_pointer
+static __always_inline unsigned long
+ftrace_regs_get_frame_pointer(const struct ftrace_regs *fregs)
+{
+	return arch_ftrace_regs(fregs)->regs.gpr[1];
+}
+
 static __always_inline void
 ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
 				    unsigned long ip)
diff --git a/arch/powerpc/kernel/trace/ftrace_entry.S b/arch/powerpc/kernel/trace/ftrace_entry.S
index 3565c67fc638..eafbfb7584ed 100644
--- a/arch/powerpc/kernel/trace/ftrace_entry.S
+++ b/arch/powerpc/kernel/trace/ftrace_entry.S
@@ -409,23 +409,30 @@ EXPORT_SYMBOL(_mcount)
 _GLOBAL(return_to_handler)
 	/* need to save return values */
 #ifdef CONFIG_PPC64
-	std	r4,  -32(r1)
-	std	r3,  -24(r1)
+	stdu	r1, -SWITCH_FRAME_SIZE(r1)
+	std	r4, GPR4(r1)
+	std	r3, GPR3(r1)
+  /* Save previous stack pointer (r1) */
+	addi	r3, r1, SWITCH_FRAME_SIZE
+	std	r3, GPR1(r1)
 	/* save TOC */
-	std	r2,  -16(r1)
-	std	r31, -8(r1)
+	std	r2,  24(r1)
+	std	r31, 32(r1)
 	mr	r31, r1
-	stdu	r1, -112(r1)
-
+  /* pass ftrace_regs/pt_regs to ftrace_return_to_handler */
+	addi	r3,  r1, STACK_INT_FRAME_REGS
 	/*
 	 * We might be called from a module.
 	 * Switch to our TOC to run inside the core kernel.
 	 */
 	LOAD_PACA_TOC()
 #else
-	stwu	r1, -16(r1)
-	stw	r3, 8(r1)
-	stw	r4, 12(r1)
+	stwu	r1, -SWITCH_FRAME_SIZE(r1)
+	stw	r4, GPR4(r1)
+	stw	r3, GPR3(r1)
+	addi	r3, r1, SWITCH_FRAME_SIZE
+	stw	r3, GPR1(r1)
+	addi	r3, r1, STACK_INT_FRAME_REGS
 #endif
 
 	bl	ftrace_return_to_handler
@@ -435,15 +442,15 @@ _GLOBAL(return_to_handler)
 	mtlr	r3
 
 #ifdef CONFIG_PPC64
-	ld	r1, 0(r1)
-	ld	r4,  -32(r1)
-	ld	r3,  -24(r1)
-	ld	r2,  -16(r1)
-	ld	r31, -8(r1)
+	ld	r4,  GPR4(r1)
+	ld	r3,  GPR3(r1)
+	ld	r2,  24(r1)
+	ld	r31, 32(r1)
+	ld	r1,  0(r1)
 #else
-	lwz	r3, 8(r1)
-	lwz	r4, 12(r1)
-	addi	r1, r1, 16
+	lwz	r3, GPR3(r1)
+	lwz	r4, GPR4(r1)
+	addi	r1, r1, SWITCH_FRAME_SIZE
 #endif
 
 	/* Jump back to real return address */
-- 
2.43.5

Re: [PATCH 1/2] powerpc/ftrace: support CONFIG_FUNCTION_GRAPH_RETVAL

[Hari Bathini]

On 28/05/25 7:18 pm, Aditya Bodkhe wrote:
> From: Aditya Bodkhe <aditya.b1@linux.ibm.com>
> 
> commit a1be9ccc57f0 ("function_graph: Support recording and printing the
> return value of function") introduced support for function graph return
> value tracing.
> 
> Additionally, commit a3ed4157b7d8 ("fgraph: Replace fgraph_ret_regs with
> ftrace_regs") further refactored and optimized the implementation,
> making `struct fgraph_ret_regs` unnecessary.
> 
> This patch enables the above modifications for powerpc64, ensuring that
> function graph return value tracing is available on this architecture.
> 
> After this patch, v6.14+ kernel can also be built with FPROBE on powerpc
> but there are a few other build and runtime dependencies for FPROBE to
> work properly. The next patch addresses them.
> 
> Signed-off-by: Aditya Bodkhe <aditya.b1@linux.ibm.com>

Except for a couple of minor nits below..

Reviewed-by: Hari Bathini <hbathini@linux.ibm.com>

> ---
>   arch/powerpc/Kconfig                     |  1 +
>   arch/powerpc/include/asm/ftrace.h        | 15 +++++++++
>   arch/powerpc/kernel/trace/ftrace_entry.S | 41 ++++++++++++++----------
>   3 files changed, 40 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index c3e0cc83f120..9163521bc4b9 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -250,6 +250,7 @@ config PPC
>   	select HAVE_FUNCTION_ARG_ACCESS_API
>   	select HAVE_FUNCTION_DESCRIPTORS	if PPC64_ELF_ABI_V1
>   	select HAVE_FUNCTION_ERROR_INJECTION
> +	select HAVE_FUNCTION_GRAPH_FREGS
>   	select HAVE_FUNCTION_GRAPH_TRACER
>   	select HAVE_FUNCTION_TRACER		if !COMPILE_TEST && (PPC64 || (PPC32 && CC_IS_GCC))
>   	select HAVE_GCC_PLUGINS			if GCC_VERSION >= 50200   # plugin support on gcc <= 5.1 is buggy on PPC
> diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
> index 82da7c7a1d12..6ffc9c9cf4e3 100644
> --- a/arch/powerpc/include/asm/ftrace.h
> +++ b/arch/powerpc/include/asm/ftrace.h
> @@ -50,6 +50,21 @@ static __always_inline struct pt_regs *arch_ftrace_get_regs(struct ftrace_regs *
>   		asm volatile("mfmsr %0" : "=r" ((_regs)->msr));	\
>   	} while (0)
>   
> +#undef ftrace_regs_get_return_value
> +static __always_inline unsigned long
> +ftrace_regs_get_return_value(const struct ftrace_regs *fregs)
> +{
> +	return arch_ftrace_regs(fregs)->regs.gpr[3];
> +}
> +#define ftrace_regs_get_return_value ftrace_regs_get_return_value
> +
> +#undef ftrace_regs_get_frame_pointer
> +static __always_inline unsigned long
> +ftrace_regs_get_frame_pointer(const struct ftrace_regs *fregs)
> +{
> +	return arch_ftrace_regs(fregs)->regs.gpr[1];
> +}
> +
>   static __always_inline void
>   ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
>   				    unsigned long ip)
> diff --git a/arch/powerpc/kernel/trace/ftrace_entry.S b/arch/powerpc/kernel/trace/ftrace_entry.S
> index 3565c67fc638..eafbfb7584ed 100644
> --- a/arch/powerpc/kernel/trace/ftrace_entry.S
> +++ b/arch/powerpc/kernel/trace/ftrace_entry.S
> @@ -409,23 +409,30 @@ EXPORT_SYMBOL(_mcount)
>   _GLOBAL(return_to_handler)
>   	/* need to save return values */
>   #ifdef CONFIG_PPC64
> -	std	r4,  -32(r1)
> -	std	r3,  -24(r1)
> +	stdu	r1, -SWITCH_FRAME_SIZE(r1)
> +	std	r4, GPR4(r1)
> +	std	r3, GPR3(r1)

> +  /* Save previous stack pointer (r1) */

Please use tab instead of "  " before the comment.

> +	addi	r3, r1, SWITCH_FRAME_SIZE
> +	std	r3, GPR1(r1)
>   	/* save TOC */
> -	std	r2,  -16(r1)
> -	std	r31, -8(r1)
> +	std	r2,  24(r1)
> +	std	r31, 32(r1)
>   	mr	r31, r1
> -	stdu	r1, -112(r1)
> -
> +  /* pass ftrace_regs/pt_regs to ftrace_return_to_handler */
> +	addi	r3,  r1, STACK_INT_FRAME_REGS

Have a newline here

>   	/*
>   	 * We might be called from a module.
>   	 * Switch to our TOC to run inside the core kernel.
>   	 */
>   	LOAD_PACA_TOC()
>   #else
> -	stwu	r1, -16(r1)
> -	stw	r3, 8(r1)
> -	stw	r4, 12(r1)
> +	stwu	r1, -SWITCH_FRAME_SIZE(r1)
> +	stw	r4, GPR4(r1)
> +	stw	r3, GPR3(r1)
> +	addi	r3, r1, SWITCH_FRAME_SIZE
> +	stw	r3, GPR1(r1)
> +	addi	r3, r1, STACK_INT_FRAME_REGS
>   #endif
>   
>   	bl	ftrace_return_to_handler
> @@ -435,15 +442,15 @@ _GLOBAL(return_to_handler)
>   	mtlr	r3
>   
>   #ifdef CONFIG_PPC64
> -	ld	r1, 0(r1)
> -	ld	r4,  -32(r1)
> -	ld	r3,  -24(r1)
> -	ld	r2,  -16(r1)
> -	ld	r31, -8(r1)
> +	ld	r4,  GPR4(r1)
> +	ld	r3,  GPR3(r1)
> +	ld	r2,  24(r1)
> +	ld	r31, 32(r1)
> +	ld	r1,  0(r1)
>   #else
> -	lwz	r3, 8(r1)
> -	lwz	r4, 12(r1)
> -	addi	r1, r1, 16
> +	lwz	r3, GPR3(r1)
> +	lwz	r4, GPR4(r1)
> +	addi	r1, r1, SWITCH_FRAME_SIZE
>   #endif
>   
>   	/* Jump back to real return address */

- Hari

Re: [PATCH 1/2] powerpc/ftrace: support CONFIG_FUNCTION_GRAPH_RETVAL

[Christophe Leroy]

Le 28/05/2025 à 15:48, Aditya Bodkhe a écrit :
> [Vous ne recevez pas souvent de courriers de adityab1@linux.ibm.com. Découvrez pourquoi ceci est important à https://aka.ms/LearnAboutSenderIdentification ]
> 
> From: Aditya Bodkhe <aditya.b1@linux.ibm.com>
> 
> commit a1be9ccc57f0 ("function_graph: Support recording and printing the
> return value of function") introduced support for function graph return
> value tracing.
> 
> Additionally, commit a3ed4157b7d8 ("fgraph: Replace fgraph_ret_regs with
> ftrace_regs") further refactored and optimized the implementation,
> making `struct fgraph_ret_regs` unnecessary.
> 
> This patch enables the above modifications for powerpc64, ensuring that
> function graph return value tracing is available on this architecture.

Why only powerpc64 ?

I see nothing specific to powerpc64 in your patch, will it work on 
powerpc32 too ?

> 
> After this patch, v6.14+ kernel can also be built with FPROBE on powerpc
> but there are a few other build and runtime dependencies for FPROBE to
> work properly. The next patch addresses them.
> 
> Signed-off-by: Aditya Bodkhe <aditya.b1@linux.ibm.com>
> ---
>   arch/powerpc/Kconfig                     |  1 +
>   arch/powerpc/include/asm/ftrace.h        | 15 +++++++++
>   arch/powerpc/kernel/trace/ftrace_entry.S | 41 ++++++++++++++----------
>   3 files changed, 40 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index c3e0cc83f120..9163521bc4b9 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -250,6 +250,7 @@ config PPC
>          select HAVE_FUNCTION_ARG_ACCESS_API
>          select HAVE_FUNCTION_DESCRIPTORS        if PPC64_ELF_ABI_V1
>          select HAVE_FUNCTION_ERROR_INJECTION
> +       select HAVE_FUNCTION_GRAPH_FREGS
>          select HAVE_FUNCTION_GRAPH_TRACER
>          select HAVE_FUNCTION_TRACER             if !COMPILE_TEST && (PPC64 || (PPC32 && CC_IS_GCC))
>          select HAVE_GCC_PLUGINS                 if GCC_VERSION >= 50200   # plugin support on gcc <= 5.1 is buggy on PPC
> diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
> index 82da7c7a1d12..6ffc9c9cf4e3 100644
> --- a/arch/powerpc/include/asm/ftrace.h
> +++ b/arch/powerpc/include/asm/ftrace.h
> @@ -50,6 +50,21 @@ static __always_inline struct pt_regs *arch_ftrace_get_regs(struct ftrace_regs *
>                  asm volatile("mfmsr %0" : "=r" ((_regs)->msr)); \
>          } while (0)
> 
> +#undef ftrace_regs_get_return_value
> +static __always_inline unsigned long
> +ftrace_regs_get_return_value(const struct ftrace_regs *fregs)
> +{
> +       return arch_ftrace_regs(fregs)->regs.gpr[3];
> +}
> +#define ftrace_regs_get_return_value ftrace_regs_get_return_value
> +
> +#undef ftrace_regs_get_frame_pointer
> +static __always_inline unsigned long
> +ftrace_regs_get_frame_pointer(const struct ftrace_regs *fregs)
> +{
> +       return arch_ftrace_regs(fregs)->regs.gpr[1];
> +}
> +

Why unset and redefine ftrace_regs_get_return_value() and 
ftrace_regs_get_frame_pointer() ? Please explain why the default ones 
can't be used on powerpc.

>   static __always_inline void
>   ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
>                                      unsigned long ip)
> diff --git a/arch/powerpc/kernel/trace/ftrace_entry.S b/arch/powerpc/kernel/trace/ftrace_entry.S
> index 3565c67fc638..eafbfb7584ed 100644
> --- a/arch/powerpc/kernel/trace/ftrace_entry.S
> +++ b/arch/powerpc/kernel/trace/ftrace_entry.S
> @@ -409,23 +409,30 @@ EXPORT_SYMBOL(_mcount)
>   _GLOBAL(return_to_handler)
>          /* need to save return values */
>   #ifdef CONFIG_PPC64
> -       std     r4,  -32(r1)
> -       std     r3,  -24(r1)
> +       stdu    r1, -SWITCH_FRAME_SIZE(r1)
> +       std     r4, GPR4(r1)
> +       std     r3, GPR3(r1)
> +  /* Save previous stack pointer (r1) */
> +       addi    r3, r1, SWITCH_FRAME_SIZE
> +       std     r3, GPR1(r1)
>          /* save TOC */
> -       std     r2,  -16(r1)
> -       std     r31, -8(r1)
> +       std     r2,  24(r1)
> +       std     r31, 32(r1)
>          mr      r31, r1
> -       stdu    r1, -112(r1)
> -
> +  /* pass ftrace_regs/pt_regs to ftrace_return_to_handler */
> +       addi    r3,  r1, STACK_INT_FRAME_REGS

Some of the changes seems to only be renaming and should be done in a 
cleanup/preparatory patch in order to only focus on real necessary 
changes in this patch.

>          /*
>           * We might be called from a module.
>           * Switch to our TOC to run inside the core kernel.
>           */
>          LOAD_PACA_TOC()
>   #else
> -       stwu    r1, -16(r1)
> -       stw     r3, 8(r1)
> -       stw     r4, 12(r1)
> +       stwu    r1, -SWITCH_FRAME_SIZE(r1)

Why do we need such a big frame size just to save two registers ?

> +       stw     r4, GPR4(r1)
> +       stw     r3, GPR3(r1)
> +       addi    r3, r1, SWITCH_FRAME_SIZE
> +       stw     r3, GPR1(r1)
 > +       addi    r3, r1, STACK_INT_FRAME_REGS

Why is this needed ?

>   #endif
> 
>          bl      ftrace_return_to_handler
> @@ -435,15 +442,15 @@ _GLOBAL(return_to_handler)
>          mtlr    r3
> 
>   #ifdef CONFIG_PPC64
> -       ld      r1, 0(r1)
> -       ld      r4,  -32(r1)
> -       ld      r3,  -24(r1)
> -       ld      r2,  -16(r1)
> -       ld      r31, -8(r1)
> +       ld      r4,  GPR4(r1)
> +       ld      r3,  GPR3(r1)
> +       ld      r2,  24(r1)
> +       ld      r31, 32(r1)
> +       ld      r1,  0(r1)
>   #else
> -       lwz     r3, 8(r1)
> -       lwz     r4, 12(r1)
> -       addi    r1, r1, 16
> +       lwz     r3, GPR3(r1)
> +       lwz     r4, GPR4(r1)
> +       addi    r1, r1, SWITCH_FRAME_SIZE
>   #endif
> 
>          /* Jump back to real return address */
> --
> 2.43.5
> 

Re: [PATCH 1/2] powerpc/ftrace: support CONFIG_FUNCTION_GRAPH_RETVAL

[Aditya Bodkhe]

On 03/06/25 2:22 pm, Christophe Leroy wrote:
>
>
> Le 28/05/2025 à 15:48, Aditya Bodkhe a écrit :
>> [Vous ne recevez pas souvent de courriers de adityab1@linux.ibm.com. 
>> Découvrez pourquoi ceci est important à 
>> https://aka.ms/LearnAboutSenderIdentification ]
>>
>> From: Aditya Bodkhe <aditya.b1@linux.ibm.com>
>>
>> commit a1be9ccc57f0 ("function_graph: Support recording and printing the
>> return value of function") introduced support for function graph return
>> value tracing.
>>
>> Additionally, commit a3ed4157b7d8 ("fgraph: Replace fgraph_ret_regs with
>> ftrace_regs") further refactored and optimized the implementation,
>> making `struct fgraph_ret_regs` unnecessary.
>>
>> This patch enables the above modifications for powerpc64, ensuring that
>> function graph return value tracing is available on this architecture.
>
> Why only powerpc64 ?
>
> I see nothing specific to powerpc64 in your patch, will it work on 
> powerpc32 too ?
>
That's a oversight on my part . This patch necessary changes for 
powerpc32 bit and tested this feature to be working as expected on the same.
>>
>> After this patch, v6.14+ kernel can also be built with FPROBE on powerpc
>> but there are a few other build and runtime dependencies for FPROBE to
>> work properly. The next patch addresses them.
>>
>> Signed-off-by: Aditya Bodkhe <aditya.b1@linux.ibm.com>
>> ---
>>   arch/powerpc/Kconfig                     |  1 +
>>   arch/powerpc/include/asm/ftrace.h        | 15 +++++++++
>>   arch/powerpc/kernel/trace/ftrace_entry.S | 41 ++++++++++++++----------
>>   3 files changed, 40 insertions(+), 17 deletions(-)
>>
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index c3e0cc83f120..9163521bc4b9 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -250,6 +250,7 @@ config PPC
>>          select HAVE_FUNCTION_ARG_ACCESS_API
>>          select HAVE_FUNCTION_DESCRIPTORS        if PPC64_ELF_ABI_V1
>>          select HAVE_FUNCTION_ERROR_INJECTION
>> +       select HAVE_FUNCTION_GRAPH_FREGS
>>          select HAVE_FUNCTION_GRAPH_TRACER
>>          select HAVE_FUNCTION_TRACER             if !COMPILE_TEST && 
>> (PPC64 || (PPC32 && CC_IS_GCC))
>>          select HAVE_GCC_PLUGINS                 if GCC_VERSION >= 
>> 50200   # plugin support on gcc <= 5.1 is buggy on PPC
>> diff --git a/arch/powerpc/include/asm/ftrace.h 
>> b/arch/powerpc/include/asm/ftrace.h
>> index 82da7c7a1d12..6ffc9c9cf4e3 100644
>> --- a/arch/powerpc/include/asm/ftrace.h
>> +++ b/arch/powerpc/include/asm/ftrace.h
>> @@ -50,6 +50,21 @@ static __always_inline struct pt_regs 
>> *arch_ftrace_get_regs(struct ftrace_regs *
>>                  asm volatile("mfmsr %0" : "=r" ((_regs)->msr)); \
>>          } while (0)
>>
>> +#undef ftrace_regs_get_return_value
>> +static __always_inline unsigned long
>> +ftrace_regs_get_return_value(const struct ftrace_regs *fregs)
>> +{
>> +       return arch_ftrace_regs(fregs)->regs.gpr[3];
>> +}
>> +#define ftrace_regs_get_return_value ftrace_regs_get_return_value
>> +
>> +#undef ftrace_regs_get_frame_pointer
>> +static __always_inline unsigned long
>> +ftrace_regs_get_frame_pointer(const struct ftrace_regs *fregs)
>> +{
>> +       return arch_ftrace_regs(fregs)->regs.gpr[1];
>> +}
>> +
> Why unset and redefine ftrace_regs_get_return_value() and 
> ftrace_regs_get_frame_pointer() ? Please explain why the default ones 
> can't be used on powerpc.
>
Because for powerpc currently for ftrace_regs_get_return_value() this 
function regs_return_value() is getting called and it's implementation 
returns -regs.gpr[3] if is_syscall_success() returns false . This was 
causing fails in ftrace selftests .

Also for ftrace_regs_get_frame_pointer() current implementation was 
always returning 0 hence we had to change that too .

>>   static __always_inline void
>>   ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
>>                                      unsigned long ip)
>> diff --git a/arch/powerpc/kernel/trace/ftrace_entry.S 
>> b/arch/powerpc/kernel/trace/ftrace_entry.S
>> index 3565c67fc638..eafbfb7584ed 100644
>> --- a/arch/powerpc/kernel/trace/ftrace_entry.S
>> +++ b/arch/powerpc/kernel/trace/ftrace_entry.S
>> @@ -409,23 +409,30 @@ EXPORT_SYMBOL(_mcount)
>>   _GLOBAL(return_to_handler)
>>          /* need to save return values */
>>   #ifdef CONFIG_PPC64
>> -       std     r4,  -32(r1)
>> -       std     r3,  -24(r1)
>> +       stdu    r1, -SWITCH_FRAME_SIZE(r1)
>> +       std     r4, GPR4(r1)
>> +       std     r3, GPR3(r1)
>> +  /* Save previous stack pointer (r1) */
>> +       addi    r3, r1, SWITCH_FRAME_SIZE
>> +       std     r3, GPR1(r1)
>>          /* save TOC */
>> -       std     r2,  -16(r1)
>> -       std     r31, -8(r1)
>> +       std     r2,  24(r1)
>> +       std     r31, 32(r1)
>>          mr      r31, r1
>> -       stdu    r1, -112(r1)
>> -
>> +  /* pass ftrace_regs/pt_regs to ftrace_return_to_handler */
>> +       addi    r3,  r1, STACK_INT_FRAME_REGS
>
> Some of the changes seems to only be renaming and should be done in a 
> cleanup/preparatory patch in order to only focus on real necessary 
> changes in this patch.
>
Now the way we are setting up the frame we cannot have negative offsets 
, hence we used offsets which are defined already.
>>          /*
>>           * We might be called from a module.
>>           * Switch to our TOC to run inside the core kernel.
>>           */
>>          LOAD_PACA_TOC()
>>   #else
>> -       stwu    r1, -16(r1)
>> -       stw     r3, 8(r1)
>> -       stw     r4, 12(r1)
>> +       stwu    r1, -SWITCH_FRAME_SIZE(r1)
> Why do we need such a big frame size just to save two registers ?
>
This Frame size is needed because we need pt_regs as part of frame , are 
you saying instead of SWITCH_FRAME_SIZE for 32 bit architecture we 
should just setup a frame with size of pt_regs because ftrace_regs size 
is same as pt_regs on ppc
>> +       stw     r4, GPR4(r1)
>> +       stw     r3, GPR3(r1)
>> +       addi    r3, r1, SWITCH_FRAME_SIZE
>> +       stw     r3, GPR1(r1)
> > +       addi    r3, r1, STACK_INT_FRAME_REGS
>
> Why is this needed ?
>
The function ftrace_return_to_handler takes pointer to pt_regs as 
arguement so we are setting that up in stack and passing that pointer.
>>   #endif
>>
>>          bl      ftrace_return_to_handler
>> @@ -435,15 +442,15 @@ _GLOBAL(return_to_handler)
>>          mtlr    r3
>>
>>   #ifdef CONFIG_PPC64
>> -       ld      r1, 0(r1)
>> -       ld      r4,  -32(r1)
>> -       ld      r3,  -24(r1)
>> -       ld      r2,  -16(r1)
>> -       ld      r31, -8(r1)
>> +       ld      r4,  GPR4(r1)
>> +       ld      r3,  GPR3(r1)
>> +       ld      r2,  24(r1)
>> +       ld      r31, 32(r1)
>> +       ld      r1,  0(r1)
>>   #else
>> -       lwz     r3, 8(r1)
>> -       lwz     r4, 12(r1)
>> -       addi    r1, r1, 16
>> +       lwz     r3, GPR3(r1)
>> +       lwz     r4, GPR4(r1)
>> +       addi    r1, r1, SWITCH_FRAME_SIZE
>>   #endif
>>
>>          /* Jump back to real return address */
>> -- 
>> 2.43.5
>>
>

[PATCH 1/2] powerpc/ftrace: support CONFIG_FUNCTION_GRAPH_RETVAL

[Aditya Bodkhe]

commit a1be9ccc57f0 ("function_graph: Support recording and printing the
return value of function") introduced support for function graph return
value tracing.

Additionally, commit a3ed4157b7d8 ("fgraph: Replace fgraph_ret_regs with
ftrace_regs") further refactored and optimized the implementation,
making `struct fgraph_ret_regs` unnecessary.

This patch enables the above modifications for powerpc64, ensuring that
function graph return value tracing is available on this architecture.

After this patch, v6.14+ kernel can also be built with FPROBE on powerpc
but there are a few other build and runtime dependencies for FPROBE to
work properly. The next patch addresses them.

Signed-off-by: Aditya Bodkhe <adityab1@linux.ibm.com>
---
 arch/powerpc/Kconfig                     |  1 +
 arch/powerpc/include/asm/ftrace.h        | 15 +++++++++
 arch/powerpc/kernel/trace/ftrace_entry.S | 41 ++++++++++++++----------
 3 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index c3e0cc83f120..9163521bc4b9 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -250,6 +250,7 @@ config PPC
 	select HAVE_FUNCTION_ARG_ACCESS_API
 	select HAVE_FUNCTION_DESCRIPTORS	if PPC64_ELF_ABI_V1
 	select HAVE_FUNCTION_ERROR_INJECTION
+	select HAVE_FUNCTION_GRAPH_FREGS
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER		if !COMPILE_TEST && (PPC64 || (PPC32 && CC_IS_GCC))
 	select HAVE_GCC_PLUGINS			if GCC_VERSION >= 50200   # plugin support on gcc <= 5.1 is buggy on PPC
diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
index 82da7c7a1d12..6ffc9c9cf4e3 100644
--- a/arch/powerpc/include/asm/ftrace.h
+++ b/arch/powerpc/include/asm/ftrace.h
@@ -50,6 +50,21 @@ static __always_inline struct pt_regs *arch_ftrace_get_regs(struct ftrace_regs *
 		asm volatile("mfmsr %0" : "=r" ((_regs)->msr));	\
 	} while (0)
 
+#undef ftrace_regs_get_return_value
+static __always_inline unsigned long
+ftrace_regs_get_return_value(const struct ftrace_regs *fregs)
+{
+	return arch_ftrace_regs(fregs)->regs.gpr[3];
+}
+#define ftrace_regs_get_return_value ftrace_regs_get_return_value
+
+#undef ftrace_regs_get_frame_pointer
+static __always_inline unsigned long
+ftrace_regs_get_frame_pointer(const struct ftrace_regs *fregs)
+{
+	return arch_ftrace_regs(fregs)->regs.gpr[1];
+}
+
 static __always_inline void
 ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
 				    unsigned long ip)
diff --git a/arch/powerpc/kernel/trace/ftrace_entry.S b/arch/powerpc/kernel/trace/ftrace_entry.S
index 3565c67fc638..eafbfb7584ed 100644
--- a/arch/powerpc/kernel/trace/ftrace_entry.S
+++ b/arch/powerpc/kernel/trace/ftrace_entry.S
@@ -409,23 +409,30 @@ EXPORT_SYMBOL(_mcount)
 _GLOBAL(return_to_handler)
 	/* need to save return values */
 #ifdef CONFIG_PPC64
-	std	r4,  -32(r1)
-	std	r3,  -24(r1)
+	stdu	r1, -SWITCH_FRAME_SIZE(r1)
+	std	r4, GPR4(r1)
+	std	r3, GPR3(r1)
+  /* Save previous stack pointer (r1) */
+	addi	r3, r1, SWITCH_FRAME_SIZE
+	std	r3, GPR1(r1)
 	/* save TOC */
-	std	r2,  -16(r1)
-	std	r31, -8(r1)
+	std	r2,  24(r1)
+	std	r31, 32(r1)
 	mr	r31, r1
-	stdu	r1, -112(r1)
-
+  /* pass ftrace_regs/pt_regs to ftrace_return_to_handler */
+	addi	r3,  r1, STACK_INT_FRAME_REGS
 	/*
 	 * We might be called from a module.
 	 * Switch to our TOC to run inside the core kernel.
 	 */
 	LOAD_PACA_TOC()
 #else
-	stwu	r1, -16(r1)
-	stw	r3, 8(r1)
-	stw	r4, 12(r1)
+	stwu	r1, -SWITCH_FRAME_SIZE(r1)
+	stw	r4, GPR4(r1)
+	stw	r3, GPR3(r1)
+	addi	r3, r1, SWITCH_FRAME_SIZE
+	stw	r3, GPR1(r1)
+	addi	r3, r1, STACK_INT_FRAME_REGS
 #endif
 
 	bl	ftrace_return_to_handler
@@ -435,15 +442,15 @@ _GLOBAL(return_to_handler)
 	mtlr	r3
 
 #ifdef CONFIG_PPC64
-	ld	r1, 0(r1)
-	ld	r4,  -32(r1)
-	ld	r3,  -24(r1)
-	ld	r2,  -16(r1)
-	ld	r31, -8(r1)
+	ld	r4,  GPR4(r1)
+	ld	r3,  GPR3(r1)
+	ld	r2,  24(r1)
+	ld	r31, 32(r1)
+	ld	r1,  0(r1)
 #else
-	lwz	r3, 8(r1)
-	lwz	r4, 12(r1)
-	addi	r1, r1, 16
+	lwz	r3, GPR3(r1)
+	lwz	r4, GPR4(r1)
+	addi	r1, r1, SWITCH_FRAME_SIZE
 #endif
 
 	/* Jump back to real return address */
-- 
2.50.0

[PATCH 2/2] powerpc/fprobe: fix updated fprobe for function-graph tracer

[Aditya Bodkhe]

From: Hari Bathini <hbathini@linux.ibm.com>

Since commit 4346ba160409 ("fprobe: Rewrite fprobe on function-graph
tracer"), FPROBE depends on HAVE_FUNCTION_GRAPH_FREGS. With previous
patch adding HAVE_FUNCTION_GRAPH_FREGS for powerpc, FPROBE can be
enabled on powerpc. But with the commit b5fa903b7f7c ("fprobe: Add
fprobe_header encoding feature"), asm/fprobe.h header is needed to
define arch dependent encode/decode macros. The fprobe header MSB
pattern on powerpc is not 0xf. So, define FPROBE_HEADER_MSB_PATTERN
expected on powerpc.

Also, commit 762abbc0d09f ("fprobe: Use ftrace_regs in fprobe exit
handler") introduced HAVE_FTRACE_REGS_HAVING_PT_REGS for archs that
have pt_regs in ftrace_regs. Advertise that on powerpc to reuse
common definitions like ftrace_partial_regs().

Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
Signed-off-by: Aditya Bodkhe <adityab1@linux.ibm.com>
---
 arch/powerpc/Kconfig              |  1 +
 arch/powerpc/include/asm/fprobe.h | 12 ++++++++++++
 2 files changed, 13 insertions(+)
 create mode 100644 arch/powerpc/include/asm/fprobe.h

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 9163521bc4b9..2203e4fb64c1 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -246,6 +246,7 @@ config PPC
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS
 	select HAVE_GUP_FAST
 	select HAVE_FTRACE_GRAPH_FUNC
+	select HAVE_FTRACE_REGS_HAVING_PT_REGS
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_FUNCTION_ARG_ACCESS_API
 	select HAVE_FUNCTION_DESCRIPTORS	if PPC64_ELF_ABI_V1
diff --git a/arch/powerpc/include/asm/fprobe.h b/arch/powerpc/include/asm/fprobe.h
new file mode 100644
index 000000000000..d64bc28fb3d3
--- /dev/null
+++ b/arch/powerpc/include/asm/fprobe.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_PPC_FPROBE_H
+#define _ASM_PPC_FPROBE_H
+
+#include <asm-generic/fprobe.h>
+
+#ifdef CONFIG_64BIT
+#undef FPROBE_HEADER_MSB_PATTERN
+#define FPROBE_HEADER_MSB_PATTERN	(PAGE_OFFSET & ~FPROBE_HEADER_MSB_MASK)
+#endif
+
+#endif /* _ASM_PPC_FPROBE_H */
-- 
2.50.0

Re: [PATCH 1/2] powerpc/ftrace: support CONFIG_FUNCTION_GRAPH_RETVAL

[Aditya Bodkhe]

Posted wrong version by mistake please ignore .

On 07/07/25 12:48 pm, Aditya Bodkhe wrote:
> commit a1be9ccc57f0 ("function_graph: Support recording and printing the
> return value of function") introduced support for function graph return
> value tracing.
>
> Additionally, commit a3ed4157b7d8 ("fgraph: Replace fgraph_ret_regs with
> ftrace_regs") further refactored and optimized the implementation,
> making `struct fgraph_ret_regs` unnecessary.
>
> This patch enables the above modifications for powerpc64, ensuring that
> function graph return value tracing is available on this architecture.
>
> After this patch, v6.14+ kernel can also be built with FPROBE on powerpc
> but there are a few other build and runtime dependencies for FPROBE to
> work properly. The next patch addresses them.
>
> Signed-off-by: Aditya Bodkhe <adityab1@linux.ibm.com>
> ---
>   arch/powerpc/Kconfig                     |  1 +
>   arch/powerpc/include/asm/ftrace.h        | 15 +++++++++
>   arch/powerpc/kernel/trace/ftrace_entry.S | 41 ++++++++++++++----------
>   3 files changed, 40 insertions(+), 17 deletions(-)
>
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index c3e0cc83f120..9163521bc4b9 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -250,6 +250,7 @@ config PPC
>   	select HAVE_FUNCTION_ARG_ACCESS_API
>   	select HAVE_FUNCTION_DESCRIPTORS	if PPC64_ELF_ABI_V1
>   	select HAVE_FUNCTION_ERROR_INJECTION
> +	select HAVE_FUNCTION_GRAPH_FREGS
>   	select HAVE_FUNCTION_GRAPH_TRACER
>   	select HAVE_FUNCTION_TRACER		if !COMPILE_TEST && (PPC64 || (PPC32 && CC_IS_GCC))
>   	select HAVE_GCC_PLUGINS			if GCC_VERSION >= 50200   # plugin support on gcc <= 5.1 is buggy on PPC
> diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
> index 82da7c7a1d12..6ffc9c9cf4e3 100644
> --- a/arch/powerpc/include/asm/ftrace.h
> +++ b/arch/powerpc/include/asm/ftrace.h
> @@ -50,6 +50,21 @@ static __always_inline struct pt_regs *arch_ftrace_get_regs(struct ftrace_regs *
>   		asm volatile("mfmsr %0" : "=r" ((_regs)->msr));	\
>   	} while (0)
>   
> +#undef ftrace_regs_get_return_value
> +static __always_inline unsigned long
> +ftrace_regs_get_return_value(const struct ftrace_regs *fregs)
> +{
> +	return arch_ftrace_regs(fregs)->regs.gpr[3];
> +}
> +#define ftrace_regs_get_return_value ftrace_regs_get_return_value
> +
> +#undef ftrace_regs_get_frame_pointer
> +static __always_inline unsigned long
> +ftrace_regs_get_frame_pointer(const struct ftrace_regs *fregs)
> +{
> +	return arch_ftrace_regs(fregs)->regs.gpr[1];
> +}
> +
>   static __always_inline void
>   ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
>   				    unsigned long ip)
> diff --git a/arch/powerpc/kernel/trace/ftrace_entry.S b/arch/powerpc/kernel/trace/ftrace_entry.S
> index 3565c67fc638..eafbfb7584ed 100644
> --- a/arch/powerpc/kernel/trace/ftrace_entry.S
> +++ b/arch/powerpc/kernel/trace/ftrace_entry.S
> @@ -409,23 +409,30 @@ EXPORT_SYMBOL(_mcount)
>   _GLOBAL(return_to_handler)
>   	/* need to save return values */
>   #ifdef CONFIG_PPC64
> -	std	r4,  -32(r1)
> -	std	r3,  -24(r1)
> +	stdu	r1, -SWITCH_FRAME_SIZE(r1)
> +	std	r4, GPR4(r1)
> +	std	r3, GPR3(r1)
> +  /* Save previous stack pointer (r1) */
> +	addi	r3, r1, SWITCH_FRAME_SIZE
> +	std	r3, GPR1(r1)
>   	/* save TOC */
> -	std	r2,  -16(r1)
> -	std	r31, -8(r1)
> +	std	r2,  24(r1)
> +	std	r31, 32(r1)
>   	mr	r31, r1
> -	stdu	r1, -112(r1)
> -
> +  /* pass ftrace_regs/pt_regs to ftrace_return_to_handler */
> +	addi	r3,  r1, STACK_INT_FRAME_REGS
>   	/*
>   	 * We might be called from a module.
>   	 * Switch to our TOC to run inside the core kernel.
>   	 */
>   	LOAD_PACA_TOC()
>   #else
> -	stwu	r1, -16(r1)
> -	stw	r3, 8(r1)
> -	stw	r4, 12(r1)
> +	stwu	r1, -SWITCH_FRAME_SIZE(r1)
> +	stw	r4, GPR4(r1)
> +	stw	r3, GPR3(r1)
> +	addi	r3, r1, SWITCH_FRAME_SIZE
> +	stw	r3, GPR1(r1)
> +	addi	r3, r1, STACK_INT_FRAME_REGS
>   #endif
>   
>   	bl	ftrace_return_to_handler
> @@ -435,15 +442,15 @@ _GLOBAL(return_to_handler)
>   	mtlr	r3
>   
>   #ifdef CONFIG_PPC64
> -	ld	r1, 0(r1)
> -	ld	r4,  -32(r1)
> -	ld	r3,  -24(r1)
> -	ld	r2,  -16(r1)
> -	ld	r31, -8(r1)
> +	ld	r4,  GPR4(r1)
> +	ld	r3,  GPR3(r1)
> +	ld	r2,  24(r1)
> +	ld	r31, 32(r1)
> +	ld	r1,  0(r1)
>   #else
> -	lwz	r3, 8(r1)
> -	lwz	r4, 12(r1)
> -	addi	r1, r1, 16
> +	lwz	r3, GPR3(r1)
> +	lwz	r4, GPR4(r1)
> +	addi	r1, r1, SWITCH_FRAME_SIZE
>   #endif
>   
>   	/* Jump back to real return address */