Commit d733f18a authored by Aditya Bodkhe's avatar Aditya Bodkhe Committed by Madhavan Srinivasan
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powerpc/ftrace: support CONFIG_FUNCTION_GRAPH_RETVAL 



commit a1be9ccc ("function_graph: Support recording and printing the
return value of function") introduced support for function graph return
value tracing.

Additionally, commit a3ed4157 ("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 powerpc all, ensuring that
function graph return value tracing is available on this architecture.

In this patch we have redefined two functions:
- 'ftrace_regs_get_return_value()' - the existing implementation on
ppc returns -ve of return value based on some conditions not
relevant to our patch.
- 'ftrace_regs_get_frame_pointer()' - always returns 0 in current code .

We also allocate stack space to equivalent of 'SWITCH_FRAME_SIZE',
allowing us to directly use predefined offsets like 'GPR3' and 'GPR4'
this keeps code clean and consistent with already defined offsets .

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.

Tested-by: default avatarVenkat Rao Bagalkote <venkat88@linux.ibm.com>
Reviewed-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: default avatarAditya Bodkhe <adityab1@linux.ibm.com>
Signed-off-by: default avatarMadhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250916044035.29033-1-adityab1@linux.ibm.com
parent b137312f

arch/powerpc/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -246,6 +246,7 @@ 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

arch/powerpc/include/asm/ftrace.h

+15 −0
Original line number Diff line number Diff line
@@ -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)

arch/powerpc/kernel/trace/ftrace_entry.S

+25 −17
Original line number Diff line number Diff line
@@ -409,23 +409,31 @@ 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)

	/* pass ftrace_regs/pt_regs to ftrace_return_to_handler */

	addi	r3, r1, STACK_INT_FRAME_REGS

#endif



	bl	ftrace_return_to_handler
@@ -435,15 +443,15 @@ _GLOBAL(return_to_handler) 
	mtlr	r3



#ifdef CONFIG_PPC64

	ld	r4,  GPR4(r1)

	ld	r3,  GPR3(r1)

	ld	r2,  24(r1)

	ld	r31, 32(r1)

	ld	r1,  0(r1)

	ld	r4,  -32(r1)

	ld	r3,  -24(r1)

	ld	r2,  -16(r1)

	ld	r31, -8(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 */