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 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: Venkat Rao Bagalkote <venka...@linux.ibm.com>
Reviewed-by: Christophe Leroy <christophe.le...@csgroup.eu>
Signed-off-by: Aditya Bodkhe <adity...@linux.ibm.com>
---
Changelog:
v3 -> v4:
- commit a41de5ccff85 ("arch/powerpc: Remove support for older GCC
and binutils") which is already part of -next has removed the check for
GCC_VERSION in Kconfig which is causing error for git am when applying v3.
So rebased it to powerpc -next as v4
v3:https://lore.kernel.org/all/20250909045615.50251-1-adity...@linux.ibm.com/
v2 -> v3:
- Rebase on Linux 6.17-rc4
v2:https://lore.kernel.org/all/20250722085648.1640-1-adity...@linux.ibm.com/
v1 -> v2:
- Added explanation for redefining ftrace_regs_get_return_value()
and ftrace_regs_get_frame_pointer()
- Explained why stack space equivalent to 'SWITCH_FRAME_SIZE' is allocated.
v1:https://lore.kernel.org/all/20250528134820.74121-1-adity...@linux.ibm.com/
---
arch/powerpc/Kconfig | 1 +
arch/powerpc/include/asm/ftrace.h | 15 +++++++++
arch/powerpc/kernel/trace/ftrace_entry.S | 42 ++++++++++++++----------
3 files changed, 41 insertions(+), 17 deletions(-)
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index ba9750c8e0cd..449404d3932b 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -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
diff --git a/arch/powerpc/include/asm/ftrace.h
b/arch/powerpc/include/asm/ftrace.h
index bd61a230b19d..5984eaa75ce8 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..6599fe3c6234 100644
--- a/arch/powerpc/kernel/trace/ftrace_entry.S
+++ b/arch/powerpc/kernel/trace/ftrace_entry.S
@@ -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 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 */
--
2.51.0
