[PATCH] ARM: ftrace: Implement HAVE_FUNCTION_GRAPH_FREGS
From: Richard Weinberger <richard@nod.at>
Date: 2025-08-18 10:40:29
Also in:
linux-trace-kernel, lkml
Subsystem:
arm port, function hooks (ftrace), the rest · Maintainers:
Russell King, Steven Rostedt, Masami Hiramatsu, Linus Torvalds
Enable support for ftrace's funcgraph-retval feature by capturing r0-r3 and fp. Since ARM does not provide its own __arch_ftrace_regs structure, we instead populate pt_regs with the registers required by ftrace. Cc: Donglin Peng <redacted> Signed-off-by: Richard Weinberger <richard@nod.at> --- I noticed that funcgraph-retval is not available on ARM. There was a patch [0] to enable the feature, but it never made it upstream. Since then, the infrastructure around CONFIG_FUNCTION_GRAPH_RETVAL has changed, so I have reimplemented the original patch. Donglin Peng, your change also captured the link register, but it seems it was never used. Therefore, I skipped storing LR. Thanks, //richard [0]: https://lore.kernel.org/all/c61eb9290c3e817d4d70c429c0e987e3ec51a3c4.1680954589.git.pengdonglin@sangfor.com.cn/ (local) --- arch/arm/Kconfig | 1 + arch/arm/kernel/entry-ftrace.S | 18 ++++++++++++++---- 2 files changed, 15 insertions(+), 4 deletions(-)
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index b1f3df39ed406..ba84c6f7f5f7a 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig@@ -108,6 +108,7 @@ config ARM select HAVE_GUP_FAST if ARM_LPAE select HAVE_FUNCTION_ERROR_INJECTION select HAVE_FUNCTION_GRAPH_TRACER + select HAVE_FUNCTION_GRAPH_FREGS select HAVE_FUNCTION_TRACER if !XIP_KERNEL select HAVE_GCC_PLUGINS select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S
index bc598e3d8dd23..e24ee559af81d 100644
--- a/arch/arm/kernel/entry-ftrace.S
+++ b/arch/arm/kernel/entry-ftrace.S@@ -257,11 +257,21 @@ ENDPROC(ftrace_graph_regs_caller) #ifdef CONFIG_FUNCTION_GRAPH_TRACER ENTRY(return_to_handler) - stmdb sp!, {r0-r3} - add r0, sp, #16 @ sp at exit of instrumented routine + mov ip, sp @ sp at exit of instrumented routine + sub sp, #PT_REGS_SIZE + str r0, [sp, #S_R0] + str r1, [sp, #S_R1] + str r2, [sp, #S_R2] + str r3, [sp, #S_R3] + str ip, [sp, #S_FP] + mov r0, sp bl ftrace_return_to_handler - mov lr, r0 @ r0 has real ret addr - ldmia sp!, {r0-r3} + mov lr, r0 @ r0 has real ret addr + ldr r3, [sp, #S_R3] + ldr r2, [sp, #S_R2] + ldr r1, [sp, #S_R1] + ldr r0, [sp, #S_R0] + add sp, sp, #PT_REGS_SIZE @ restore stack pointer ret lr ENDPROC(return_to_handler) #endif
--
2.50.1