From 1a85a03fc2fe180c1ddc91b4a801d313321d9e53 Mon Sep 17 00:00:00 2001 From: Matt Turner Date: Sun, 18 Oct 2026 10:22:05 -0400 Subject: [PATCH] alpha: fill in pc for software event samples Context switch and tracepoint events have no trap frame, so perf builds one with perf_fetch_caller_regs(). Alpha does not define perf_arch_fetch_caller_regs(), which leaves that pt_regs zeroed, and these samples report pc as 0. Record the caller's address as pc. The zero ps already marks the frame as kernel mode, and pt_regs has nowhere to keep sp, so pc is all that can be filled in. perf_fetch_caller_regs() gets that address from CALLER_ADDR0, which alpha defines as 0 when CONFIG_FRAME_POINTER is disabled. Finding the level zero return address does not need a frame pointer, so make alpha_ftrace_return_address0() available in both configurations. Only ftrace_return_address(n) still depends on frame pointers. Reported-by: Magnus Lindholm Closes: https://lore.kernel.org/all/CA%2B%3DFv5S8-Zk8-LUpZnWiBfTGSQXthepmRc_-a9O%2BpEPmVW0mRA@mail.gmail.com/ Suggested-by: Magnus Lindholm Assisted-by: Claude:claude-opus-5-5 Reviewed-by: Magnus Lindholm Acked-by: Ian Rogers Signed-off-by: Matt Turner Tested-by: Magnus Lindholm Link: https://lore.kernel.org/r/20261018-alpha-perf-regs-v3-v3-5-52be85332c57@gmail.com Signed-off-by: Magnus Lindholm --- arch/alpha/include/asm/ftrace.h | 5 ++--- arch/alpha/include/asm/perf_event.h | 7 +++++++ 2 files changed, 9 insertions(+), 3 deletions(-) diff --git a/arch/alpha/include/asm/ftrace.h b/arch/alpha/include/asm/ftrace.h index 7ec44134c804..5b75a294a7c9 100644 --- a/arch/alpha/include/asm/ftrace.h +++ b/arch/alpha/include/asm/ftrace.h @@ -2,8 +2,6 @@ #ifndef _ASM_ALPHA_FTRACE_H #define _ASM_ALPHA_FTRACE_H -#ifdef CONFIG_FRAME_POINTER - static void *alpha_ftrace_return_address0(void) noinline notrace; static void *alpha_ftrace_return_address0(void) @@ -13,6 +11,8 @@ static void *alpha_ftrace_return_address0(void) #define ftrace_return_address0 alpha_ftrace_return_address0() +#ifdef CONFIG_FRAME_POINTER + /* * __builtin_return_address() requires a constant integer argument. * Keep this as a macro so the value is seen at the callsite. @@ -21,7 +21,6 @@ static void *alpha_ftrace_return_address0(void) #else /* !CONFIG_FRAME_POINTER */ -#define ftrace_return_address0 0UL #define ftrace_return_address(n) ((void)(n), 0UL) #endif /* CONFIG_FRAME_POINTER */ diff --git a/arch/alpha/include/asm/perf_event.h b/arch/alpha/include/asm/perf_event.h index 5996e7a6757e..72536566014a 100644 --- a/arch/alpha/include/asm/perf_event.h +++ b/arch/alpha/include/asm/perf_event.h @@ -1,4 +1,11 @@ #ifndef __ASM_ALPHA_PERF_EVENT_H #define __ASM_ALPHA_PERF_EVENT_H +/* + * Software events have no trap frame, so perf_fetch_caller_regs() fills + * in a zeroed pt_regs. A zero ps already means kernel mode; only pc is + * missing. + */ +#define perf_arch_fetch_caller_regs(regs, __ip) ((regs)->pc = (__ip)) + #endif /* __ASM_ALPHA_PERF_EVENT_H */