* [PATCH v2 0/5] alpha: perf register sampling and user stack dumps
@ 2026-10-17 1:55 Matt Turner
2026-10-17 1:55 ` [PATCH v2 1/5] alpha: fix stale user_stack_pointer() Matt Turner
` (4 more replies)
0 siblings, 5 replies; 11+ messages in thread
From: Matt Turner @ 2026-10-17 1:55 UTC (permalink / raw)
To: Richard Henderson, Magnus Lindholm
Cc: linux-alpha, linux-kernel, linux-doc, linux-perf-users,
Ian Rogers, Matt Turner
This lets perf sample registers and dump the user stack on alpha, which
perf record --call-graph dwarf needs to unwind user space.
r9-r15 are not in pt_regs, so they cannot be sampled. An unwinder
therefore cannot get past a first frame that uses $15 as its frame
pointer (-O0 code or alloca).
The perf tool side is a separate patch for perf-tools-next:
https://lore.kernel.org/r/20261011-alpha-perf-tools-regs-v1-1-2a5940e22548@gmail.com
libdw also needs alpha unwinding support, which I sent to
elfutils-devel:
https://inbox.sourceware.org/elfutils-devel/20261012-alpha-v1-0-46760216dfb7@gmail.com/
---
Changes in v2:
- Patch 4: report sp as 0 for software event samples, whose pt_regs is
a per-CPU buffer rather than a trap frame (Magnus).
- New patch 5: fill in pc for those samples via
perf_arch_fetch_caller_regs() (Magnus).
- Collect trailers. Magnus's Tested-by on patch 4 dropped until he
retests the change.
- Link the perf and elfutils postings.
- Link to v1: https://lore.kernel.org/r/20261011-alpha-perf-regs-v3-v1-0-eaa625a39712@gmail.com
---
Matt Turner (5):
alpha: fix stale user_stack_pointer()
alpha: stop storing the user stack pointer in pt_regs
alpha: use user_stack_pointer() in KSTK_ESP() and dump_elf_thread()
alpha: add HAVE_PERF_REGS and HAVE_PERF_USER_STACK_DUMP support
alpha: fill in pc for software event samples
.../features/perf/perf-regs/arch-support.txt | 2 +-
.../features/perf/perf-stackdump/arch-support.txt | 2 +-
arch/alpha/Kconfig | 2 +
arch/alpha/include/asm/perf_event.h | 7 +++
arch/alpha/include/asm/processor.h | 3 +-
arch/alpha/include/asm/ptrace.h | 7 +--
arch/alpha/include/uapi/asm/perf_regs.h | 45 +++++++++++++++
arch/alpha/include/uapi/asm/ptrace.h | 2 +-
arch/alpha/kernel/Makefile | 1 +
arch/alpha/kernel/asm-offsets.c | 1 -
arch/alpha/kernel/entry.S | 5 --
arch/alpha/kernel/perf_regs.c | 64 ++++++++++++++++++++++
arch/alpha/kernel/process.c | 2 +-
arch/alpha/kernel/ptrace.c | 12 ++++
arch/alpha/kernel/traps.c | 8 ---
15 files changed, 137 insertions(+), 26 deletions(-)
---
base-commit: 8f5dbfb93440d1aba216a1a34369a65654b94be9
change-id: 20261001-alpha-perf-regs-v3-7e23508c1ca2
Best regards,
--
Matt Turner <mattst88@gmail.com>
^ permalink raw reply [flat|nested] 11+ messages in thread* [PATCH v2 1/5] alpha: fix stale user_stack_pointer() 2026-10-17 1:55 [PATCH v2 0/5] alpha: perf register sampling and user stack dumps Matt Turner @ 2026-10-17 1:55 ` Matt Turner 2026-10-17 2:00 ` sashiko-bot 2026-10-17 1:55 ` [PATCH v2 2/5] alpha: stop storing the user stack pointer in pt_regs Matt Turner ` (3 subsequent siblings) 4 siblings, 1 reply; 11+ messages in thread From: Matt Turner @ 2026-10-17 1:55 UTC (permalink / raw) To: Richard Henderson, Magnus Lindholm Cc: linux-alpha, linux-kernel, linux-doc, linux-perf-users, Ian Rogers, Matt Turner PALcode keeps the user stack pointer in the PCB, not the trap frame, so pt_regs->usp is only valid where entry code stores it: entSys, do_entArith() and do_entIF(). Interrupts, page faults and unaligned traps leave it stale, and ptrace and /proc/<pid>/syscall read it through user_stack_pointer(). A user-mode pt_regs is at the top of its task's stack, so find the thread_info from it and use rdusp() for current or pcb.usp otherwise, as KSTK_ESP() and the regset code already do. Fixes: 8a2857bc2b30 ("alpha: enable regset-based ptrace and core dumps") Assisted-by: Claude:claude-opus-5-5 Reviewed-by: Magnus Lindholm <linmag7@gmail.com> Tested-by: Magnus Lindholm <linmag7@gmail.com> Acked-by: Ian Rogers <irogers@google.com> Signed-off-by: Matt Turner <mattst88@gmail.com> --- arch/alpha/include/asm/ptrace.h | 7 +------ arch/alpha/kernel/ptrace.c | 12 ++++++++++++ 2 files changed, 13 insertions(+), 6 deletions(-) diff --git a/arch/alpha/include/asm/ptrace.h b/arch/alpha/include/asm/ptrace.h index 430e8dc27ff7..45d1229344b6 100644 --- a/arch/alpha/include/asm/ptrace.h +++ b/arch/alpha/include/asm/ptrace.h @@ -26,12 +26,7 @@ static inline unsigned long regs_return_value(struct pt_regs *regs) return regs->r0; } -/* Helpers for working with the user stack pointer */ -static inline unsigned long user_stack_pointer(struct pt_regs *regs) -{ - /* Valid for user-mode regs */ - return regs->usp; -} +unsigned long user_stack_pointer(struct pt_regs *regs); static __always_inline bool regs_irqs_disabled(struct pt_regs *regs) { diff --git a/arch/alpha/kernel/ptrace.c b/arch/alpha/kernel/ptrace.c index e1d8c2f69688..dba7e9905cfa 100644 --- a/arch/alpha/kernel/ptrace.c +++ b/arch/alpha/kernel/ptrace.c @@ -440,6 +440,18 @@ ptrace_cancel_bpt(struct task_struct * child) return (nsaved != 0); } +/* + * PALcode keeps the user stack pointer in the PCB, not the trap frame. + * A user-mode pt_regs sits at the top of its task's stack, so the + * thread_info is at the base. + */ +unsigned long user_stack_pointer(struct pt_regs *regs) +{ + struct thread_info *ti = (void *)((unsigned long)regs & -THREAD_SIZE); + + return ti == current_thread_info() ? rdusp() : ti->pcb.usp; +} + void user_enable_single_step(struct task_struct *child) { /* Mark single stepping. */ -- 2.55.0 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH v2 1/5] alpha: fix stale user_stack_pointer() 2026-10-17 1:55 ` [PATCH v2 1/5] alpha: fix stale user_stack_pointer() Matt Turner @ 2026-10-17 2:00 ` sashiko-bot 0 siblings, 0 replies; 11+ messages in thread From: sashiko-bot @ 2026-10-17 2:00 UTC (permalink / raw) To: Matt Turner; +Cc: linux-perf-users > PALcode keeps the user stack pointer in the PCB, not the trap frame, so > pt_regs->usp is only valid where entry code stores it: entSys, > do_entArith() and do_entIF(). Interrupts, page faults and unaligned > traps leave it stale, and ptrace and /proc/<pid>/syscall read it > through user_stack_pointer(). > > A user-mode pt_regs is at the top of its task's stack, so find the > thread_info from it and use rdusp() for current or pcb.usp otherwise, > as KSTK_ESP() and the regset code already do. > > Fixes: 8a2857bc2b30 ("alpha: enable regset-based ptrace and core dumps") > Assisted-by: Claude:claude-opus-5-5 > Reviewed-by: Magnus Lindholm <linmag7@gmail.com> > Tested-by: Magnus Lindholm <linmag7@gmail.com> > Acked-by: Ian Rogers <irogers@google.com> > Signed-off-by: Matt Turner <mattst88@gmail.com> Sashiko has reviewed this patch and found no issues. -- Sashiko AI review · https://sashiko.dev/#/patchset/20261016-alpha-perf-regs-v3-v2-0-17654742226a@gmail.com?part=1 ^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH v2 2/5] alpha: stop storing the user stack pointer in pt_regs 2026-10-17 1:55 [PATCH v2 0/5] alpha: perf register sampling and user stack dumps Matt Turner 2026-10-17 1:55 ` [PATCH v2 1/5] alpha: fix stale user_stack_pointer() Matt Turner @ 2026-10-17 1:55 ` Matt Turner 2026-10-17 2:00 ` sashiko-bot 2026-10-17 1:55 ` [PATCH v2 3/5] alpha: use user_stack_pointer() in KSTK_ESP() and dump_elf_thread() Matt Turner ` (2 subsequent siblings) 4 siblings, 1 reply; 11+ messages in thread From: Matt Turner @ 2026-10-17 1:55 UTC (permalink / raw) To: Richard Henderson, Magnus Lindholm Cc: linux-alpha, linux-kernel, linux-doc, linux-perf-users, Ian Rogers, Matt Turner Nothing reads pt_regs->usp now that user_stack_pointer() uses the PCB. Drop the stores, which saves a PAL_rdusp call on every syscall, and give the field back its old name. Assisted-by: Claude:claude-opus-5-5 Reviewed-by: Magnus Lindholm <linmag7@gmail.com> Tested-by: Magnus Lindholm <linmag7@gmail.com> Acked-by: Ian Rogers <irogers@google.com> Signed-off-by: Matt Turner <mattst88@gmail.com> --- arch/alpha/include/uapi/asm/ptrace.h | 2 +- arch/alpha/kernel/asm-offsets.c | 1 - arch/alpha/kernel/entry.S | 5 ----- arch/alpha/kernel/traps.c | 8 -------- 4 files changed, 1 insertion(+), 15 deletions(-) diff --git a/arch/alpha/include/uapi/asm/ptrace.h b/arch/alpha/include/uapi/asm/ptrace.h index 9d86b2a1526e..72ed913a910f 100644 --- a/arch/alpha/include/uapi/asm/ptrace.h +++ b/arch/alpha/include/uapi/asm/ptrace.h @@ -43,7 +43,7 @@ struct pt_regs { unsigned long trap_a1; unsigned long trap_a2; /* This makes the stack 16-byte aligned as GCC expects */ - unsigned long usp; + unsigned long __pad0; /* These are saved by PAL-code: */ unsigned long ps; unsigned long pc; diff --git a/arch/alpha/kernel/asm-offsets.c b/arch/alpha/kernel/asm-offsets.c index c89792c86044..22ed3c975b1c 100644 --- a/arch/alpha/kernel/asm-offsets.c +++ b/arch/alpha/kernel/asm-offsets.c @@ -30,7 +30,6 @@ static void __used foo(void) DEFINE(HAE_CACHE, offsetof(struct alpha_machine_vector, hae_cache)); DEFINE(HAE_REG, offsetof(struct alpha_machine_vector, hae_register)); - DEFINE(PT_REGS_USP, offsetof(struct pt_regs, usp)); DEFINE(TI_FLAGS, offsetof(struct thread_info, flags)); DEFINE(TI_SYSCALL_WORK, offsetof(struct thread_info, syscall_work)); diff --git a/arch/alpha/kernel/entry.S b/arch/alpha/kernel/entry.S index bfa116d455fb..790389a15c3c 100644 --- a/arch/alpha/kernel/entry.S +++ b/arch/alpha/kernel/entry.S @@ -476,11 +476,6 @@ entSys: ldq $1, 0($sp) /* syscall nr from saved r0 */ stq $1, 8($sp) /* regs->r1 = shadow syscall nr */ - mov $0, $8 - call_pal PAL_rdusp - stq $0, PT_REGS_USP($sp) - mov $8, $0 - lda $8, 0x3fff bic $sp, $8, $8 diff --git a/arch/alpha/kernel/traps.c b/arch/alpha/kernel/traps.c index cfaef96c4ce8..5882c65b7ef1 100644 --- a/arch/alpha/kernel/traps.c +++ b/arch/alpha/kernel/traps.c @@ -30,12 +30,6 @@ #include "proto.h" -static __always_inline void alpha_snapshot_usp(struct pt_regs *regs) -{ - if (user_mode(regs)) - regs->usp = rdusp(); -} - void dik_show_regs(struct pt_regs *regs, unsigned long *r9_15) { @@ -186,7 +180,6 @@ do_entArith(unsigned long summary, unsigned long write_mask, { long si_code = FPE_FLTINV; - alpha_snapshot_usp(regs); if (summary & 1) { /* Software-completion summary bit is set, so try to emulate the instruction. If the processor supports @@ -208,7 +201,6 @@ do_entIF(unsigned long type, struct pt_regs *regs) { int signo, code; - alpha_snapshot_usp(regs); if (type == 3) { /* FEN fault */ /* Irritating users can call PAL_clrfen to disable the FPU for the process. The kernel will then trap in -- 2.55.0 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH v2 2/5] alpha: stop storing the user stack pointer in pt_regs 2026-10-17 1:55 ` [PATCH v2 2/5] alpha: stop storing the user stack pointer in pt_regs Matt Turner @ 2026-10-17 2:00 ` sashiko-bot 0 siblings, 0 replies; 11+ messages in thread From: sashiko-bot @ 2026-10-17 2:00 UTC (permalink / raw) To: Matt Turner; +Cc: linux-perf-users > Nothing reads pt_regs->usp now that user_stack_pointer() uses the PCB. > Drop the stores, which saves a PAL_rdusp call on every syscall, and > give the field back its old name. > > Assisted-by: Claude:claude-opus-5-5 > Reviewed-by: Magnus Lindholm <linmag7@gmail.com> > Tested-by: Magnus Lindholm <linmag7@gmail.com> > Acked-by: Ian Rogers <irogers@google.com> > Signed-off-by: Matt Turner <mattst88@gmail.com> Sashiko has reviewed this patch and found no issues. -- Sashiko AI review · https://sashiko.dev/#/patchset/20261016-alpha-perf-regs-v3-v2-0-17654742226a@gmail.com?part=2 ^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH v2 3/5] alpha: use user_stack_pointer() in KSTK_ESP() and dump_elf_thread() 2026-10-17 1:55 [PATCH v2 0/5] alpha: perf register sampling and user stack dumps Matt Turner 2026-10-17 1:55 ` [PATCH v2 1/5] alpha: fix stale user_stack_pointer() Matt Turner 2026-10-17 1:55 ` [PATCH v2 2/5] alpha: stop storing the user stack pointer in pt_regs Matt Turner @ 2026-10-17 1:55 ` Matt Turner 2026-10-17 1:59 ` sashiko-bot 2026-10-17 1:55 ` [PATCH v2 4/5] alpha: add HAVE_PERF_REGS and HAVE_PERF_USER_STACK_DUMP support Matt Turner 2026-10-17 1:55 ` [PATCH v2 5/5] alpha: fill in pc for software event samples Matt Turner 4 siblings, 1 reply; 11+ messages in thread From: Matt Turner @ 2026-10-17 1:55 UTC (permalink / raw) To: Richard Henderson, Magnus Lindholm Cc: linux-alpha, linux-kernel, linux-doc, linux-perf-users, Ian Rogers, Matt Turner Both open-code the same PCB lookup. Assisted-by: Claude:claude-opus-5-5 Tested-by: Magnus Lindholm <linmag7@gmail.com> Reviewed-by: Magnus Lindholm <linmag7@gmail.com> Acked-by: Ian Rogers <irogers@google.com> Signed-off-by: Matt Turner <mattst88@gmail.com> --- arch/alpha/include/asm/processor.h | 3 +-- arch/alpha/kernel/process.c | 2 +- 2 files changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/alpha/include/asm/processor.h b/arch/alpha/include/asm/processor.h index c461a26d47b3..73251cd671e0 100644 --- a/arch/alpha/include/asm/processor.h +++ b/arch/alpha/include/asm/processor.h @@ -43,8 +43,7 @@ unsigned long __get_wchan(struct task_struct *p); #define KSTK_EIP(tsk) (task_pt_regs(tsk)->pc) -#define KSTK_ESP(tsk) \ - ((tsk) == current ? rdusp() : task_thread_info(tsk)->pcb.usp) +#define KSTK_ESP(tsk) user_stack_pointer(task_pt_regs(tsk)) #define cpu_relax() barrier() diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c index 06522451f018..7861c9e767b7 100644 --- a/arch/alpha/kernel/process.c +++ b/arch/alpha/kernel/process.c @@ -318,7 +318,7 @@ dump_elf_thread(elf_greg_t *dest, struct pt_regs *pt, struct thread_info *ti) dest[27] = pt->r27; dest[28] = pt->r28; dest[29] = pt->gp; - dest[30] = ti == current_thread_info() ? rdusp() : ti->pcb.usp; + dest[30] = user_stack_pointer(pt); dest[31] = pt->pc; /* Once upon a time this was the PS value. Which is stupid -- 2.55.0 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH v2 3/5] alpha: use user_stack_pointer() in KSTK_ESP() and dump_elf_thread() 2026-10-17 1:55 ` [PATCH v2 3/5] alpha: use user_stack_pointer() in KSTK_ESP() and dump_elf_thread() Matt Turner @ 2026-10-17 1:59 ` sashiko-bot 0 siblings, 0 replies; 11+ messages in thread From: sashiko-bot @ 2026-10-17 1:59 UTC (permalink / raw) To: Matt Turner; +Cc: linux-perf-users > Both open-code the same PCB lookup. > > Assisted-by: Claude:claude-opus-5-5 > Tested-by: Magnus Lindholm <linmag7@gmail.com> > Reviewed-by: Magnus Lindholm <linmag7@gmail.com> > Acked-by: Ian Rogers <irogers@google.com> > Signed-off-by: Matt Turner <mattst88@gmail.com> Sashiko has reviewed this patch and found no issues. -- Sashiko AI review · https://sashiko.dev/#/patchset/20261016-alpha-perf-regs-v3-v2-0-17654742226a@gmail.com?part=3 ^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH v2 4/5] alpha: add HAVE_PERF_REGS and HAVE_PERF_USER_STACK_DUMP support 2026-10-17 1:55 [PATCH v2 0/5] alpha: perf register sampling and user stack dumps Matt Turner ` (2 preceding siblings ...) 2026-10-17 1:55 ` [PATCH v2 3/5] alpha: use user_stack_pointer() in KSTK_ESP() and dump_elf_thread() Matt Turner @ 2026-10-17 1:55 ` Matt Turner 2026-10-17 2:08 ` sashiko-bot 2026-10-17 1:55 ` [PATCH v2 5/5] alpha: fill in pc for software event samples Matt Turner 4 siblings, 1 reply; 11+ messages in thread From: Matt Turner @ 2026-10-17 1:55 UTC (permalink / raw) To: Richard Henderson, Magnus Lindholm Cc: linux-alpha, linux-kernel, linux-doc, linux-perf-users, Ian Rogers, Matt Turner Let perf sample registers and dump the user stack, which is what the perf tool needs for --call-graph dwarf. The register indices follow the hardware numbering, so r0-r30 map directly to DWARF register numbers, with pc after them. r9-r15 are callee-saved and live in switch_stack rather than pt_regs, so they cannot be sampled. Without r15 an unwinder cannot recover the CFA of a first frame that uses $15 as its frame pointer. sp is not in pt_regs either: for user frames it comes from user_stack_pointer(), and for kernel frames (PERF_SAMPLE_REGS_INTR) it is the end of the trap frame, as in stacktrace.c. Software events such as context switches and tracepoints hand perf a per-CPU pt_regs filled in by perf_fetch_caller_regs() instead of a trap frame. It is not on the stack and has no room for sp, so report sp as 0 there rather than the address of the per-CPU buffer. Assisted-by: Claude:claude-opus-5-5 Acked-by: Ian Rogers <irogers@google.com> Signed-off-by: Matt Turner <mattst88@gmail.com> --- .../features/perf/perf-regs/arch-support.txt | 2 +- .../features/perf/perf-stackdump/arch-support.txt | 2 +- arch/alpha/Kconfig | 2 + arch/alpha/include/uapi/asm/perf_regs.h | 45 +++++++++++++++ arch/alpha/kernel/Makefile | 1 + arch/alpha/kernel/perf_regs.c | 64 ++++++++++++++++++++++ 6 files changed, 114 insertions(+), 2 deletions(-) diff --git a/Documentation/features/perf/perf-regs/arch-support.txt b/Documentation/features/perf/perf-regs/arch-support.txt index 4c9a5a012075..7d736d678fd4 100644 --- a/Documentation/features/perf/perf-regs/arch-support.txt +++ b/Documentation/features/perf/perf-regs/arch-support.txt @@ -6,7 +6,7 @@ ----------------------- | arch |status| ----------------------- - | alpha: | TODO | + | alpha: | ok | | arc: | TODO | | arm: | ok | | arm64: | ok | diff --git a/Documentation/features/perf/perf-stackdump/arch-support.txt b/Documentation/features/perf/perf-stackdump/arch-support.txt index dd362b5cb638..17b84ea7769d 100644 --- a/Documentation/features/perf/perf-stackdump/arch-support.txt +++ b/Documentation/features/perf/perf-stackdump/arch-support.txt @@ -6,7 +6,7 @@ ----------------------- | arch |status| ----------------------- - | alpha: | TODO | + | alpha: | ok | | arc: | TODO | | arm: | ok | | arm64: | ok | diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig index b2c359b947f6..8fafbfabd1e5 100644 --- a/arch/alpha/Kconfig +++ b/arch/alpha/Kconfig @@ -41,6 +41,8 @@ config ALPHA select HAVE_PAGE_SIZE_8KB select HAVE_PCSPKR_PLATFORM select HAVE_PERF_EVENTS + select HAVE_PERF_REGS + select HAVE_PERF_USER_STACK_DUMP select NEED_DMA_MAP_STATE select NEED_SG_DMA_LENGTH select GENERIC_IRQ_PROBE diff --git a/arch/alpha/include/uapi/asm/perf_regs.h b/arch/alpha/include/uapi/asm/perf_regs.h new file mode 100644 index 000000000000..da96a31b12fb --- /dev/null +++ b/arch/alpha/include/uapi/asm/perf_regs.h @@ -0,0 +1,45 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +#ifndef _UAPI_ASM_ALPHA_PERF_REGS_H +#define _UAPI_ASM_ALPHA_PERF_REGS_H + +/* + * Indices 0-30 match the hardware (and DWARF) register numbers. + * r9-r15 are not saved in pt_regs and cannot be sampled. + */ +enum perf_event_alpha_regs { + PERF_REG_ALPHA_R0, + PERF_REG_ALPHA_R1, + PERF_REG_ALPHA_R2, + PERF_REG_ALPHA_R3, + PERF_REG_ALPHA_R4, + PERF_REG_ALPHA_R5, + PERF_REG_ALPHA_R6, + PERF_REG_ALPHA_R7, + PERF_REG_ALPHA_R8, + PERF_REG_ALPHA_R9, + PERF_REG_ALPHA_R10, + PERF_REG_ALPHA_R11, + PERF_REG_ALPHA_R12, + PERF_REG_ALPHA_R13, + PERF_REG_ALPHA_R14, + PERF_REG_ALPHA_R15, + PERF_REG_ALPHA_R16, + PERF_REG_ALPHA_R17, + PERF_REG_ALPHA_R18, + PERF_REG_ALPHA_R19, + PERF_REG_ALPHA_R20, + PERF_REG_ALPHA_R21, + PERF_REG_ALPHA_R22, + PERF_REG_ALPHA_R23, + PERF_REG_ALPHA_R24, + PERF_REG_ALPHA_R25, + PERF_REG_ALPHA_R26, + PERF_REG_ALPHA_R27, + PERF_REG_ALPHA_R28, + PERF_REG_ALPHA_GP, + PERF_REG_ALPHA_SP, + PERF_REG_ALPHA_PC, + PERF_REG_ALPHA_MAX, +}; + +#endif /* _UAPI_ASM_ALPHA_PERF_REGS_H */ diff --git a/arch/alpha/kernel/Makefile b/arch/alpha/kernel/Makefile index 4ea5c189e60e..0c04b89676ed 100644 --- a/arch/alpha/kernel/Makefile +++ b/arch/alpha/kernel/Makefile @@ -18,6 +18,7 @@ obj-$(CONFIG_PCI) += pci.o pci_iommu.o pci-sysfs.o obj-$(CONFIG_SRM_ENV) += srm_env.o obj-$(CONFIG_MODULES) += module.o obj-$(CONFIG_PERF_EVENTS) += perf_event.o +obj-$(CONFIG_HAVE_PERF_REGS) += perf_regs.o obj-$(CONFIG_RTC_DRV_ALPHA) += rtc.o obj-$(CONFIG_AUDIT) += audit.o diff --git a/arch/alpha/kernel/perf_regs.c b/arch/alpha/kernel/perf_regs.c new file mode 100644 index 000000000000..33ea2e831ba0 --- /dev/null +++ b/arch/alpha/kernel/perf_regs.c @@ -0,0 +1,64 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include <linux/bits.h> +#include <linux/perf_event.h> +#include <linux/sched/task_stack.h> +#include <asm/perf_regs.h> + +#define REG(idx, field) \ + [PERF_REG_ALPHA_##idx] = offsetof(struct pt_regs, field) + +#define REG_RESERVED (~GENMASK_ULL(PERF_REG_ALPHA_MAX - 1, 0) | \ + GENMASK_ULL(PERF_REG_ALPHA_R15, PERF_REG_ALPHA_R9)) + +static const unsigned int pt_regs_offset[PERF_REG_ALPHA_MAX] = { + REG(R0, r0), REG(R1, r1), REG(R2, r2), REG(R3, r3), + REG(R4, r4), REG(R5, r5), REG(R6, r6), REG(R7, r7), + REG(R8, r8), REG(R16, r16), REG(R17, r17), REG(R18, r18), + REG(R19, r19), REG(R20, r20), REG(R21, r21), REG(R22, r22), + REG(R23, r23), REG(R24, r24), REG(R25, r25), REG(R26, r26), + REG(R27, r27), REG(R28, r28), REG(GP, gp), REG(PC, pc), +}; + +u64 perf_reg_value(struct pt_regs *regs, int idx) +{ + if (idx == PERF_REG_ALPHA_SP) { + if (user_mode(regs)) + return user_stack_pointer(regs); + /* + * Software events built by perf_fetch_caller_regs() use a + * per-CPU pt_regs rather than a trap frame, and pt_regs has + * nowhere to record sp, so report none. + */ + if (!object_is_on_stack(regs)) + return 0; + /* Same kernel sp approximation as stacktrace.c. */ + return (unsigned long)(regs + 1); + } + + if (WARN_ON_ONCE((u32)idx >= PERF_REG_ALPHA_MAX || + BIT_ULL(idx) & REG_RESERVED)) + return 0; + + return *(unsigned long *)((void *)regs + pt_regs_offset[idx]); +} + +int perf_reg_validate(u64 mask) +{ + if (!mask || mask & REG_RESERVED) + return -EINVAL; + + return 0; +} + +u64 perf_reg_abi(struct task_struct *task) +{ + return PERF_SAMPLE_REGS_ABI_64; +} + +void perf_get_regs_user(struct perf_regs *regs_user, + struct pt_regs *regs) +{ + regs_user->regs = task_pt_regs(current); + regs_user->abi = perf_reg_abi(current); +} -- 2.55.0 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH v2 4/5] alpha: add HAVE_PERF_REGS and HAVE_PERF_USER_STACK_DUMP support 2026-10-17 1:55 ` [PATCH v2 4/5] alpha: add HAVE_PERF_REGS and HAVE_PERF_USER_STACK_DUMP support Matt Turner @ 2026-10-17 2:08 ` sashiko-bot 0 siblings, 0 replies; 11+ messages in thread From: sashiko-bot @ 2026-10-17 2:08 UTC (permalink / raw) To: Matt Turner; +Cc: linux-perf-users > Let perf sample registers and dump the user stack, which is what the > perf tool needs for --call-graph dwarf. > > The register indices follow the hardware numbering, so r0-r30 map > directly to DWARF register numbers, with pc after them. r9-r15 > are callee-saved and live in switch_stack rather than pt_regs, so they > cannot be sampled. Without r15 an unwinder cannot recover the CFA of a > first frame that uses $15 as its frame pointer. > > sp is not in pt_regs either: for user frames it comes from > user_stack_pointer(), and for kernel frames (PERF_SAMPLE_REGS_INTR) it > is the end of the trap frame, as in stacktrace.c. > > Software events such as context switches and tracepoints hand perf a > per-CPU pt_regs filled in by perf_fetch_caller_regs() instead of a > trap frame. It is not on the stack and has no room for sp, so report > sp as 0 there rather than the address of the per-CPU buffer. > > Assisted-by: Claude:claude-opus-5-5 > Acked-by: Ian Rogers <irogers@google.com> > Signed-off-by: Matt Turner <mattst88@gmail.com> Sashiko has reviewed this patch and found no issues. -- Sashiko AI review · https://sashiko.dev/#/patchset/20261016-alpha-perf-regs-v3-v2-0-17654742226a@gmail.com?part=4 ^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH v2 5/5] alpha: fill in pc for software event samples 2026-10-17 1:55 [PATCH v2 0/5] alpha: perf register sampling and user stack dumps Matt Turner ` (3 preceding siblings ...) 2026-10-17 1:55 ` [PATCH v2 4/5] alpha: add HAVE_PERF_REGS and HAVE_PERF_USER_STACK_DUMP support Matt Turner @ 2026-10-17 1:55 ` Matt Turner 2026-10-17 1:59 ` sashiko-bot 4 siblings, 1 reply; 11+ messages in thread From: Matt Turner @ 2026-10-17 1:55 UTC (permalink / raw) To: Richard Henderson, Magnus Lindholm Cc: linux-alpha, linux-kernel, linux-doc, linux-perf-users, Matt Turner 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. Reported-by: Magnus Lindholm <linmag7@gmail.com> Closes: https://lore.kernel.org/all/CA%2B%3DFv5S8-Zk8-LUpZnWiBfTGSQXthepmRc_-a9O%2BpEPmVW0mRA@mail.gmail.com/ Assisted-by: Claude:claude-opus-5-5 Signed-off-by: Matt Turner <mattst88@gmail.com> --- arch/alpha/include/asm/perf_event.h | 7 +++++++ 1 file changed, 7 insertions(+) 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 */ -- 2.55.0 ^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH v2 5/5] alpha: fill in pc for software event samples 2026-10-17 1:55 ` [PATCH v2 5/5] alpha: fill in pc for software event samples Matt Turner @ 2026-10-17 1:59 ` sashiko-bot 0 siblings, 0 replies; 11+ messages in thread From: sashiko-bot @ 2026-10-17 1:59 UTC (permalink / raw) To: Matt Turner; +Cc: linux-perf-users > 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. > > Reported-by: Magnus Lindholm <linmag7@gmail.com> > Closes: https://lore.kernel.org/all/CA%2B%3DFv5S8-Zk8-LUpZnWiBfTGSQXthepmRc_-a9O%2BpEPmVW0mRA@mail.gmail.com/ > Assisted-by: Claude:claude-opus-5-5 > Signed-off-by: Matt Turner <mattst88@gmail.com> Sashiko has reviewed this patch and found no issues. -- Sashiko AI review · https://sashiko.dev/#/patchset/20261016-alpha-perf-regs-v3-v2-0-17654742226a@gmail.com?part=5 ^ permalink raw reply [flat|nested] 11+ messages in thread
end of thread, other threads:[~2026-10-17 2:08 UTC | newest] Thread overview: 11+ messages (download: mbox.gz follow: Atom feed -- links below jump to the message on this page -- 2026-10-17 1:55 [PATCH v2 0/5] alpha: perf register sampling and user stack dumps Matt Turner 2026-10-17 1:55 ` [PATCH v2 1/5] alpha: fix stale user_stack_pointer() Matt Turner 2026-10-17 2:00 ` sashiko-bot 2026-10-17 1:55 ` [PATCH v2 2/5] alpha: stop storing the user stack pointer in pt_regs Matt Turner 2026-10-17 2:00 ` sashiko-bot 2026-10-17 1:55 ` [PATCH v2 3/5] alpha: use user_stack_pointer() in KSTK_ESP() and dump_elf_thread() Matt Turner 2026-10-17 1:59 ` sashiko-bot 2026-10-17 1:55 ` [PATCH v2 4/5] alpha: add HAVE_PERF_REGS and HAVE_PERF_USER_STACK_DUMP support Matt Turner 2026-10-17 2:08 ` sashiko-bot 2026-10-17 1:55 ` [PATCH v2 5/5] alpha: fill in pc for software event samples Matt Turner 2026-10-17 1:59 ` sashiko-bot
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