From 9280e99d87ddd8c6c7fd83f9ea1585967b3dcd60 Mon Sep 17 00:00:00 2001 From: Matt Turner Date: Sun, 18 Oct 2026 10:22:04 -0400 Subject: [PATCH] alpha: add HAVE_PERF_REGS and HAVE_PERF_USER_STACK_DUMP support 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 Tested-by: Magnus Lindholm Reviewed-by: Magnus Lindholm Signed-off-by: Matt Turner Link: https://lore.kernel.org/r/20261018-alpha-perf-regs-v3-v3-4-52be85332c57@gmail.com Signed-off-by: Magnus Lindholm --- .../features/perf/perf-regs/arch-support.txt | 2 +- .../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(-) create mode 100644 arch/alpha/include/uapi/asm/perf_regs.h create mode 100644 arch/alpha/kernel/perf_regs.c 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..b6d2dcf6e184 --- /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 _ASM_ALPHA_PERF_REGS_H +#define _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 /* _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 +#include +#include +#include + +#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); +}