[PATCH 22/24] alpha: add HAVE_PERF_REGS and HAVE_PERF_USER_STACK_DUMP support

[Matt Turner <mattst88@gmail.com>]

Implement the perf register sampling interface for Alpha. This enables
perf to capture register state and user stack dumps with samples,
supporting --call-graph dwarf.

The perf_regs enum exposes the registers available in pt_regs: r0-r8,
r16-r28, gp, pc, and ps. Registers r9-r15 are callee-saved and live
in switch_stack, not pt_regs, so they are not included.

A switch statement maps perf register indices to pt_regs fields since
Alpha's pt_regs layout is non-contiguous (unlike architectures where
direct array indexing works).

Assisted-by: Claude:claude-opus-4-6
Signed-off-by: Matt Turner <mattst88@gmail.com>
---
 arch/alpha/Kconfig                      |  2 +
 arch/alpha/include/asm/perf_regs.h      |  7 ++
 arch/alpha/include/uapi/asm/perf_regs.h | 34 ++++++++++
 arch/alpha/kernel/Makefile              |  1 +
 arch/alpha/kernel/perf_regs.c           | 86 +++++++++++++++++++++++++
 5 files changed, 130 insertions(+)
 create mode 100644 arch/alpha/include/asm/perf_regs.h
 create mode 100644 arch/alpha/include/uapi/asm/perf_regs.h
 create mode 100644 arch/alpha/kernel/perf_regs.c

diff --git ./arch/alpha/Kconfig ./arch/alpha/Kconfig
index bda8443a7323..74d13a29b8a9 100644
--- ./arch/alpha/Kconfig
+++ ./arch/alpha/Kconfig
@@ -31,6 +31,8 @@ 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 ./arch/alpha/include/asm/perf_regs.h ./arch/alpha/include/asm/perf_regs.h
new file mode 100644
index 000000000000..6045da1a2a4f
--- /dev/null
+++ ./arch/alpha/include/asm/perf_regs.h
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_ALPHA_PERF_REGS_H
+#define _ASM_ALPHA_PERF_REGS_H
+
+#include <uapi/asm/perf_regs.h>
+
+#endif /* _ASM_ALPHA_PERF_REGS_H */
diff --git ./arch/alpha/include/uapi/asm/perf_regs.h ./arch/alpha/include/uapi/asm/perf_regs.h
new file mode 100644
index 000000000000..afeb6a1584cd
--- /dev/null
+++ ./arch/alpha/include/uapi/asm/perf_regs.h
@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_ASM_ALPHA_PERF_REGS_H
+#define _UAPI_ASM_ALPHA_PERF_REGS_H
+
+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_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_PC,
+	PERF_REG_ALPHA_PS,
+	PERF_REG_ALPHA_MAX,
+};
+
+#endif /* _UAPI_ASM_ALPHA_PERF_REGS_H */
diff --git ./arch/alpha/kernel/Makefile ./arch/alpha/kernel/Makefile
index 4ea5c189e60e..0c04b89676ed 100644
--- ./arch/alpha/kernel/Makefile
+++ ./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 ./arch/alpha/kernel/perf_regs.c ./arch/alpha/kernel/perf_regs.c
new file mode 100644
index 000000000000..e15081ac95e0
--- /dev/null
+++ ./arch/alpha/kernel/perf_regs.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/perf_event.h>
+#include <asm/perf_regs.h>
+#include <asm/ptrace.h>
+
+u64 perf_reg_value(struct pt_regs *regs, int idx)
+{
+	switch (idx) {
+	case PERF_REG_ALPHA_R0:
+		return regs->r0;
+	case PERF_REG_ALPHA_R1:
+		return regs->r1;
+	case PERF_REG_ALPHA_R2:
+		return regs->r2;
+	case PERF_REG_ALPHA_R3:
+		return regs->r3;
+	case PERF_REG_ALPHA_R4:
+		return regs->r4;
+	case PERF_REG_ALPHA_R5:
+		return regs->r5;
+	case PERF_REG_ALPHA_R6:
+		return regs->r6;
+	case PERF_REG_ALPHA_R7:
+		return regs->r7;
+	case PERF_REG_ALPHA_R8:
+		return regs->r8;
+	case PERF_REG_ALPHA_R16:
+		return regs->r16;
+	case PERF_REG_ALPHA_R17:
+		return regs->r17;
+	case PERF_REG_ALPHA_R18:
+		return regs->r18;
+	case PERF_REG_ALPHA_R19:
+		return regs->r19;
+	case PERF_REG_ALPHA_R20:
+		return regs->r20;
+	case PERF_REG_ALPHA_R21:
+		return regs->r21;
+	case PERF_REG_ALPHA_R22:
+		return regs->r22;
+	case PERF_REG_ALPHA_R23:
+		return regs->r23;
+	case PERF_REG_ALPHA_R24:
+		return regs->r24;
+	case PERF_REG_ALPHA_R25:
+		return regs->r25;
+	case PERF_REG_ALPHA_R26:
+		return regs->r26;
+	case PERF_REG_ALPHA_R27:
+		return regs->r27;
+	case PERF_REG_ALPHA_R28:
+		return regs->r28;
+	case PERF_REG_ALPHA_GP:
+		return regs->gp;
+	case PERF_REG_ALPHA_PC:
+		return regs->pc;
+	case PERF_REG_ALPHA_PS:
+		return regs->ps;
+	default:
+		WARN_ON_ONCE(1);
+		return 0;
+	}
+}
+
+#define REG_RESERVED (~((1ULL << PERF_REG_ALPHA_MAX) - 1))
+
+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);
+}
-- 
2.54.0