[PATCH v3 0/5] alpha: perf register sampling and user stack dumps

[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@xxxxxxxxx

libdw also needs alpha unwinding support, which I sent to
elfutils-devel:

  https://inbox.sourceware.org/elfutils-devel/20261012-alpha-v1-0-46760216dfb7@xxxxxxxxx/

---
Changes in v3:
- Patch 4: rename the uapi <asm/perf_regs.h> include guard from
  _UAPI_ASM_ALPHA_PERF_REGS_H to _ASM_ALPHA_PERF_REGS_H, matching
  x86, arm64 and most other architectures. headers_install strips
  the _UAPI prefix, so installed headers were fine, but code built
  against the uapi directory in the kernel tree saw a different
  guard. elfutils tests for _ASM_ALPHA_PERF_REGS_H, and without the
  rename it disabled alpha perf sample unwinding in that case
  (Magnus).
- Patch 5: make alpha_ftrace_return_address0() available without
  CONFIG_FRAME_POINTER. CALLER_ADDR0 was 0 in that configuration, so
  software event samples still reported pc as 0 (Magnus).
- Collect trailers.
- Link to v2: https://lore.kernel.org/r/20261016-alpha-perf-regs-v3-v2-0-17654742226a@xxxxxxxxx

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@xxxxxxxxx

---
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/ftrace.h                    |  5 +-
 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 ---
 16 files changed, 139 insertions(+), 29 deletions(-)
---
base-commit: 8f5dbfb93440d1aba216a1a34369a65654b94be9
change-id: 20261001-alpha-perf-regs-v3-7e23508c1ca2

Best regards,
-- 
Matt Turner <mattst88@xxxxxxxxx>