On 04/07/2022 15:53, Andrew Kilroy wrote: > This patch series addresses issues that perf has when attempting to show > userspace stacks in the presence of pointer authentication on arm64. > > Depending on whether libunwind or libdw is used, perf incorrectly > displays the userspace stack in 'perf report --stdio'. With libunwind, > only the leaf function is shown. > > | > ---0x200000004005bf > 0x200000004005bf > my_leaf_function > > With libdw, only the leaf function is shown even though there are > callers in the application. > > | > ---my_leaf_function > > > The reason perf cannot show the stack upon a perf report --stdio is > because the unwinders are given instruction pointers which contain a > pointer authentication code (PAC). For the libraries to correctly > unwind, they need to know which bits of the instruction pointer to turn > off. > > The kernel exposes the set of PAC bits via the NT_ARM_PAC_MASK regset. > It is expected that this may vary per-task in future. The kernel also > exposes which pointer authentication keys are enabled via the > NT_ARM_PAC_ENABLED_KEYS regset, and this can change dynamically. These > are per-task state which perf would need to sample. > > It's not always feasible for perf to acquire these regsets via ptrace. > When sampling system-wide or with inherited events this may require a > large volume of ptrace requests, and by the time the perf tool processes > a sample for a task, that task might already have terminated. > > Instead, these patches allow this state to be sampled into the perf > ringbuffer, where it can be consumed more easily by the perf tool. > > The first patch changes the kernel to send the authentication PAC masks > to userspace perf via the perf ring buffer. This is published in the > sample, using a new sample field PERF_SAMPLE_ARCH_1. > > The subsequent patches are changes to userspace perf to > > 1) request the PERF_SAMPLE_ARCH_1 > 2) supply the instruction mask to libunwind > 3) ensure perf can cope with an older kernel that does not know about > the PERF_SAMPLE_ARCH_1 sample field. > 4) checks if the version of libunwind has the capability to accept > an instruction mask from perf and if so enable the feature. > > These changes depend on a change to libunwind, that is yet to be > released, although the patch has been merged. > > https://github.com/libunwind/libunwind/pull/360 > For the whole set: Reviewed-by: James Clark <james.clark@xxxxxxx> I checked that the new test passes on an AWS Graviton 3 instance and with a build of mainline libunwind. I also checked that the PAC masks on the samples look sensible. The tests also still pass when run on N1SDP which doesn't have pointer authentication. > > Andrew Kilroy (6): > perf arm64: Send pointer auth masks to ring buffer > perf evsel: Do not request ptrauth sample field if not supported > perf tools: arm64: Read ptrauth data from kernel > perf libunwind: Feature check for libunwind ptrauth callback > perf libunwind: arm64 pointer authentication > perf tools: Print ptrauth struct in perf report > > German Gomez (2): > perf test: Update arm64 tests to expect ptrauth masks > perf test arm64: Test unwinding with PACs on gcc & clang compilers > > arch/arm64/include/asm/arch_sample_data.h | 38 ++++++ > arch/arm64/kernel/Makefile | 2 +- > arch/arm64/kernel/arch_sample_data.c | 37 ++++++ > include/linux/perf_event.h | 24 ++++ > include/uapi/linux/perf_event.h | 5 +- > kernel/events/core.c | 35 ++++++ > tools/build/Makefile.feature | 2 + > tools/build/feature/Makefile | 4 + > tools/build/feature/test-all.c | 5 + > .../feature/test-libunwind-arm64-ptrauth.c | 26 ++++ > tools/include/uapi/linux/perf_event.h | 5 +- > tools/perf/Makefile.config | 10 ++ > tools/perf/Makefile.perf | 1 + > tools/perf/tests/Build | 1 + > tools/perf/tests/arm_unwind_pac.c | 113 ++++++++++++++++++ > tools/perf/tests/arm_unwind_pac.sh | 57 +++++++++ > tools/perf/tests/attr/README | 1 + > .../attr/test-record-graph-default-aarch64 | 3 +- > tools/perf/tests/attr/test-record-graph-dwarf | 1 + > .../attr/test-record-graph-dwarf-aarch64 | 13 ++ > .../tests/attr/test-record-graph-fp-aarch64 | 3 +- > tools/perf/tests/builtin-test.c | 1 + > tools/perf/tests/sample-parsing.c | 2 +- > tools/perf/tests/tests.h | 1 + > tools/perf/util/event.h | 8 ++ > tools/perf/util/evsel.c | 64 ++++++++++ > tools/perf/util/evsel.h | 1 + > tools/perf/util/perf_event_attr_fprintf.c | 2 +- > tools/perf/util/session.c | 15 +++ > tools/perf/util/unwind-libunwind-local.c | 12 ++ > 30 files changed, 485 insertions(+), 7 deletions(-) > create mode 100644 arch/arm64/include/asm/arch_sample_data.h > create mode 100644 arch/arm64/kernel/arch_sample_data.c > create mode 100644 tools/build/feature/test-libunwind-arm64-ptrauth.c > create mode 100644 tools/perf/tests/arm_unwind_pac.c > create mode 100755 tools/perf/tests/arm_unwind_pac.sh > create mode 100644 tools/perf/tests/attr/test-record-graph-dwarf-aarch64 >
