Perf tool bpf selftests revealed a broken uapi for s390 and arm64. With the BPF_PROG_TYPE_PERF_EVENT program type the bpf_perf_event structure exports the pt_regs structure for all architectures.
This fails for s390 and arm64 because pt_regs are not part of the user api and kept in-kernel only. To mitigate the broken uapi, introduce a wrapper that exports pt_regs in an asm-generic way. For arm64, export the exising user_pt_regs structure. For s390, introduce a user_pt_regs structure that exports the beginning of pt_regs.
Note that user_pt_regs must export from the beginning of pt_regs as BPF_PROG_TYPE_PERF_EVENT program type is not the only type for running BPF programs.
Some more background: For the bpf_perf_event, there is a uapi definition that is passed to the BPF program. For other "probe" points like trace points, kprobes, and uprobes, there is no uapi and the BPF program is always passed pt_regs (which is OK as the BPF program runs in the kernel context). The perf tool can attach BPF programs to all of these "probe" points and, optionally, can create a BPF prologue to access particular arguments (passed as registers). For this, it uses DWARF/CFI information to obtain the register and calls a perf-arch backend function, regs_query_register_offset(). This function returns the index into (user_)pt_regs for a particular register. Then, perf creates a BPF prologue that accesses this register based on the passed stucture from the "probe" point.
Part of this series, are also updates to the testing and bpf selftest to deal with asm-specifics. To complete the bpf support in perf, the the regs_query_register_offset function is added for s390 to support BPF prologue creation.
Hendrik Brueckner (5): bpf: correct broken uapi for BPF_PROG_TYPE_PERF_EVENT program type s390/bpf: correct broken uapi for BPF_PROG_TYPE_PERF_EVENT program type arm64/bpf: correct broken uapi for BPF_PROG_TYPE_PERF_EVENT program type selftests/bpf: sync kernel headers and introduce arch support in Makefile perf s390: add regs_query_register_offset()
arch/arm64/include/asm/perf_event.h | 2 + arch/arm64/include/uapi/asm/bpf_perf_event.h | 9 + arch/s390/include/asm/perf_event.h | 1 + arch/s390/include/asm/ptrace.h | 11 +- arch/s390/include/uapi/asm/bpf_perf_event.h | 9 + arch/s390/include/uapi/asm/ptrace.h | 11 + include/linux/perf_event.h | 6 +- include/uapi/asm-generic/bpf_perf_event.h | 9 + include/uapi/linux/bpf_perf_event.h | 5 +- kernel/events/core.c | 2 +- tools/arch/arm64/include/uapi/asm/bpf_perf_event.h | 9 + tools/arch/s390/include/uapi/asm/bpf_perf_event.h | 9 + tools/arch/s390/include/uapi/asm/ptrace.h | 471 +++++++++++++++++++++ tools/include/uapi/asm-generic/bpf_perf_event.h | 9 + tools/include/uapi/linux/bpf_perf_event.h | 6 +- tools/perf/arch/s390/Makefile | 1 + tools/perf/arch/s390/util/dwarf-regs.c | 32 +- tools/perf/check-headers.sh | 1 + tools/testing/selftests/bpf/Makefile | 14 +- 19 files changed, 602 insertions(+), 15 deletions(-) create mode 100644 arch/arm64/include/uapi/asm/bpf_perf_event.h create mode 100644 arch/s390/include/uapi/asm/bpf_perf_event.h create mode 100644 include/uapi/asm-generic/bpf_perf_event.h create mode 100644 tools/arch/arm64/include/uapi/asm/bpf_perf_event.h create mode 100644 tools/arch/s390/include/uapi/asm/bpf_perf_event.h create mode 100644 tools/arch/s390/include/uapi/asm/ptrace.h create mode 100644 tools/include/uapi/asm-generic/bpf_perf_event.h