Currently, BPF programs can access register values from struct pt_regs. Fetching other registers is not supported. For some usecases this limits the usefulness of BPF programs. This series adds a helper meant to fetch any register value for the architecture the program is running on. Concrete motivating usecase: Tracing programs often attach to User Statically-Defined Tracing (USDT) probes, which can pass arguments using registers. The registers used to pass arguments for a specific probe are determined at compile-time. Although general-purpose registers which can be accessed via pt_regs are usually chosen, register pressure can cause others to be used. Recently we saw this happening in a Fedora libpthread library [0], where a xmm register was used. Similarly, floating-point arguments in USDTs will result in use of xmm register [1]. Since there is no way to access the registers used to pass these arguments, BPF programs can't use them. Another usecase: rdtsc access. Initially the helper was meant to narrowly address the USDT xmm usecase but conversation with Andrii highlighted the usefulness of a more general helper. Although only x86 SSE reg fetching is added in this patchset, the path forward for adding other register sets and architectures should be clear. Feedback from someone familiar with s390 or other arch regarding whether the helper would be usable for other archs in current form would be appreciated. Summary of patches: Patch 1 moves a header so fpregs_state_valid helper can be used. Patches 2 and 3 contain the meat of the kernel- and libbpf-side changes, respectively. Libbpf-side changes add use of the helper to usdt lib in order to address USDT xmm issue that originally prompted this work. Patches 4 and 5 add tests. Submitted as RFC for early feedback while failing usdt12 prog verification is addressed (see patch 3). [0] - https://github.com/iovisor/bcc/pull/3880 [1] - https://github.com/iovisor/bcc/issues/3875 Dave Marchevsky (5): x86/fpu: Move context.h to include/asm bpf: add get_reg_val helper libbpf: usdt lib wiring of xmm reads selftests/bpf: Add test for USDT parse of xmm reg selftests/bpf: get_reg_val test exercising fxsave fetch .../x86/{kernel => include/asm}/fpu/context.h | 2 + arch/x86/kernel/fpu/core.c | 2 +- arch/x86/kernel/fpu/regset.c | 2 +- arch/x86/kernel/fpu/signal.c | 2 +- arch/x86/kernel/fpu/xstate.c | 2 +- include/linux/bpf.h | 1 + include/uapi/linux/bpf.h | 40 +++++ kernel/trace/bpf_trace.c | 148 ++++++++++++++++++ kernel/trace/bpf_trace.h | 1 + net/bpf/bpf_dummy_struct_ops.c | 13 ++ tools/include/uapi/linux/bpf.h | 40 +++++ tools/lib/bpf/usdt.bpf.h | 36 +++-- tools/lib/bpf/usdt.c | 51 +++++- tools/testing/selftests/bpf/Makefile | 8 +- .../selftests/bpf/bpf_testmod/bpf_testmod.c | 13 ++ tools/testing/selftests/bpf/prog_tests/usdt.c | 49 ++++++ .../selftests/bpf/progs/test_urandom_usdt.c | 37 +++++ tools/testing/selftests/bpf/test_progs.c | 7 + tools/testing/selftests/bpf/urandom_read.c | 3 + .../selftests/bpf/urandom_read_lib_xmm.c | 62 ++++++++ 20 files changed, 499 insertions(+), 20 deletions(-) rename arch/x86/{kernel => include/asm}/fpu/context.h (96%) create mode 100644 tools/testing/selftests/bpf/urandom_read_lib_xmm.c -- 2.30.2
