Messages in this thread | | | Subject | struct pt_regs missing in /usr/include/ tree for eBPF program compile | From | Thomas-Mich Richter <> | Date | Wed, 2 Aug 2017 13:22:36 +0200 |
| |
I work on the perf tool and its bpf support for IBM s390 and came across a strange issue compiling tools/testing/selftests/bpf/test_verifier.c on s390x.
This is the compile error: gcc -Wall -O2 -I../../../include/uapi -I../../../lib -I../../../../include/generated -DHAVE_GENHDR -I../../../include test_verifier.c /root/linux-devel/tools/testing/selftests/bpf/libbpf.a -lcap -lelf -o /root/linux-devel/tools/testing/selftests/bpf/test_verifier In file included from test_verifier.c:63:0: ../../../include/uapi/linux/bpf_perf_event.h:14:17: error: field ‘regs’ has incomplete type struct pt_regs regs;
This shows up in test case "unpriv: spill/fill of different pointers ldx" at line 1811. This issue is located in file /usr/include/linux/bpf_perf_event.h which is a copy of the linux kernels include/uapi/linux/bpf_perf_event.h.
It contains: struct bpf_perf_event_data { struct pt_regs regs; __u64 sample_period; };
On s390 struct pt_regs is not exported to user space and does not appear anywhere in /usr/include. How about other architectures beside Intel? As far as I know 1. the struct pt_regs contains only kernel registers, no user space registers? 2. Is part of the kernel API and should not be exported at all?
When I investigated the kernel side of the bpf() system call, the test case ends up in functions pe_prog_is_valid_access() and pe_prog_convert_ctx_access() via syscall(bpf) +--> bpf_prog_load() +--> find_prog_type() to load eBPF type specific verifiers | pe_prog_is_valid_access() and pe_prog_convert_ctx_access() +--> bpf_check() to verify (and modify) the eBPF +--> check_vfg() +--> do_check() +--> check_xadd() +--> check_mem_access() +--> check_ctx_access() +--> env->prog->aux->ops->is_valid_access which is set to pe_prog_is_valid_access()
Now this last function expects and verifies struct pt_regs via struct member offsets which needs a correct struct pt_regs previously setup by user space eBPF program.
This also requires a correct struct pt_regs in /usr/include/linux/bpf_perf_event.h (which includes /usr/include/{linux,asm,sym}/ptrace.h
How to achieve this on a platform which does not export struct pt_regs to the user?
Thanks a lot for your help.
-- Thomas Richter, Dept 3303, IBM LTC Boeblingen Germany -- Vorsitzende des Aufsichtsrats: Martina Koederitz Geschäftsführung: Dirk Wittkopp Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294
| |