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
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