bpf: add bpf_get_stack helper

Currently, stackmap and bpf_get_stackid helper are provided for bpf program to get the stack trace. This approach has a limitation though. If two stack traces have the same hash, only one will get stored in the stackmap table regardless of whether BPF_F_REUSE_STACKID is specified or not, so some stack traces may be missing from user perspective.

This patch implements a new helper, bpf_get_stack, will send stack traces directly to bpf program. The bpf program is able to see all stack traces, and then can do in-kernel processing or send stack traces to user space through shared map or bpf_perf_event_output.

Patches #1 and #2 implemented the core kernel support. Patch #3 removes two never-hit branches in verifier. Patches #4 and #5 are two verifier improves to make bpf programming easier. Patch #6 synced the new helper to tools headers. Patch #7 moved perf_event polling code and ksym lookup code from samples/bpf to tools/testing/selftests/bpf. Patch #8 added a verifier test in tools/bpf for new verifier change. Patches #9 and #10 added tests for raw tracepoint prog and tracepoint prog respectively.

Changelogs:
v8 -> v9:
. make function perf_event_mmap (in trace_helpers.c) extern
to decouple perf_event_mmap and perf_event_poller.
. add jit enabled handling for kernel stack verification
in Patch #9. Since we did not have a good way to verify jit enabled kernel stack, just return true if the kernel stack is not empty.
. In path #9, using raw_syscalls/sys_enter instead of
sched/sched_switch, removed calling cmd
"task 1 dd if=/dev/zero of=/dev/null" which is left with dangling process after the program exited.

v7 -> v8:
. rebase on top of latest bpf-next
. simplify BPF_ARSH dst_reg->smin_val/smax_value tracking . rewrite the description of bpf_get_stack() in uapi bpf.h
based on new format.
v6 -> v7:
. do perf callchain buffer allocation inside the
verifier. so if the prog->has_callchain_buf is set, it is guaranteed that the buffer has been allocated.
. change condition "trace_nr <= skip" to "trace_nr < skip"
so that for zero size buffer, return 0 instead of -EFAULT
v5 -> v6:
. after refining return register smax_value and umax_value
for helpers bpf_get_stack and bpf_probe_read_str, bounds and var_off of the return register are further refined.
. added missing commit message for tools header sync commit. . removed one unnecessary empty line.
v4 -> v5:
. relied on dst_reg->var_off to refine umin_val/umax_val
in verifier handling BPF_ARSH value range tracking, suggested by Edward.
v3 -> v4:
. fixed a bug when meta ptr is set to NULL in check_func_arg. . introduced tnum_arshift and added detailed comments for
the underlying implementation
. avoided using VLA in tools/bpf test_progs.
v2 -> v3:
. used meta to track helper memory size argument
. implemented range checking for ARSH in verifier
. moved perf event polling and ksym related functions
from samples/bpf to tools/bpf
. added test to compare build id's between bpf_get_stackid
and bpf_get_stack
v1 -> v2:
. fixed compilation error when CONFIG_PERF_EVENTS is not enabled

Yonghong Song (10):
bpf: change prototype for stack_map_get_build_id_offset
bpf: add bpf_get_stack helper
bpf/verifier: refine retval R0 state for bpf_get_stack helper
bpf: remove never-hit branches in verifier adjust_scalar_min_max_vals bpf/verifier: improve register value range tracking with ARSH tools/bpf: add bpf_get_stack helper to tools headers samples/bpf: move common-purpose trace functions to selftests tools/bpf: add a verifier test case for bpf_get_stack helper and ARSH tools/bpf: add a test for bpf_get_stack with raw tracepoint prog tools/bpf: add a test for bpf_get_stack with tracepoint prog

 include/linux/bpf.h                                |   1 +
 include/linux/filter.h                             |   3 +-
 include/linux/tnum.h                               |   4 +-
 include/uapi/linux/bpf.h                           |  42 +++-
 kernel/bpf/core.c                                  |   5 +
 kernel/bpf/stackmap.c                              |  80 ++++++-
 kernel/bpf/tnum.c                                  |  10 +
 kernel/bpf/verifier.c                              |  80 ++++++-
 kernel/trace/bpf_trace.c                           |  50 ++++-
 samples/bpf/Makefile                               |  11 +-
 samples/bpf/bpf_load.c                             |  63 ------
 samples/bpf/bpf_load.h                             |   7 -
 samples/bpf/offwaketime_user.c                     |   1 +
 samples/bpf/sampleip_user.c                        |   1 +
 samples/bpf/spintest_user.c                        |   1 +
 samples/bpf/trace_event_user.c                     |   1 +
 samples/bpf/trace_output_user.c                    | 110 +---------
 tools/include/uapi/linux/bpf.h                     |  42 +++-
 tools/testing/selftests/bpf/Makefile               |   4 +-
 tools/testing/selftests/bpf/bpf_helpers.h          |   2 +
 tools/testing/selftests/bpf/test_get_stack_rawtp.c | 102 +++++++++
 tools/testing/selftests/bpf/test_progs.c           | 242 +++++++++++++++++++--
 .../selftests/bpf/test_stacktrace_build_id.c       |  20 +-
 tools/testing/selftests/bpf/test_stacktrace_map.c  |  19 +-
 tools/testing/selftests/bpf/test_verifier.c        |  45 ++++
 tools/testing/selftests/bpf/trace_helpers.c        | 180 +++++++++++++++
 tools/testing/selftests/bpf/trace_helpers.h        |  23 ++
 27 files changed, 927 insertions(+), 222 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/test_get_stack_rawtp.c
 create mode 100644 tools/testing/selftests/bpf/trace_helpers.c
 create mode 100644 tools/testing/selftests/bpf/trace_helpers.h

2.9.5