opensnoop to trace openat

rename name builtin to probe

Use env to find bpftrace

Fixlets

Ensure no garbage in struct sigaction.
Valgrind was complaining:

==21435== Syscall param rt_sigaction(act->sa_mask) points to uninitialised byte(s)
==21435==    at 0x95ED000: __libc_sigaction (in /usr/lib64/libc-2.27.so)
==21435==    by 0x594E99: main
==21435==  Address 0x1ffefff8e8 is on thread 1's stack
==21435==  in frame #0, created by __libc_sigaction (???:)

Valgrind was complaining:

==8428== 32,816 bytes in 1 blocks are definitely lost in loss record 983 of 985
==8428==    at 0x4C2EDA7: malloc (vg_replace_malloc.c:299)
==8428==    by 0x96779A5: __alloc_dir (in /usr/lib64/libc-2.27.so)
==8428==    by 0x9677AAC: opendir_tail (in /usr/lib64/libc-2.27.so)
==8428==    by 0x59EC50: bpftrace::list_dir(...)
==8428==    by 0x59ED5F: bpftrace::list_probes(...)
==8428==    by 0x594993: main

cppcheck was complaining:

[attached_probe.cpp:206]: (warning) %d in format string (no. 1) requires 'int *' but the argument type is 'unsigned int *'.
[attached_probe.cpp:206]: (warning) %d in format string (no. 2) requires 'int *' but the argument type is 'unsigned int *'.
[attached_probe.cpp:206]: (warning) %d in format string (no. 3) requires 'int *' but the argument type is 'unsigned int *'.

While at it, check uname() and sscanf() return values to avoid garbage.

Valgrind was complaining:
==9103== Warning: invalid file descriptor -1 in syscall close()
==9103== Warning: invalid file descriptor -1 in syscall close()

issue 174 make resolve_kname match exact string

probe type short names 

Add file globbing search semantics to list_probes()

Support printf("%s") for stack and ustack

This works similarly to how printf'ing a Type::usym works.

When verifying the printf format string we treat stack and ustack as
Type::string. BPFtrace:get_arg_values now knows how to resolve these.

Fixes #10

This makes cgroupid function to work fine when building with alpine.

Allow '.' in idents for golang

Supports:
- LLVM 5 (static build)
- LLVM 5
- LLVM 6
- LLVM 7

ClangParser: Don't exit if kernel headers are not found

When specifying a string literal attach point do not try to expand
wildcards if they are present.

This specifically is required for Go methods on pointer receivers,
which have a '*' in their symbol name.

Allow quoted string attach points so that you can match more than
[a-Z0-9].

This specific issue that this fixes is attaching to go
functions. These symbols are in the format '<package>.<function>' and
can contain unicode letters and digits.

Implement function cgroupid(path) -> cgroup id

Mention the `cgroup` variable and the `cgroupid` function alongside an
example that uses them both.

Currently used image of alpine has a version of musl libc that does
not have name_to_handle_at function that is required to resolve the
cgroup id. In such case we just use an implementation that says that
resolving cgroupid is not supported.

We will wrap the file_handle struct in the next commit. The struct has
a flexible array member, which is not supported by C++. Compiler may
complain about using it when allocated on stack, even indirectly as a
member of a struct. I'm not sure if using this kind of types is even a
defined behavior…