[Bug bpf/28285] New: Allow stapbpf backend to handle $arg1, $arg2, ...

[Bug bpf/28285] New: Allow stapbpf backend to handle $arg1, $arg2, ...

[wcohen at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28285

            Bug ID: 28285
           Summary: Allow stapbpf backend to handle $arg1, $arg2, ...
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: bpf
          Assignee: systemtap at sourceware dot org
          Reporter: wcohen at redhat dot com
  Target Milestone: ---

The stapbpf backend doesn't handle $argn (for example $arg2 in
gmalloc_watch.stp example below).  A number of the tapsets use $argn to access
values passed into functions.  The bpf backend should be able to access those
simple arguments also, but currently it fails.  This can be demonstrated with
some of the systemtap examples:

$ sudo dnf install glib2-devel
$ cd /usr/share/systemtap/testsuite/systemtap.examples/
$ sudo stap --bpf apps/gmalloc_watch.stp -T 1
semantic error: unhandled statement or expression type: identifier '$arg2' at
/usr/share/systemtap/tapset/x86_64/libglib-2.0.so.0.6800.4.stp:31:13
        source:   n_bytes = $arg2; 
                            ^

Pass 4: compilation failed.  [man error::pass4]
$ sudo stap  --bpf apps/stap_time.stp 
semantic error: unhandled statement or expression type: identifier '$arg1' at
/usr/share/systemtap/tapset/stap_staticmarkers.stp:18:12
        source:         session = $arg1
                                  ^

Pass 4: compilation failed.  [man error::pass4]


On the same machine the linux kernel module version things work fine:

$ sudo stap  apps/gmalloc_watch.stp -T 1
g_malloc: pid=2077 n_bytes=72
$ sudo stap  apps/stap_time.stp -T 1
$

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[Bug bpf/28285] Allow stapbpf backend to handle $arg1, $arg2, ...

[wcohen at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=28285

--- Comment #1 from William Cohen <wcohen at redhat dot com> ---
The issue is occuring because tapsets.cxx is writing the code for the access to
the argument in tapsets.cxx
sdt_uprobe_var_expanding_visitor::try_parse_arg_register  around line 7053. 
Later on the bpf-translate.cxx has no way of converting that magic string
containing the code to access an SDT marker argument into bpf.

There is similar generation of strings containing code in the following sdt
methods:


sdt_uprobe_var_expanding_visitor::try_parse_arg_register (target_symbol *e,
                                                          const string& asmarg,
                                                          long precision)

sdt_uprobe_var_expanding_visitor::try_parse_arg_offset_register (target_symbol
*e,
                                                                 const string&
asmarg,
                                                                 long
precision)

sdt_uprobe_var_expanding_visitor::try_parse_arg_effective_addr (target_symbol
*e,
                                                                const string&
asmarg,
                                                                long precision)

sdt_uprobe_var_expanding_visitor::try_parse_arg_varname (target_symbol *e,
                                                         const string& asmarg,
                                                         long precision)

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