bpf translation error handling: try tracking derived_probe token

BPF translation internals involve data structures that do not track
the staptree level entities they are based on.  So when an error
occurs, there's no quick way to mapping it back to the token, for an
ideal error message.  translate_bpf_pass() now tries to track a
last-token* as it goes translating all the probe bodies to bpf, so
that a semantic_error can be synthesized if needed.

This is still far from ideal; a single exception causes giving up
trying all the remaining probes; and all begin/end probes are
translated into single larger bpf programs, so it's harder to narrow
down the cause.  Baby steps.

diff --git a/bpf-translate.cxx b/bpf-translate.cxx
index 7dfbf00e66863a3214f3886e113cd50615a5ef0d..7491c647cfed04e45dd87ff62b6b0e8743dd0541 100644 (file)
--- a/bpf-translate.cxx
+++ b/bpf-translate.cxx
@@ -2225,6 +2225,7 @@ translate_bpf_pass (systemtap_session& s)
   BPF_Output eo(fd);
   globals glob;
   int ret = 0;
+  const token* t = 0;
   try
     {
       translate_globals(glob, s);
@@ -2238,6 +2239,7 @@ translate_bpf_pass (systemtap_session& s)
 
           if (!init.empty())
             {
+              t = begin_v[0]->tok;
               program p;
               translate_init_and_probe_v(p, glob, init, begin_v);
               p.generate();
@@ -2245,6 +2247,7 @@ translate_bpf_pass (systemtap_session& s)
             }
           else if (!begin_v.empty())
             {
+              t = begin_v[0]->tok;
               program p;
               translate_probe_v(p, glob, begin_v);
               p.generate();
@@ -2253,6 +2256,7 @@ translate_bpf_pass (systemtap_session& s)
 
           if (!end_v.empty())
             {
+              t = end_v[0]->tok;
               program p;
               translate_probe_v(p, glob, end_v);
               p.generate();
@@ -2267,6 +2271,7 @@ translate_bpf_pass (systemtap_session& s)
 
           for (auto i = kprobe_v.begin(); i != kprobe_v.end(); ++i)
             {
+              t = i->first->tok;
               program p;
               translate_probe(p, glob, i->first);
               p.generate();
@@ -2293,7 +2298,8 @@ translate_bpf_pass (systemtap_session& s)
     }
   catch (const std::runtime_error &e)
     {
-      std::cerr << "bpf translation internal error: " << e.what() << std::endl;
+      semantic_error er(ERR_SRC, _F("bpf translation failure: %s", e.what()), t);
+      s.print_error(er);
       ret = 1;
     }
   catch (...)