[Qemu-devel] [PATCH for-2.10 1/2] trace: use static event ID mapping in simpletrace.stp

[Stefan Hajnoczi <stefanha@redhat.com>]

Commit 7f1b588f20d027730676e627713ae3bbf6baab04 ("trace: emit name <->
ID mapping in simpletrace header") broke the SystemTap flight recorder
because event mapping records may no longer be present in the ring
buffer when the trace is analyzed.  This means simpletrace.py
--no-header does not know the event ID mapping needed to pretty-print
the trace.

Instead of numbering events dynamically, use a static event ID mapping
as dictated by the event order in the trace-events-all file.

The simpletrace.py script also uses trace-events-all so the next patch
will fix the simpletrace.py --no-header option to take advantage of this
knowledge.

Cc: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 scripts/tracetool/format/simpletrace_stap.py | 36 ++++++++++++----------------
 1 file changed, 15 insertions(+), 21 deletions(-)

diff --git a/scripts/tracetool/format/simpletrace_stap.py b/scripts/tracetool/format/simpletrace_stap.py
index 144b704bcd..6cfdc32867 100644
--- a/scripts/tracetool/format/simpletrace_stap.py
+++ b/scripts/tracetool/format/simpletrace_stap.py
@@ -22,33 +22,18 @@ def global_var_name(name):
     return probeprefix().replace(".", "_") + "_" + name
 
 def generate(events, backend, group):
-    id_map = global_var_name("event_name_to_id_map")
-    next_id = global_var_name("event_next_id")
-    map_func = global_var_name("simple_trace_map_event")
+    id_map = global_var_name("id_map")
+
     out('/* This file is autogenerated by tracetool, do not edit. */',
         '',
         'global %(id_map)s',
-        'global %(next_id)s',
-        'function %(map_func)s(name)',
         '',
-        '{',
-        '    if (!([name] in %(id_map)s)) {',
-        '        %(id_map)s[name] = %(next_id)s',
-        '        name_len = strlen(name)',
-        '        printf("%%8b%%8b%%4b%%.*s", 0, ',
-        '               %(next_id)s, name_len, name_len, name)',
-        '        %(next_id)s = %(next_id)s + 1',
-        '    }',
-        '    return %(id_map)s[name]',
-        '}',
         'probe begin',
         '{',
         '    printf("%%8b%%8b%%8b", 0xffffffffffffffff, 0xf2b177cb0aa429b4, 4)',
         '}',
         '',
-        id_map=id_map,
-        next_id=next_id,
-        map_func=map_func)
+        id_map=id_map)
 
     for event_id, e in enumerate(events):
         if 'disable' in e.properties:
@@ -56,11 +41,20 @@ def generate(events, backend, group):
 
         out('probe %(probeprefix)s.simpletrace.%(name)s = %(probeprefix)s.%(name)s ?',
             '{',
-            '    id = %(map_func)s("%(name)s")',
             probeprefix=probeprefix(),
-            map_func=map_func,
             name=e.name)
 
+        out('    if (!(["%(name)s"] in %(id_map)s)) {',
+            '        %(id_map)s["%(name)s"] = 1',
+            '        printf("%%8b%%8b%%4b%%.*s", 0, ',
+            '               %(event_id)s, %(name_len)s, %(name_len)s,',
+            '               "%(name)s")',
+            '    }',
+            id_map=id_map,
+            name=e.name,
+            name_len=len(e.name),
+            event_id=event_id)
+
         # Calculate record size
         sizes = ['24'] # sizeof(TraceRecord)
         for type_, name in e.args:
@@ -77,7 +71,7 @@ def generate(events, backend, group):
         sizestr = ' + '.join(sizes)
 
         # Generate format string and value pairs for record header and arguments
-        fields = [('8b', 'id'),
+        fields = [('8b', str(event_id)),
                   ('8b', 'gettimeofday_ns()'),
                   ('4b', sizestr),
                   ('4b', 'pid()')]
-- 
2.13.4