[Qemu-devel] [PATCH for 2.10] trace: ensure unique function / variable names per .stp file

[Qemu-devel] [PATCH for 2.10] trace: ensure unique function / variable names per .stp file

[Daniel P. Berrange]

The simpletrace compatibility code for systemtap creates a
function and some global variables for mapping to event ID
numbers. We generate multiple -simpletrace.stp files though,
one per target and systemtap considers functions & variables
to be globally scoped, not per file. So if trying to use the
simpletrace compat probes, systemtap will complain:

 # stap -e 'probe qemu.system.arm.simpletrace.visit_type_str { print( "hello")}'
 semantic error: conflicting global variables: identifier 'event_name_to_id_map' at /usr/share/systemtap/tapset/qemu-aarch64-simpletrace.stp:3:8
        source: global event_name_to_id_map
                       ^
 identifier 'event_name_to_id_map' at /usr/share/systemtap/tapset/qemu-system-arm-simpletrace.stp:3:8
        source: global event_name_to_id_map
                       ^

 WARNING: cross-file global variable reference to identifier 'event_name_to_id_map' at /usr/share/systemtap/tapset/qemu-system-arm-simpletrace.stp:3:8 from: identifier 'event_name_to_id_map' at /usr/share/systemtap/tapset/qemu-aarch64-simpletrace.stp:8:21
 source:     if (!([name] in event_name_to_id_map)) {
                             ^
 WARNING: cross-file global variable reference to identifier 'event_next_id' at /usr/share/systemtap/tapset/qemu-system-arm-simpletrace.stp:4:8 from: identifier 'event_next_id' at :9:38
 source:         event_name_to_id_map[name] = event_next_id
                                              ^

We already have a string used to prefix probe names, so just
replace '.' with '_' to get a function / variable name prefix

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 scripts/tracetool/format/simpletrace_stap.py | 29 ++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/scripts/tracetool/format/simpletrace_stap.py b/scripts/tracetool/format/simpletrace_stap.py
index c35e662e00..144b704bcd 100644
--- a/scripts/tracetool/format/simpletrace_stap.py
+++ b/scripts/tracetool/format/simpletrace_stap.py
@@ -18,29 +18,37 @@ from tracetool.backend.dtrace import binary, probeprefix
 from tracetool.backend.simple import is_string
 from tracetool.format.stap import stap_escape
 
+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")
     out('/* This file is autogenerated by tracetool, do not edit. */',
         '',
-        'global event_name_to_id_map',
-        'global event_next_id',
-        'function simple_trace_map_event(name)',
+        'global %(id_map)s',
+        'global %(next_id)s',
+        'function %(map_func)s(name)',
         '',
         '{',
-        '    if (!([name] in event_name_to_id_map)) {',
-        '        event_name_to_id_map[name] = event_next_id',
+        '    if (!([name] in %(id_map)s)) {',
+        '        %(id_map)s[name] = %(next_id)s',
         '        name_len = strlen(name)',
         '        printf("%%8b%%8b%%4b%%.*s", 0, ',
-        '               event_next_id, name_len, name_len, name)',
-        '        event_next_id = event_next_id + 1',
+        '               %(next_id)s, name_len, name_len, name)',
+        '        %(next_id)s = %(next_id)s + 1',
         '    }',
-        '    return event_name_to_id_map[name]',
+        '    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)
 
     for event_id, e in enumerate(events):
         if 'disable' in e.properties:
@@ -48,8 +56,9 @@ def generate(events, backend, group):
 
         out('probe %(probeprefix)s.simpletrace.%(name)s = %(probeprefix)s.%(name)s ?',
             '{',
-            '    id = simple_trace_map_event("%(name)s")',
+            '    id = %(map_func)s("%(name)s")',
             probeprefix=probeprefix(),
+            map_func=map_func,
             name=e.name)
 
         # Calculate record size
-- 
2.13.3

Re: [Qemu-devel] [PATCH for 2.10] trace: ensure unique function / variable names per .stp file

[Stefan Hajnoczi]

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On Fri, Jul 28, 2017 at 02:36:57PM +0100, Daniel P. Berrange wrote:
> The simpletrace compatibility code for systemtap creates a
> function and some global variables for mapping to event ID
> numbers. We generate multiple -simpletrace.stp files though,
> one per target and systemtap considers functions & variables
> to be globally scoped, not per file. So if trying to use the
> simpletrace compat probes, systemtap will complain:
> 
>  # stap -e 'probe qemu.system.arm.simpletrace.visit_type_str { print( "hello")}'
>  semantic error: conflicting global variables: identifier 'event_name_to_id_map' at /usr/share/systemtap/tapset/qemu-aarch64-simpletrace.stp:3:8
>         source: global event_name_to_id_map
>                        ^
>  identifier 'event_name_to_id_map' at /usr/share/systemtap/tapset/qemu-system-arm-simpletrace.stp:3:8
>         source: global event_name_to_id_map
>                        ^
> 
>  WARNING: cross-file global variable reference to identifier 'event_name_to_id_map' at /usr/share/systemtap/tapset/qemu-system-arm-simpletrace.stp:3:8 from: identifier 'event_name_to_id_map' at /usr/share/systemtap/tapset/qemu-aarch64-simpletrace.stp:8:21
>  source:     if (!([name] in event_name_to_id_map)) {
>                              ^
>  WARNING: cross-file global variable reference to identifier 'event_next_id' at /usr/share/systemtap/tapset/qemu-system-arm-simpletrace.stp:4:8 from: identifier 'event_next_id' at :9:38
>  source:         event_name_to_id_map[name] = event_next_id
>                                               ^
> 
> We already have a string used to prefix probe names, so just
> replace '.' with '_' to get a function / variable name prefix
> 
> Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
> ---
>  scripts/tracetool/format/simpletrace_stap.py | 29 ++++++++++++++++++----------
>  1 file changed, 19 insertions(+), 10 deletions(-)

Thanks, applied to my tracing tree:
https://github.com/stefanha/qemu/commits/tracing

Stefan

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