Add -finfo-table-map which maps info tables to source positions

This new flag embeds a lookup table from the address of an info table
to information about that info table.

The main interface for consulting the map is the `lookupIPE` C function

> InfoProvEnt * lookupIPE(StgInfoTable *info)

The `InfoProvEnt` has the following structure:

> typedef struct InfoProv_{
>     char * table_name;
>     char * closure_desc;
>     char * ty_desc;
>     char * label;
>     char * module;
>     char * srcloc;
> } InfoProv;
>
> typedef struct InfoProvEnt_ {
>     StgInfoTable * info;
>     InfoProv prov;
>     struct InfoProvEnt_ *link;
> } InfoProvEnt;

The source positions are approximated in a similar way to the source
positions for DWARF debugging information. They are only approximate but
in our experience provide a good enough hint about where the problem
might be. It is therefore recommended to use this flag in conjunction
with `-g<n>` for more accurate locations.

The lookup table is also emitted into the eventlog when it is available
as it is intended to be used with the `-hi` profiling mode.

Using this flag will significantly increase the size of the resulting
object file but only by a factor of 2-3x in our experience.

2 files changed, 42 insertions, 0 deletions

diff --git a/rts/eventlog/EventLog.c b/rts/eventlog/EventLog.c
index c1eda283f5..0a1ed09f6f 100644
--- a/rts/eventlog/EventLog.c
+++ b/rts/eventlog/EventLog.c
@@ -165,6 +165,7 @@ char *EventDesc[] = {
   [EVENT_HACK_BUG_T9003]      = "Empty event for bug #9003",
   [EVENT_HEAP_PROF_BEGIN]     = "Start of heap profile",
   [EVENT_HEAP_PROF_COST_CENTRE]   = "Cost center definition",
+  [EVENT_IPE]                     = "Info Table Source Position",
   [EVENT_HEAP_PROF_SAMPLE_BEGIN]  = "Start of heap profile sample",
   [EVENT_HEAP_BIO_PROF_SAMPLE_BEGIN]  = "Start of heap profile (biographical) sample",
   [EVENT_HEAP_PROF_SAMPLE_END]    = "End of heap profile sample",
@@ -497,6 +498,9 @@ init_event_types(void)
         case EVENT_HEAP_PROF_COST_CENTRE:
             eventTypes[t].size = EVENT_SIZE_DYNAMIC;
             break;
+        case EVENT_IPE:
+            eventTypes[t].size = EVENT_SIZE_DYNAMIC;
+            break;
 
         case EVENT_HEAP_PROF_SAMPLE_BEGIN:
             eventTypes[t].size = 8;
@@ -1640,6 +1644,36 @@ void postTickyCounterSamples(StgEntCounter *counters)
     RELEASE_LOCK(&eventBufMutex);
 }
 #endif /* TICKY_TICKY */
+void postIPE(StgWord64 info,
+             const char *table_name,
+             const char *closure_desc,
+             const char *ty_desc,
+             const char *label,
+             const char *module,
+             const char *srcloc)
+{
+    ACQUIRE_LOCK(&eventBufMutex);
+    StgWord table_name_len = strlen(table_name);
+    StgWord closure_desc_len = strlen(closure_desc);
+    StgWord ty_desc_len = strlen(ty_desc);
+    StgWord label_len = strlen(label);
+    StgWord module_len = strlen(module);
+    StgWord srcloc_len = strlen(srcloc);
+    // 8 for the info word
+    // 6 for the number of strings in the payload as postString adds 1 to the length
+    StgWord len = 8+table_name_len+closure_desc_len+ty_desc_len+label_len+module_len+srcloc_len+6;
+    ensureRoomForVariableEvent(&eventBuf, len);
+    postEventHeader(&eventBuf, EVENT_IPE);
+    postPayloadSize(&eventBuf, len);
+    postWord64(&eventBuf, info);
+    postString(&eventBuf, table_name);
+    postString(&eventBuf, closure_desc);
+    postString(&eventBuf, ty_desc);
+    postString(&eventBuf, label);
+    postString(&eventBuf, module);
+    postString(&eventBuf, srcloc);
+    RELEASE_LOCK(&eventBufMutex);
+}
 
 void printAndClearEventBuf (EventsBuf *ebuf)
 {
diff --git a/rts/eventlog/EventLog.h b/rts/eventlog/EventLog.h
index a412b491bb..b0675db14d 100644
--- a/rts/eventlog/EventLog.h
+++ b/rts/eventlog/EventLog.h
@@ -171,6 +171,14 @@ void postProfSampleCostCentre(Capability *cap,
 void postProfBegin(void);
 #endif /* PROFILING */
 
+void postIPE(StgWord64 info,
+             const char *table_name,
+             const char *closure_desc,
+             const char *ty_desc,
+             const char *label,
+             const char *module,
+             const char *srcloc);
+
 void postConcUpdRemSetFlush(Capability *cap);
 void postConcMarkEnd(StgWord32 marked_obj_count);
 void postNonmovingHeapCensus(int log_blk_size,