Don't truncate traceEvents to 512 bytes (#8309)

Summary:
Don't call postLogMsg to post a user msg, because it truncates messages to
512 bytes.

Rename traceCap_stderr and trace_stderr to vtraceCap_stderr and trace_stderr,
to signal that they take a va_list (similar to vdebugBelch vs debugBelch).

See #3874 for the original reason behind traceFormatUserMsg.

See the commit msg in #9395 (d360d440) for a discussion about using
null-terminated strings vs strings with an explicit length.

Test Plan:
Run `cabal install ghc-events` and inspect the result of `ghc-events show` on
an eventlog file created with `ghc -eventlog Test.hs` and `./Test +RTS -l`,
where Test.hs contains:

```
import Debug.Trace
main = traceEvent (replicate 510 'a' ++ "bcd") $ return ()
```

Depends on D655.

Reviewers: austin

Reviewed By: austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D656

GHC Trac Issues: #8309

1 files changed, 18 insertions, 21 deletions

diff --git a/rts/Trace.c b/rts/Trace.c
index a0783f3400..bd4d332eac 100644
--- a/rts/Trace.c
+++ b/rts/Trace.c
@@ -622,7 +622,7 @@ void traceTaskDelete_ (Task *task)
 }
 
 #ifdef DEBUG
-static void traceCap_stderr(Capability *cap, char *msg, va_list ap)
+static void vtraceCap_stderr(Capability *cap, char *msg, va_list ap)
 {
     ACQUIRE_LOCK(&trace_utx);
 
@@ -633,6 +633,14 @@ static void traceCap_stderr(Capability *cap, char *msg, va_list ap)
 
     RELEASE_LOCK(&trace_utx);
 }
+
+static void traceCap_stderr(Capability *cap, char *msg, ...)
+{
+  va_list ap;
+  va_start(ap,msg);
+  vtraceCap_stderr(cap, msg, ap);
+  va_end(ap);
+}
 #endif
 
 void traceCap_(Capability *cap, char *msg, ...)
@@ -642,7 +650,7 @@ void traceCap_(Capability *cap, char *msg, ...)
 
 #ifdef DEBUG
     if (RtsFlags.TraceFlags.tracing == TRACE_STDERR) {
-        traceCap_stderr(cap, msg, ap);
+        vtraceCap_stderr(cap, msg, ap);
     } else
 #endif
     {
@@ -653,7 +661,7 @@ void traceCap_(Capability *cap, char *msg, ...)
 }
 
 #ifdef DEBUG
-static void trace_stderr(char *msg, va_list ap)
+static void vtrace_stderr(char *msg, va_list ap)
 {
     ACQUIRE_LOCK(&trace_utx);
 
@@ -672,7 +680,7 @@ void trace_(char *msg, ...)
 
 #ifdef DEBUG
     if (RtsFlags.TraceFlags.tracing == TRACE_STDERR) {
-        trace_stderr(msg, ap);
+        vtrace_stderr(msg, ap);
     } else
 #endif
     {
@@ -682,32 +690,24 @@ void trace_(char *msg, ...)
     va_end(ap);
 }
 
-static void traceFormatUserMsg(Capability *cap, char *msg, ...)
+void traceUserMsg(Capability *cap, char *msg)
 {
-    va_list ap;
-    va_start(ap,msg);
-
     /* Note: normally we don't check the TRACE_* flags here as they're checked
        by the wrappers in Trace.h. But traceUserMsg is special since it has no
        wrapper (it's called from cmm code), so we check TRACE_user here
      */
 #ifdef DEBUG
     if (RtsFlags.TraceFlags.tracing == TRACE_STDERR && TRACE_user) {
-        traceCap_stderr(cap, msg, ap);
+        // Use "%s" as format string to ignore format specifiers in msg (#3874).
+        traceCap_stderr(cap, "%s", msg);
     } else
 #endif
     {
         if (eventlog_enabled && TRACE_user) {
-            postUserMsg(cap, msg, ap);
+            postUserEvent(cap, EVENT_USER_MSG, msg);
         }
     }
     dtraceUserMsg(cap->no, msg);
-    va_end(ap);
-}
-
-void traceUserMsg(Capability *cap, char *msg)
-{
-    traceFormatUserMsg(cap, "%s", msg);
 }
 
 void traceUserMarker(Capability *cap, char *markername)
@@ -717,15 +717,12 @@ void traceUserMarker(Capability *cap, char *markername)
      */
 #ifdef DEBUG
     if (RtsFlags.TraceFlags.tracing == TRACE_STDERR && TRACE_user) {
-        ACQUIRE_LOCK(&trace_utx);
-        tracePreface();
-        debugBelch("cap %d: User marker: %s\n", cap->no, markername);
-        RELEASE_LOCK(&trace_utx);
+        traceCap_stderr(cap, "User marker: %s", markername);
     } else
 #endif
     {
         if (eventlog_enabled && TRACE_user) {
-            postUserMarker(cap, markername);
+            postUserEvent(cap, EVENT_USER_MARKER, markername);
         }
     }
     dtraceUserMarker(cap->no, markername);