rts: Always truncate output fileswip/T16993

Previously there were numerous places in the RTS where we would fopen
with the "w" flag string. This is wrong as it will not truncate the
file. Consequently if we write less data than the previous length of the
file we will leave garbage at its end.

Fixes #16993.

1 files changed, 2 insertions, 2 deletions

diff --git a/rts/RtsFlags.c b/rts/RtsFlags.c
index 8d9b052bc7..5cdf08e9a5 100644
--- a/rts/RtsFlags.c
+++ b/rts/RtsFlags.c
@@ -1745,7 +1745,7 @@ openStatsFile (char *filename,           // filename, or NULL
         f = NULL; /* NULL means use debugBelch */
     } else {
         if (*filename != '\0') {  /* stats file specified */
-            f = __rts_fopen (filename,"w");
+            f = __rts_fopen (filename,"w+");
         } else {
             if (filename_fmt == NULL) {
                 errorBelch("Invalid stats filename format (NULL)\n");
@@ -1755,7 +1755,7 @@ openStatsFile (char *filename,           // filename, or NULL
             char stats_filename[STATS_FILENAME_MAXLEN];
             snprintf(stats_filename, STATS_FILENAME_MAXLEN, filename_fmt,
                 prog_name);
-            f = __rts_fopen (stats_filename,"w");
+            f = __rts_fopen (stats_filename,"w+");
         }
         if (f == NULL) {
             errorBelch("Can't open stats file %s\n", filename);