fixes #25306; Dangling pointers in stack traces with -d:nimStackTraceOverride

lib/system.nim

@@ -553,6 +553,9 @@ type
   CatchableError* = object of Exception ## \
     ## Abstract class for all exceptions that are catchable.
 
+when defined(nimStackTraceOverride):
+  proc `=copy`*(x: var StackTraceEntry, y: StackTraceEntry) {.error.}
+
 when defined(nimIcIntegrityChecks):
   include "system/exceptions"
 

lib/system/stacktraces.nim

@@ -29,6 +29,9 @@ when defined(nimStackTraceOverride):
       proc (programCounters: seq[cuintptr_t], maxLength: cint): seq[StackTraceEntry] {.
         nimcall, gcsafe, raises: [], tags: [], noinline.}
 
+
+  const NimStackTraceMsgs = compileOption("stacktraceMsgs")
+
   # Default procedures (not normally used, because people opting in on this
   # override are supposed to register their own versions).
   var
@@ -65,6 +68,23 @@ when defined(nimStackTraceOverride):
     for i in 0..<programCounters.len:
       s.add(StackTraceEntry(programCounter: cast[uint](programCounters[i])))
 
+  proc copyStackTraceEntry(x: ptr StackTraceEntry): StackTraceEntry =
+    result = StackTraceEntry(line: x.line, programCounter: x.programCounter,
+                             procnameStr: x.procnameStr, filenameStr: x.filenameStr
+    )
+    when NimStackTraceMsgs:
+      result.frameMsg = x.frameMsg
+
+    # points `procname`, `filename` to its own corresponding fields
+    # to avoid dangling pointers # bug #25306 18039
+    result.procname = result.procnameStr.cstring
+    result.filename = result.filenameStr.cstring
+
+  proc copyStackTraceEntrySeq(result: var seq[StackTraceEntry]; s: seq[StackTraceEntry]) =
+    for i in 0..<s.len:
+      let entry = addr s[i]
+      result.add(copyStackTraceEntry entry)
+
   # We may have more stack trace lines in the output, due to inlined procedures.
   proc addDebuggingInfo*(s: seq[StackTraceEntry]): seq[StackTraceEntry] =
     var programCounters: seq[cuintptr_t]
@@ -75,10 +95,10 @@ when defined(nimStackTraceOverride):
       if entry.procname.isNil and entry.programCounter != 0:
         programCounters.add(cast[cuintptr_t](entry.programCounter))
       elif entry.procname.isNil and (entry.line == reraisedFromBegin or entry.line == reraisedFromEnd):
-        result.add(stackTraceOverrideGetDebuggingInfo(programCounters, maxStackTraceLines))
+        result.copyStackTraceEntrySeq(stackTraceOverrideGetDebuggingInfo(programCounters, maxStackTraceLines))
         programCounters = @[]
-        result.add(entry[])
+        result.add(copyStackTraceEntry entry)
       else:
-        result.add(entry[])
+        result.add(copyStackTraceEntry entry)
     if programCounters.len > 0:
-      result.add(stackTraceOverrideGetDebuggingInfo(programCounters, maxStackTraceLines))
+      result.copyStackTraceEntrySeq(stackTraceOverrideGetDebuggingInfo(programCounters, maxStackTraceLines))