From 2ac055383f4619cea09988aa79c2b4324c1bfb40 Mon Sep 17 00:00:00 2001
From: bbbradsmith <bbbradsmith@users.noreply.github.com>
Date: Sun, 19 Feb 2023 08:14:04 -0500
Subject: [PATCH 1/2] ld65 fix overwrite segments adding wrong padding or
 causing internal errors

---
 src/ld65/config.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/src/ld65/config.c b/src/ld65/config.c
index c22ced1ef..c101bd1c6 100644
--- a/src/ld65/config.c
+++ b/src/ld65/config.c
@@ -1945,6 +1945,10 @@ unsigned CfgProcess (void)
             /* Remember the start address before handling this segment */
             unsigned long StartAddr = Addr;
 
+            /* For computing FillLevel */
+            unsigned long FillLevel;
+            unsigned long FillAdded = 0;
+
             /* Take note of "overwrite" segments and make sure there are no
             ** other segment types following them in current memory region.
             */
@@ -2081,14 +2085,19 @@ unsigned CfgProcess (void)
             /* Increment the fill level of the memory area; and, check for an
             ** overflow.
             */
-            M->FillLevel = Addr + S->Seg->Size - M->Start;
-            if (M->FillLevel > M->Size && (M->Flags & MF_OVERFLOW) == 0) {
+            FillLevel = Addr + S->Seg->Size - M->Start;
+            if (FillLevel > M->Size && (M->Flags & MF_OVERFLOW) == 0) {
                 ++Overflows;
                 M->Flags |= MF_OVERFLOW;
                 CfgWarning (GetSourcePos (M->LI),
                             "Segment '%s' overflows memory area '%s' by %lu byte%c",
                             GetString (S->Name), GetString (M->Name),
-                            M->FillLevel - M->Size, (M->FillLevel - M->Size == 1) ? ' ' : 's');
+                            FillLevel - M->Size, (FillLevel - M->Size == 1) ? ' ' : 's');
+            }
+            if (FillLevel > M->FillLevel) {
+                /* Regular segments increase FillLevel. Overwrite segments may increase but not decrease FillLevel. */
+                FillAdded = FillLevel - M->FillLevel;
+                M->FillLevel = FillLevel;
             }
 
             /* If requested, define symbols for the start and size of the
@@ -2107,13 +2116,14 @@ unsigned CfgProcess (void)
             Addr += S->Seg->Size;
 
             /* If this segment will go out to the file, or its place
-            ** in the file will be filled, then increase the file size,
-            ** unless it's an OVERWRITE segment.
+            ** in the file will be filled, then increase the file size.
+            ** An OVERWRITE segment will only increase the size if it overlapped some of the fill area.
             */
             if (S->Load == M &&
-                ((S->Flags & SF_BSS) == 0 || (M->Flags & MF_FILL) != 0) &&
-                    (S->Flags & SF_OVERWRITE) == 0) {
-                M->F->Size += Addr - StartAddr;
+                ((S->Flags & SF_BSS) == 0 || (M->Flags & MF_FILL) != 0)) {
+                M->F->Size += (!(S->Flags & SF_OVERWRITE)) ?
+                    (Addr - StartAddr) :
+                    FillAdded;
             }
         }
 

From 4fc19a3d4c27d193297e928171f85ab361ac2ae7 Mon Sep 17 00:00:00 2001
From: bbbradsmith <bbbradsmith@users.noreply.github.com>
Date: Sun, 19 Feb 2023 08:37:07 -0500
Subject: [PATCH 2/2] ld65 overwrite segment should pad with fill value if the
 desired seek position is beyond the end of the file so far

---
 src/ld65/bin.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/ld65/bin.c b/src/ld65/bin.c
index bd822cc23..15b534f66 100644
--- a/src/ld65/bin.c
+++ b/src/ld65/bin.c
@@ -193,8 +193,16 @@ static void BinWriteMem (BinDesc* D, MemoryArea* M)
                     NewAddr += M->Start;
                 }
                 if (DoWrite || (M->Flags & MF_FILL) != 0) {
-                    /* Seek in "overwrite" segments */
                     if (S->Flags & SF_OVERWRITE) {
+                        /* Seek in "overwrite" segments. Fill if the seek position has not been reached yet. */
+                        unsigned long FileLength;
+                        unsigned long SeekTarget = NewAddr - M->Start + M->FileOffs;
+                        fseek (D->F, 0, SEEK_END);
+                        FileLength = ftell (D->F);
+                        if (SeekTarget > FileLength) {
+                            WriteMult (D->F, M->FillVal, SeekTarget - FileLength);
+                            PrintNumVal ("SF_OVERWRITE", SeekTarget - FileLength);
+                        }
                         fseek (D->F, NewAddr - M->Start + M->FileOffs, SEEK_SET);
                     } else {
                         WriteMult (D->F, M->FillVal, NewAddr-Addr);