From e9db34ffd3fdfdf637533d4899b81fa130e86684 Mon Sep 17 00:00:00 2001
From: Scott Duensing <scott.duensing@gmail.com>
Date: Thu, 23 Jul 2026 18:50:40 -0500
Subject: [PATCH] libc fseek issues fixed.

---
 runtime/src/libc.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/runtime/src/libc.c b/runtime/src/libc.c
index 467f8aa..198e6dd 100644
--- a/runtime/src/libc.c
+++ b/runtime/src/libc.c
@@ -57,6 +57,17 @@ typedef struct {
     u16            refNum;
     unsigned long  position;
 } __GsosMarkRecGS;
+// SetMark ($2016) / SetEOF ($2018) take a positioning base word followed
+// by a displacement long -- NOT the bare-position layout that GetMark
+// ($2017) / GetEOF ($2019) return.  These calls require pCount=3; the
+// Get side keeps the 3-field records above.  base=0 means "displacement
+// measured from the start of the file".
+typedef struct {
+    u16            pCount;
+    u16            refNum;
+    u16            base;
+    unsigned long  displacement;
+} __GsosSetPosRecGS;
 typedef struct {
     u16            pCount;
     void          *pathname;
@@ -140,8 +151,8 @@ extern u16 gsosRead   (__GsosIORecGS     *p) __attribute__((weak, retain, used))
 extern u16 gsosWrite  (__GsosIORecGS     *p) __attribute__((weak, retain, used));
 extern u16 gsosClose  (__GsosRefNumRecGS *p) __attribute__((weak, retain, used));
 extern u16 gsosGetEOF (__GsosEOFRecGS    *p) __attribute__((weak, retain, used));
-extern u16 gsosSetEOF (__GsosEOFRecGS    *p) __attribute__((weak, retain, used));
-extern u16 gsosSetMark(__GsosMarkRecGS   *p) __attribute__((weak, retain, used));
+extern u16 gsosSetEOF (__GsosSetPosRecGS *p) __attribute__((weak, retain, used));
+extern u16 gsosSetMark(__GsosSetPosRecGS *p) __attribute__((weak, retain, used));
 extern u16 gsosGetMark(__GsosMarkRecGS   *p) __attribute__((weak, retain, used));
 extern u16 gsosCreate    (__GsosCreateParm    *p) __attribute__((weak, retain, used));
 extern u16 gsosDestroy   (__GsosDestroyParm   *p) __attribute__((weak, retain, used));
@@ -1573,14 +1584,14 @@ FILE *fopen(const char *path, const char *mode) {
     f->refNum   = op.refNum;
     if (truncate) {
         // "w" / "w+" — truncate to zero length.
-        __GsosEOFRecGS e = { 2, op.refNum, 0 };
+        __GsosSetPosRecGS e = { 3, op.refNum, 0, 0 };
         if (gsosSetEOF(&e) != 0) f->err = 1;
     }
     if (append) {
         // "a" / "a+" — position at end-of-file.
         __GsosEOFRecGS e = { 2, op.refNum, 0 };
         if (gsosGetEOF(&e) == 0) {
-            __GsosMarkRecGS m = { 2, op.refNum, e.eof };
+            __GsosSetPosRecGS m = { 3, op.refNum, 0, e.eof };
             gsosSetMark(&m);
         }
     }
@@ -1709,7 +1720,7 @@ int fseek(FILE *stream, long offset, int whence) {
         }
         long target = base + offset;
         if (target < 0) return -1;
-        __GsosMarkRecGS m = { 2, stream->refNum, (unsigned long)target };
+        __GsosSetPosRecGS m = { 3, stream->refNum, 0, (unsigned long)target };
         if (gsosSetMark(&m) != 0) return -1;
         stream->eof = 0;
         stream->unget = -1;
@@ -1956,7 +1967,7 @@ static unsigned char __renameCopyBuf[RENAME_COPY_BUF_SZ];
 // use stack-resident parm blocks (smaller scope, less BSS).
 static __GsosIORecGS      __rcIORec;
 static __GsosRefNumRecGS  __rcRefRec;
-static __GsosEOFRecGS     __rcEofRec;
+static __GsosSetPosRecGS  __rcEofRec;
 static __GsosDestroyParm  __rcDestroy;
 
 // Tear-down on any mid-flow failure.  Closes both refs (best-effort)
@@ -1990,7 +2001,7 @@ static int __renameCopyDelete(const char *src, const char *dst) {
         return -1;
     }
     u16 dstRef = dstOpen.refNum;
-    __rcEofRec.pCount = 2; __rcEofRec.refNum = dstRef; __rcEofRec.eof = 0;
+    __rcEofRec.pCount = 3; __rcEofRec.refNum = dstRef; __rcEofRec.base = 0; __rcEofRec.displacement = 0;
     if (gsosSetEOF(&__rcEofRec) != 0) {
         __renameCleanup(srcRef, dstRef, dst);
         errno = 5;