From 2d6ca8a7b2e24e1b5670529c220f50ef23f1652e Mon Sep 17 00:00:00 2001
From: Stephen Heumann <stephenheumann@gmail.com>
Date: Sat, 2 Jul 2022 22:09:56 -0500
Subject: [PATCH] Do not set read/write error indicator if ftell cannot get the
 file mark.

This is not really an IO operation on the file, and accordingly the C standards do not describe the error indicator as being set here. In particular, you cannot get the mark for a character device, but that is expected behavior, not really an error condition.

errno is still set, indicating that the ftell operation failed.
---
 stdio.asm | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/stdio.asm b/stdio.asm
index 5ba27ad..072b0ea 100644
--- a/stdio.asm
+++ b/stdio.asm
@@ -2008,8 +2008,8 @@ lb0      ldy   #FILE_file               get the file's mark
          sta   gmRefNum
          OSGet_Mark gm
          bcc   lb1
-         ph4   <stream
-         jsr   ~ioerror
+         lda   #EIO
+         sta   >errno
          bra   rts
 
 lb1      move4 gmPosition,pos           set the position