From: Paul Eggert <eggert@cs.ucla.edu>
Date: Mon, 21 Jul 2025 21:56:43 +0000 (-0700)
Subject: insert-file-contents shrinking Solaris file fix
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=850c271a48a9227c3b743987b745bf46a232c966;p=emacs.git

insert-file-contents shrinking Solaris file fix

This is related to recent fixes for Bug#77315.
* src/fileio.c (Finsert_file_contents): Defend against
a file shrinking to be smaller than its initial offset.
This can happen only on platforms like Solaris where
the initial offset can be positive.

(cherry picked from commit 8393e469e7f1771b4e167392eef169ab51c047b2)
---

diff --git a/src/fileio.c b/src/fileio.c
index 2c60405ef35..7312efb6244 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -4529,8 +4529,9 @@ by calling `format-decode', which see.  */)
 		    {
 		      /* Shrink the file's head if the file shrank to
 			 be smaller than its head.  */
-		      if (endpos - beg_offset < same_at_start - BEGV_BYTE)
-			same_at_start = endpos - beg_offset + BEGV_BYTE;
+		      off_t offset_from_beg = endpos - beg_offset;
+		      if (offset_from_beg < same_at_start - BEGV_BYTE)
+			same_at_start = max (0, offset_from_beg) + BEGV_BYTE;
 		    }
 		}
 	    }