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.

1 files changed, 3 insertions, 2 deletions

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;
                     }
                 }
             }