tty: vt: conmakehash: cope with abs_srctree no longer in env

conmakehash uses getenv("abs_srctree") from the environment to strip
the absolute path from the generated sources.
However since commit e2bad14 ("kbuild: unexport abs_srctree and
abs_objtree") this environment variable no longer gets set.
Instead use basename() to indicate the used file in a comment of the
generated source file.

Fixes: 3bd85c6 ("tty: vt: conmakehash: Don't mention the full path of the input in output")
Cc: stable <stable@kernel.org>
Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Link: https://lore.kernel.org/stable/20240725132056.9151-1-max.oss.09%40gmail.com
Link: https://lore.kernel.org/r/20240725132056.9151-1-max.oss.09@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: MaxKrummenacher

drivers/tty/vt/conmakehash.c

@@ -11,6 +11,8 @@
  * Copyright (C) 1995-1997 H. Peter Anvin
  */
 
+#include <libgen.h>
+#include <linux/limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <sysexits.h>
@@ -76,8 +78,8 @@ static void addpair(int fp, int un)
 int main(int argc, char *argv[])
 {
   FILE *ctbl;
-  const char *tblname, *rel_tblname;
-  const char *abs_srctree;
+  const char *tblname;
+  char base_tblname[PATH_MAX];
   char buffer[65536];
   int fontlen;
   int i, nuni, nent;
@@ -102,16 +104,6 @@ int main(int argc, char *argv[])
 	}
     }
 
-  abs_srctree = getenv("abs_srctree");
-  if (abs_srctree && !strncmp(abs_srctree, tblname, strlen(abs_srctree)))
-    {
-      rel_tblname = tblname + strlen(abs_srctree);
-      while (*rel_tblname == '/')
-	++rel_tblname;
-    }
-  else
-    rel_tblname = tblname;
-
   /* For now we assume the default font is always 256 characters. */
   fontlen = 256;
 
@@ -253,6 +245,8 @@ int main(int argc, char *argv[])
   for ( i = 0 ; i < fontlen ; i++ )
     nuni += unicount[i];
 
+  strncpy(base_tblname, tblname, PATH_MAX);
+  base_tblname[PATH_MAX - 1] = 0;
   printf("\
 /*\n\
  * Do not edit this file; it was automatically generated by\n\
@@ -264,7 +258,7 @@ int main(int argc, char *argv[])
 #include <linux/types.h>\n\
 \n\
 u8 dfont_unicount[%d] = \n\
-{\n\t", rel_tblname, fontlen);
+{\n\t", basename(base_tblname), fontlen);
 
   for ( i = 0 ; i < fontlen ; i++ )
     {