[binutils-gdb] avoid bogus format-overflow error

[Alan Modra]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=9c7ed7b7fdbe4e25b4bad5e64f5d37936e4c9045

commit 9c7ed7b7fdbe4e25b4bad5e64f5d37936e4c9045
Author: Alan Modra <amodra@gmail.com>
Date:   Mon Apr 21 09:03:52 2025 +0930

    avoid bogus format-overflow error
    
    Seen on x86_64-linux Ubuntu 24.04.2 using gcc-13.3.0 with
    CFLAGS="-m32 -g -O2 -fsanitize=address,undefined"
    
    In function ‘sprintf’,
        inlined from ‘s_mri_for’ at gas/config/tc-m68k.c:6941:5:
    /usr/include/bits/stdio2.h:30:10: error: null destination pointer [-Werror=format-overflow=]
       30 |   return __builtin___sprintf_chk (__s, __USE_FORTIFY_LEVEL - 1,
          |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       31 |                                   __glibc_objsize (__s), __fmt,
          |                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
       32 |                                   __va_arg_pack ());
          |                                   ~~~~~~~~~~~~~~~~~
    
    Rewrite the code without sprintf, as in other parts of s_mri_for.
    See also commit 760fb390fd4c and following commits.
    
    Note that adding -D_FORTIFY_SOURCE=0 to CFLAGS (which is a good idea
    when building with sanitizers) merely transforms the sprintf_chk error
    here into one regarding plain sprintf.

Diff:
---
 gas/config/tc-m68k.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/gas/config/tc-m68k.c b/gas/config/tc-m68k.c
index 0f36741fec1..46b26d4f38a 100644
--- a/gas/config/tc-m68k.c
+++ b/gas/config/tc-m68k.c
@@ -6754,7 +6754,6 @@ s_mri_for (int qual)
   struct mri_control_info *n;
   char *buf;
   char *s;
-  char ex[2];
 
   /* The syntax is
        FOR.q var = init { TO | DOWNTO } end [ BY by ] DO.e
@@ -6935,12 +6934,14 @@ s_mri_for (int qual)
   mri_assemble (buf);
 
   /* bcc bottom.  */
-  ex[0] = TOLOWER (extent);
-  ex[1] = '\0';
-  if (up)
-    sprintf (buf, "blt%s %s", ex, n->bottom);
-  else
-    sprintf (buf, "bgt%s %s", ex, n->bottom);
+  s = buf;
+  *s++ = 'b';
+  *s++ = up ? 'l' : 'g';
+  *s++ = 't';
+  if (extent != '\0')
+    *s++ = TOLOWER (extent);
+  *s++ = ' ';
+  strcpy (s, n->bottom);
   mri_assemble (buf);
 
   /* Put together the add or sub instruction used by ENDF.  */