ar: Fix GCC7 -Wformat-length issues.

GCC7 adds warnings for snprintf formatting into too small buffers.
Fix the two issues pointed out by the new warning. The ar header
fields are fixed length containing left-justified strings without
zero terminator. snprintf always adds a '\0' char at the end (which
we then don't copy into the ar header field) and numbers are decimal
strings of fixed 10 chars  (-Wformat-length thinks formatting
them as size_t might overflow the buffer on 64bit arches).

Signed-off-by: Mark Wielaard <[email protected]>

Author: Mark Wielaard

src/ChangeLog

@@ -1,3 +1,10 @@
+2016-11-10  Mark Wielaard  <[email protected]>
+
+	* ar.c (write_member): Make sure tmpbuf is large enough to contain
+	a starting '/' and ending '\0' char.
+	(do_oper_insert): Likewise.
+	* arlib.c (arlib_finalize): Format tmpbuf as PRId32 decimal.
+
 2016-11-02  Mark Wielaard  <[email protected]>
 
 	* addr2line.c (handle_address): Add fallthrough comment.

src/ar.c

@@ -1,5 +1,5 @@
 /* Create, modify, and extract from archives.
-   Copyright (C) 2005-2012 Red Hat, Inc.
+   Copyright (C) 2005-2012, 2016 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <[email protected]>, 2005.
 
@@ -853,7 +853,10 @@ write_member (struct armem *memb, off_t *startp, off_t *lenp, Elf *elf,
 	      off_t end_off, int newfd)
 {
   struct ar_hdr arhdr;
-  char tmpbuf[sizeof (arhdr.ar_name) + 1];
+  /* The ar_name is not actually zero teminated, but we need that for
+     snprintf.  Also if the name is too long, then the string starts
+     with '/' plus an index off number (decimal).  */
+  char tmpbuf[sizeof (arhdr.ar_name) + 2];
 
   bool changed_header = memb->long_name_off != -1;
   if (changed_header)
@@ -1455,7 +1458,11 @@ do_oper_insert (int oper, const char *arfname, char **argv, int argc,
 
 	      /* Create the header.  */
 	      struct ar_hdr arhdr;
-	      char tmpbuf[sizeof (arhdr.ar_name) + 1];
+	      /* The ar_name is not actually zero teminated, but we
+		 need that for snprintf.  Also if the name is too
+		 long, then the string starts with '/' plus an index
+		 off number (decimal).  */
+	      char tmpbuf[sizeof (arhdr.ar_name) + 2];
 	      if (all->long_name_off == -1)
 		{
 		  size_t namelen = strlen (all->name);
@@ -1465,7 +1472,7 @@ do_oper_insert (int oper, const char *arfname, char **argv, int argc,
 		}
 	      else
 		{
-		  snprintf (tmpbuf, sizeof (arhdr.ar_name) + 1, "/%-*ld",
+		  snprintf (tmpbuf, sizeof (tmpbuf), "/%-*ld",
 			    (int) sizeof (arhdr.ar_name), all->long_name_off);
 		  memcpy (arhdr.ar_name, tmpbuf, sizeof (arhdr.ar_name));
 		}

src/arlib.c

@@ -1,5 +1,5 @@
 /* Functions to handle creation of Linux archives.
-   Copyright (C) 2007-2012 Red Hat, Inc.
+   Copyright (C) 2007-2012, 2016 Red Hat, Inc.
    This file is part of elfutils.
    Written by Ulrich Drepper <[email protected]>, 2007.
 
@@ -23,6 +23,7 @@
 #include <assert.h>
 #include <error.h>
 #include <gelf.h>
+#include <inttypes.h>
 #include <libintl.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -107,6 +108,9 @@ arlib_init (void)
 void
 arlib_finalize (void)
 {
+  /* Note that the size is stored as decimal string in 10 chars,
+     without zero terminator (we add + 1 here only so snprintf can
+     put it at the end, we then don't use it when we memcpy it).  */
   char tmpbuf[sizeof (((struct ar_hdr *) NULL)->ar_size) + 1];
 
   symtab.longnameslen = obstack_object_size (&symtab.longnamesob);
@@ -121,9 +125,9 @@ arlib_finalize (void)
 
       symtab.longnames = obstack_finish (&symtab.longnamesob);
 
-      int s = snprintf (tmpbuf, sizeof (tmpbuf), "%-*zu",
+      int s = snprintf (tmpbuf, sizeof (tmpbuf), "%-*" PRIu32 "",
 			(int) sizeof (((struct ar_hdr *) NULL)->ar_size),
-			symtab.longnameslen - sizeof (struct ar_hdr));
+			(uint32_t) (symtab.longnameslen - sizeof (struct ar_hdr)));
       memcpy (&((struct ar_hdr *) symtab.longnames)->ar_size, tmpbuf, s);
     }
 
@@ -169,10 +173,10 @@ arlib_finalize (void)
 
   /* See comment for ar_date above.  */
   memcpy (&((struct ar_hdr *) symtab.symsoff)->ar_size, tmpbuf,
-	  snprintf (tmpbuf, sizeof (tmpbuf), "%-*zu",
+	  snprintf (tmpbuf, sizeof (tmpbuf), "%-*" PRIu32 "",
 		    (int) sizeof (((struct ar_hdr *) NULL)->ar_size),
-		    symtab.symsofflen + symtab.symsnamelen
-		    - sizeof (struct ar_hdr)));
+		    (uint32_t) (symtab.symsofflen + symtab.symsnamelen
+				- sizeof (struct ar_hdr))));
 }