[PATCH 2/2] [gdbsupport] Fix UB in print-utils.cc:int_string

[Tom de Vries]

When building gdb with -fsanitize=undefined, I run into:
...
(gdb) PASS: gdb.ada/access_to_packed_array.exp: set logging enabled on
maint print symbols^M
print-utils.cc:281:29:runtime error: negation of -9223372036854775808 cannot \
  be represented in type 'long int'; cast to an unsigned type to negate this \
  value to itself
(gdb) FAIL: gdb.ada/access_to_packed_array.exp: maint print symbols
...

By running in a debug session, we find that this happens during printing of:
...
   typedef system.storage_elements.storage_offset: \
     range -9223372036854775808 .. 9223372036854775807;
...
Possibly, an ada test-case could be created that exercises this in isolation.

The problem is here in int_string, where we negate a val with type LONGEST:
...
         return decimal2str ("-", -val, width);
...

Fix this by, as recommend, using "-(ULONGEST)val" instead.

Tested on x86_64-linux.
---
 gdbsupport/print-utils.cc | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/gdbsupport/print-utils.cc b/gdbsupport/print-utils.cc
index 73ff1afda30..7bbb6deea74 100644
--- a/gdbsupport/print-utils.cc
+++ b/gdbsupport/print-utils.cc
@@ -278,7 +278,11 @@ int_string (LONGEST val, int radix, int is_signed, int width,
     case 10:
       {
 	if (is_signed && val < 0)
-	  return decimal2str ("-", -val, width);
+	  /* Cast to unsigned before negating, to prevent runtime error:
+	     negation of -9223372036854775808 cannot be represented in type
+	     'long int'; cast to an unsigned type to negate this value to
+	     itself.  */
+	  return decimal2str ("-", -(ULONGEST)val, width);
 	else
 	  return decimal2str ("", val, width);
       }
-- 
2.35.3