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

[Tom de Vries <tdevries@suse.de>]

On 5/17/22 17:40, Tom de Vries via Gdb-patches wrote:
> 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.

Committed.

Thanks,
- Tom

> ---
>   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);
>         }