[committed][PATCH 1/2] [gdb/exp] Fix UB in scalar_binop

[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 -q -batch -ex "p -(-0x7fffffffffffffff - 1)"
> src/gdb/valarith.c:1385:10: runtime error: signed integer overflow: \
>    0 - -9223372036854775808 cannot be represented in type 'long int'
> $1 = -9223372036854775808
> ...
> 
> Fix this by performing the substraction in scalar_binop using unsigned types.
> 
> Tested on x86_64-linux.

Committed.

Thanks,
- Tom

> ---
>   gdb/testsuite/gdb.base/arithmet.exp | 2 ++
>   gdb/valarith.c                      | 5 ++++-
>   2 files changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/testsuite/gdb.base/arithmet.exp b/gdb/testsuite/gdb.base/arithmet.exp
> index b6009a36235..4905c2e2706 100644
> --- a/gdb/testsuite/gdb.base/arithmet.exp
> +++ b/gdb/testsuite/gdb.base/arithmet.exp
> @@ -98,3 +98,5 @@ gdb_test "print x-(y+w)"  "3"
>   gdb_test "print x/(y*w)"  "0"
>   gdb_test "print x-(y/w)"  "9"
>   gdb_test "print (x+y)*w" "42"
> +
> +gdb_test "p /x -(-0x7fffffffffffffff - 1)" " = 0x8000000000000000"
> diff --git a/gdb/valarith.c b/gdb/valarith.c
> index 6210267826e..526cc02599e 100644
> --- a/gdb/valarith.c
> +++ b/gdb/valarith.c
> @@ -1382,7 +1382,10 @@ scalar_binop (struct value *arg1, struct value *arg2, enum exp_opcode op)
>   	      break;
>   
>   	    case BINOP_SUB:
> -	      v = v1 - v2;
> +	      /* Avoid runtime error: signed integer overflow: \
> +		 0 - -9223372036854775808 cannot be represented in type
> +		 'long int'.  */
> +	      v = (ULONGEST)v1 - (ULONGEST)v2;
>   	      break;
>   
>   	    case BINOP_MUL:
> 
> base-commit: a1f2ddd38378c8db63e75daa28b7e304c2fd774f