Hello Rouven,
On 9/21/19 9:47 AM, Rouven Czerwinski wrote:
> Hi Ahmad,
>
> On Fri, 2019-09-20 at 09:58 +0200, Ahmad Fatoum wrote:
>> The __ubsan_handle_shift_out_of_bounds handler would be called for
>> code
>> shifting a one into the sign bit like (1 << 31), which is all too
>> common
>> in barebox. It's technically UB, but it's so prevalent that it's
>> highly
>> unlikely to be treated by a compiler as anything else than the
>> standard-compliant (1U << 31).
>>
>> Check for this case here and ignore it selectively.
>
> Shouldn't we rather fix the the (1 << 31) to be (1U <<31)?
Well, we could of course convert all bitwise operations to act on unsigned
integers or to use the BIT() macro, but that's possibly thousands of instances.
A very tedious work I'd rather not be doing... :D
>
>> Signed-off-by: Ahmad Fatoum <ahmad@xxxxxx>
>> ---
>> lib/ubsan.c | 20 ++++++++++++++++++++
>> 1 file changed, 20 insertions(+)
>>
>> diff --git a/lib/ubsan.c b/lib/ubsan.c
>> index 89ca6e580bce..41a5731dda66 100644
>> --- a/lib/ubsan.c
>> +++ b/lib/ubsan.c
>> @@ -382,6 +382,26 @@ void __ubsan_handle_shift_out_of_bounds(struct
>> shift_out_of_bounds_data *data,
>> if (suppress_report(&data->location))
>> return;
>>
>> + /* This handler would be called for code shifting a one into
>> the
>> + * sign bit like (1 << 31), which is all too common in barebox.
>> + * It's technically UB, but it's so prevalent that it's highly
>> + * unlikely to be treated by a compiler as anything else than
>> the
>> + * standard-compliant (1U << 31). Thus check for this case here
>> + * and ignore it selectively
>> + */
>> + if (type_is_signed(lhs_type)) {
>> + s_max lhs_int, rhs_int;
>> +
>> + lhs_int = get_signed_val(lhs_type, lhs);
>> + rhs_int = get_signed_val(rhs_type, rhs);
>> +
>> + if (fls(lhs_int) + rhs_int == type_bit_width(lhs_type))
>> {
>> + pr_debug("signed left shift of %lld by %lld
>> ignored.\n",
>> + (s64)lhs_int, (s64)rhs_int);
>> + return;
>> + }
>> + }
>> +
>> ubsan_prologue(&data->location, &flags);
>>
>> val_to_string(rhs_str, sizeof(rhs_str), rhs_type, rhs);
>
> - rcz
>
>
> _______________________________________________
> barebox mailing list
> barebox@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/barebox
>
--
Pengutronix e.K. | |
Industrial Linux Solutions | http://www.pengutronix.de/ |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
_______________________________________________
barebox mailing list
barebox@xxxxxxxxxxxxxxxxxxx
http://lists.infradead.org/mailman/listinfo/barebox
