[vbox-dev] Fwd: Bug report (minor)

[Frank Mehnert]

On Saturday 01 May 2010, TwoThe wrote:
> Type: Bug
> Severity: minor
> Component: VirtualBox OSE
> Host: Ubuntu 64
>
> In file src/VBox/Devices/PC/DevAPIC.cpp:
>
>    897        case 0x0d:
>    !898           val = apic->log_dest << 24;
>    899            break;
>
> In line 898 "apic->log_dest" with type "unsigned char" (8 bits, unsigned)
> is promoted in "apic->log_dest << 24" to type "int" (32 bits, signed), then
> sign-extended to type "unsigned long long" (64 bits, unsigned). If
> "apic->log_dest << 24" is greater than 0x7FFFFFFF, the upper bits of the
> result will all be 1.

Confirmed.

> The same happens in the next case:
>    900        case 0x0e:
>    901            /* Bottom 28 bits are always 1 */
>    !902           val = (apic->dest_mode << 28) | 0xfffffff;
>    903            break;
>
> In line 902 "apic->dest_mode" with type "unsigned char" (8 bits, unsigned)
> is promoted in "(apic->dest_mode << 28) | 0xfffffff" to type "int" (32
> bits, signed), then sign-extended to type "unsigned long long" (64 bits,
> unsigned). If "(apic->dest_mode << 28) | 0xfffffff" is greater than
> 0x7FFFFFFF, the upper bits of the result will all be 1.
>
> In both cases the value should be cast to the target value (unsigned long
> long) first before shifting.

Confirmed.

Kind regards,

Frank
-- 
Dr.-Ing. Frank Mehnert

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Sun Microsystems GmbH, Sonnenallee 1, 85551 Kirchheim-Heimstetten
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