Re: [Qemu-devel] [PATCH] hw/ide/ahci.c: Fix shift left into sign bit

[John Snow]

On 10/16/2015 01:48 PM, Peter Maydell wrote:
> Avoid undefined behaviour from shifting left into the sign bit:
> 
> hw/ide/ahci.c:551:36: runtime error: left shift of 255 by 24 places cannot be 
> represented in type 'int'
> 
> (Unfortunately C's promotion rules mean that in the expression
> "some_uint8_t_variable << 24" the LHS gets promoted to signed
> int before shifting.)
> 
> Signed-off-by: Peter Maydell <address@hidden>
> ---
> clang's undefined sanitizer produces a lot of copies of this warning during
> 'make check'...
> 
>  hw/ide/ahci.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/ide/ahci.c b/hw/ide/ahci.c
> index 796be15..21f76ed 100644
> --- a/hw/ide/ahci.c
> +++ b/hw/ide/ahci.c
> @@ -548,7 +548,7 @@ static void ahci_init_d2h(AHCIDevice *ad)
>          ad->init_d2h_sent = true;
>          /* We're emulating receiving the first Reg H2D Fis from the device;
>           * Update the SIG register, but otherwise proceed as normal. */
> -        pr->sig = (ide_state->hcyl << 24) |
> +        pr->sig = ((uint32_t)ide_state->hcyl << 24) |
>              (ide_state->lcyl << 16) |
>              (ide_state->sector << 8) |
>              (ide_state->nsector & 0xFF);
> 

Reviewed-by: John Snow <address@hidden>

Since the "patches" tool seems to still be hiccuping, do you want to
just apply this directly?

--js