Re: [Qemu-devel] [PATCH] hw/i386: Use unaligned store functions building acpi tables

[Peter Maydell]

On 12 March 2014 22:25, Richard Henderson <address@hidden> wrote:
> Hosts that don't support native unaligned stores will SIGBUS
> without additional help.
>
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  hw/i386/acpi-build.c | 29 +++++++++++++++--------------
>  1 file changed, 15 insertions(+), 14 deletions(-)
>
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index b1a7ebb..d636115 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -886,22 +886,24 @@ static void build_pci_bus_end(PCIBus *bus, void 
> *bus_state)
>
>  static void patch_pci_windows(PcPciInfo *pci, uint8_t *start, unsigned size)
>  {
> -    *ACPI_BUILD_PTR(start, size, acpi_pci32_start[0], uint32_t) =
> -        cpu_to_le32(pci->w32.begin);
> +    /* Note that these pointers are unaligned, so we must use routines
> +       that take care for unaligned stores on the host.  */
>
> -    *ACPI_BUILD_PTR(start, size, acpi_pci32_end[0], uint32_t) =
> -        cpu_to_le32(pci->w32.end - 1);
> +    stl_le_p(ACPI_BUILD_PTR(start, size, acpi_pci32_start[0], uint32_t),
> +             pci->w32.begin);
> +    stl_le_p(ACPI_BUILD_PTR(start, size, acpi_pci32_end[0], uint32_t),
> +             pci->w32.end - 1);

See the mail thread on Michael's original patch -- he didn't like
this because we end up writing the size of the store twice
(once in the "l" suffix in the function name and once by passing
a type to the ACP_BUILD_PTR function.

(That thread also has my personal preferred option in the comments,
which uses stl_le_p and friends but via a wrapping macro.)

Also you'll find this doesn't apply because a fix has already been
committed on master...

> -    *(uint16_t *)(ssdt_ptr + *ssdt_isa_pest) =
> -        cpu_to_le16(misc->pvpanic_port);
> +    stw_le_p(ssdt_ptr + *ssdt_isa_pest, misc->pvpanic_port);

Patch on list to fix this too I think.

thanks
-- PMM