Re: [Qemu-devel] [PATCH v2 5/8] hw: arm: Convert the RSDP build to the buid_append_foo() API

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 29 Nov 2018 14:24:25 +0100
Samuel Ortiz <sameo@linux.intel.com> wrote:

> Instead of filling a mapped and packed C structure field in random order
> and being careful about endianness and sizes, build_rsdp() now uses
> build_append_int_noprefix() to compose RSDP table.
> 
> This makes for an easier to review and maintain code that is almost
> matching 1:1 the ACPI spec itself.
nit if you happen to respin:
 This makes review and maintaining code easier and ..

> Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
> ---
>  hw/arm/virt-acpi-build.c | 42 +++++++++++++++++++++-------------------
>  1 file changed, 22 insertions(+), 20 deletions(-)
> 
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index ce8bfa5a37..4782aea4fe 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -368,35 +368,37 @@ static void acpi_dsdt_add_power_button(Aml *scope)
>  
>  /* RSDP */
>  static void
> -build_rsdp(GArray *rsdp_table, BIOSLinker *linker, AcpiRsdpData *rsdp_data)
> +build_rsdp(GArray *tbl, BIOSLinker *linker, AcpiRsdpData *rsdp_data)
>  {
> -    AcpiRsdpDescriptor *rsdp = acpi_data_push(rsdp_table, sizeof *rsdp);
> -    unsigned xsdt_pa_size = sizeof(rsdp->xsdt_physical_address);
> -    unsigned xsdt_pa_offset =
> -        (char *)&rsdp->xsdt_physical_address - rsdp_table->data;
> -
> -    bios_linker_loader_alloc(linker, ACPI_BUILD_RSDP_FILE, rsdp_table, 16,
> +    bios_linker_loader_alloc(linker, ACPI_BUILD_RSDP_FILE, tbl, 16,
>                               true /* fseg memory */);
>  
> -    memcpy(&rsdp->signature, "RSD PTR ", sizeof(rsdp->signature));
> -    memcpy(rsdp->oem_id, rsdp_data->oem_id, sizeof(rsdp->oem_id));
> -    rsdp->length = cpu_to_le32(sizeof(*rsdp));
> -    rsdp->revision = rsdp_data->revision;
> +    g_array_append_vals(tbl, "RSD PTR ", 8); /* Signature */
> +    build_append_int_noprefix(tbl, 0, 1); /* Checksum */
> +    g_array_append_vals(tbl, rsdp_data->oem_id, 6); /* OEMID */
> +    build_append_int_noprefix(tbl, rsdp_data->revision, 1); /* Revision */
> +    build_append_int_noprefix(tbl, 0, 4); /* RsdtAddress */
> +    build_append_int_noprefix(tbl, 36, 4); /* Length */
>  
> -    /* Address to be filled by Guest linker */
> -    bios_linker_loader_add_pointer(linker,
> -        ACPI_BUILD_RSDP_FILE, xsdt_pa_offset, xsdt_pa_size,
> -        ACPI_BUILD_TABLE_FILE, *rsdp_data->xsdt_tbl_offset);
> +    /* XSDT address to be filled by guest linker */
> +    build_append_int_noprefix(tbl, 0, 8); /* XsdtAddress */
> +    bios_linker_loader_add_pointer(linker, ACPI_BUILD_RSDP_FILE,
> +                                   24, 8,
> +                                   ACPI_BUILD_TABLE_FILE,
> +                                   *rsdp_data->xsdt_tbl_offset);
>  
> -    /* Checksum to be filled by Guest linker */
> +    build_append_int_noprefix(tbl, 0, 1); /* Extended Checksum */
> +    build_append_int_noprefix(tbl, 0, 3); /* Reserved */
> +
> +    /* Checksum to be filled by guest linker */
>      bios_linker_loader_add_checksum(linker, ACPI_BUILD_RSDP_FILE,
> -        (char *)rsdp - rsdp_table->data, 20 /* ACPI rev 1.0 RSDP size */,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
this is always 0 with all current users and you a replacing it with 0
constant. That's fine but that assumes that above condition stays always true.
I'd add assert at the beginning of function to make sure that
tbl length is 0
or as an alternative
 build_rsdp(...)
 {
   start_off = tbl->len;
   ...
   bios_linker_loader_add_checksum(linker, ACPI_BUILD_RSDP_FILE, start_off, 20 ...

so it won't explode even if RSDP isn't at the beginning of file.
If you go for the later than bios_linker_loader_add_pointer() will also need similar treatment

> -        (char *)&rsdp->checksum - rsdp_table->data);
> +                                    0, 20, /* ACPI rev 1.0 RSDP size */
> +                                    8);
>  
>      /* Extended checksum to be filled by Guest linker */
>      bios_linker_loader_add_checksum(linker, ACPI_BUILD_RSDP_FILE,
> -        (char *)rsdp - rsdp_table->data, 36 /* ACPI rev 2.0 RSDP size */,
> -        (char *)&rsdp->extended_checksum - rsdp_table->data);
> +                                    0, 36, /* ACPI rev 2.0 RSDP size */
> +                                    32);
>  }
>  
>  static void