Re: [Xen-devel] [PATCH] libxl/arm: Fix build on arm64 + acpi w/ gcc 8.2

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Tue, 14 Aug 2018, Christopher Clark wrote:
> Add zero-padding to #defined ACPI table strings that are copied. 
> Provides sufficient characters to satisfy the length required to
> fully populate the destination and prevent array-bounds warnings.
> 
> Signed-off-by: Christopher Clark <christopher.clark6@xxxxxxxxxxxxxx>
> ---
> 
> Please add this patch to the backport list for the next minor 4.11
> release.
> 
> Prior to this: gcc 8.2 objects to memcpy past bounds:
> 
> | libxl_arm_acpi.c: In function 'make_acpi_header':
> | libxl_arm_acpi.c:208:5: error: 'memcpy' forming offset [5, 6] is out
> of the bounds [0, 4] [-Werror=array-bounds]
> |      memcpy(h->oem_id, ACPI_OEM_ID, sizeof(h->oem_id));
> |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> | libxl_arm_acpi.c:209:5: error: 'memcpy' forming offset [5, 8] is out
> of the bounds [0, 4] [-Werror=array-bounds]
> |      memcpy(h->oem_table_id, ACPI_OEM_TABLE_ID,
> sizeof(h->oem_table_id));
> |
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> | libxl_arm_acpi.c:211:5: error: 'memcpy' forming offset 4 is out of the
> bounds [0, 3] [-Werror=array-bounds]
> |      memcpy(h->asl_compiler_id, ACPI_ASL_COMPILER_ID,
> |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> |             sizeof(h->asl_compiler_id));
> |             ~~~~~~~~~~~~~~~~~~~~~~~~~~~
> | In function 'make_acpi_rsdp.isra.4',
> |     inlined from 'libxl__prepare_acpi' at libxl_arm_acpi.c:389:5:
> | libxl_arm_acpi.c:193:5: error: 'memcpy' forming offset [5, 6] is out
> of the bounds [0, 4] [-Werror=array-bounds]
> |      memcpy(rsdp->oem_id, ACPI_OEM_ID, sizeof(rsdp->oem_id));
> |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>  tools/libxl/libxl_arm_acpi.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/libxl/libxl_arm_acpi.c b/tools/libxl/libxl_arm_acpi.c
> index 636f724..eeca1de 100644
> --- a/tools/libxl/libxl_arm_acpi.c
> +++ b/tools/libxl/libxl_arm_acpi.c
> @@ -48,9 +48,9 @@ extern const unsigned char dsdt_anycpu_arm[];
>  _hidden
>  extern const int dsdt_anycpu_arm_len;
>  
> -#define ACPI_OEM_ID "Xen"
> -#define ACPI_OEM_TABLE_ID "ARM"
> -#define ACPI_ASL_COMPILER_ID "XL"
> +#define ACPI_OEM_ID "Xen\0\0"
> +#define ACPI_OEM_TABLE_ID "ARM\0\0\0\0"
> +#define ACPI_ASL_COMPILER_ID "XL\0"
>  
>  enum {
>      RSDP,

Thank you for the patch! These changes should fix the errors.
Alternatively, changing the three memcpy's in the following way would
also work:

  memcpy(rsdp->oem_id, ACPI_OEM_ID, sizeof(ACPI_OEM_ID));

I don't have an opinion on which way is best so:

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

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