[PATCH v2] libxl/arm: Fix build on arm64 + acpi w/ gcc 8.2

[Matt Weber <matthew.weber@rockwellcollins.com>]

From: Christopher Clark <christopher.w.clark@gmail.com>

[modified for Xen 4.11 to add required: #include <xen-tools/libs.h>]

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.
Add BUILD_BUG_ON sizeof checks for compile-time length checking.

Signed-off-by: Christopher Clark <christopher.clark6@baesystems.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Matt Weber <matthew.weber@rockwellcollins.com>
---
v2: add BUILD_BUG_ON length checks, requested by Wei.

v1: 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 | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/tools/libxl/libxl_arm_acpi.c b/tools/libxl/libxl_arm_acpi.c
index 636f724..8924396 100644
--- a/tools/libxl/libxl_arm_acpi.c
+++ b/tools/libxl/libxl_arm_acpi.c
@@ -29,6 +29,7 @@ typedef int64_t s64;
 
 #include <acpi/acconfig.h>
 #include <acpi/actbl.h>
+#include <xen-tools/libs.h>
 
 #ifndef BITS_PER_LONG
 #ifdef _LP64
@@ -48,9 +49,9 @@ 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,
@@ -190,6 +191,7 @@ static void make_acpi_rsdp(libxl__gc *gc, struct xc_dom_image *dom,
     struct acpi_table_rsdp *rsdp = (void *)dom->acpi_modules[0].data + offset;
 
     memcpy(rsdp->signature, "RSD PTR ", sizeof(rsdp->signature));
+    BUILD_BUG_ON(sizeof(ACPI_OEM_ID) != sizeof(rsdp->oem_id));
     memcpy(rsdp->oem_id, ACPI_OEM_ID, sizeof(rsdp->oem_id));
     rsdp->length = acpitables[RSDP].size;
     rsdp->revision = 0x02;
@@ -205,9 +207,12 @@ static void make_acpi_header(struct acpi_table_header *h, const char *sig,
     memcpy(h->signature, sig, 4);
     h->length = len;
     h->revision = rev;
+    BUILD_BUG_ON(sizeof(ACPI_OEM_ID) != sizeof(h->oem_id));
     memcpy(h->oem_id, ACPI_OEM_ID, sizeof(h->oem_id));
+    BUILD_BUG_ON(sizeof(ACPI_OEM_TABLE_ID) != sizeof(h->oem_table_id));
     memcpy(h->oem_table_id, ACPI_OEM_TABLE_ID, sizeof(h->oem_table_id));
     h->oem_revision = 0;
+    BUILD_BUG_ON(sizeof(ACPI_ASL_COMPILER_ID) != sizeof(h->asl_compiler_id));
     memcpy(h->asl_compiler_id, ACPI_ASL_COMPILER_ID,
            sizeof(h->asl_compiler_id));
     h->asl_compiler_revision = 0;

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