xen/arm: Fix MISRA regression on R1.1, flexible array member not at the end

Commit 2209c1e35b ("xen/arm: Introduce a generic way to access memory
bank structures") introduced a MISRA regression for Rule 1.1 because a
flexible array member is introduced in the middle of a struct, furthermore
this is using a GCC extension that is going to be deprecated in GCC 14 and
a warning to identify such cases will be present
(-Wflex-array-member-not-at-end) to identify such cases.

In order to fix this issue, use the macro __struct_group to create a
structure 'struct membanks_hdr' which will hold the common data among
structures using the 'struct membanks' interface.

Modify the 'struct shared_meminfo' and 'struct meminfo' to use this new
structure, effectively removing the flexible array member from the middle
of the structure and modify the code accessing the .common field to use
the macro container_of to maintain the functionality of the interface.

Given this change, container_of needs to be supplied with a type and so
the macro 'kernel_info_get_mem' inside arm/include/asm/kernel.h can't be
an option since it uses const and non-const types for struct membanks, so
introduce two static inline, one of which will keep the const qualifier.

Given the complexity of the interface, which carries a lot of benefit but
on the other hand could be prone to developer confusion if the access is
open-coded, introduce two static inline helper for the
'struct kernel_info' .shm_mem member and get rid the open-coding
shm_mem.common access.

Fixes: 2209c1e35b ("xen/arm: Introduce a generic way to access memory bank structures")
Reported-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>

xen/arch/arm/acpi/domain_build.c

@@ -451,7 +451,7 @@ static int __init estimate_acpi_efi_size(struct domain *d,
     struct acpi_table_rsdp *rsdp_tbl;
     struct acpi_table_header *table;
 
-    efi_size = estimate_efi_size(kernel_info_get_mem(kinfo)->nr_banks);
+    efi_size = estimate_efi_size(kernel_info_get_mem_const(kinfo)->nr_banks);
 
     acpi_size = ROUNDUP(sizeof(struct acpi_table_fadt), 8);
     acpi_size += ROUNDUP(sizeof(struct acpi_table_stao), 8);

xen/arch/arm/domain_build.c

@@ -805,7 +805,7 @@ int __init make_memory_node(const struct kernel_info *kinfo, int addrcells,
      * static shared memory banks need to be listed as /memory node, so when
      * this function is handling the normal memory, add the banks.
      */
-    if ( mem == kernel_info_get_mem(kinfo) )
+    if ( mem == kernel_info_get_mem_const(kinfo) )
         shm_mem_node_fill_reg_range(kinfo, reg, &nr_cells, addrcells,
                                     sizecells);
 
@@ -884,7 +884,7 @@ static int __init find_unallocated_memory(const struct kernel_info *kinfo,
 {
     const struct membanks *mem = bootinfo_get_mem();
     const struct membanks *mem_banks[] = {
-        kernel_info_get_mem(kinfo),
+        kernel_info_get_mem_const(kinfo),
         bootinfo_get_reserved_mem(),
 #ifdef CONFIG_STATIC_SHM
         bootinfo_get_shmem(),
@@ -1108,7 +1108,7 @@ static int __init find_domU_holes(const struct kernel_info *kinfo,
     uint64_t bankend;
     const uint64_t bankbase[] = GUEST_RAM_BANK_BASES;
     const uint64_t banksize[] = GUEST_RAM_BANK_SIZES;
-    const struct membanks *kinfo_mem = kernel_info_get_mem(kinfo);
+    const struct membanks *kinfo_mem = kernel_info_get_mem_const(kinfo);
     int res = -ENOENT;
 
     for ( i = 0; i < GUEST_RAM_BANKS; i++ )

xen/arch/arm/include/asm/kernel.h

@@ -80,7 +80,16 @@ struct kernel_info {
     };
 };
 
-#define kernel_info_get_mem(kinfo) (&(kinfo)->mem.common)
+static inline struct membanks *kernel_info_get_mem(struct kernel_info *kinfo)
+{
+    return container_of(&kinfo->mem.common, struct membanks, common);
+}
+
+static inline const struct membanks *
+kernel_info_get_mem_const(const struct kernel_info *kinfo)
+{
+    return container_of(&kinfo->mem.common, const struct membanks, common);
+}
 
 #ifdef CONFIG_STATIC_SHM
 #define KERNEL_INFO_SHM_MEM_INIT .shm_mem.common.max_banks = NR_SHMEM_BANKS,

xen/arch/arm/include/asm/setup.h

@@ -64,18 +64,20 @@ struct membank {
 };
 
 struct membanks {
-    unsigned int nr_banks;
-    unsigned int max_banks;
+    __struct_group(membanks_hdr, common, ,
+        unsigned int nr_banks;
+        unsigned int max_banks;
+    );
     struct membank bank[];
 };
 
 struct meminfo {
-    struct membanks common;
+    struct membanks_hdr common;
     struct membank bank[NR_MEM_BANKS];
 };
 
 struct shared_meminfo {
-    struct membanks common;
+    struct membanks_hdr common;
     struct membank bank[NR_SHMEM_BANKS];
     struct shmem_membank_extra extra[NR_SHMEM_BANKS];
 };
@@ -166,25 +168,25 @@ extern domid_t max_init_domid;
 
 static inline struct membanks *bootinfo_get_mem(void)
 {
-    return &bootinfo.mem.common;
+    return container_of(&bootinfo.mem.common, struct membanks, common);
 }
 
 static inline struct membanks *bootinfo_get_reserved_mem(void)
 {
-    return &bootinfo.reserved_mem.common;
+    return container_of(&bootinfo.reserved_mem.common, struct membanks, common);
 }
 
 #ifdef CONFIG_ACPI
 static inline struct membanks *bootinfo_get_acpi(void)
 {
-    return &bootinfo.acpi.common;
+    return container_of(&bootinfo.acpi.common, struct membanks, common);
 }
 #endif
 
 #ifdef CONFIG_STATIC_SHM
 static inline struct membanks *bootinfo_get_shmem(void)
 {
-    return &bootinfo.shmem.common;
+    return container_of(&bootinfo.shmem.common, struct membanks, common);
 }
 
 static inline struct shmem_membank_extra *bootinfo_get_shmem_extra(void)

xen/arch/arm/include/asm/static-shmem.h

@@ -45,6 +45,18 @@ int make_shm_resv_memory_node(const struct kernel_info *kinfo, int addrcells,
 void shm_mem_node_fill_reg_range(const struct kernel_info *kinfo, __be32 *reg,
                                  int *nr_cells, int addrcells, int sizecells);
 
+static inline struct membanks *
+kernel_info_get_shm_mem(struct kernel_info *kinfo)
+{
+    return container_of(&kinfo->shm_mem.common, struct membanks, common);
+}
+
+static inline const struct membanks *
+kernel_info_get_shm_mem_const(const struct kernel_info *kinfo)
+{
+    return container_of(&kinfo->shm_mem.common, const struct membanks, common);
+}
+
 #else /* !CONFIG_STATIC_SHM */
 
 /* Worst case /memory node reg element: (addrcells + sizecells) */

xen/arch/arm/static-shmem.c

@@ -172,16 +172,16 @@ static int __init assign_shared_memory(struct domain *d,
 }
 
 static int __init
-append_shm_bank_to_domain(struct shared_meminfo *kinfo_shm_mem, paddr_t start,
+append_shm_bank_to_domain(struct kernel_info *kinfo, paddr_t start,
                           paddr_t size, const char *shm_id)
 {
-    struct membanks *shm_mem = &kinfo_shm_mem->common;
+    struct membanks *shm_mem = kernel_info_get_shm_mem(kinfo);
     struct shmem_membank_extra *shm_mem_extra;
 
     if ( shm_mem->nr_banks >= shm_mem->max_banks )
         return -ENOMEM;
 
-    shm_mem_extra = &kinfo_shm_mem->extra[shm_mem->nr_banks];
+    shm_mem_extra = &kinfo->shm_mem.extra[shm_mem->nr_banks];
 
     shm_mem->bank[shm_mem->nr_banks].start = start;
     shm_mem->bank[shm_mem->nr_banks].size = size;
@@ -289,8 +289,7 @@ int __init process_shm(struct domain *d, struct kernel_info *kinfo,
          * Record static shared memory region info for later setting
          * up shm-node in guest device tree.
          */
-        ret = append_shm_bank_to_domain(&kinfo->shm_mem, gbase, psize,
-                                        shm_id);
+        ret = append_shm_bank_to_domain(kinfo, gbase, psize, shm_id);
         if ( ret )
             return ret;
     }
@@ -301,7 +300,7 @@ int __init process_shm(struct domain *d, struct kernel_info *kinfo,
 int __init make_shm_resv_memory_node(const struct kernel_info *kinfo,
                                      int addrcells, int sizecells)
 {
-    const struct membanks *mem = &kinfo->shm_mem.common;
+    const struct membanks *mem = kernel_info_get_shm_mem_const(kinfo);
     void *fdt = kinfo->fdt;
     unsigned int i = 0;
     int res = 0;
@@ -517,7 +516,7 @@ int __init process_shm_node(const void *fdt, int node, uint32_t address_cells,
 int __init make_resv_memory_node(const struct kernel_info *kinfo, int addrcells,
                                  int sizecells)
 {
-    const struct membanks *mem = &kinfo->shm_mem.common;
+    const struct membanks *mem = kernel_info_get_shm_mem_const(kinfo);
     void *fdt = kinfo->fdt;
     int res = 0;
     /* Placeholder for reserved-memory\0 */
@@ -579,7 +578,7 @@ void __init init_sharedmem_pages(void)
 int __init remove_shm_from_rangeset(const struct kernel_info *kinfo,
                                     struct rangeset *rangeset)
 {
-    const struct membanks *shm_mem = &kinfo->shm_mem.common;
+    const struct membanks *shm_mem = kernel_info_get_shm_mem_const(kinfo);
     unsigned int i;
 
     /* Remove static shared memory regions */
@@ -607,7 +606,7 @@ int __init remove_shm_from_rangeset(const struct kernel_info *kinfo,
 int __init remove_shm_holes_for_domU(const struct kernel_info *kinfo,
                                      struct membanks *ext_regions)
 {
-    const struct membanks *shm_mem = &kinfo->shm_mem.common;
+    const struct membanks *shm_mem = kernel_info_get_shm_mem_const(kinfo);
     struct rangeset *guest_holes;
     unsigned int i;
     paddr_t start;
@@ -673,7 +672,7 @@ void __init shm_mem_node_fill_reg_range(const struct kernel_info *kinfo,
                                         __be32 *reg, int *nr_cells,
                                         int addrcells, int sizecells)
 {
-    const struct membanks *mem = &kinfo->shm_mem.common;
+    const struct membanks *mem = kernel_info_get_shm_mem_const(kinfo);
     unsigned int i;
     __be32 *cells;