arm: boot: Support big-endian elfs

Support ARM big-endian ELF files in system-mode emulation. When loading
an elf, determine the endianness mode expected by the elf, and set the
relevant CPU state accordingly.

With this, big-endian modes are now fully supported via system-mode LE,
so there is no need to restrict the elf loading to the TARGET
endianness so the ifdeffery on TARGET_WORDS_BIGENDIAN goes away.

Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: fix typo in comments]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/arm/boot.c

@@ -518,9 +518,34 @@ static void do_cpu_reset(void *opaque)
     cpu_reset(cs);
     if (info) {
         if (!info->is_linux) {
+            int i;
             /* Jump to the entry point.  */
             uint64_t entry = info->entry;
 
+            switch (info->endianness) {
+            case ARM_ENDIANNESS_LE:
+                env->cp15.sctlr_el[1] &= ~SCTLR_E0E;
+                for (i = 1; i < 4; ++i) {
+                    env->cp15.sctlr_el[i] &= ~SCTLR_EE;
+                }
+                env->uncached_cpsr &= ~CPSR_E;
+                break;
+            case ARM_ENDIANNESS_BE8:
+                env->cp15.sctlr_el[1] |= SCTLR_E0E;
+                for (i = 1; i < 4; ++i) {
+                    env->cp15.sctlr_el[i] |= SCTLR_EE;
+                }
+                env->uncached_cpsr |= CPSR_E;
+                break;
+            case ARM_ENDIANNESS_BE32:
+                env->cp15.sctlr_el[1] |= SCTLR_B;
+                break;
+            case ARM_ENDIANNESS_UNKNOWN:
+                break; /* Board's decision */
+            default:
+                g_assert_not_reached();
+            }
+
             if (!env->aarch64) {
                 env->thumb = info->entry & 1;
                 entry &= 0xfffffffe;
@@ -638,6 +663,62 @@ static int do_arm_linux_init(Object *obj, void *opaque)
     return 0;
 }
 
+static uint64_t arm_load_elf(struct arm_boot_info *info, uint64_t *pentry,
+                             uint64_t *lowaddr, uint64_t *highaddr,
+                             int elf_machine)
+{
+    bool elf_is64;
+    union {
+        Elf32_Ehdr h32;
+        Elf64_Ehdr h64;
+    } elf_header;
+    int data_swab = 0;
+    bool big_endian;
+    uint64_t ret = -1;
+    Error *err = NULL;
+
+
+    load_elf_hdr(info->kernel_filename, &elf_header, &elf_is64, &err);
+    if (err) {
+        return ret;
+    }
+
+    if (elf_is64) {
+        big_endian = elf_header.h64.e_ident[EI_DATA] == ELFDATA2MSB;
+        info->endianness = big_endian ? ARM_ENDIANNESS_BE8
+                                      : ARM_ENDIANNESS_LE;
+    } else {
+        big_endian = elf_header.h32.e_ident[EI_DATA] == ELFDATA2MSB;
+        if (big_endian) {
+            if (bswap32(elf_header.h32.e_flags) & EF_ARM_BE8) {
+                info->endianness = ARM_ENDIANNESS_BE8;
+            } else {
+                info->endianness = ARM_ENDIANNESS_BE32;
+                /* In BE32, the CPU has a different view of the per-byte
+                 * address map than the rest of the system. BE32 ELF files
+                 * are organised such that they can be programmed through
+                 * the CPU's per-word byte-reversed view of the world. QEMU
+                 * however loads ELF files independently of the CPU. So
+                 * tell the ELF loader to byte reverse the data for us.
+                 */
+                data_swab = 2;
+            }
+        } else {
+            info->endianness = ARM_ENDIANNESS_LE;
+        }
+    }
+
+    ret = load_elf(info->kernel_filename, NULL, NULL,
+                   pentry, lowaddr, highaddr, big_endian, elf_machine,
+                   1, data_swab);
+    if (ret <= 0) {
+        /* The header loaded but the image didn't */
+        exit(1);
+    }
+
+    return ret;
+}
+
 static void arm_load_kernel_notify(Notifier *notifier, void *data)
 {
     CPUState *cs;
@@ -647,7 +728,6 @@ static void arm_load_kernel_notify(Notifier *notifier, void *data)
     uint64_t elf_entry, elf_low_addr, elf_high_addr;
     int elf_machine;
     hwaddr entry, kernel_load_offset;
-    int big_endian;
     static const ARMInsnFixup *primary_loader;
     ArmLoadKernelNotifier *n = DO_UPCAST(ArmLoadKernelNotifier,
                                          notifier, notifier);
@@ -733,12 +813,6 @@ static void arm_load_kernel_notify(Notifier *notifier, void *data)
     if (info->nb_cpus == 0)
         info->nb_cpus = 1;
 
-#ifdef TARGET_WORDS_BIGENDIAN
-    big_endian = 1;
-#else
-    big_endian = 0;
-#endif
-
     /* We want to put the initrd far enough into RAM that when the
      * kernel is uncompressed it will not clobber the initrd. However
      * on boards without much RAM we must ensure that we still leave
@@ -753,9 +827,8 @@ static void arm_load_kernel_notify(Notifier *notifier, void *data)
         MIN(info->ram_size / 2, 128 * 1024 * 1024);
 
     /* Assume that raw images are linux kernels, and ELF images are not.  */
-    kernel_size = load_elf(info->kernel_filename, NULL, NULL, &elf_entry,
+    kernel_size = arm_load_elf(info, &elf_entry, &elf_low_addr,
-                           &elf_low_addr, &elf_high_addr, big_endian,
+                               &elf_high_addr, elf_machine);
-                           elf_machine, 1, 0);
     if (kernel_size > 0 && have_dtb(info)) {
         /* If there is still some room left at the base of RAM, try and put
          * the DTB there like we do for images loaded with -bios or -pflash.

include/hw/arm/arm.h

@@ -16,6 +16,13 @@
 #include "qemu/notify.h"
 #include "cpu.h"
 
+typedef enum {
+    ARM_ENDIANNESS_UNKNOWN = 0,
+    ARM_ENDIANNESS_LE,
+    ARM_ENDIANNESS_BE8,
+    ARM_ENDIANNESS_BE32,
+} arm_endianness;
+
 /* armv7m.c */
 DeviceState *armv7m_init(MemoryRegion *system_memory, int mem_size, int num_irq,
                       const char *kernel_filename, const char *cpu_model);
@@ -103,6 +110,8 @@ struct arm_boot_info {
      * changing to non-secure state if implementing a non-secure boot
      */
     bool secure_board_setup;
+
+    arm_endianness endianness;
 };
 
 /**