[Qemu-devel] [PATCH] arm_boot: Change initrd load address to "halfway through RAM"

[Peter Maydell <peter.maydell@linaro.org>]

To avoid continually having to bump the initrd load address
to account for larger kernel images, put the initrd halfway
through RAM. This allows large kernels on new boards with lots
of RAM to work OK, without breaking existing usecases for
boards with only 32MB of RAM.

Note that this change fixes in passing a bug where we were
passing an overly large max_size to load_image_targphys()
for the initrd, which meant that we wouldn't correctly refuse
to load an enormous initrd that didn't actually fit into RAM.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
Cole: does this fix the problems you see?

 hw/arm-misc.h |    1 +
 hw/arm_boot.c |   35 ++++++++++++++++++++---------------
 2 files changed, 21 insertions(+), 15 deletions(-)

diff --git a/hw/arm-misc.h b/hw/arm-misc.h
index d02f7f0..adb1665 100644
--- a/hw/arm-misc.h
+++ b/hw/arm-misc.h
@@ -56,6 +56,7 @@ struct arm_boot_info {
                                      const struct arm_boot_info *info);
     /* Used internally by arm_boot.c */
     int is_linux;
+    hwaddr initrd_start;
     hwaddr initrd_size;
     hwaddr entry;
 };
diff --git a/hw/arm_boot.c b/hw/arm_boot.c
index 09bf6c5..83bdf16 100644
--- a/hw/arm_boot.c
+++ b/hw/arm_boot.c
@@ -18,7 +18,6 @@
 
 #define KERNEL_ARGS_ADDR 0x100
 #define KERNEL_LOAD_ADDR 0x00010000
-#define INITRD_LOAD_ADDR 0x00d00000
 
 /* The worlds second smallest bootloader.  Set r0-r2, then jump to kernel.  */
 static uint32_t bootloader[] = {
@@ -109,7 +108,7 @@ static void set_kernel_args(const struct arm_boot_info *info)
         /* ATAG_INITRD2 */
         WRITE_WORD(p, 4);
         WRITE_WORD(p, 0x54420005);
-        WRITE_WORD(p, info->loader_start + INITRD_LOAD_ADDR);
+        WRITE_WORD(p, info->initrd_start);
         WRITE_WORD(p, initrd_size);
     }
     if (info->kernel_cmdline && *info->kernel_cmdline) {
@@ -185,10 +184,11 @@ static void set_kernel_args_old(const struct arm_boot_info *info)
     /* pages_in_vram */
     WRITE_WORD(p, 0);
     /* initrd_start */
-    if (initrd_size)
-        WRITE_WORD(p, info->loader_start + INITRD_LOAD_ADDR);
-    else
+    if (initrd_size) {
+        WRITE_WORD(p, info->initrd_start);
+    } else {
         WRITE_WORD(p, 0);
+    }
     /* initrd_size */
     WRITE_WORD(p, initrd_size);
     /* rd_start */
@@ -281,14 +281,13 @@ static int load_dtb(hwaddr addr, const struct arm_boot_info *binfo)
 
     if (binfo->initrd_size) {
         rc = qemu_devtree_setprop_cell(fdt, "/chosen", "linux,initrd-start",
-                binfo->loader_start + INITRD_LOAD_ADDR);
+                binfo->initrd_start);
         if (rc < 0) {
             fprintf(stderr, "couldn't set /chosen/linux,initrd-start\n");
         }
 
         rc = qemu_devtree_setprop_cell(fdt, "/chosen", "linux,initrd-end",
-                    binfo->loader_start + INITRD_LOAD_ADDR +
-                    binfo->initrd_size);
+                    binfo->initrd_start + binfo->initrd_size);
         if (rc < 0) {
             fprintf(stderr, "couldn't set /chosen/linux,initrd-end\n");
         }
@@ -375,6 +374,14 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info *info)
     big_endian = 0;
 #endif
 
+    /* Put the initrd halfway through RAM; this means that on
+     * most boards we will not be in danger of overlapping the
+     * initrd with the kernel, but will still work OK on models
+     * with only small amounts of RAM (which can be assumed to
+     * have correspondingly small kernels).
+     */
+    info->initrd_start = info->loader_start + (info->ram_size / 2);
+
     /* Assume that raw images are linux kernels, and ELF images are not.  */
     kernel_size = load_elf(info->kernel_filename, NULL, NULL, &elf_entry,
                            NULL, NULL, big_endian, ELF_MACHINE, 1);
@@ -398,10 +405,9 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info *info)
     if (is_linux) {
         if (info->initrd_filename) {
             initrd_size = load_image_targphys(info->initrd_filename,
-                                              info->loader_start
-                                              + INITRD_LOAD_ADDR,
-                                              info->ram_size
-                                              - INITRD_LOAD_ADDR);
+                                              info->initrd_start,
+                                              info->ram_size -
+                                              info->initrd_start);
             if (initrd_size < 0) {
                 fprintf(stderr, "qemu: could not load initrd '%s'\n",
                         info->initrd_filename);
@@ -419,9 +425,8 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info *info)
          */
         if (info->dtb_filename) {
             /* Place the DTB after the initrd in memory */
-            hwaddr dtb_start = TARGET_PAGE_ALIGN(info->loader_start
-                                                             + INITRD_LOAD_ADDR
-                                                             + initrd_size);
+            hwaddr dtb_start = TARGET_PAGE_ALIGN(info->initrd_start +
+                                                 initrd_size);
             if (load_dtb(dtb_start, info)) {
                 exit(1);
             }
-- 
1.7.9.5