Re: [Xen-devel] [PATCH v3] xen/arm: build as zImage

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 27 Nov 2012, Stefano Stabellini wrote:
> +     .word (_end - _start)        /* zImage end address */

Actually the assembler has problems digesting this expression.
This patch actually compiles:

---

xen/arm: build as zImage

The zImage format is extremely simple: it only consists of a magic
number and 2 addresses in a specific position (see
http://www.simtec.co.uk/products/SWLINUX/files/booting_article.html#d0e309).

Some bootloaders expect a zImage; considering that it doesn't cost us
much to build Xen compatible with the format, make it so.

Changes in v3:
- pass the correct size;
- go back to the original no-ops plus branch for consistency with Linux.

Changes in v2:
- code style;
- pass 0 a start address.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

diff --git a/xen/arch/arm/head.S b/xen/arch/arm/head.S
index 25c4cfe..6cb5d1b 100644
--- a/xen/arch/arm/head.S
+++ b/xen/arch/arm/head.S
@@ -22,6 +22,8 @@
 #include <asm/processor-ca15.h>
 #include <asm/asm_defns.h>
 
+#define ZIMAGE_MAGIC_NUMBER 0x016f2818
+
 #define PT_PT  0xe7f /* nG=1, AF=1, SH=10, AP=01, NS=1, ATTR=111, T=1, P=1 */
 #define PT_MEM 0xe7d /* nG=1, AF=1, SH=10, AP=01, NS=1, ATTR=111, T=0, P=1 */
 #define PT_DEV 0xe71 /* nG=1, AF=1, SH=10, AP=01, NS=1, ATTR=100, T=0, P=1 */
@@ -52,6 +54,22 @@
         * or the initial pagetable code below will need adjustment. */
        .global start
 start:
+
+       /* zImage magic header, see:
+        * 
http://www.simtec.co.uk/products/SWLINUX/files/booting_article.html#d0e309
+        */
+       .rept 7
+       mov   r0, r0
+       .endr
+       mov   r0, r0
+       b     past_zImage
+
+       .word ZIMAGE_MAGIC_NUMBER    /* Magic numbers to help the loader */
+       .word 0x00000000             /* absolute load/run zImage address or
+                                     * 0 for PiC */
+       .word (_end - start)         /* zImage end address */
+
+past_zImage:
        cpsid aif                    /* Disable all interrupts */
 
        /* Save the bootloader arguments in less-clobberable registers */

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