[PATCH] i386: Implement CONFIG_PHYSICAL_ALIGN

o Now CONFIG_PHYSICAL_START is being replaced with CONFIG_PHYSICAL_ALIGN.
  Hardcoding the kernel physical start value creates a problem in relocatable
  kernel context due to boot loader limitations. For ex, if somebody
  compiles a relocatable kernel to be run from address 4MB, but this kernel
  will run from location 1MB as grub loads the kernel at physical address
  1MB. Kernel thinks that I am a relocatable kernel and I should run from
  the address I have been loaded at. So somebody wanting to run kernel
  from 4MB alignment location (for improved performance regions) can't do
  that.

o Hence, Eric proposed that probably CONFIG_PHYSICAL_ALIGN will make
  more sense in relocatable kernel context. At run time kernel will move
  itself to a physical addr location which meets user specified alignment
  restrictions.

Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andi Kleen <ak@suse.de>

1 files changed, 14 insertions, 12 deletions

diff --git a/arch/i386/boot/compressed/head.S b/arch/i386/boot/compressed/head.S
index e4dd7a6b9b0f..f395a4bb38bb 100644
--- a/arch/i386/boot/compressed/head.S
+++ b/arch/i386/boot/compressed/head.S
@@ -26,6 +26,7 @@
 #include <linux/linkage.h>
 #include <asm/segment.h>
 #include <asm/page.h>
+#include <asm/boot.h>
 
 .section ".text.head"
         .globl startup_32
@@ -52,17 +53,17 @@ startup_32:
 1:      popl %ebp
         subl $1b, %ebp
 
-/* Compute the delta between where we were compiled to run at
- * and where the code will actually run at.
+/* %ebp contains the address we are loaded at by the boot loader and %ebx
+ * contains the address where we should move the kernel image temporarily
+ * for safe in-place decompression.
  */
-        /* Start with the delta to where the kernel will run at.  If we are
-         * a relocatable kernel this is the delta to our load address otherwise
-         * this is the delta to CONFIG_PHYSICAL start.
-         */
+
 #ifdef CONFIG_RELOCATABLE
-        movl %ebp, %ebx
+        movl    %ebp, %ebx
+        addl    $(CONFIG_PHYSICAL_ALIGN - 1), %ebx
+        andl    $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebx
 #else
-        movl $(CONFIG_PHYSICAL_START - startup_32), %ebx
+        movl $LOAD_PHYSICAL_ADDR, %ebx
 #endif
 
         /* Replace the compressed data size with the uncompressed size */
@@ -94,9 +95,10 @@ startup_32:
 /* Compute the kernel start address.
  */
 #ifdef CONFIG_RELOCATABLE
-        leal    startup_32(%ebp), %ebp
+        addl    $(CONFIG_PHYSICAL_ALIGN - 1), %ebp
+        andl    $(~(CONFIG_PHYSICAL_ALIGN - 1)), %ebp
 #else
-        movl    $CONFIG_PHYSICAL_START, %ebp
+        movl    $LOAD_PHYSICAL_ADDR, %ebp
 #endif
 
 /*
@@ -150,8 +152,8 @@ relocated:
  * and where it was actually loaded.
  */
         movl %ebp, %ebx
-        subl $CONFIG_PHYSICAL_START, %ebx
-
+        subl $LOAD_PHYSICAL_ADDR, %ebx
+        jz   2f         /* Nothing to be done if loaded at compiled addr. */
 /*
  * Process relocations.
  */