[PATCH] i386: Restore CONFIG_PHYSICAL_START option

o Relocatable bzImage support had got rid of CONFIG_PHYSICAL_START option
  thinking that now this option is not required as people can build a
  second kernel as relocatable and load it anywhere. So need of compiling
  the kernel for a custom address was gone. But Magnus uses vmlinux images
  for second kernel in Xen environment and he wants to continue to use
  it.

o Restoring the CONFIG_PHYSICAL_START option for the time being. I think
  down the line we can get rid of it.

Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 43 insertions, 1 deletions

diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
index 0d67a0a115..0dfee81281 100644
--- a/arch/i386/Kconfig
+++ b/arch/i386/Kconfig
@@ -777,6 +777,47 @@ config CRASH_DUMP
           PHYSICAL_START.
           For more details see Documentation/kdump/kdump.txt
 
+config PHYSICAL_START
+        hex "Physical address where the kernel is loaded" if (EMBEDDED || CRASH_DUMP)
+        default "0x100000"
+        help
+          This gives the physical address where the kernel is loaded.
+
+          If kernel is a not relocatable (CONFIG_RELOCATABLE=n) then
+          bzImage will decompress itself to above physical address and
+          run from there. Otherwise, bzImage will run from the address where
+          it has been loaded by the boot loader and will ignore above physical
+          address.
+
+          In normal kdump cases one does not have to set/change this option
+          as now bzImage can be compiled as a completely relocatable image
+          (CONFIG_RELOCATABLE=y) and be used to load and run from a different
+          address. This option is mainly useful for the folks who don't want
+          to use a bzImage for capturing the crash dump and want to use a
+          vmlinux instead. vmlinux is not relocatable hence a kernel needs
+          to be specifically compiled to run from a specific memory area
+          (normally a reserved region) and this option comes handy.
+
+          So if you are using bzImage for capturing the crash dump, leave
+          the value here unchanged to 0x100000 and set CONFIG_RELOCATABLE=y.
+          Otherwise if you plan to use vmlinux for capturing the crash dump
+          change this value to start of the reserved region (Typically 16MB
+          0x1000000). In other words, it can be set based on the "X" value as
+          specified in the "crashkernel=YM@XM" command line boot parameter
+          passed to the panic-ed kernel. Typically this parameter is set as
+          crashkernel=64M@16M. Please take a look at
+          Documentation/kdump/kdump.txt for more details about crash dumps.
+
+          Usage of bzImage for capturing the crash dump is recommended as
+          one does not have to build two kernels. Same kernel can be used
+          as production kernel and capture kernel. Above option should have
+          gone away after relocatable bzImage support is introduced. But it
+          is present because there are users out there who continue to use
+          vmlinux for dump capture. This option should go away down the
+          line.
+
+          Don't change this unless you know what you are doing.
+
 config RELOCATABLE
         bool "Build a relocatable kernel(EXPERIMENTAL)"
         depends on EXPERIMENTAL
diff --git a/include/asm-i386/boot.h b/include/asm-i386/boot.h
index 8ce79a6fa8..e7686d0a84 100644
--- a/include/asm-i386/boot.h
+++ b/include/asm-i386/boot.h
@@ -13,7 +13,8 @@
 #define ASK_VGA         0xfffd          /* ask for it at bootup */
 
 /* Physical address where kenrel should be loaded. */
-#define LOAD_PHYSICAL_ADDR ((0x100000 + CONFIG_PHYSICAL_ALIGN - 1) \
+#define LOAD_PHYSICAL_ADDR ((CONFIG_PHYSICAL_START \
+                                + (CONFIG_PHYSICAL_ALIGN - 1)) \
                                 & ~(CONFIG_PHYSICAL_ALIGN - 1))
 
 #endif /* _LINUX_BOOT_H */