x86, boot: Update comments about entries for 64bit image

Now 64bit entry is fixed on 0x200, can not be changed anymore.

Update the comments to reflect that.

Also put info about it in boot.txt

-v2: fix some grammar error

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1359058816-7615-27-git-send-email-yinghai@kernel.org
Cc: Rob Landley <rob@landley.net>
Cc: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 13 insertions, 9 deletions

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 5c80b94f6c4a..d9ae9a4ffcb9 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -37,6 +37,12 @@
         __HEAD
         .code32
 ENTRY(startup_32)
+        /*
+         * 32bit entry is 0 and it is ABI so immutable!
+         * If we come here directly from a bootloader,
+         * kernel(text+data+bss+brk) ramdisk, zero_page, command line
+         * all need to be under the 4G limit.
+         */
         cld
         /*
          * Test KEEP_SEGMENTS flag to see if the bootloader is asking
@@ -182,20 +188,18 @@ ENTRY(startup_32)
         lret
 ENDPROC(startup_32)
 
-        /*
-         * Be careful here startup_64 needs to be at a predictable
-         * address so I can export it in an ELF header.  Bootloaders
-         * should look at the ELF header to find this address, as
-         * it may change in the future.
-         */
         .code64
         .org 0x200
 ENTRY(startup_64)
         /*
+         * 64bit entry is 0x200 and it is ABI so immutable!
          * We come here either from startup_32 or directly from a
-         * 64bit bootloader.  If we come here from a bootloader we depend on
-         * an identity mapped page table being provied that maps our
-         * entire text+data+bss and hopefully all of memory.
+         * 64bit bootloader.
+         * If we come here from a bootloader, kernel(text+data+bss+brk),
+         * ramdisk, zero_page, command line could be above 4G.
+         * We depend on an identity mapped page table being provided
+         * that maps our entire kernel(text+data+bss+brk), zero page
+         * and command line.
          */
 #ifdef CONFIG_EFI_STUB
         /*