x86 setup: set %ebx == %ebp == %edi == 0 on protected mode entry

In accordance with the newly formalized 32-bit boot protocol, set
%ebx == %ebp == %edi == 0 in order to support future extensions to the
protocol.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/x86/boot/pmjump.S b/arch/x86/boot/pmjump.S
index 26baeab3a4d4..fa6bed1fac14 100644
--- a/arch/x86/boot/pmjump.S
+++ b/arch/x86/boot/pmjump.S
@@ -28,11 +28,13 @@
  * void protected_mode_jump(u32 entrypoint, u32 bootparams);
  */
 protected_mode_jump:
-        xorl    %ebx, %ebx              # Flag to indicate this is a boot
         movl    %edx, %esi              # Pointer to boot_params table
         movl    %eax, 2f                # Patch ljmpl instruction
 
         movw    $__BOOT_DS, %cx
+        xorl    %ebx, %ebx              # Per the 32-bit boot protocol
+        xorl    %ebp, %ebp              # Per the 32-bit boot protocol
+        xorl    %edi, %edi              # Per the 32-bit boot protocol
 
         movl    %cr0, %edx
         orb     $1, %dl                 # Protected mode (PE) bit