Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/hpa/linux-2.6-x86setup

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/hpa/linux-2.6-x86setup:
  x86 setup: don't recalculate ss:esp unless really necessary

1 files changed, 16 insertions, 25 deletions

diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 6ef5a060fa11..4cc5b0411db5 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -236,39 +236,30 @@ start_of_setup:
         movw    %ax, %es
         cld
 
-# Apparently some ancient versions of LILO invoked the kernel
-# with %ss != %ds, which happened to work by accident for the
-# old code.  If the CAN_USE_HEAP flag is set in loadflags, or
-# %ss != %ds, then adjust the stack pointer.
+# Apparently some ancient versions of LILO invoked the kernel with %ss != %ds,
+# which happened to work by accident for the old code.  Recalculate the stack
+# pointer if %ss is invalid.  Otherwise leave it alone, LOADLIN sets up the
+# stack behind its own code, so we can't blindly put it directly past the heap.
 
-        # Smallest possible stack we can tolerate
-        movw    $(_end+STACK_SIZE), %cx
-
-        movw    heap_end_ptr, %dx
-        addw    $512, %dx
-        jnc     1f
-        xorw    %dx, %dx        # Wraparound - whole segment available
-1:      testb   $CAN_USE_HEAP, loadflags
-        jnz     2f
-
-        # No CAN_USE_HEAP
         movw    %ss, %dx
         cmpw    %ax, %dx        # %ds == %ss?
         movw    %sp, %dx
-        # If so, assume %sp is reasonably set, otherwise use
-        # the smallest possible stack.
-        jne     4f              # -> Smallest possible stack...
+        je      2f              # -> assume %sp is reasonably set
+
+        # Invalid %ss, make up a new stack
+        movw    $_end, %dx
+        testb   $CAN_USE_HEAP, loadflags
+        jz      1f
+        movw    heap_end_ptr, %dx
+1:      addw    $STACK_SIZE, %dx
+        jnc     2f
+        xorw    %dx, %dx        # Prevent wraparound
 
-        # Make sure the stack is at least minimum size.  Take a value
-        # of zero to mean "full segment."
-2:
+2:      # Now %dx should point to the end of our stack space
         andw    $~3, %dx        # dword align (might as well...)
         jnz     3f
         movw    $0xfffc, %dx    # Make sure we're not zero
-3:      cmpw    %cx, %dx
-        jnb     5f
-4:      movw    %cx, %dx        # Minimum value we can possibly use
-5:      movw    %ax, %ss
+3:      movw    %ax, %ss
         movzwl  %dx, %esp       # Clear upper half of %esp
         sti                     # Now we should have a working stack