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-rw-r--r--arch/x86/boot/header.S41
1 files changed, 16 insertions, 25 deletions
diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 6ef5a060fa1..4cc5b0411db 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