linux-kernel - [PATCH] [10/12] x86_64: Add warning in Documentation that zero-page is not a stable ABI

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Message-Id: <20070809124138.1F2E114F3B@wotan.suse.de>
Date:	Thu,  9 Aug 2007 14:41:38 +0200 (CEST)
From:	Andi Kleen <ak@...e.de>
To:	patches@...-64.org, linux-kernel@...r.kernel.org
Subject: [PATCH] [10/12] x86_64: Add warning in Documentation that zero-page is not a stable ABI


Some people writing boot loaders seem to falsely belief the 32bit zero page is a 
stable interface for out of tree code like the real mode boot protocol. Add a comment 
clarifying that is not true.

Signed-off-by: Andi Kleen <ak@...e.de>

---
 Documentation/i386/zero-page.txt |   10 ++++++++++
 1 file changed, 10 insertions(+)

Index: linux/Documentation/i386/zero-page.txt
===================================================================
--- linux.orig/Documentation/i386/zero-page.txt
+++ linux/Documentation/i386/zero-page.txt
@@ -1,3 +1,13 @@
+---------------------------------------------------------------------------
+!!!!!!!!!!!!!!!WARNING!!!!!!!!
+The zero page is a kernel internal data structure, not a stable ABI.  It might change
+without warning and the kernel has no way to detect old version of it.
+If you're writing some external code like a boot loader you should only use
+the stable versioned real mode boot protocol described in boot.txt. Otherwise the kernel
+might break you at any time.
+!!!!!!!!!!!!!WARNING!!!!!!!!!!!
+----------------------------------------------------------------------------
+
 Summary of boot_params layout (kernel point of view)
      ( collected by Hans Lermen and Martin Mares )
  
-
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