linux-kernel - [PATCH v3 3/5] x86/asm: Error out if asm/jump

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Message-Id: <99407f0ac7fa3ab03a3d31ce076d47b5c2f44795.1447361906.git.luto@kernel.org>
Date:	Thu, 12 Nov 2015 12:59:02 -0800
From:	Andy Lutomirski <luto@...nel.org>
To:	x86@...nel.org, linux-kernel@...r.kernel.org
Cc:	Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>
Subject: [PATCH v3 3/5] x86/asm: Error out if asm/jump_label.h is included inappropriately

Rather than potentially generating incorrect code on a
non-HAVE_JUMP_LABEL kernel if someone includes asm/jump_label.h,
error out.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/include/asm/jump_label.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index 5daeca3d0f9e..96872dc96597 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -1,6 +1,19 @@
 #ifndef _ASM_X86_JUMP_LABEL_H
 #define _ASM_X86_JUMP_LABEL_H
 
+#ifndef HAVE_JUMP_LABEL
+/*
+ * For better or for worse, if jump labels (the gcc extension) are missing,
+ * then the entire static branch patching infrastructure is compiled out.
+ * If that happens, the code in here will malfunction.  Raise a compiler
+ * error instead.
+ *
+ * In theory, jump labels and the static branch patching infrastructure
+ * could be decoupled to fix this.
+ */
+#error asm/jump_label.h included on a non-jump-label kernel
+#endif
+
 #ifndef __ASSEMBLY__
 
 #include <linux/stringify.h>
-- 
2.5.0

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