linux-kernel - [PATCH 4/8] x86: add .broken section to the vDSO linker script

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Date:	Fri, 12 Jun 2009 15:25:38 +0200
From:	Petr Tesarik <ptesarik@...e.cz>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	Roland McGrath <roland@...hat.com>,
	Petr Tesarik <ptesarik@...e.cz>
Subject: [PATCH 4/8] x86: add .broken section to the vDSO linker script

This section should not contain anything unless the vDSO is
broken. It is intended to hold sections which are known not
to work correctly inside a vDSO.

If such a "broken" section is found at link-time, the linker
issues an error with a hint how to find out more.

Signed-off-by: Petr Tesarik <ptesarik@...e.cz>
---
 arch/x86/vdso/vdso-layout.lds.S |   22 ++++++++++++++++++++++
 1 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/arch/x86/vdso/vdso-layout.lds.S b/arch/x86/vdso/vdso-layout.lds.S
index 0386c92..23da4a1 100644
--- a/arch/x86/vdso/vdso-layout.lds.S
+++ b/arch/x86/vdso/vdso-layout.lds.S
@@ -70,8 +70,30 @@ SECTIONS
 	.text : {
 		*(.text* .gnu.linkonce.t.*)
 	} :text	=0x90909090
+
+	/* Some sections require some additional work from the dynamic
+	 * linker to work properly. However, there is no dynamic-link
+	 * pass for the vDSO, so these sections will not work.
+	 * Put them into a special section and raise a link-time error
+	 * if they get used by accident.
+	 */
+	.broken : {
+	}
 }
 
+/* This assert is triggered if the linker finds a section in one of its
+ * input files which is known not to work inside a vDSO.
+ *
+ * To see which is the offending sections, you may:
+ *   a. use objdump -h on the object files which make up the vDSO, or
+ *   b. add -Wl,-M to VDSO_LDFLAGS and examine the linker map.
+ *
+ * See individual comments in the definition of the .broken section
+ * above for more information on why any given section is considered
+ * "broken".
+ */
+ASSERT(!SIZEOF(.broken), "The vdso linker script found a section that is bad. See vdso-layout.lds.S for details.");
+
 /*
  * Very old versions of ld do not recognize this name token; use the constant.
  */
-- 
1.6.0.2

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