linux-kernel - [PATCH] x86: clean up vdso-layout.lds.S

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Date:	Mon, 01 Jun 2009 16:05:15 +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>
Subject: [PATCH] x86: clean up vdso-layout.lds.S

The handling of various sections in the VDSO linker script
looks pretty haphazard. This patch cleans it up in this
regards:

 - re-order sections to more closely match the result of
   a normal shared link
 - discard sections which are not useful to user-space
 - issue a linker error if a section is encountered which
   is known not to work
 - check that the .got section is empty, except for the
   three entries defined by the ABI

Signed-off-by: Petr Tesarik <ptesarik@...e.cz>

---
 Makefile          |    5 ++--
 vdso-layout.lds.S |   57 +++++++++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 51 insertions(+), 11 deletions(-)

diff --git a/arch/x86/vdso/Makefile b/arch/x86/vdso/Makefile
index 16a9020..8c7f06a 100644
--- a/arch/x86/vdso/Makefile
+++ b/arch/x86/vdso/Makefile
@@ -23,7 +23,8 @@ $(obj)/vdso.o: $(obj)/vdso.so
 
 targets += vdso.so vdso.so.dbg vdso.lds $(vobjs-y)
 
-export CPPFLAGS_vdso.lds += -P -C
+vdso-cppflags = -P -C
+export CPPFLAGS_vdso.lds += -m64 $(vdso-cppflags)
 
 VDSO_LDFLAGS_vdso.lds = -m elf_x86_64 -Wl,-soname=linux-vdso.so.1 \
 		      	-Wl,-z,max-page-size=4096 -Wl,-z,common-page-size=4096
@@ -68,7 +69,7 @@ vdso32.so-$(VDSO32-y)		+= sysenter
 
 vdso32-images			= $(vdso32.so-y:%=vdso32-%.so)
 
-CPPFLAGS_vdso32.lds = $(CPPFLAGS_vdso.lds)
+CPPFLAGS_vdso32.lds = -m32 $(vdso-cppflags)
 VDSO_LDFLAGS_vdso32.lds = -m elf_i386 -Wl,-soname=linux-gate.so.1
 
 # This makes sure the $(obj) subdirectory exists even though vdso32/
diff --git a/arch/x86/vdso/vdso-layout.lds.S b/arch/x86/vdso/vdso-layout.lds.S
index 634a2cf..1f4b215 100644
--- a/arch/x86/vdso/vdso-layout.lds.S
+++ b/arch/x86/vdso/vdso-layout.lds.S
@@ -22,16 +22,15 @@ SECTIONS
 	.eh_frame	: { KEEP (*(.eh_frame)) }	:text
 
 	.dynamic	: { *(.dynamic) }		:text	:dynamic
+	.got		: { *(.got.plt) *(.got) }	:text
 
-	.rodata		: { *(.rodata*) }		:text
+	.rodata		: {
+		*(.rodata .rodata.* .gnu.linkonce.r.*)
+	}
 	.data		: {
-	      *(.data*)
-	      *(.sdata*)
-	      *(.got.plt) *(.got)
-	      *(.gnu.linkonce.d.*)
-	      *(.bss*)
-	      *(.dynbss*)
-	      *(.gnu.linkonce.b.*)
+		*(.data .data.* .gnu.linkonce.d.*)
+		*(.bss .bss.* .gnu.linkonce.b.*)
+		*(COMMON)
 	}
 
 	.altinstructions	: { *(.altinstructions) }
@@ -43,9 +42,49 @@ SECTIONS
 	 */
 	. = ALIGN(0x100);
 
-	.text		: { *(.text*) }			:text	=0x90909090
+	.text		: {
+		*(.text .text.* .gnu.linkonce.t.*)
+	}						:text	=0x90909090
+
+	/* We would need a more sophisticated dynamic linker for the
+	 * vDSO to make the following sections work.  Put them into
+	 * a special section and raise a link-time error if they get
+	 * used.
+	 */
+	.broken		: {
+		/* Code in the Procedure Linkage Table will segfault */
+		*(.plt)
+
+		/* Relocation will not be done, so any pointers will
+		 * still point to the prelinked address, which is wrong
+		 */
+		*(.data.rel.ro*)
+		*(.gnu.linkonce.d.rel.ro.*)
+
+		/* Initialization/termination won't work this way */
+		*(.init) *(.fini)
+		*(.preinit_array) *(.init_array*)
+		*(.fini_array*)
+
+		/* Thread-local data cannot be defined like this */
+		*(.tdata .tdata.* .gnu.linkonce.td.*)
+		*(.tbss .tbss.* .gnu.linkonce.tb.*)
+		*(.tcommon)
+	}
+
+	/* These sections are not useful */
+	/DISCARD/	: {
+		*(.gnu.warning.*)
+		*(.note.GNU-stack)
+	}
 }
 
+ASSERT(!SIZEOF(.broken), "VDSO contains sections that don't work properly");
+
+/* Check that GOT has only the three entries defined by the ABI */
+ASSERT(SIZEOF(.got) == 3*__SIZEOF_POINTER__,
+	"Found extra GOT entries. Check your use of external vars.");
+
 /*
  * Very old versions of ld do not recognize this name token; use the constant.
  */


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