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Date: Thu, 14 May 2009 15:06:53 +0200
From: Petr Tesarik <ptesarik@...e.cz>
To: linux-kernel@...r.kernel.org, linux-x86_64@...r.kernel.org,
mingo@...e.hu, andi@...stfloor.org
Cc: zwane@....linux.org.uk, roland@...hat.com,
Petr Tesarik <ptesarik@...e.cz>
Subject: [PATCH 3/4] x86-64: link vDSO into the kernel with relocations
Preserve relocation info about the sections in the vDSO.
This is achieved by linking the vDSO twice.
First link produces a complete vdso.so as seen by user-space.
This image is used to:
- determine the final layout of the vDSO
(extracted by nm to vdso-syms.h)
- obtain the ELF headers and linker-generated sections
(copied by the assembler .incbin directive to .vdso_head and
.vdso_tail sections of vdso-parts.o)
The second link combines the head and tail portions with the
rodata, data and text sections of the object which make up the vDSO,
but doesn't produce a shared library, but a relocatable object for
further linking.
Advantages of this approach:
1. No run-time bloat. All that can be done at link time is done
at link time.
2. No user-space bloat. Only those sections which are needed by
user-space are mapped into the process space.
3. Possibility to re-use the technique for more general linking,
e.g. get rid of VMAGIC and run-time vDSO "resolving" of vDSO
variables in init_vdso_vars().
Signed-off-by: Petr Tesarik <ptesarik@...e.cz>
---
arch/x86/vdso/.gitignore | 1 +
arch/x86/vdso/Makefile | 25 ++++++++++----
arch/x86/vdso/vdso-layout.lds.S | 16 +++++++++
arch/x86/vdso/vdso-parts.S | 7 ++++
arch/x86/vdso/vdso-reloc.lds.S | 66 +++++++++++++++++++++++++++++++++++++++
arch/x86/vdso/vdso.S | 10 ------
arch/x86/vdso/vdso.lds.S | 1 +
7 files changed, 109 insertions(+), 17 deletions(-)
create mode 100644 arch/x86/vdso/vdso-parts.S
create mode 100644 arch/x86/vdso/vdso-reloc.lds.S
delete mode 100644 arch/x86/vdso/vdso.S
diff --git a/arch/x86/vdso/.gitignore b/arch/x86/vdso/.gitignore
index 6ac0a86..9d887a8 100644
--- a/arch/x86/vdso/.gitignore
+++ b/arch/x86/vdso/.gitignore
@@ -1,4 +1,5 @@
vdso.lds
+vdso-reloc.lds
vdso-syms.h
vdso32-syms.h
vdso32-syscall-syms.h
diff --git a/arch/x86/vdso/Makefile b/arch/x86/vdso/Makefile
index 550dca0..194db49 100644
--- a/arch/x86/vdso/Makefile
+++ b/arch/x86/vdso/Makefile
@@ -19,17 +19,17 @@ obj-$(VDSO32-y) += vdso32.o vdso32-setup.o
vobjs := $(foreach F,$(vobjs-y),$(obj)/$F)
-$(obj)/vdso.o: $(obj)/vdso.so
+#
+# Rules for the vDSO as visible to user-space
+#
targets += vdso.so vdso.so.dbg vdso.lds $(vobjs-y)
export CPPFLAGS_vdso.lds += -P -C
-VDSO_LDFLAGS_vdso.lds = -m elf_x86_64 -Wl,-soname=linux-vdso.so.1 \
+VDSO_LDFLAGS_vdso.lds = -shared -m elf_x86_64 -Wl,-soname=linux-vdso.so.1 \
-Wl,-z,max-page-size=4096 -Wl,-z,common-page-size=4096
-$(obj)/vdso.o: $(src)/vdso.S $(obj)/vdso.so
-
$(obj)/vdso.so.dbg: $(src)/vdso.lds $(vobjs) FORCE
$(call if_changed,vdso)
@@ -42,9 +42,20 @@ CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
$(vobjs): KBUILD_CFLAGS += $(CFL)
-targets += vdso-syms.h
+#
+# Rules for the vDSO as linked into the kernel
+#
+
+targets += vdso-syms.h vdso-parts.o vdso-reloc.lds
+
+$(obj)/vdso-parts.o: $(obj)/vdso-syms.h $(obj)/vdso.so
$(obj)/vma.o: $(obj)/vdso-syms.h
+export CPPFLAGS_vdso-reloc.lds += -P -C
+VDSO_LDFLAGS_vdso.o = -r -m elf_x86_64
+$(obj)/vdso.o: $(src)/vdso-reloc.lds $(vobjs) $(obj)/vdso-parts.o
+ $(call if_changed,vdso)
+
#
# Match symbols in the DSO that look like VDSO*; produce a file of constants.
#
@@ -68,7 +79,7 @@ vdso32.so-$(VDSO32-y) += sysenter
vdso32-images = $(vdso32.so-y:%=vdso32-%.so)
CPPFLAGS_vdso32.lds = $(CPPFLAGS_vdso.lds)
-VDSO_LDFLAGS_vdso32.lds = -m elf_i386 -Wl,-soname=linux-gate.so.1
+VDSO_LDFLAGS_vdso32.lds = -shared -m elf_i386 -Wl,-soname=linux-gate.so.1
# This makes sure the $(obj) subdirectory exists even though vdso32/
# is not a kbuild sub-make subdirectory.
@@ -122,7 +133,7 @@ quiet_cmd_vdso = VDSO $@
$(VDSO_LDFLAGS) $(VDSO_LDFLAGS_$(filter %.lds,$(^F))) \
-Wl,-T,$(filter %.lds,$^) $(filter %.o,$^)
-VDSO_LDFLAGS = -fPIC -shared $(call ld-option, -Wl$(comma)--hash-style=sysv)
+VDSO_LDFLAGS = -fPIC $(call ld-option, -Wl$(comma)--hash-style=sysv)
#
# Install the unstripped copy of vdso*.so listed in $(vdso-install-y).
diff --git a/arch/x86/vdso/vdso-layout.lds.S b/arch/x86/vdso/vdso-layout.lds.S
index aaa3026..c2c6aef 100644
--- a/arch/x86/vdso/vdso-layout.lds.S
+++ b/arch/x86/vdso/vdso-layout.lds.S
@@ -4,6 +4,12 @@
* This script controls its layout.
*/
+#ifdef VDSO_MARK_SECTIONS
+# define MARK(sym) VDSO_ ## sym = .;
+#else
+# define MARK(sym)
+#endif
+
SECTIONS
{
. = VDSO_PRELINK + SIZEOF_HEADERS;
@@ -27,17 +33,25 @@ SECTIONS
.got.plt : { *(.got.plt) }
.dynbss : { *(.dynbss) }
+ /* IMPORTANT
+ * If you change the link order here, make sure you also
+ * reflect your changes in vdso-reloc.lds.S.
+ */
.rodata : {
+ MARK(rodata_start)
*(.rodata*)
*(.gnu.linkonce.r.*)
+ MARK(rodata_end)
}
.data : {
+ MARK(data_start)
*(.data*)
*(.sdata*)
*(.gnu.linkonce.d.*)
*(.bss*)
*(.sbss*)
*(.gnu.linkonce.b.*)
+ MARK(data_end)
}
/*
@@ -47,8 +61,10 @@ SECTIONS
. = ALIGN(0x100);
.text : {
+ MARK(text_start)
*(.text*)
*(.gnu.linkonce.t.*)
+ MARK(text_end)
} :text =0x90909090
/DISCARD/ : {
diff --git a/arch/x86/vdso/vdso-parts.S b/arch/x86/vdso/vdso-parts.S
new file mode 100644
index 0000000..6c34c5e
--- /dev/null
+++ b/arch/x86/vdso/vdso-parts.S
@@ -0,0 +1,7 @@
+#include "vdso-syms.h"
+
+ .section .vdso_head,"a"
+ .incbin "arch/x86/vdso/vdso.so", 0, VDSO_rodata_start-VDSO64_PRELINK
+
+ .section .vdso_tail,"a"
+ .incbin "arch/x86/vdso/vdso.so", VDSO_text_end-VDSO64_PRELINK
diff --git a/arch/x86/vdso/vdso-reloc.lds.S b/arch/x86/vdso/vdso-reloc.lds.S
new file mode 100644
index 0000000..44e0fb5
--- /dev/null
+++ b/arch/x86/vdso/vdso-reloc.lds.S
@@ -0,0 +1,66 @@
+#include "vdso-syms.h"
+
+#define STRINGIFY(x) #x
+
+/* Choose a name which is not a valid C identifier to prevent conflicts */
+#define MARKER(sym) STRINGIFY(.vdso. ## sym)
+
+/* Saved value from vdso-syms.h */
+#define VDSOSYM(sym) (VDSO_ ## sym - VDSO64_PRELINK)
+
+/* Older binutils do not allow ASSERT() inside SECTIONS, so we must
+ * save the current pointer and check it later at file level.
+ */
+#define MARK(sym) MARKER(sym) = .;
+#define CHECK(sym) \
+ ASSERT(VDSOSYM(sym) == MARKER(sym) - vdso_start, \
+ STRINGIFY(sym in kernel does not match the pre-linked image))
+
+SECTIONS {
+ .init.data : {
+ FILL(0);
+
+ vdso_start = .;
+ *(.vdso_head)
+
+ /* .rodata */
+ MARK(rodata_start)
+ *(.rodata*)
+ *(.gnu.linkonce.r.*)
+ MARK(rodata_end)
+
+ /* .data */
+ MARK(data_start)
+ *(.data*)
+ *(.sdata*)
+ *(.gnu.linkonce.d.*)
+ *(.bss*)
+ *(.sbss*)
+ *(.gnu.linkonce.b.*)
+ MARK(data_end)
+
+ /* .text */
+ . = ALIGN(. - vdso_start,0x100);
+ FILL(0x90909090);
+ MARK(text_start)
+ *(.text*)
+ *(.gnu.linkonce.t.*)
+ MARK(text_end)
+
+ *(.vdso_tail)
+ vdso_end = .;
+ } =0x90909090
+
+ .altinstructions : { *(.altinstructions) }
+ .altinstr_replacement : { *(.altinstr_replacement) }
+
+ /* The custom vDSO note section is not understood in vmlinux */
+ /DISCARD/ : { *(.note.Linux) }
+}
+
+CHECK(rodata_start)
+CHECK(rodata_end)
+CHECK(data_start)
+CHECK(data_end)
+CHECK(text_start)
+CHECK(text_end)
diff --git a/arch/x86/vdso/vdso.S b/arch/x86/vdso/vdso.S
deleted file mode 100644
index 1d3aa6b..0000000
--- a/arch/x86/vdso/vdso.S
+++ /dev/null
@@ -1,10 +0,0 @@
-#include <linux/init.h>
-
-__INITDATA
-
- .globl vdso_start, vdso_end
-vdso_start:
- .incbin "arch/x86/vdso/vdso.so"
-vdso_end:
-
-__FINIT
diff --git a/arch/x86/vdso/vdso.lds.S b/arch/x86/vdso/vdso.lds.S
index 4e5dd3b..d5cf24f 100644
--- a/arch/x86/vdso/vdso.lds.S
+++ b/arch/x86/vdso/vdso.lds.S
@@ -9,6 +9,7 @@
*/
#define VDSO_PRELINK 0xffffffffff700000
+#define VDSO_MARK_SECTIONS 1
#include "vdso-layout.lds.S"
/*
--
1.6.0.2
--
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