x86 vDSO: new layout

This revamps the vDSO linker script to lay things out with the best
packing of the data and good, separate alignment of the code.  The
rigid layout using VDSO_TEXT_OFFSET no longer matters to the kernel.
I've moved the layout parts of the linker script into a new include
file, vdso-layout.lds.S; this is in preparation for sharing the script
for the 32-bit vDSO builds too.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 25 insertions, 77 deletions

diff --git a/arch/x86/vdso/vdso.lds.S b/arch/x86/vdso/vdso.lds.S
index d40d0e906190..4e5dd3b4de7f 100644
--- a/arch/x86/vdso/vdso.lds.S
+++ b/arch/x86/vdso/vdso.lds.S
@@ -1,89 +1,37 @@
 /*
- * Linker script for vsyscall DSO.  The vsyscall page is an ELF shared
- * object prelinked to its virtual address, and with only one read-only
- * segment (that fits in one page).  This script controls its layout.
+ * Linker script for 64-bit vDSO.
+ * We #include the file to define the layout details.
+ * Here we only choose the prelinked virtual address.
+ *
+ * This file defines the version script giving the user-exported symbols in
+ * the DSO.  We can define local symbols here called VDSO* to make their
+ * values visible using the asm-x86/vdso.h macros from the kernel proper.
  */
-#include <asm/asm-offsets.h>
-#include "voffset.h"
 
 #define VDSO_PRELINK 0xffffffffff700000
+#include "vdso-layout.lds.S"
 
 /*
- * Symbols we define here called VDSO* get their values into vdso-syms.lds
- * and become visible to the kernel itself.
+ * This controls what userland symbols we export from the vDSO.
  */
-VDSO64_PRELINK = VDSO_PRELINK;
-
-#define VEXTERN(x)      VDSO64_ ## x = vdso_ ## x;
-#include "vextern.h"
-#undef  VEXTERN
-
-SECTIONS
-{
-  . = VDSO_PRELINK + SIZEOF_HEADERS;
-
-  .hash           : { *(.hash) }                :text
-  .gnu.hash       : { *(.gnu.hash) }
-  .dynsym         : { *(.dynsym) }
-  .dynstr         : { *(.dynstr) }
-  .gnu.version    : { *(.gnu.version) }
-  .gnu.version_d  : { *(.gnu.version_d) }
-  .gnu.version_r  : { *(.gnu.version_r) }
-
-  /* This linker script is used both with -r and with -shared.
-     For the layouts to match, we need to skip more than enough
-     space for the dynamic symbol table et al.  If this amount
-     is insufficient, ld -shared will barf.  Just increase it here.  */
-  . = VDSO_PRELINK + VDSO_TEXT_OFFSET;
-
-  .text           : { *(.text*) }               :text
-  .rodata         : { *(.rodata*) }             :text
-  .data           : {
-        *(.data*)
-        *(.sdata*)
-        *(.bss*)
-        *(.dynbss*)
-  }                                             :text
-
-  .altinstructions : { *(.altinstructions) }            :text
-  .altinstr_replacement  : { *(.altinstr_replacement) } :text
-
-  .note           : { *(.note.*) }              :text :note
-  .eh_frame_hdr   : { *(.eh_frame_hdr) }        :text :eh_frame_hdr
-  .eh_frame       : { KEEP (*(.eh_frame)) }     :text
-  .dynamic        : { *(.dynamic) }             :text :dynamic
-  .useless        : {
-        *(.got.plt) *(.got)
-        *(.gnu.linkonce.d.*)
-        *(.gnu.linkonce.b.*)
-  }                                             :text
+VERSION {
+        LINUX_2.6 {
+        global:
+                clock_gettime;
+                __vdso_clock_gettime;
+                gettimeofday;
+                __vdso_gettimeofday;
+                getcpu;
+                __vdso_getcpu;
+        local: *;
+        };
 }
 
-/*
- * We must supply the ELF program headers explicitly to get just one
- * PT_LOAD segment, and set the flags explicitly to make segments read-only.
- */
-PHDRS
-{
-  text PT_LOAD FILEHDR PHDRS FLAGS(5); /* PF_R|PF_X */
-  dynamic PT_DYNAMIC FLAGS(4); /* PF_R */
-  note PT_NOTE FLAGS(4); /* PF_R */
-  eh_frame_hdr 0x6474e550; /* PT_GNU_EH_FRAME, but ld doesn't match the name */
-}
+VDSO64_PRELINK = VDSO_PRELINK;
 
 /*
- * This controls what symbols we export from the DSO.
+ * Define VDSO64_x for each VEXTERN(x), for use via VDSO64_SYMBOL.
  */
-VERSION
-{
-  LINUX_2.6 {
-    global:
-        clock_gettime;
-        __vdso_clock_gettime;
-        gettimeofday;
-        __vdso_gettimeofday;
-        getcpu;
-        __vdso_getcpu;
-    local: *;
-  };
-}
+#define VEXTERN(x)      VDSO64_ ## x = vdso_ ## x;
+#include "vextern.h"
+#undef  VEXTERN