[PATCH] x86_64 vDSO: use initdata

[PATCH] x86_64 vDSO: use initdata

[Roland McGrath]

The 64-bit vDSO image is in a special ".vdso" section for no reason
I can determine.  Furthermore, the location of the vdso_end symbol
includes some wrongly-calculated padding space in the image, which
is then (correctly) rounded to page size, resulting in an extra page
of zeros in the image mapped in to user processes.

This changes it to put the vdso.so image into normal initdata as we
have always done for the 32-bit vDSO images.  The extra padding is
gone, so the user VMA is one page instead of two.  The image that
was already copied around at boot time is now in initdata, so we
recover that wasted space after boot.

Signed-off-by: Roland McGrath <roland@redhat.com>
---
 arch/x86/kernel/vmlinux_64.lds.S |    6 ------
 arch/x86/vdso/vdso.S             |   10 +++++++++-
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/vmlinux_64.lds.S b/arch/x86/kernel/vmlinux_64.lds.S
index b7ab3c3..fad3674 100644
--- a/arch/x86/kernel/vmlinux_64.lds.S
+++ b/arch/x86/kernel/vmlinux_64.lds.S
@@ -209,12 +209,6 @@ SECTIONS
 	EXIT_DATA
   }
 
-/* vdso blob that is mapped into user space */
-  vdso_start = . ;
-  .vdso  : AT(ADDR(.vdso) - LOAD_OFFSET) { *(.vdso) }
-  . = ALIGN(PAGE_SIZE);
-  vdso_end = .;
-
 #ifdef CONFIG_BLK_DEV_INITRD
   . = ALIGN(PAGE_SIZE);
   __initramfs_start = .;
diff --git a/arch/x86/vdso/vdso.S b/arch/x86/vdso/vdso.S
index 4b1620a..1d3aa6b 100644
--- a/arch/x86/vdso/vdso.S
+++ b/arch/x86/vdso/vdso.S
@@ -1,2 +1,10 @@
-	.section ".vdso","a"
+#include <linux/init.h>
+
+__INITDATA
+
+	.globl vdso_start, vdso_end
+vdso_start:
 	.incbin "arch/x86/vdso/vdso.so"
+vdso_end:
+
+__FINIT

Re: [PATCH] x86_64 vDSO: use initdata

[Ingo Molnar]

* Roland McGrath <roland@redhat.com> wrote:

> The 64-bit vDSO image is in a special ".vdso" section for no reason I 
> can determine.  Furthermore, the location of the vdso_end symbol 
> includes some wrongly-calculated padding space in the image, which is 
> then (correctly) rounded to page size, resulting in an extra page of 
> zeros in the image mapped in to user processes.
> 
> This changes it to put the vdso.so image into normal initdata as we 
> have always done for the 32-bit vDSO images.  The extra padding is 
> gone, so the user VMA is one page instead of two.  The image that was 
> already copied around at boot time is now in initdata, so we recover 
> that wasted space after boot.

thanks Roland, applied. I suspect this will need a few days of test-time 
as we change the user-space vma layout. (not in material ways though)

	Ingo