[PATCH] i386 : Make arch/x86/kernel/acpi/wakeup_32.S use a separate text section

[PATCH] i386 : Make arch/x86/kernel/acpi/wakeup_32.S use a separate text section

[Eric Dumazet]

While examining vmlinux namelist on i386 (nm -v vmlinux) I noticed :

c01021d0 t es7000_rename_gsi
c010221a T es7000_start_cpu
<Big Hole>
c0103000 T thread_saved_pc

and 

c0113218 T acpi_restore_state_mem
c0113219 T acpi_save_state_mem
<Big Hole>
c0114000 t wakeup_code

This is because arch/x86/kernel/acpi/wakeup_32.S forces a .text alignment
of 4096 bytes. (I have no idea if it is really needed, since 
arch/x86/kernel/acpi/wakeup_64.S uses a 16 bytes alignment *only*)

So arch/x86/kernel/built-in.o also has this alignment

arch/x86/kernel/built-in.o:     file format elf32-i386

Sections:
Idx Name          Size      VMA       LMA       File off  Algn
  0 .text         00018c94  00000000  00000000  00001000  2**12
                  CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE

But as arch/x86/kernel/acpi/wakeup_32.o is not the first object linked
into arch/x86/kernel/built-in.o, linker had to build several holes to meet
alignement requirements, because of .o nestings in the kbuild process.

This can be solved by using a special section, .text.page_aligned, so that
no holes are needed.


# size vmlinux.before vmlinux.after
   text    data     bss     dec     hex filename
4619942  422838  458752 5501532  53f25c vmlinux.before
4610534  422838  458752 5492124  53cd9c vmlinux.after

This saves 9408 bytes

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

diff --git a/arch/x86/kernel/acpi/wakeup_32.S b/arch/x86/kernel/acpi/wakeup_32.S
index 1e931aa..f53e327 100644
--- a/arch/x86/kernel/acpi/wakeup_32.S
+++ b/arch/x86/kernel/acpi/wakeup_32.S
@@ -1,4 +1,4 @@
-.text
+	.section .text.page_aligned
 #include <linux/linkage.h>
 #include <asm/segment.h>
 #include <asm/page.h>
diff --git a/arch/x86/kernel/vmlinux_32.lds.S b/arch/x86/kernel/vmlinux_32.lds.S
index 7d72cce..113a831 100644
--- a/arch/x86/kernel/vmlinux_32.lds.S
+++ b/arch/x86/kernel/vmlinux_32.lds.S
@@ -44,6 +44,8 @@ SECTIONS
 
   /* read-only */
   .text : AT(ADDR(.text) - LOAD_OFFSET) {
+	. = ALIGN(4096); /* not really needed, already page aligned */
+	*(.text.page_aligned)
 	TEXT_TEXT
 	SCHED_TEXT
 	LOCK_TEXT

Re: [PATCH] i386 : Make arch/x86/kernel/acpi/wakeup_32.S use a separate text section

[Ingo Molnar]

* Eric Dumazet <dada1@cosmosbay.com> wrote:

> # size vmlinux.before vmlinux.after
>    text    data     bss     dec     hex filename
> 4619942  422838  458752 5501532  53f25c vmlinux.before
> 4610534  422838  458752 5492124  53cd9c vmlinux.after
> 
> This saves 9408 bytes

that's nice! Applied it to x86.git. I'm wondering, do we have other such 
cases? page alignment requirements are quite often for various CPU data 
structures.

	Ingo

Re: [PATCH] i386 : Make arch/x86/kernel/acpi/wakeup_32.S use a separate text section

[Matt Mackall]

On Sat, 2008-01-05 at 16:11 +0100, Ingo Molnar wrote:
> * Eric Dumazet <dada1@cosmosbay.com> wrote:
> 
> > # size vmlinux.before vmlinux.after
> >    text    data     bss     dec     hex filename
> > 4619942  422838  458752 5501532  53f25c vmlinux.before
> > 4610534  422838  458752 5492124  53cd9c vmlinux.after
> > 
> > This saves 9408 bytes
> 
> that's nice! Applied it to x86.git. I'm wondering, do we have other such 
> cases? page alignment requirements are quite often for various CPU data 
> structures.

They slip in from time to time, it would be nice to automate checking
for them.

-- 
Mathematics is the supreme nostalgia of our time.

Re: [PATCH] i386 : Make arch/x86/kernel/acpi/wakeup_32.S use a separate text section

[Pavel Machek]

On Thu 2008-01-03 21:04:26, Eric Dumazet wrote:
> While examining vmlinux namelist on i386 (nm -v vmlinux) I noticed :
> 
> c01021d0 t es7000_rename_gsi
> c010221a T es7000_start_cpu
> <Big Hole>
> c0103000 T thread_saved_pc
> 
> and 
> 
> c0113218 T acpi_restore_state_mem
> c0113219 T acpi_save_state_mem
> <Big Hole>
> c0114000 t wakeup_code
> 
> This is because arch/x86/kernel/acpi/wakeup_32.S forces a .text alignment
> of 4096 bytes. (I have no idea if it is really needed, since 
> arch/x86/kernel/acpi/wakeup_64.S uses a 16 bytes alignment *only*)
> 
> So arch/x86/kernel/built-in.o also has this alignment
> 
> arch/x86/kernel/built-in.o:     file format elf32-i386
> 
> Sections:
> Idx Name          Size      VMA       LMA       File off  Algn
>   0 .text         00018c94  00000000  00000000  00001000  2**12
>                   CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
> 
> But as arch/x86/kernel/acpi/wakeup_32.o is not the first object linked
> into arch/x86/kernel/built-in.o, linker had to build several holes to meet
> alignement requirements, because of .o nestings in the kbuild process.
> 
> This can be solved by using a special section, .text.page_aligned, so that
> no holes are needed.
> 
> 
> # size vmlinux.before vmlinux.after
>    text    data     bss     dec     hex filename
> 4619942  422838  458752 5501532  53f25c vmlinux.before
> 4610534  422838  458752 5492124  53cd9c vmlinux.after
> 
> This saves 9408 bytes
> 
> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

Seems okay to me, but I did not test it.

> diff --git a/arch/x86/kernel/acpi/wakeup_32.S b/arch/x86/kernel/acpi/wakeup_32.S
> index 1e931aa..f53e327 100644
> --- a/arch/x86/kernel/acpi/wakeup_32.S
> +++ b/arch/x86/kernel/acpi/wakeup_32.S
> @@ -1,4 +1,4 @@
> -.text
> +	.section .text.page_aligned
>  #include <linux/linkage.h>
>  #include <asm/segment.h>
>  #include <asm/page.h>
> diff --git a/arch/x86/kernel/vmlinux_32.lds.S b/arch/x86/kernel/vmlinux_32.lds.S
> index 7d72cce..113a831 100644
> --- a/arch/x86/kernel/vmlinux_32.lds.S
> +++ b/arch/x86/kernel/vmlinux_32.lds.S
> @@ -44,6 +44,8 @@ SECTIONS
>  
>    /* read-only */
>    .text : AT(ADDR(.text) - LOAD_OFFSET) {
> +	. = ALIGN(4096); /* not really needed, already page aligned */
> +	*(.text.page_aligned)
>  	TEXT_TEXT
>  	SCHED_TEXT
>  	LOCK_TEXT
> 
> --
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-- 
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