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Add support for compiling with -ffunction-sections -fdata-sections

From:  Tim Abbott <tabbott@MIT.EDU>
To:  Linus Torvalds <torvalds@linux-foundation.org>
Subject:  [PATCH 0/4] Add support for compiling with -ffunction-sections -fdata-sections
Date:  Tue, 24 Mar 2009 01:28:41 -0400
Message-ID:  <1237872525-31014-1-git-send-email-tabbott@mit.edu>
Cc:  Linux kernel mailing list <linux-kernel@vger.kernel.org>, Tim Abbott <tabbott@mit.edu>, Anders Kaseorg <andersk@mit.edu>, Waseem Daher <wdaher@mit.edu>, Denys Vlasenko <vda.linux@googlemail.com>, Rusty Russell <rusty@rustcorp.com.au>, Andi Kleen <andi@firstfloor.org>, "H. Peter Anvin" <hpa@zytor.com>
Archive-link:  Article

Hi Linus,

I'd like to see this patch series merged for 2.6.30.  It applies on
top of your current master (aka v2.6.29).  Patch 1/4 would benefit
from special treatment during the merge window, since it makes many
small changes in lots of files, and thus is likely to conflict with
other changes; the other patches are fairly small.

The purpose of this patch series is to make it possible to build the
kernel with "gcc -ffunction-sections -fdata-sections".  There are two
major applications for this functionality: decreasing vmlinux image
size with --gc-sections, and Ksplice.

The original motivation for this functionality was to allow using the
linker's unused section garbage collection support (ld --gc-sections)
in order to get a smaller vmlinux image for embedded systems.  People
have been developing patches for supporting building the kernel with
-ffunction-sections -fdata-sections for this purpose for a few years
now (e.g. [1]).  The most recent previous set of patches for
--gc-sections was by Denys Vlasenko, and saved 10% on vmlinux size
with CONFIG_MODULES=n and 1% with CONFIG_MODULES=y [2,3,4].  The
primary source of complexity in the various patch series for doing
section garbage collection has been in the patches adding support for
compiling the kernel with -ffunction-sections -fdata-sections, so
merging this patch series should be a big step towards those
significant savings in kernel image size.

[1] <http://lkml.org/lkml/2006/6/4/169>
[2] <http://lkml.org/lkml/2007/9/5/90>
[3] <http://lkml.org/lkml/2007/9/7/110>
[4] <http://lkml.org/lkml/2008/7/1/499>

Support for building the kernel with -ffunction-sections
-fdata-sections is the only significant prerequisite change currently
required by Ksplice.  Ksplice is a system for updating the Linux
kernel without rebooting [5].

[5] <http://lkml.org/lkml/2009/2/24/362> is the latest version of the
Ksplice patch series

Patches 1/4, 2/4, and 3/4 are independent of each other, but
all three are prerequisites for patch 4/4.

--

Anders Kaseorg (1):
  modpost: Check the section flags, not name, to catch missing
    "ax"/"aw"

Denys Vlasenko (1):
  modpost: support objects with more than 64k sections

Tim Abbott (1):
  Make section names compatible with -ffunction-sections
    -fdata-sections

Waseem Daher (1):
  x86: Add an option to compile with -ffunction-sections
    -fdata-sections

 Documentation/mutex-design.txt              |    4 +-
 Makefile                                    |    4 +
 arch/alpha/kernel/head.S                    |    2 +-
 arch/alpha/kernel/init_task.c               |    2 +-
 arch/alpha/kernel/vmlinux.lds.S             |   14 ++--
 arch/arm/kernel/head-nommu.S                |    2 +-
 arch/arm/kernel/head.S                      |    2 +-
 arch/arm/kernel/init_task.c                 |    2 +-
 arch/arm/kernel/vmlinux.lds.S               |   14 ++--
 arch/arm/mm/proc-v6.S                       |    2 +-
 arch/arm/mm/proc-v7.S                       |    2 +-
 arch/arm/mm/tlb-v6.S                        |    2 +-
 arch/arm/mm/tlb-v7.S                        |    2 +-
 arch/avr32/kernel/init_task.c               |    2 +-
 arch/avr32/kernel/vmlinux.lds.S             |    6 +-
 arch/avr32/mm/init.c                        |    2 +-
 arch/blackfin/kernel/vmlinux.lds.S          |    2 +-
 arch/cris/kernel/process.c                  |    2 +-
 arch/cris/kernel/vmlinux.lds.S              |    2 +-
 arch/frv/kernel/break.S                     |    4 +-
 arch/frv/kernel/entry.S                     |    2 +-
 arch/frv/kernel/head-mmu-fr451.S            |    2 +-
 arch/frv/kernel/head-uc-fr401.S             |    2 +-
 arch/frv/kernel/head-uc-fr451.S             |    2 +-
 arch/frv/kernel/head-uc-fr555.S             |    2 +-
 arch/frv/kernel/head.S                      |    4 +-
 arch/frv/kernel/init_task.c                 |    2 +-
 arch/frv/kernel/vmlinux.lds.S               |   18 ++--
 arch/frv/mm/tlb-miss.S                      |    2 +-
 arch/h8300/boot/compressed/head.S           |    2 +-
 arch/h8300/boot/compressed/vmlinux.lds      |    2 +-
 arch/h8300/kernel/init_task.c               |    2 +-
 arch/h8300/kernel/vmlinux.lds.S             |    2 +-
 arch/ia64/include/asm/asmmacro.h            |   12 +-
 arch/ia64/include/asm/cache.h               |    2 +-
 arch/ia64/include/asm/percpu.h              |    2 +-
 arch/ia64/kernel/Makefile                   |    2 +-
 arch/ia64/kernel/gate-data.S                |    2 +-
 arch/ia64/kernel/gate.S                     |    8 +-
 arch/ia64/kernel/gate.lds.S                 |   10 +-
 arch/ia64/kernel/head.S                     |    2 +-
 arch/ia64/kernel/init_task.c                |    4 +-
 arch/ia64/kernel/ivt.S                      |    2 +-
 arch/ia64/kernel/minstate.h                 |    4 +-
 arch/ia64/kernel/paravirtentry.S            |    2 +-
 arch/ia64/kernel/vmlinux.lds.S              |   48 ++++----
 arch/ia64/kvm/vmm_ivt.S                     |    2 +-
 arch/ia64/xen/xensetup.S                    |    2 +-
 arch/m32r/kernel/head.S                     |    2 +-
 arch/m32r/kernel/init_task.c                |    2 +-
 arch/m32r/kernel/vmlinux.lds.S              |    8 +-
 arch/m68k/kernel/head.S                     |    2 +-
 arch/m68k/kernel/process.c                  |    2 +-
 arch/m68k/kernel/sun3-head.S                |    2 +-
 arch/m68k/kernel/vmlinux-std.lds            |    6 +-
 arch/m68k/kernel/vmlinux-sun3.lds           |    4 +-
 arch/m68knommu/kernel/init_task.c           |    2 +-
 arch/m68knommu/kernel/vmlinux.lds.S         |    6 +-
 arch/m68knommu/platform/68360/head-ram.S    |    2 +-
 arch/m68knommu/platform/68360/head-rom.S    |    2 +-
 arch/mips/kernel/init_task.c                |    2 +-
 arch/mips/kernel/vmlinux.lds.S              |    8 +-
 arch/mips/lasat/image/head.S                |    2 +-
 arch/mips/lasat/image/romscript.normal      |    2 +-
 arch/mn10300/kernel/head.S                  |    2 +-
 arch/mn10300/kernel/init_task.c             |    2 +-
 arch/mn10300/kernel/vmlinux.lds.S           |   16 ++--
 arch/parisc/include/asm/cache.h             |    2 +-
 arch/parisc/include/asm/system.h            |    2 +-
 arch/parisc/kernel/head.S                   |    2 +-
 arch/parisc/kernel/init_task.c              |    8 +-
 arch/parisc/kernel/vmlinux.lds.S            |   26 +++---
 arch/powerpc/include/asm/cache.h            |    2 +-
 arch/powerpc/include/asm/page_64.h          |    2 +-
 arch/powerpc/include/asm/ppc_asm.h          |    4 +-
 arch/powerpc/kernel/head_32.S               |    2 +-
 arch/powerpc/kernel/head_40x.S              |    2 +-
 arch/powerpc/kernel/head_44x.S              |    2 +-
 arch/powerpc/kernel/head_8xx.S              |    2 +-
 arch/powerpc/kernel/head_fsl_booke.S        |    2 +-
 arch/powerpc/kernel/init_task.c             |    2 +-
 arch/powerpc/kernel/machine_kexec_64.c      |    2 +-
 arch/powerpc/kernel/vdso.c                  |    2 +-
 arch/powerpc/kernel/vdso32/vdso32_wrapper.S |    2 +-
 arch/powerpc/kernel/vdso64/vdso64_wrapper.S |    2 +-
 arch/powerpc/kernel/vmlinux.lds.S           |   28 +++---
 arch/s390/include/asm/cache.h               |    2 +-
 arch/s390/kernel/head.S                     |    2 +-
 arch/s390/kernel/init_task.c                |    2 +-
 arch/s390/kernel/vdso.c                     |    2 +-
 arch/s390/kernel/vdso32/vdso32_wrapper.S    |    2 +-
 arch/s390/kernel/vdso64/vdso64_wrapper.S    |    2 +-
 arch/s390/kernel/vmlinux.lds.S              |   20 ++--
 arch/sh/include/asm/cache.h                 |    2 +-
 arch/sh/kernel/cpu/sh5/entry.S              |    4 +-
 arch/sh/kernel/head_32.S                    |    2 +-
 arch/sh/kernel/head_64.S                    |    2 +-
 arch/sh/kernel/init_task.c                  |    2 +-
 arch/sh/kernel/irq.c                        |    4 +-
 arch/sh/kernel/vmlinux_32.lds.S             |   14 ++--
 arch/sh/kernel/vmlinux_64.lds.S             |   14 ++--
 arch/sparc/boot/btfixupprep.c               |    4 +-
 arch/sparc/include/asm/cache.h              |    2 +-
 arch/sparc/kernel/head_32.S                 |    4 +-
 arch/sparc/kernel/head_64.S                 |    2 +-
 arch/sparc/kernel/init_task.c               |    2 +-
 arch/sparc/kernel/vmlinux.lds.S             |   14 ++--
 arch/um/include/asm/common.lds.S            |    4 +-
 arch/um/kernel/dyn.lds.S                    |    4 +-
 arch/um/kernel/init_task.c                  |    4 +-
 arch/um/kernel/uml.lds.S                    |    4 +-
 arch/x86/Kconfig                            |    1 +
 arch/x86/boot/compressed/head_32.S          |    2 +-
 arch/x86/boot/compressed/head_64.S          |    2 +-
 arch/x86/boot/compressed/relocs.c           |    2 +-
 arch/x86/boot/compressed/vmlinux.scr        |    2 +-
 arch/x86/boot/compressed/vmlinux_32.lds     |   14 ++-
 arch/x86/boot/compressed/vmlinux_64.lds     |   10 +-
 arch/x86/include/asm/cache.h                |    4 +-
 arch/x86/kernel/acpi/wakeup_32.S            |    2 +-
 arch/x86/kernel/head_32.S                   |    6 +-
 arch/x86/kernel/head_64.S                   |    4 +-
 arch/x86/kernel/init_task.c                 |    4 +-
 arch/x86/kernel/traps.c                     |    2 +-
 arch/x86/kernel/vmlinux_32.lds.S            |   37 ++++---
 arch/x86/kernel/vmlinux_64.lds.S            |   27 +++---
 arch/xtensa/kernel/head.S                   |    2 +-
 arch/xtensa/kernel/init_task.c              |    2 +-
 arch/xtensa/kernel/vmlinux.lds.S            |    6 +-
 include/asm-frv/init.h                      |    8 +-
 include/asm-generic/vmlinux.lds.h           |   19 ++--
 include/linux/cache.h                       |    2 +-
 include/linux/init.h                        |    8 +-
 include/linux/linkage.h                     |    4 +-
 include/linux/percpu.h                      |   10 +-
 include/linux/spinlock.h                    |    2 +-
 kernel/module.c                             |    2 +-
 lib/Kconfig.debug                           |   18 +++
 scripts/mod/file2alias.c                    |    6 +-
 scripts/mod/modpost.c                       |  155 ++++++++++++++++-----------
 scripts/mod/modpost.h                       |   43 ++++++++
 scripts/recordmcount.pl                     |    6 +-
 142 files changed, 515 insertions(+), 409 deletions(-)



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