lkml.org 
[lkml]   [2018]   [Jun]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Subject[PATCH v9 0/6] add support for relative references in special sections
    Date
    This adds support for emitting special sections such as initcall arrays,
    PCI fixups and tracepoints as relative references rather than absolute
    references. This reduces the size by 50% on 64-bit architectures, but
    more importantly, it removes the need for carrying relocation metadata
    for these sections in relocatable kernels (e.g., for KASLR) that needs
    to be fixed up at boot time. On arm64, this reduces the vmlinux footprint
    of such a reference by 8x (8 byte absolute reference + 24 byte RELA entry
    vs 4 byte relative reference)

    Patch #3 was sent out before as a single patch. This series supersedes
    the previous submission. This version makes relative ksymtab entries
    dependent on the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS rather
    than trying to infer from kbuild test robot replies for which architectures
    it should be blacklisted.

    Patch #1 introduces the new Kconfig symbol HAVE_ARCH_PREL32_RELOCATIONS,
    and sets it for the main architectures that are expected to benefit the
    most from this feature, i.e., 64-bit architectures or ones that use
    runtime relocations.

    Patch #2 add support for #define'ing __DISABLE_EXPORTS to get rid of
    ksymtab/kcrctab sections in decompressor and EFI stub objects when
    rebuilding existing C files to run in a different context.

    Patches #4 - #6 implement relative references for initcalls, PCI fixups
    and tracepoints, respectively, all of which produce sections with order
    ~1000 entries on an arm64 defconfig kernel with tracing enabled. This
    means we save about 28 KB of vmlinux space for each of these patches.

    [From the v7 series blurb, which included the jump_label patches as well]:
    For the arm64 kernel, all patches combined reduce the memory footprint of
    vmlinux by about 1.3 MB (using a config copied from Ubuntu that has KASLR
    enabled), of which ~1 MB is the size reduction of the RELA section in .init,
    and the remaining 300 KB is reduction of .text/.data.

    Branch:
    git://git.kernel.org/pub/scm/linux/kernel/git/ardb/linux.git relative-special-sections-v9

    Changes since v8:
    - add Nico's ack (#2)
    - drop 'const' qualifier from __ADDRESSABLE(sym) to prevent mismatching
    attributes for the .discard section (#3)
    - drop all uses of VMLINUX_SYMBOL_STR(), which is on its way out (#3 - #6)

    Changes since v7:
    - dropped the jump_label patches, these will be revisited in a separate series
    - reorder __DISABLE_EXPORTS with __KSYM_DEPS__ check in #2
    - use offset_to_ptr() helper function to abstract the relative pointer
    conversion [int *off -> (ulong)off + *off] (#3 - #6)
    - rebase onto v4.16-rc3

    Changes since v6:
    - drop S390 from patch #1 introducing HAVE_ARCH_PREL32_RELOCATIONS: kbuild
    robot threw me some s390 curveballs, and given that s390 does not define
    CONFIG_RELOCATABLE in the first place, it does not benefit as much from
    relative references as arm64, x86 and power do
    - add patch to allow symbol exports to be disabled at compilation unit
    granularity (#2)
    - get rid of arm64 vmlinux.lds.S hunk to ensure code generated by __ADDRESSABLE
    gets discarded from the EFI stub - it is no longer needed after adding #2 (#1)
    - change _ADDRESSABLE() to emit a data reference, not a code reference - this
    is another simplification made possible by patch #2 (#3)
    - add Steven's ack to #6
    - split x86 jump_label patch into two (#9, #10)

    Changes since v5:
    - add missing jump_label prototypes to s390 jump_label.h (#6)
    - fix inverted condition in call to jump_entry_is_module_init() (#6)

    Changes since v4:
    - add patches to convert x86 and arm64 to use relative references for jump
    tables (#6 - #8)
    - rename PCI patch and add Bjorn's ack (#4)
    - rebase onto v4.15-rc5

    Changes since v3:
    - fix module unload issue in patch #5 reported by Jessica, by reusing the
    updated routine for_each_tracepoint_range() for the quiescent check at
    module unload time; this requires this routine to be moved before
    tracepoint_module_going() in kernel/tracepoint.c
    - add Jessica's ack to #2
    - rebase onto v4.14-rc1

    Changes since v2:
    - Revert my slightly misguided attempt to appease checkpatch, which resulted
    in needless churn and worse code. This v3 is based on v1 with a few tweaks
    that were actually reasonable checkpatch warnings: unnecessary braces (as
    pointed out by Ingo) and other minor whitespace misdemeanors.

    Changes since v1:
    - Remove checkpatch errors to the extent feasible: in some cases, this
    involves moving extern declarations into C files, and switching to
    struct definitions rather than typedefs. Some errors are impossible
    to fix: please find the remaining ones after the diffstat.
    - Used 'int' instead if 'signed int' for the various offset fields: there
    is no ambiguity between architectures regarding its signedness (unlike
    'char')
    - Refactor the different patches to be more uniform in the way they define
    the section entry type and accessors in the .h file, and avoid the need to
    add #ifdefs to the C code.

    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Michael Ellerman <mpe@ellerman.id.au>
    Cc: Thomas Garnier <thgarnie@google.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: "Serge E. Hallyn" <serge@hallyn.com>
    Cc: Bjorn Helgaas <bhelgaas@google.com>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Russell King <linux@armlinux.org.uk>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Petr Mladek <pmladek@suse.com>
    Cc: Ingo Molnar <mingo@redhat.com>
    Cc: James Morris <jmorris@namei.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Nicolas Pitre <nico@linaro.org>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Jessica Yu <jeyu@kernel.org>

    Cc: linux-arm-kernel@lists.infradead.org
    Cc: linux-kernel@vger.kernel.org
    Cc: linuxppc-dev@lists.ozlabs.org
    Cc: x86@kernel.org

    Ard Biesheuvel (6):
    arch: enable relative relocations for arm64, power and x86
    module: allow symbol exports to be disabled
    module: use relative references for __ksymtab entries
    init: allow initcall tables to be emitted using relative references
    PCI: Add support for relative addressing in quirk tables
    kernel: tracepoints: add support for relative references

    arch/Kconfig | 10 ++++
    arch/arm64/Kconfig | 1 +
    arch/powerpc/Kconfig | 1 +
    arch/x86/Kconfig | 1 +
    arch/x86/boot/compressed/kaslr.c | 5 +-
    arch/x86/include/asm/Kbuild | 1 +
    arch/x86/include/asm/export.h | 5 --
    drivers/firmware/efi/libstub/Makefile | 3 +-
    drivers/pci/quirks.c | 12 +++--
    include/asm-generic/export.h | 12 ++++-
    include/linux/compiler.h | 19 +++++++
    include/linux/export.h | 57 +++++++++++++++-----
    include/linux/init.h | 44 +++++++++++----
    include/linux/pci.h | 20 +++++++
    include/linux/tracepoint.h | 19 +++++--
    init/main.c | 32 +++++------
    kernel/module.c | 32 ++++++++---
    kernel/printk/printk.c | 16 +++---
    kernel/tracepoint.c | 49 +++++++++--------
    security/security.c | 17 +++---
    20 files changed, 255 insertions(+), 101 deletions(-)
    delete mode 100644 arch/x86/include/asm/export.h

    --
    2.11.0

    \
     
     \ /
      Last update: 2018-06-26 20:29    [W:2.770 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site