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 relocatables kernels (e.g., for KASLR) that need to fix up these absolute references 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 #2 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. Patches #3 - #5 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. Patches #6 - #8 have been added in v5, and implement relative references in jump tables for arm64 and x86. On arm64, this results in significant space savings (650+ KB on a typical distro kernel). On x86, the savings are not as impressive, but still worthwhile. (Note that these patches do not rely on CONFIG_HAVE_ARCH_PREL32_RELOCATIONS, given that the inline asm that is emitted is already per-arch) 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-v6 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: "H. Peter Anvin" <[email protected]> Cc: Ralf Baechle <[email protected]> Cc: Arnd Bergmann <[email protected]> Cc: Heiko Carstens <[email protected]> Cc: Kees Cook <[email protected]> Cc: Will Deacon <[email protected]> Cc: Michael Ellerman <[email protected]> Cc: Thomas Garnier <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: "Serge E. Hallyn" <[email protected]> Cc: Bjorn Helgaas <[email protected]> Cc: Benjamin Herrenschmidt <[email protected]> Cc: Russell King <[email protected]> Cc: Paul Mackerras <[email protected]> Cc: Catalin Marinas <[email protected]> Cc: "David S. Miller" <[email protected]> Cc: Petr Mladek <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: James Morris <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Nicolas Pitre <[email protected]> Cc: Josh Poimboeuf <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Martin Schwidefsky <[email protected]> Cc: Sergey Senozhatsky <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Jessica Yu <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Ard Biesheuvel (8): arch: enable relative relocations for arm64, power, x86, s390 and x86 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 kernel/jump_label: abstract jump_entry member accessors arm64/kernel: jump_label: use relative references x86/kernel: jump_table: use relative references arch/Kconfig | 10 ++++ arch/arm/include/asm/jump_label.h | 27 +++++++++ arch/arm64/Kconfig | 1 + arch/arm64/include/asm/jump_label.h | 48 +++++++++++++--- arch/arm64/kernel/jump_label.c | 22 +++++++- arch/arm64/kernel/vmlinux.lds.S | 2 +- arch/mips/include/asm/jump_label.h | 27 +++++++++ arch/powerpc/Kconfig | 1 + arch/powerpc/include/asm/jump_label.h | 27 +++++++++ arch/s390/Kconfig | 1 + arch/s390/include/asm/jump_label.h | 20 +++++++ arch/sparc/include/asm/jump_label.h | 27 +++++++++ arch/tile/include/asm/jump_label.h | 27 +++++++++ arch/x86/Kconfig | 1 + arch/x86/include/asm/Kbuild | 1 + arch/x86/include/asm/export.h | 5 -- arch/x86/include/asm/jump_label.h | 56 +++++++++++++++---- arch/x86/kernel/jump_label.c | 59 ++++++++++++++------ drivers/pci/quirks.c | 13 ++++- include/asm-generic/export.h | 12 +++- include/linux/compiler.h | 11 ++++ include/linux/export.h | 46 +++++++++++---- include/linux/init.h | 44 +++++++++++---- include/linux/pci.h | 20 +++++++ include/linux/tracepoint.h | 19 +++++-- init/main.c | 32 +++++------ kernel/jump_label.c | 38 ++++++------- kernel/module.c | 33 +++++++++-- kernel/printk/printk.c | 4 +- kernel/tracepoint.c | 50 +++++++++-------- security/security.c | 4 +- tools/objtool/special.c | 4 +- 32 files changed, 544 insertions(+), 148 deletions(-) delete mode 100644 arch/x86/include/asm/export.h -- 2.11.0
