From patchwork Fri Aug 5 12:12:00 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nicholas Piggin X-Patchwork-Id: 9265323 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 2B99F60760 for ; Fri, 5 Aug 2016 12:13:02 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1A4FE283E4 for ; Fri, 5 Aug 2016 12:13:02 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 0EE0828400; Fri, 5 Aug 2016 12:13:02 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=2.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED, FREEMAIL_FROM, RCVD_IN_DNSWL_HI, T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 028CC283E4 for ; Fri, 5 Aug 2016 12:13:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161098AbcHEMM6 (ORCPT ); Fri, 5 Aug 2016 08:12:58 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:34340 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934333AbcHEMMz (ORCPT ); Fri, 5 Aug 2016 08:12:55 -0400 Received: by mail-pf0-f194.google.com with SMTP id g202so20126012pfb.1; Fri, 05 Aug 2016 05:12:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=NfgmW4ejJ9+o25+smPitwFwpcSLucpXi9+8fJrMutCU=; b=YcrJMKHaBYT2w/xG1bjehTxTrbH9v5h+DThAIK2cAPvGiF7wmBg0Kr0g7JeAUeaAN6 u0uwugbH7SLQB4nWH3/2R5/tHEru5mTL+gq7803hinr2rXLEDb8aYVD6m/5hbneK6ZKk KJjKQaMBoQ1ZfvYxPjdrI+0ojqFF+3Eoxx6LWj7+GYrmg7zw9dcL+dPnmYuiq/IEta9b VZ+FkB9EckvrfngfsWBkgOaPa9tNpVtVOp2slJu/HVb9hr2hRzsh7gTff6JwCRkS4zDX dT8EsafmgUlMGuYn+4eQQ3h0mlvx7HI0+tOLQWbu20sP4l2HyXO/smOE7CAYHZIai1ZO pwBw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=NfgmW4ejJ9+o25+smPitwFwpcSLucpXi9+8fJrMutCU=; b=FHr6rhWx5J7PKlTw71GxF1O2RIhGXh3EWKXFULC1yHh6m2CpTNqLrHVQ4OJxRw8XOo 1hN3nCue1+2z2aajGnMDd1VTXN9YGFAks3b2wHwKozZg1gCYUqLeaL8qrFIAhfu7sjdE qxR5uelGVw/9pNujDbvUnm5kXNK11xtkFPyyz4xSK6Pbx5qKJHf5Fua0i/B1TOg+zLsm FMQtJNCXRoffJQSeUq5IwvA03Taic1BIkqxgAS+ftWUEmRYCDCEaJVg86vOovLKotyTF Mi42pI6GJGPamQLmK69QKWqko0VTEpDI4aUz3uNjy/XIy+PC9i/D43s5bWUxWZ60XGjE PfyA== X-Gm-Message-State: AEkoousHQkJcI4bjSqhY1UUsHTirCTN2GIUdjZHLupnZzqg+FU6JQBP+t2tJXbf40654ZA== X-Received: by 10.98.16.75 with SMTP id y72mr134721918pfi.50.1470399169818; Fri, 05 Aug 2016 05:12:49 -0700 (PDT) Received: from roar.ozlabs.ibm.com ([122.99.82.10]) by smtp.gmail.com with ESMTPSA id m65sm27669685pfg.79.2016.08.05.05.12.44 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 05 Aug 2016 05:12:49 -0700 (PDT) From: Nicholas Piggin To: linux-kbuild@vger.kernel.org Cc: Nicholas Piggin , linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Stephen Rothwell , Arnd Bergmann , Nicolas Pitre , Segher Boessenkool , Alan Modra Subject: [PATCH 2/5] kbuild: allow archs to select build for link dead code/data elimination Date: Fri, 5 Aug 2016 22:12:00 +1000 Message-Id: <1470399123-8455-3-git-send-email-npiggin@gmail.com> X-Mailer: git-send-email 2.8.1 In-Reply-To: <1470399123-8455-1-git-send-email-npiggin@gmail.com> References: <1470399123-8455-1-git-send-email-npiggin@gmail.com> Sender: linux-kbuild-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kbuild@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Introduce LINKER_DCE option for architectures to select if they want to build with -ffunction-sections, -fdata-sections, and link with --gc-sections. It requires some work (documented) to ensure all unreferenced entrypoints are live, and requires toolchain and build verification, so it is made a per-arch option for now. On a random powerpc64le build, this yelds a significant size saving, it boots and runs fine, but there is a lot I haven't tested as yet, so these savings may be reduced if there are bugs in the link. text data bss dec filename 11169741 1180744 1923176 14273661 vmlinux 10445269 1004127 1919707 13369103 vmlinux.dce ~700K text, ~170K data, 6% removed from kernel image size. Signed-off-by: Nicholas Piggin --- Makefile | 10 ++++++++ arch/Kconfig | 13 ++++++++++ include/asm-generic/vmlinux.lds.h | 52 ++++++++++++++++++++++----------------- include/linux/compiler.h | 18 ++++++++++++++ include/linux/export.h | 30 +++++++++++----------- include/linux/init.h | 38 ++++++++++------------------ init/Makefile | 2 ++ 7 files changed, 100 insertions(+), 63 deletions(-) diff --git a/Makefile b/Makefile index b409076..d5ef31a 100644 --- a/Makefile +++ b/Makefile @@ -618,6 +618,11 @@ include arch/$(SRCARCH)/Makefile KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) +ifdef CONFIG_LINKER_DCE +KBUILD_CFLAGS += $(call cc-option,-ffunction-sections,) +KBUILD_CFLAGS += $(call cc-option,-fdata-sections,) +endif + ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE KBUILD_CFLAGS += -Os $(call cc-disable-warning,maybe-uninitialized,) else @@ -819,6 +824,11 @@ LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\ KBUILD_LDFLAGS_MODULE += $(LDFLAGS_BUILD_ID) LDFLAGS_vmlinux += $(LDFLAGS_BUILD_ID) +ifdef CONFIG_LINKER_DCE +# LDFLAGS_MODULE += $(call ld-option, --gc-sections,) +LDFLAGS_vmlinux += $(call ld-option, --gc-sections,) +endif + ifeq ($(CONFIG_STRIP_ASM_SYMS),y) LDFLAGS_vmlinux += $(call ld-option, -X,) endif diff --git a/arch/Kconfig b/arch/Kconfig index 1330bf4..a49092b 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -430,6 +430,19 @@ config THIN_ARCHIVES Select this if the architecture wants to use thin archives instead of ld -r to create the built-in.o files. +config LINKER_DCE + bool + help + Select this if the architecture wants to do dead code and + data elimination with the linker by compiling with + -ffunction-sections -fdata-sections and linking with + --gc-sections. + + This requires that the arch annotates or otherwise protects + its external entry points from being discarded. Linker scripts + must also merge .text.*, .data.*, and .bss.* correctly into + output sections. + config HAVE_CONTEXT_TRACKING bool help diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 6a67ab9..a66ffe9 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -196,9 +196,14 @@ *(.dtb.init.rodata) \ VMLINUX_SYMBOL(__dtb_end) = .; -/* .data section */ +/* + * .data section + * -fdata-sections generates .data.identifier which needs to be pulled in + * with .data, but don't want to pull in .data..stuff which has its own + * requirements. Same for bss. + */ #define DATA_DATA \ - *(.data) \ + *(.data .data.[0-9a-zA-Z_]*) \ *(.ref.data) \ *(.data..shared_aligned) /* percpu related */ \ MEM_KEEP(init.data) \ @@ -312,76 +317,76 @@ /* Kernel symbol table: Normal symbols */ \ __ksymtab : AT(ADDR(__ksymtab) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___ksymtab) = .; \ - *(SORT(___ksymtab+*)) \ + KEEP(*(SORT(___ksymtab+*))) \ VMLINUX_SYMBOL(__stop___ksymtab) = .; \ } \ \ /* Kernel symbol table: GPL-only symbols */ \ __ksymtab_gpl : AT(ADDR(__ksymtab_gpl) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___ksymtab_gpl) = .; \ - *(SORT(___ksymtab_gpl+*)) \ + KEEP(*(SORT(___ksymtab_gpl+*))) \ VMLINUX_SYMBOL(__stop___ksymtab_gpl) = .; \ } \ \ /* Kernel symbol table: Normal unused symbols */ \ __ksymtab_unused : AT(ADDR(__ksymtab_unused) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___ksymtab_unused) = .; \ - *(SORT(___ksymtab_unused+*)) \ + KEEP(*(SORT(___ksymtab_unused+*))) \ VMLINUX_SYMBOL(__stop___ksymtab_unused) = .; \ } \ \ /* Kernel symbol table: GPL-only unused symbols */ \ __ksymtab_unused_gpl : AT(ADDR(__ksymtab_unused_gpl) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___ksymtab_unused_gpl) = .; \ - *(SORT(___ksymtab_unused_gpl+*)) \ + KEEP(*(SORT(___ksymtab_unused_gpl+*))) \ VMLINUX_SYMBOL(__stop___ksymtab_unused_gpl) = .; \ } \ \ /* Kernel symbol table: GPL-future-only symbols */ \ __ksymtab_gpl_future : AT(ADDR(__ksymtab_gpl_future) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___ksymtab_gpl_future) = .; \ - *(SORT(___ksymtab_gpl_future+*)) \ + KEEP(*(SORT(___ksymtab_gpl_future+*))) \ VMLINUX_SYMBOL(__stop___ksymtab_gpl_future) = .; \ } \ \ /* Kernel symbol table: Normal symbols */ \ __kcrctab : AT(ADDR(__kcrctab) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___kcrctab) = .; \ - *(SORT(___kcrctab+*)) \ + KEEP(*(SORT(___kcrctab+*))) \ VMLINUX_SYMBOL(__stop___kcrctab) = .; \ } \ \ /* Kernel symbol table: GPL-only symbols */ \ __kcrctab_gpl : AT(ADDR(__kcrctab_gpl) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___kcrctab_gpl) = .; \ - *(SORT(___kcrctab_gpl+*)) \ + KEEP(*(SORT(___kcrctab_gpl+*))) \ VMLINUX_SYMBOL(__stop___kcrctab_gpl) = .; \ } \ \ /* Kernel symbol table: Normal unused symbols */ \ __kcrctab_unused : AT(ADDR(__kcrctab_unused) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___kcrctab_unused) = .; \ - *(SORT(___kcrctab_unused+*)) \ + KEEP(*(SORT(___kcrctab_unused+*))) \ VMLINUX_SYMBOL(__stop___kcrctab_unused) = .; \ } \ \ /* Kernel symbol table: GPL-only unused symbols */ \ __kcrctab_unused_gpl : AT(ADDR(__kcrctab_unused_gpl) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___kcrctab_unused_gpl) = .; \ - *(SORT(___kcrctab_unused_gpl+*)) \ + KEEP(*(SORT(___kcrctab_unused_gpl+*))) \ VMLINUX_SYMBOL(__stop___kcrctab_unused_gpl) = .; \ } \ \ /* Kernel symbol table: GPL-future-only symbols */ \ __kcrctab_gpl_future : AT(ADDR(__kcrctab_gpl_future) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__start___kcrctab_gpl_future) = .; \ - *(SORT(___kcrctab_gpl_future+*)) \ + KEEP(*(SORT(___kcrctab_gpl_future+*))) \ VMLINUX_SYMBOL(__stop___kcrctab_gpl_future) = .; \ } \ \ /* Kernel symbol table: strings */ \ __ksymtab_strings : AT(ADDR(__ksymtab_strings) - LOAD_OFFSET) { \ - *(__ksymtab_strings) \ + KEEP(*(__ksymtab_strings)) \ } \ \ /* __*init sections */ \ @@ -416,7 +421,7 @@ #define SECURITY_INIT \ .security_initcall.init : AT(ADDR(.security_initcall.init) - LOAD_OFFSET) { \ VMLINUX_SYMBOL(__security_initcall_start) = .; \ - *(.security_initcall.init) \ + KEEP(*(.security_initcall.init)) \ VMLINUX_SYMBOL(__security_initcall_end) = .; \ } @@ -424,7 +429,7 @@ * during second ld run in second ld pass when generating System.map */ #define TEXT_TEXT \ ALIGN_FUNCTION(); \ - *(.text.hot .text .text.fixup .text.unlikely) \ + *(.text.hot .text .text.fixup .text.unlikely .text.*) \ *(.ref.text) \ MEM_KEEP(init.text) \ MEM_KEEP(exit.text) \ @@ -519,6 +524,7 @@ /* init and exit section handling */ #define INIT_DATA \ + KEEP(*(SORT(___kentry+*))) \ *(.init.data) \ MEM_DISCARD(init.data) \ KERNEL_CTORS() \ @@ -581,7 +587,7 @@ BSS_FIRST_SECTIONS \ *(.bss..page_aligned) \ *(.dynbss) \ - *(.bss) \ + *(.bss .bss.[0-9a-zA-Z_]*) \ *(COMMON) \ } @@ -664,12 +670,12 @@ #define INIT_CALLS_LEVEL(level) \ VMLINUX_SYMBOL(__initcall##level##_start) = .; \ - *(.initcall##level##.init) \ - *(.initcall##level##s.init) \ + KEEP(*(.initcall##level##.init)) \ + KEEP(*(.initcall##level##s.init)) \ #define INIT_CALLS \ VMLINUX_SYMBOL(__initcall_start) = .; \ - *(.initcallearly.init) \ + KEEP(*(.initcallearly.init)) \ INIT_CALLS_LEVEL(0) \ INIT_CALLS_LEVEL(1) \ INIT_CALLS_LEVEL(2) \ @@ -683,21 +689,21 @@ #define CON_INITCALL \ VMLINUX_SYMBOL(__con_initcall_start) = .; \ - *(.con_initcall.init) \ + KEEP(*(.con_initcall.init)) \ VMLINUX_SYMBOL(__con_initcall_end) = .; #define SECURITY_INITCALL \ VMLINUX_SYMBOL(__security_initcall_start) = .; \ - *(.security_initcall.init) \ + KEEP(*(.security_initcall.init)) \ VMLINUX_SYMBOL(__security_initcall_end) = .; #ifdef CONFIG_BLK_DEV_INITRD #define INIT_RAM_FS \ . = ALIGN(4); \ VMLINUX_SYMBOL(__initramfs_start) = .; \ - *(.init.ramfs) \ + KEEP(*(.init.ramfs)) \ . = ALIGN(8); \ - *(.init.ramfs.info) + KEEP(*(.init.ramfs.info)) #else #define INIT_RAM_FS #endif diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 793c082..8404d93 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -184,6 +184,24 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); # define unreachable() do { } while (1) #endif +/* + * KENTRY - kernel entry point + * This can be used to annotate symbols (functions or data) that are used + * without their linker symbol being referenced. For example, interrupt vector + * handlers, or functions in the kernel image that are found programatically. + * This can be avoided if the symbols are marked as KEEP() in the linker script. + * For example the architecture could KEEP() its entire exception vector + * code rather than annotate each one. + */ +#ifndef KENTRY +# define KENTRY(sym) \ + extern typeof(sym) sym; \ + static const unsigned long __kentry_##sym \ + __used \ + __attribute__((section("___kentry" "+" #sym ), used)) \ + = (unsigned long)&sym; +#endif + #ifndef RELOC_HIDE # define RELOC_HIDE(ptr, off) \ ({ unsigned long __ptr; \ diff --git a/include/linux/export.h b/include/linux/export.h index 2f9ccbe..0d1ccdd 100644 --- a/include/linux/export.h +++ b/include/linux/export.h @@ -1,5 +1,6 @@ #ifndef _LINUX_EXPORT_H #define _LINUX_EXPORT_H + /* * Export symbols from the kernel to modules. Forked from module.h * to reduce the amount of pointless cruft we feed to gcc when only @@ -42,27 +43,26 @@ extern struct module __this_module; #ifdef CONFIG_MODVERSIONS /* Mark the CRC weak since genksyms apparently decides not to * generate a checksums for some symbols */ -#define __CRC_SYMBOL(sym, sec) \ - extern __visible void *__crc_##sym __attribute__((weak)); \ - static const unsigned long __kcrctab_##sym \ - __used \ - __attribute__((section("___kcrctab" sec "+" #sym), unused)) \ +#define __CRC_SYMBOL(sym, sec) \ + extern __visible void *__crc_##sym __attribute__((weak)); \ + static const unsigned long __kcrctab_##sym \ + __used \ + __attribute__((section("___kcrctab" sec "+" #sym), used)) \ = (unsigned long) &__crc_##sym; #else #define __CRC_SYMBOL(sym, sec) #endif /* For every exported symbol, place a struct in the __ksymtab section */ -#define ___EXPORT_SYMBOL(sym, sec) \ - extern typeof(sym) sym; \ - __CRC_SYMBOL(sym, sec) \ - static const char __kstrtab_##sym[] \ - __attribute__((section("__ksymtab_strings"), aligned(1))) \ - = VMLINUX_SYMBOL_STR(sym); \ - extern const struct kernel_symbol __ksymtab_##sym; \ - __visible const struct kernel_symbol __ksymtab_##sym \ - __used \ - __attribute__((section("___ksymtab" sec "+" #sym), unused)) \ +#define ___EXPORT_SYMBOL(sym, sec) \ + extern typeof(sym) sym; \ + __CRC_SYMBOL(sym, sec) \ + static const char __kstrtab_##sym[] \ + __attribute__((section("__ksymtab_strings"), aligned(1))) \ + = VMLINUX_SYMBOL_STR(sym); \ + static const struct kernel_symbol __ksymtab_##sym \ + __used \ + __attribute__((section("___ksymtab" sec "+" #sym), used)) \ = { (unsigned long)&sym, __kstrtab_##sym } #if defined(__KSYM_DEPS__) diff --git a/include/linux/init.h b/include/linux/init.h index aedb254..9abd61f 100644 --- a/include/linux/init.h +++ b/include/linux/init.h @@ -156,24 +156,8 @@ extern bool initcall_debug; #ifndef __ASSEMBLY__ -#ifdef CONFIG_LTO -/* Work around a LTO gcc problem: when there is no reference to a variable - * in a module it will be moved to the end of the program. This causes - * reordering of initcalls which the kernel does not like. - * Add a dummy reference function to avoid this. The function is - * deleted by the linker. - */ -#define LTO_REFERENCE_INITCALL(x) \ - ; /* yes this is needed */ \ - static __used __exit void *reference_##x(void) \ - { \ - return &x; \ - } -#else -#define LTO_REFERENCE_INITCALL(x) -#endif - -/* initcalls are now grouped by functionality into separate +/* + * initcalls are now grouped by functionality into separate * subsections. Ordering inside the subsections is determined * by link order. * For backwards compatibility, initcall() puts the call in @@ -181,12 +165,16 @@ extern bool initcall_debug; * * The `id' arg to __define_initcall() is needed so that multiple initcalls * can point at the same handler without causing duplicate-symbol build errors. + * + * Initcalls are run by placing pointers in initcall sections that the + * kernel iterates at runtime. The linker can do dead code / data elimination + * and remove that completely, so the initcall sections have to be marked + * as KEEP() in the linker script. */ #define __define_initcall(fn, id) \ static initcall_t __initcall_##fn##id __used \ - __attribute__((__section__(".initcall" #id ".init"))) = fn; \ - LTO_REFERENCE_INITCALL(__initcall_##fn##id) + __attribute__((__section__(".initcall" #id ".init"))) = fn; /* * Early initcalls run before initializing SMP. @@ -222,15 +210,15 @@ extern bool initcall_debug; #define __initcall(fn) device_initcall(fn) -#define __exitcall(fn) \ +#define __exitcall(fn) \ static exitcall_t __exitcall_##fn __exit_call = fn -#define console_initcall(fn) \ - static initcall_t __initcall_##fn \ +#define console_initcall(fn) \ + static initcall_t __initcall_##fn \ __used __section(.con_initcall.init) = fn -#define security_initcall(fn) \ - static initcall_t __initcall_##fn \ +#define security_initcall(fn) \ + static initcall_t __initcall_##fn \ __used __section(.security_initcall.init) = fn struct obs_kernel_param { diff --git a/init/Makefile b/init/Makefile index 7bc47ee..c4fb455 100644 --- a/init/Makefile +++ b/init/Makefile @@ -2,6 +2,8 @@ # Makefile for the linux kernel. # +ccflags-y := -fno-function-sections -fno-data-sections + obj-y := main.o version.o mounts.o ifneq ($(CONFIG_BLK_DEV_INITRD),y) obj-y += noinitramfs.o