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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:message-id:mime-version:subject:from :to:cc; bh=9znxVvQ/9PAVTHgEOV292+fDBKHMlDcfsU9d9H/6O4k=; b=OQJmprItKi83gKmDg2PmRfmV0zUU72XvnqEdH9Mcffw9T3WwTY1YVRtXAWThhGwb0n jqbrZhfzLGBOOqYhNyLlT9gJaXKrktkEPO94Zuv5e+wwomu4dvfJSVBVfg/VNeyEiOYr 4IFFIqVlqDT7wySbUN/86+DdpjjiL4XMEtpR552Vr0XPi58pJV4BwYYFdO+eJWuckwww KixMGfOwQyWFfMAWQqb1z3g9lDNkVc103R1TC2dwOAPRWUntWNwwYkN3T9ZnpGpgfn8h T4M7vZc8Rja0EPsF1f3LNLWSpmShX+a8VUKnhUIpJFkTYuHebSktAdQOgAcCV5DPASJ9 uKWw== X-Gm-Message-State: AOAM530W90NWF3BMfRi0B8u6eh2k11xPW3Qk8Bvba/f5r/XRwnssMyMm /UaPMSQrGAjUqAxrpSWbzSlZWFiNNbv8vyKTT5M= X-Google-Smtp-Source: ABdhPJz0ek2SN2U3fjfWQhqwMXyCIcZwDvklDVCCSVaJyxuiJlfb7KJJKz1h/PtZ4xu/S0R9tK22wDIg3yDTEgQwy4E= X-Received: from samitolvanen1.mtv.corp.google.com ([2620:15c:201:2:f693:9fff:fef4:1b6d]) (user=samitolvanen job=sendgmr) by 2002:a25:22d5:: with SMTP id i204mr22729999ybi.0.1607712395089; Fri, 11 Dec 2020 10:46:35 -0800 (PST) Date: Fri, 11 Dec 2020 10:46:17 -0800 Message-Id: <20201211184633.3213045-1-samitolvanen@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.29.2.576.ga3fc446d84-goog Subject: [PATCH v9 00/16] Add support for Clang LTO From: Sami Tolvanen To: Masahiro Yamada , Steven Rostedt , Will Deacon X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201211_134639_504971_D3C32260 X-CRM114-Status: GOOD ( 29.32 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Kees Cook , "Paul E. McKenney" , kernel-hardening@lists.openwall.com, Peter Zijlstra , Greg Kroah-Hartman , linux-kbuild@vger.kernel.org, Nick Desaulniers , linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, clang-built-linux@googlegroups.com, Sami Tolvanen , Josh Poimboeuf , linux-arm-kernel@lists.infradead.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org This patch series adds support for building the kernel with Clang's Link Time Optimization (LTO). In addition to performance, the primary motivation for LTO is to allow Clang's Control-Flow Integrity (CFI) to be used in the kernel. Google has shipped millions of Pixel devices running three major kernel versions with LTO+CFI since 2018. Most of the patches are build system changes for handling LLVM bitcode, which Clang produces with LTO instead of ELF object files, postponing ELF processing until a later stage, and ensuring initcall ordering. Note that arm64 support depends on Will's memory ordering patches [1]. I will post x86_64 patches separately after we have fixed the remaining objtool warnings [2][3]. [1] https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/lto [2] https://lore.kernel.org/lkml/20201120040424.a3wctajzft4ufoiw@treble/ [3] https://git.kernel.org/pub/scm/linux/kernel/git/jpoimboe/linux.git/log/?h=objtool-vmlinux You can also pull this series from https://github.com/samitolvanen/linux.git lto-v9 --- Changes in v9: - Added HAS_LTO_CLANG dependencies to LLVM=1 and LLVM_IAS=1 to avoid issues with mismatched toolchains. - Dropped the .mod patch as Masahiro landed a better solution to the split line issue in commit 7d32358be8ac ("kbuild: avoid split lines in .mod files"). - Updated CC_FLAGS_LTO to use -fvisibility=hidden to avoid weak symbol visibility issues with ThinLTO on x86. - Changed LTO_CLANG_FULL to depend on !COMPILE_TEST to prevent timeouts in automated testing. - Added a dependency to CPU_LITTLE_ENDIAN to ARCH_SUPPORTS_LTO_CLANG in arch/arm64/Kconfig. - Added a default symbol list to fix an issue with TRIM_UNUSED_KSYMS. Changes in v8: - Cleaned up the LTO Kconfig options based on suggestions from Nick and Kees. - Dropped the patch to disable LTO for the arm64 nVHE KVM code as David pointed out it's not needed anymore. Changes in v7: - Rebased to master again. - Added back arm64 patches as the prerequisites are now staged, and dropped x86_64 support until the remaining objtool issues are resolved. - Dropped ifdefs from module.lds.S. Changes in v6: - Added the missing --mcount flag to patch 5. - Dropped the arm64 patches from this series and will repost them later. Changes in v5: - Rebased on top of tip/master. - Changed the command line for objtool to use --vmlinux --duplicate to disable warnings about retpoline thunks and to fix .orc_unwind generation for vmlinux.o. - Added --noinstr flag to objtool, so we can use --vmlinux without also enabling noinstr validation. - Disabled objtool's unreachable instruction warnings with LTO to disable false positives for the int3 padding in vmlinux.o. - Added ANNOTATE_RETPOLINE_SAFE annotations to the indirect jumps in x86 assembly code to fix objtool warnings with retpoline. - Fixed modpost warnings about missing version information with CONFIG_MODVERSIONS. - Included Makefile.lib into Makefile.modpost for ld_flags. Thanks to Sedat for pointing this out. - Updated the help text for ThinLTO to better explain the trade-offs. - Updated commit messages with better explanations. Changes in v4: - Fixed a typo in Makefile.lib to correctly pass --no-fp to objtool. - Moved ftrace configs related to generating __mcount_loc to Kconfig, so they are available also in Makefile.modfinal. - Dropped two prerequisite patches that were merged to Linus' tree. Changes in v3: - Added a separate patch to remove the unused DISABLE_LTO treewide, as filtering out CC_FLAGS_LTO instead is preferred. - Updated the Kconfig help to explain why LTO is behind a choice and disabled by default. - Dropped CC_FLAGS_LTO_CLANG, compiler-specific LTO flags are now appended directly to CC_FLAGS_LTO. - Updated $(AR) flags as KBUILD_ARFLAGS was removed earlier. - Fixed ThinLTO cache handling for external module builds. - Rebased on top of Masahiro's patch for preprocessing modules.lds, and moved the contents of module-lto.lds to modules.lds.S. - Moved objtool_args to Makefile.lib to avoid duplication of the command line parameters in Makefile.modfinal. - Clarified in the commit message for the initcall ordering patch that the initcall order remains the same as without LTO. - Changed link-vmlinux.sh to use jobserver-exec to control the number of jobs started by generate_initcall_ordering.pl. - Dropped the x86/relocs patch to whitelist L4_PAGE_OFFSET as it's no longer needed with ToT kernel. - Disabled LTO for arch/x86/power/cpu.c to work around a Clang bug with stack protector attributes. Changes in v2: - Fixed -Wmissing-prototypes warnings with W=1. - Dropped cc-option from -fsplit-lto-unit and added .thinlto-cache scrubbing to make distclean. - Added a comment about Clang >=11 being required. - Added a patch to disable LTO for the arm64 KVM nVHE code. - Disabled objtool's noinstr validation with LTO unless enabled. - Included Peter's proposed objtool mcount patch in the series and replaced recordmcount with the objtool pass to avoid whitelisting relocations that are not calls. - Updated several commit messages with better explanations. Sami Tolvanen (16): tracing: move function tracer options to Kconfig kbuild: add support for Clang LTO kbuild: lto: fix module versioning kbuild: lto: limit inlining kbuild: lto: merge module sections kbuild: lto: add a default list of used symbols init: lto: ensure initcall ordering init: lto: fix PREL32 relocations PCI: Fix PREL32 relocations for LTO modpost: lto: strip .lto from module names scripts/mod: disable LTO for empty.c efi/libstub: disable LTO drivers/misc/lkdtm: disable LTO for rodata.o arm64: vdso: disable LTO arm64: disable recordmcount with DYNAMIC_FTRACE_WITH_REGS arm64: allow LTO to be selected .gitignore | 1 + Makefile | 45 +++-- arch/Kconfig | 90 +++++++++ arch/arm64/Kconfig | 4 + arch/arm64/kernel/vdso/Makefile | 3 +- drivers/firmware/efi/libstub/Makefile | 2 + drivers/misc/lkdtm/Makefile | 1 + include/asm-generic/vmlinux.lds.h | 11 +- include/linux/init.h | 79 +++++++- include/linux/pci.h | 19 +- init/Kconfig | 1 + kernel/trace/Kconfig | 16 ++ scripts/Makefile.build | 48 ++++- scripts/Makefile.lib | 6 +- scripts/Makefile.modfinal | 9 +- scripts/Makefile.modpost | 25 ++- scripts/generate_initcall_order.pl | 270 ++++++++++++++++++++++++++ scripts/link-vmlinux.sh | 70 ++++++- scripts/lto-used-symbollist | 5 + scripts/mod/Makefile | 1 + scripts/mod/modpost.c | 16 +- scripts/mod/modpost.h | 9 + scripts/mod/sumversion.c | 6 +- scripts/module.lds.S | 24 +++ 24 files changed, 696 insertions(+), 65 deletions(-) create mode 100755 scripts/generate_initcall_order.pl create mode 100644 scripts/lto-used-symbollist base-commit: 33dc9614dc208291d0c4bcdeb5d30d481dcd2c4c