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From: Sami Tolvanen <samitolvanen@google.com>
To: Masahiro Yamada <masahiroy@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>
Cc: Will Deacon <will@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	clang-built-linux@googlegroups.com,
	kernel-hardening@lists.openwall.com, linux-arch@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-pci@vger.kernel.org, x86@kernel.org,
	Sami Tolvanen <samitolvanen@google.com>
Subject: [PATCH v6 11/25] kbuild: lto: postpone objtool
Date: Mon, 12 Oct 2020 17:31:49 -0700
Message-ID: <20201013003203.4168817-12-samitolvanen@google.com> (raw)
In-Reply-To: <20201013003203.4168817-1-samitolvanen@google.com>

With LTO, LLVM bitcode won't be compiled into native code until
modpost_link, or modfinal for modules. This change postpones calls
to objtool until after these steps, and moves objtool_args to
Makefile.lib, so the arguments can be reused in Makefile.modfinal.

As we didn't have objects to process earlier, we use --duplicate
when processing vmlinux.o. This change also disables unreachable
instruction warnings with LTO to avoid warnings about the int3
padding between functions.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
---
 arch/Kconfig              |  2 +-
 scripts/Makefile.build    | 22 ++--------------------
 scripts/Makefile.lib      | 11 +++++++++++
 scripts/Makefile.modfinal | 19 ++++++++++++++++---
 scripts/link-vmlinux.sh   | 28 +++++++++++++++++++++++++---
 5 files changed, 55 insertions(+), 27 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index caeb6feb517e..74cbd6e3b116 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -612,7 +612,7 @@ config LTO_CLANG
 	depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
 	depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
 	depends on ARCH_SUPPORTS_LTO_CLANG
-	depends on !FTRACE_MCOUNT_RECORD
+	depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
 	depends on !KASAN
 	depends on !GCOV_KERNEL
 	select LTO
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index e08e66413dbe..ab0ddf4884fd 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -218,30 +218,11 @@ cmd_record_mcount = $(if $(findstring $(strip $(CC_FLAGS_FTRACE)),$(_c_flags)),
 endif # CONFIG_FTRACE_MCOUNT_USE_RECORDMCOUNT
 
 ifdef CONFIG_STACK_VALIDATION
+ifndef CONFIG_LTO_CLANG
 ifneq ($(SKIP_STACK_VALIDATION),1)
 
 __objtool_obj := $(objtree)/tools/objtool/objtool
 
-objtool_args = $(if $(CONFIG_UNWINDER_ORC),orc generate,check)
-
-objtool_args += $(if $(part-of-module), --module,)
-
-ifndef CONFIG_FRAME_POINTER
-objtool_args += --no-fp
-endif
-ifdef CONFIG_GCOV_KERNEL
-objtool_args += --no-unreachable
-endif
-ifdef CONFIG_RETPOLINE
-  objtool_args += --retpoline
-endif
-ifdef CONFIG_X86_SMAP
-  objtool_args += --uaccess
-endif
-ifdef CONFIG_FTRACE_MCOUNT_USE_OBJTOOL
-  objtool_args += --mcount
-endif
-
 # 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
 # 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file
 # 'OBJECT_FILES_NON_STANDARD_foo.o := 'n': override directory skip for a file
@@ -253,6 +234,7 @@ objtool_obj = $(if $(patsubst y%,, \
 	$(__objtool_obj))
 
 endif # SKIP_STACK_VALIDATION
+endif # CONFIG_LTO_CLANG
 endif # CONFIG_STACK_VALIDATION
 
 # Rebuild all objects when objtool changes, or is enabled/disabled.
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 3d599716940c..ecb97c9f5feb 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -216,6 +216,17 @@ dtc_cpp_flags  = -Wp,-MMD,$(depfile).pre.tmp -nostdinc                    \
 		 $(addprefix -I,$(DTC_INCLUDE))                          \
 		 -undef -D__DTS__
 
+# Objtool arguments are also needed for modfinal with LTO, so we define
+# then here to avoid duplication.
+objtool_args =								\
+	$(if $(CONFIG_UNWINDER_ORC),orc generate,check)			\
+	$(if $(part-of-module), --module,)				\
+	$(if $(CONFIG_FRAME_POINTER),, --no-fp)				\
+	$(if $(CONFIG_GCOV_KERNEL), --no-unreachable,)			\
+	$(if $(CONFIG_RETPOLINE), --retpoline,)				\
+	$(if $(CONFIG_X86_SMAP), --uaccess,)				\
+	$(if $(CONFIG_FTRACE_MCOUNT_USE_OBJTOOL), --mcount,)
+
 # Useful for describing the dependency of composite objects
 # Usage:
 #   $(call multi_depend, multi_used_targets, suffix_to_remove, suffix_to_add)
diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index 2cb9a1d88434..1bd2953b11c4 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -9,7 +9,7 @@ __modfinal:
 include $(objtree)/include/config/auto.conf
 include $(srctree)/scripts/Kbuild.include
 
-# for c_flags
+# for c_flags and objtool_args
 include $(srctree)/scripts/Makefile.lib
 
 # find all modules listed in modules.order
@@ -34,10 +34,23 @@ ifdef CONFIG_LTO_CLANG
 # With CONFIG_LTO_CLANG, reuse the object file we compiled for modpost to
 # avoid a second slow LTO link
 prelink-ext := .lto
-endif
+
+# ELF processing was skipped earlier because we didn't have native code,
+# so let's now process the prelinked binary before we link the module.
+
+ifdef CONFIG_STACK_VALIDATION
+ifneq ($(SKIP_STACK_VALIDATION),1)
+cmd_ld_ko_o +=								\
+	$(objtree)/tools/objtool/objtool $(objtool_args)		\
+		$(@:.ko=$(prelink-ext).o);
+
+endif # SKIP_STACK_VALIDATION
+endif # CONFIG_STACK_VALIDATION
+
+endif # CONFIG_LTO_CLANG
 
 quiet_cmd_ld_ko_o = LD [M]  $@
-      cmd_ld_ko_o =                                                     \
+      cmd_ld_ko_o +=							\
 	$(LD) -r $(KBUILD_LDFLAGS)					\
 		$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE)		\
 		-T scripts/module.lds -o $@ $(filter %.o, $^);		\
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 5ace1dc43993..7f4d19271180 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -89,14 +89,36 @@ modpost_link()
 
 objtool_link()
 {
+	local objtoolcmd;
 	local objtoolopt;
 
+	if [ "${CONFIG_LTO_CLANG} ${CONFIG_STACK_VALIDATION}" = "y y" ]; then
+		# Don't perform vmlinux validation unless explicitly requested,
+		# but run objtool on vmlinux.o now that we have an object file.
+		if [ -n "${CONFIG_UNWINDER_ORC}" ]; then
+			objtoolcmd="orc generate"
+		fi
+
+		objtoolopt="${objtoolopt} --duplicate"
+
+		if [ -n "${CONFIG_FTRACE_MCOUNT_USE_OBJTOOL}" ]; then
+			objtoolopt="${objtoolopt} --mcount"
+		fi
+	fi
+
 	if [ -n "${CONFIG_VMLINUX_VALIDATION}" ]; then
-		objtoolopt="check --vmlinux --noinstr"
+		objtoolopt="${objtoolopt} --noinstr"
+	fi
+
+	if [ -n "${objtoolopt}" ]; then
+		if [ -z "${objtoolcmd}" ]; then
+			objtoolcmd="check"
+		fi
+		objtoolopt="${objtoolopt} --vmlinux"
 		if [ -z "${CONFIG_FRAME_POINTER}" ]; then
 			objtoolopt="${objtoolopt} --no-fp"
 		fi
-		if [ -n "${CONFIG_GCOV_KERNEL}" ]; then
+		if [ -n "${CONFIG_GCOV_KERNEL}" ] || [ -n "${CONFIG_LTO_CLANG}" ]; then
 			objtoolopt="${objtoolopt} --no-unreachable"
 		fi
 		if [ -n "${CONFIG_RETPOLINE}" ]; then
@@ -106,7 +128,7 @@ objtool_link()
 			objtoolopt="${objtoolopt} --uaccess"
 		fi
 		info OBJTOOL ${1}
-		tools/objtool/objtool ${objtoolopt} ${1}
+		tools/objtool/objtool ${objtoolcmd} ${objtoolopt} ${1}
 	fi
 }
 
-- 
2.28.0.1011.ga647a8990f-goog


  parent reply index

Thread overview: 71+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-13  0:31 [PATCH v6 00/25] Add support for Clang LTO Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 01/25] kbuild: preprocess module linker script Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 02/25] objtool: Add a pass for generating __mcount_loc Sami Tolvanen
2020-10-14 16:50   ` Ingo Molnar
2020-10-14 18:21     ` Peter Zijlstra
2020-10-15 20:10       ` Josh Poimboeuf
2020-10-13  0:31 ` [PATCH v6 03/25] objtool: Don't autodetect vmlinux.o Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 04/25] tracing: move function tracer options to Kconfig Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 05/25] tracing: add support for objtool mcount Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 06/25] x86, build: use " Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 07/25] treewide: remove DISABLE_LTO Sami Tolvanen
2020-10-14 22:43   ` Kees Cook
2020-10-17  1:46     ` Masahiro Yamada
2020-10-13  0:31 ` [PATCH v6 08/25] kbuild: add support for Clang LTO Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 09/25] kbuild: lto: fix module versioning Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 10/25] objtool: Split noinstr validation from --vmlinux Sami Tolvanen
2020-10-13  0:31 ` Sami Tolvanen [this message]
2020-10-13  0:31 ` [PATCH v6 12/25] kbuild: lto: limit inlining Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 13/25] kbuild: lto: merge module sections Sami Tolvanen
2020-10-14 22:49   ` Kees Cook
2020-10-20 16:42     ` Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 14/25] kbuild: lto: remove duplicate dependencies from .mod files Sami Tolvanen
2020-10-14 22:50   ` Kees Cook
2020-10-13  0:31 ` [PATCH v6 15/25] init: lto: ensure initcall ordering Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 16/25] init: lto: fix PREL32 relocations Sami Tolvanen
2020-10-14 22:53   ` Kees Cook
2020-10-15  0:12   ` Jann Horn
2020-10-13  0:31 ` [PATCH v6 17/25] PCI: Fix PREL32 relocations for LTO Sami Tolvanen
2020-10-14 22:58   ` Kees Cook
2020-10-13  0:31 ` [PATCH v6 18/25] modpost: lto: strip .lto from module names Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 19/25] scripts/mod: disable LTO for empty.c Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 20/25] efi/libstub: disable LTO Sami Tolvanen
2020-10-13  0:31 ` [PATCH v6 21/25] drivers/misc/lkdtm: disable LTO for rodata.o Sami Tolvanen
2020-10-13  0:32 ` [PATCH v6 22/25] x86/asm: annotate indirect jumps Sami Tolvanen
2020-10-14 22:46   ` Kees Cook
2020-10-14 23:23   ` Jann Horn
2020-10-15 10:22     ` Peter Zijlstra
2020-10-15 20:39       ` Josh Poimboeuf
2020-10-20 16:45         ` Sami Tolvanen
2020-10-20 18:52           ` Josh Poimboeuf
2020-10-20 19:24             ` Sami Tolvanen
2020-10-21  8:56               ` Peter Zijlstra
2020-10-21  9:08                 ` Peter Zijlstra
2020-10-21  9:32                 ` Peter Zijlstra
2020-10-21 21:27                   ` Josh Poimboeuf
2020-10-22  7:25                     ` Peter Zijlstra
2020-10-23 17:48                       ` Sami Tolvanen
2020-10-23 18:04                         ` Nick Desaulniers
2020-10-21 15:01                 ` Sami Tolvanen
2020-10-22  0:22                 ` Sami Tolvanen
2020-10-23 17:36                   ` Sami Tolvanen
2020-11-09 23:11                     ` Sami Tolvanen
2020-11-10  2:29                       ` Josh Poimboeuf
2020-11-10  3:18                         ` Nick Desaulniers
2020-11-10  4:48                         ` Sami Tolvanen
2020-11-10 16:11                           ` Josh Poimboeuf
2020-11-10 17:46                         ` Josh Poimboeuf
2020-11-10 18:59                           ` Sami Tolvanen
2020-11-13 19:54                             ` Josh Poimboeuf
2020-11-13 20:24                               ` Sami Tolvanen
2020-11-13 20:52                                 ` Josh Poimboeuf
2020-11-13 22:34                                 ` Josh Poimboeuf
2020-11-13 22:54                                   ` Sami Tolvanen
2020-11-13 22:56                                     ` Josh Poimboeuf
2020-11-13 23:31                                   ` Sami Tolvanen
2020-11-14  0:49                                     ` Josh Poimboeuf
2020-10-21  9:51             ` Peter Zijlstra
2020-10-21 18:30               ` Josh Poimboeuf
2020-10-13  0:32 ` [PATCH v6 23/25] x86, vdso: disable LTO only for vDSO Sami Tolvanen
2020-10-13  0:32 ` [PATCH v6 24/25] x86, cpu: disable LTO for cpu.c Sami Tolvanen
2020-10-13  0:32 ` [PATCH v6 25/25] x86, build: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen

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