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From:   Xin Li <xin3.li@intel.com>
To:     linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
        linux-kbuild@vger.kernel.org, x86@kernel.org
Cc:     nathan@kernel.org, keescook@chromium.org,
        andrew.cooper3@citrix.com, hpa@zytor.com, peterz@infradead.org
Subject: [PATCH 1/1] kbuild: upgrade the orphan section warning to an error if CONFIG_WERROR is set
Date:   Fri, 21 Oct 2022 20:05:19 -0700
Message-Id: <20221022030519.9505-2-xin3.li@intel.com>
In-Reply-To: <20221022030519.9505-1-xin3.li@intel.com>
References: <20221022030519.9505-1-xin3.li@intel.com>
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Andrew Cooper suggested upgrading the orphan section warning to a hard link
error. However Nathan Chancellor said outright turning the warning into an
error with no escape hatch might be too aggressive, as we have had these
warnings triggered by new compiler generated sections, and suggested turning
orphan sections into an error only if CONFIG_WERROR is set. Kees Cook echoed
and emphasized that the mandate from Linus is that we should avoid breaking
builds. It wrecks bisection, it causes problems across compiler versions, etc.

Thus upgrade the orphan section warning to a hard link error only if
CONFIG_WERROR is set.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Suggested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Xin Li <xin3.li@intel.com>
---
 Makefile                          | 2 +-
 arch/arm/boot/compressed/Makefile | 2 +-
 arch/arm64/kernel/vdso/Makefile   | 2 +-
 arch/arm64/kernel/vdso32/Makefile | 2 +-
 arch/x86/boot/compressed/Makefile | 2 +-
 init/Kconfig                      | 9 ++++++---
 6 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/Makefile b/Makefile
index f41ec8c8426b..b6716a64519f 100644
--- a/Makefile
+++ b/Makefile
@@ -1118,7 +1118,7 @@ endif
 # We never want expected sections to be placed heuristically by the
 # linker. All sections should be explicitly named in the linker script.
 ifdef CONFIG_LD_ORPHAN_WARN
-LDFLAGS_vmlinux += --orphan-handling=warn
+LDFLAGS_vmlinux += --orphan-handling=$(if $(CONFIG_WERROR),error,warn)
 endif
 
 # Align the bit size of userspace programs with the kernel
diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index 41bcbb460fac..c97db8b14c4f 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -123,7 +123,7 @@ LDFLAGS_vmlinux += --no-undefined
 LDFLAGS_vmlinux += -X
 # Report orphan sections
 ifdef CONFIG_LD_ORPHAN_WARN
-LDFLAGS_vmlinux += --orphan-handling=warn
+LDFLAGS_vmlinux += --orphan-handling=$(if $(CONFIG_WERROR),error,warn)
 endif
 # Next argument is a linker script
 LDFLAGS_vmlinux += -T
diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
index 619e2dc7ee14..c8fcc06b5037 100644
--- a/arch/arm64/kernel/vdso/Makefile
+++ b/arch/arm64/kernel/vdso/Makefile
@@ -27,7 +27,7 @@ ldflags-y := -shared -soname=linux-vdso.so.1 --hash-style=sysv	\
 	     -Bsymbolic --build-id=sha1 -n $(btildflags-y)
 
 ifdef CONFIG_LD_ORPHAN_WARN
-  ldflags-y += --orphan-handling=warn
+  ldflags-y += --orphan-handling=$(if $(CONFIG_WERROR),error,warn)
 endif
 
 ldflags-y += -T
diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
index 36c8f66cad25..fa157366e814 100644
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -104,7 +104,7 @@ VDSO_AFLAGS += -D__ASSEMBLY__
 VDSO_LDFLAGS += -Bsymbolic --no-undefined -soname=linux-vdso.so.1
 VDSO_LDFLAGS += -z max-page-size=4096 -z common-page-size=4096
 VDSO_LDFLAGS += -shared --hash-style=sysv --build-id=sha1
-VDSO_LDFLAGS += --orphan-handling=warn
+VDSO_LDFLAGS += --orphan-handling=$(if $(CONFIG_WERROR),error,warn)
 
 
 # Borrow vdsomunge.c from the arm vDSO
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 3a261abb6d15..a1a8bec61c10 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -68,7 +68,7 @@ KBUILD_LDFLAGS += $(call ld-option,--no-ld-generated-unwind-info)
 # address by the bootloader.
 LDFLAGS_vmlinux := -pie $(call ld-option, --no-dynamic-linker)
 ifdef CONFIG_LD_ORPHAN_WARN
-LDFLAGS_vmlinux += --orphan-handling=warn
+LDFLAGS_vmlinux += --orphan-handling=$(if $(CONFIG_WERROR),error,warn)
 endif
 LDFLAGS_vmlinux += -z noexecstack
 ifeq ($(CONFIG_LD_IS_BFD),y)
diff --git a/init/Kconfig b/init/Kconfig
index abf65098f1b6..8f4b838ece47 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -159,10 +159,12 @@ config WERROR
 	help
 	  A kernel build should not cause any compiler warnings, and this
 	  enables the '-Werror' (for C) and '-Dwarnings' (for Rust) flags
-	  to enforce that rule by default.
+	  to enforce that rule by default. Certain warnings from other tools
+	  such as the linker may be upgraded to errors with this option as
+	  well.
 
-	  However, if you have a new (or very old) compiler with odd and
-	  unusual warnings, or you have some architecture with problems,
+	  However, if you have a new (or very old) compiler or linker with odd
+	  and unusual warnings, or you have some architecture with problems,
 	  you may need to disable this config option in order to
 	  successfully build the kernel.
 
@@ -1454,6 +1456,7 @@ config LD_ORPHAN_WARN
 	def_bool y
 	depends on ARCH_WANT_LD_ORPHAN_WARN
 	depends on $(ld-option,--orphan-handling=warn)
+	depends on $(ld-option,--orphan-handling=error)
 
 config SYSCTL
 	bool
-- 
2.34.1