[1/1] kbuild: upgrade the orphan section warning to an error if CONFIG_WERROR is set

  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(-)
  

On Fri, Oct 21, 2022 at 08:05:19PM -0700, Xin Li wrote:
> 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>

Thanks for the patch!

Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>

We could deduplicate the '$(if $(CONFIG_WERROR),error,warn)' logic if we
hoisted it into Kconfig by having something like

    config LD_ORPHAN_WARN_LEVEL
        string
        depends on LD_ORPHAN_WARN
        default "error" if WERROR
        default "warn"

in init/Kconfig then using it everywhere like

    --orphan-handling=$(CONFIG_LD_ORPHAN_WARN_LEVEL)

but I will let others decide if they would prefer that over the
direction we went here.

Cheers,
Nathan

> ---
>  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
> 
>
  

On Mon, Oct 24, 2022 at 10:29:55AM -0700, Nathan Chancellor wrote:
> On Fri, Oct 21, 2022 at 08:05:19PM -0700, Xin Li wrote:
> > 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>
> 
> Thanks for the patch!
> 
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> Tested-by: Nathan Chancellor <nathan@kernel.org>
> 
> We could deduplicate the '$(if $(CONFIG_WERROR),error,warn)' logic if we
> hoisted it into Kconfig by having something like
> 
>     config LD_ORPHAN_WARN_LEVEL
>         string
>         depends on LD_ORPHAN_WARN
>         default "error" if WERROR
>         default "warn"
> 
> in init/Kconfig then using it everywhere like
> 
>     --orphan-handling=$(CONFIG_LD_ORPHAN_WARN_LEVEL)
> 
> but I will let others decide if they would prefer that over the
> direction we went here.

I think this makes it look cleaner, yeah.
  

> On Mon, Oct 24, 2022 at 10:29:55AM -0700, Nathan Chancellor wrote:
> > On Fri, Oct 21, 2022 at 08:05:19PM -0700, Xin Li wrote:
> > > 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>
> >
> > Thanks for the patch!
> >
> > Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> > Tested-by: Nathan Chancellor <nathan@kernel.org>
> >
> > We could deduplicate the '$(if $(CONFIG_WERROR),error,warn)' logic if
> > we hoisted it into Kconfig by having something like
> >
> >     config LD_ORPHAN_WARN_LEVEL
> >         string
> >         depends on LD_ORPHAN_WARN
> >         default "error" if WERROR
> >         default "warn"
> >
> > in init/Kconfig then using it everywhere like
> >
> >     --orphan-handling=$(CONFIG_LD_ORPHAN_WARN_LEVEL)
> >
> > but I will let others decide if they would prefer that over the
> > direction we went here.
> 
> I think this makes it look cleaner, yeah.

Agree this looks much cleaner.

> 
> --
> Kees Cook