Re: [PATCH 4/4] kbuild: include Makefile.compiler only when compiler is required

(CC: Will and ARM ML)


On Fri, Mar 19, 2021 at 6:14 AM Nathan Chancellor [off-list ref] wrote:

On Sun, Feb 28, 2021 at 03:10:28PM +0900, Masahiro Yamada wrote:

quoted

Since commit f2f02ebd8f38 ("kbuild: improve cc-option to clean up all
temporary files"), running 'make kernelversion' in a read-only source
tree emits a bunch of warnings:

  mkdir: cannot create directory '.tmp_12345': Permission denied

Non-build targets such as kernelversion, clean, help, etc. do not
need to evaluate $(call cc-option,) and friends. Do not include
Makefile.compiler so $(call cc-option,) becomes no-op.

This not only fix the warnings, but also runs non-build targets much
faster.

Basically, all installation targets should also be non-build targets.
Unfortunately, vdso_install requires the compiler because it builds
vdso before installtion. This is a problem that must be fixed by a
separate patch.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

I am not adding Reported-by for now because a reporter sent me
an email privately.

If he allows me to add Reported-by, I will add it to record
the credit.

(Perhaps, another person might have reported a similar issue
somewhere, but my memory is obsure. I cannot recall it.)


 Makefile | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/Makefile b/Makefile
index eec7a94f5c33..20724711dc71 100644
--- a/Makefile
+++ b/Makefile

@@ -263,6 +263,10 @@ no-dot-config-targets := $(clean-targets) \
                       $(version_h) headers headers_% archheaders archscripts \
                       %asm-generic kernelversion %src-pkg dt_binding_check \
                       outputmakefile
+# Installation targets should not require compiler. Unfortunately, vdso_install
+# is an exception where build artifacts may be updated. This must be fixed.
+no-compiler-targets := $(no-dot-config-targets) install dtbs_install \
+                     headers_install modules_install kernelrelease image_name
 no-sync-config-targets := $(no-dot-config-targets) %install kernelrelease \
                        image_name
 single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.s %.symtypes %/

@@ -270,6 +274,7 @@ single-targets := %.a %.i %.ko %.lds %.ll %.lst %.mod %.o %.s %.symtypes %/
 config-build :=
 mixed-build  :=
 need-config  := 1
+need-compiler        := 1
 may-sync-config      := 1
 single-build :=

@@ -279,6 +284,12 @@ ifneq ($(filter $(no-dot-config-targets), $(MAKECMDGOALS)),)
      endif
 endif

+ifneq ($(filter $(no-compiler-targets), $(MAKECMDGOALS)),)
+     ifeq ($(filter-out $(no-compiler-targets), $(MAKECMDGOALS)),)
+             need-compiler :=
+     endif
+endif
+
 ifneq ($(filter $(no-sync-config-targets), $(MAKECMDGOALS)),)
      ifeq ($(filter-out $(no-sync-config-targets), $(MAKECMDGOALS)),)
              may-sync-config :=

@@ -584,7 +595,9 @@ endif

 # Include this also for config targets because some architectures need
 # cc-cross-prefix to determine CROSS_COMPILE.
+ifdef need-compiler
 include $(srctree)/scripts/Makefile.compiler
+endif

 ifdef config-build
 # ===========================================================================
--

2.27.0

Hi Masahiro,

I see a new warning in my builds on arm64 now when running
'modules_install' or 'dtbs_install' because ld-option evaluates to
nothing, which triggers the warning in arch/arm64/Makefile:

$ make -skj"$(nproc)" \
ARCH=arm64 \
CROSS_COMPILE=aarch64-linux- \
INSTALL_DTBS_PATH=rootfs \
INSTALL_MOD_PATH=rootfs \
O=build/arm64 \
distclean defconfig all modules_install dtbs_install
...
/home/nathan/cbl/src/linux-next/arch/arm64/Makefile:25: ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum
/home/nathan/cbl/src/linux-next/arch/arm64/Makefile:25: ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum

$ sed -n '23,29p' arch/arm64/Makefile
ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
  ifeq ($(call ld-option, --fix-cortex-a53-843419),)
$(warning ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum)
  else
LDFLAGS_vmlinux += --fix-cortex-a53-843419
  endif
endif

I am not sure how this should be resolved, hence just the report.

Cheers,
Nathan

I see this a few lines below:

ifeq ($(CONFIG_ARM64_USE_LSE_ATOMICS), y)
  ifneq ($(CONFIG_ARM64_LSE_ATOMICS), y)
$(warning LSE atomics not supported by binutils)
  endif
endif


We can move ld-option evaluation to Kconfig.

ifeq ($(CONFIG_ARM64_ERRATUM_843419),y)
  ifneq ($(CONFIG_ARM64_LD_HAS_FIX_ERRATUM_843419,y))
$(warning ld does not support --fix-cortex-a53-843419; kernel may be
susceptible to erratum)
  else
LDFLAGS_vmlinux += --fix-cortex-a53-843419
  endif
endif


I do not know what CONFIG name is preferred.



-- 
Best Regards
Masahiro Yamada

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