r365703 breaks multi_v7_defconfig

[nathanchance]

See my comment: https://reviews.llvm.org/D64527#1580070

[nickdesaulniers]

For bugs involving cc-option, ld-option, and what looks like here as-option I have https://stackoverflow.com/questions/16467718/how-to-print-out-a-variable-in-makefile bookmarked and set as my homepage 🤡 .

What I typically do to debug these is:

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index ee58cde8ee3b..ca4ab9b0fcbc 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -102,6 +102,8 @@ try-run = $(shell set -e;           \
 # Usage: cflags-y += $(call as-option,-Wa$(comma)-isa=foo,)
 
 as-option = $(call try-run,\
+       $(info $$KBUILD_CFLAGS are [${KBUILD_CFLAGS}]) \
+       $(info $$1 is [${1}]) \
        $(CC) $(KBUILD_CFLAGS) $(1) -c -x assembler /dev/null -o "$$TMP",$(1),$(2))
 
 # as-instr

Then I rerun make:

$ ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- make CC=clang -j71
$KBUILD_CFLAGS are [-Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Wno-format-security -std=gnu89 --target=arm-linux-gnueabi --prefix=/usr/bin/ --gcc-toolchain=/usr -no-integrated-as -fno-dwarf2-cfi-asm ]
$1 is [-Wa,-mno-warn-deprecated]
  UPD     include/config/kernel.release
  UPD     include/generated/utsrelease.h
  CC      scripts/mod/devicetable-offsets.s
  CC      scripts/mod/empty.o
clang-9: error: unsupported argument '-mno-warn-deprecated' to option 'Wa,'
clang-9: error: unsupported argument '-mno-warn-deprecated' to option 'Wa,'

Then I manually recreate the exact command as-option did:

$ clang -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Wno-format-security -std=gnu89 --target=arm-linux-gnueabi --prefix=/usr/bin/ --gcc-toolchain=/usr -no-integrated-as -fno-dwarf2-cfi-asm -Wa,-mno-warn-deprecated -c -x assembler /dev/null

huh, would've expected that to fail (it does not). Since I can repro w/ make, let's try V=1:

$ clang -Wp,-MD,scripts/mod/.empty.o.d  -nostdinc -isystem /android0/llvm-project/llvm/build/lib/clang/9.0.0/include -I./arch/arm/include -I./arch/arm/include/generated  -I./include -I./arch/arm/include/uapi -I./arch/arm/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/kconfig.h -include ./include/linux/compiler_types.h -D__KERNEL__ -mlittle-endian -Qunused-arguments -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Wno-format-security -std=gnu89 --target=arm-linux-gnueabi --prefix=/usr/bin/ --gcc-toolchain=/usr -no-integrated-as -fno-dwarf2-cfi-asm -mabi=aapcs-linux -mfpu=vfp -funwind-tables -marm -Wa,-mno-warn-deprecated -D__LINUX_ARM_ARCH__=7 -march=armv7-a -msoft-float -Uarm -O2 -fstack-protector-strong -Wno-format-invalid-specifier -Wno-gnu -Wno-tautological-compare -mno-global-merge -fomit-frame-pointer -Wdeclaration-after-statement -Wvla -Wno-pointer-sign -Wno-initializer-overrides -Wno-unused-value -Wno-format -Wno-sign-compare -Wno-format-zero-length -Wno-uninitialized    -DKBUILD_BASENAME='"empty"' -DKBUILD_MODNAME='"empty"' -c -o scripts/mod/empty.o scripts/mod/empty.c
clang-9: error: unsupported argument '-mno-warn-deprecated' to option 'Wa,'

changing the input from scripts/mod/empty.c to /dev/null makes the error go away. Reducing the flags and giving it a garbage .c file as input leads to:

$ clang -Wa,-mno-warn-deprecated -c hello.c 
clang-9: error: unsupported argument '-mno-warn-deprecated' to option 'Wa,'
$ clang -Wa,-mno-warn-deprecated -c /dev/null
clang-9: warning: /dev/null: 'linker' input unused [-Wunused-command-line-argument]
clang-9: warning: argument unused during compilation: '-Wa,-mno-warn-deprecated' [-Wunused-command-line-argument]

[nickdesaulniers]

$ arm-linux-gnueabi-as -mno-warn-deprecated /dev/null

So I think as-option needs the 055efab treatment.

[nickdesaulniers]

https://github.com/ClangBuiltLinux/llvm-project/blob/8955be68cfca54e5f1195bfb338cc49164d929a3/clang/lib/Driver/ToolChains/Clang.cpp#L2225-L2226 is where this is coming from.

[nathanchance]

I don't think we can nuke as-option in the same way as cc-ldoption as we can't use $(AS) like $(CC) or $(LD) according to @masahir0y:

The assembler files in the kernel are *.S instead of *.s, so they must
be preprocessed. Since 'as' of GNU binutils is not able to preprocess,
we always use $(CC) as an assembler driver.

https://lore.kernel.org/lkml/20190706162508.8529-1-yamada.masahiro@socionext.com/

[nickdesaulniers]

Fix: https://reviews.llvm.org/D64655

[nathanchance]

The problematic commit was reverted: llvm/llvm-project@a3aa67b