linux-kernel - x86 - weird cross-compile build problem with try-run next-20210602

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Date:   Fri, 04 Jun 2021 16:33:30 -0400
From:   "Valdis Klētnieks" <valdis.kletnieks@...edu>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>
cc:     linux-kernel@...r.kernel.org, x86@...nel.org
Subject: x86 - weird cross-compile build problem with try-run next-20210602

I built a gcc 11.1 cross-compiler targeting x86_64, and builds
were throwing an error message:

Makefile:149: CONFIG_X86_X32 enabled but no binutils support

so I added some debugging to arch/x86/Makefile:

ifdef CONFIG_X86_X32
        x32_ld_ok := $(call try-run,\
                        /bin/echo -e '1: .quad 1b' | \ 
                        $(CC) $(KBUILD_AFLAGS) -c -x assembler -o "$$TMP" - && \
                        $(OBJCOPY) -O elf32-x86-64 "$$TMP" "$$TMP.o" && \
                        $(LD) -m elf32_x86_64 "$$TMP.o" -o "$$TMP",y,n)
 $(warning x32_ld_ok is +$(x32_ld_ok)+ with CC=$(CC) $(KBUILD_AFLAGS) OBJ=$(OBJCOPY) LD=$(LD) )
        ifeq ($(x32_ld_ok),y)
                CONFIG_X86_X32_ABI := y

and that throws:

arch/x86/Makefile:143: x32_ld_ok is ++ with CC=x86_64-unknown-linux-gnu-gcc -D__ASSEMBLY__ -fno-PIE -m64 OBJ=x86_64-unknown-linux-gnu-objcopy LD=x86_64-unknown-linux-gnu-ld 

Anybody have a clue why $(x32_ld_ok)  is null rather than 'y' or 'n'?

(It's totally possible that my cross-compiler is broken, but I still don't see how
try-run would return null rather than 'n' in that case...  I built a shell script that did the
test and that ended with $? == 0, but had a warning msg:

+ /bin/echo -e '1: .quad 1b'
+ x86_64-unknown-linux-gnu-gcc -D__ASSEMBLY__ -fno-PIE -m64 -c -x assembler -o /tmp/z97 -
+ x86_64-unknown-linux-gnu-objcopy -O elf32-x86-64 /tmp/z97 /tmp/z99.o
+ x86_64-unknown-linux-gnu-ld -m elf32_x86_64 /tmp/z99.o -o /tmp/z98
x86_64-unknown-linux-gnu-ld: warning: cannot find entry symbol _start; defaulting to 0000000000401000
echo $?
+ echo 0
0