linux-kernel - Re: [PATCH 1/2] ARM: fix nm error message when GNU Make >= 4.4 is used

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Message-ID: <CAK7LNARcmJUO9hnEngnRkFcTU-OUDduu7AaPfpDd7BFvf85K6g@mail.gmail.com>
Date:   Sun, 8 Jan 2023 18:50:53 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Nathan Chancellor <nathan@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <n.schier@....de>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Russell King <linux@...linux.org.uk>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Xin Li <xin3.li@...el.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] ARM: fix nm error message when GNU Make >= 4.4 is used

On Sun, Jan 8, 2023 at 6:20 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> Nathan Chancellor reports an error message from $(NM) if GNU Make 4.4
> is used to build the ARM decompressor.
>
>   $ make-4.4 ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- O=build defconfig all
>     [snip]
>     LD      vmlinux
>     NM      System.map
>     SORTTAB vmlinux
>     OBJCOPY arch/arm/boot/Image
>     Kernel: arch/arm/boot/Image is ready
>   arm-linux-gnueabi-nm: 'arch/arm/boot/compressed/../../../../vmlinux': No such file
>   /bin/sh: 1: arithmetic expression: expecting primary: " "
>     LDS     arch/arm/boot/compressed/vmlinux.lds
>     AS      arch/arm/boot/compressed/head.o
>     GZIP    arch/arm/boot/compressed/piggy_data
>     AS      arch/arm/boot/compressed/piggy.o
>     CC      arch/arm/boot/compressed/misc.o
>
> This occurs with GNU Make commit 98da874c4303 ("[SV 10593] Export
> variables to $(shell ...) commands"), and the O= option is needed to
> reproduce it. The generated zImage is correct despite the error message.
>
> As the commit description of 98da874c4303 [1] says, exported variables
> are passed down to $(shell ) functions, which means exported recursive
> variables might be expanded earlier than before, in the parse stage.
>
> The following test code demonstrates the change for GNU Make 4.4.
>
> [Test Makefile]
>
>   $(shell echo hello > foo)
>   export foo = $(shell cat bar/../foo)
>   $(shell mkdir bar)
>
>   all:
>           @echo $(foo)
>
> [GNU Make 4.3]
>
>   $ rm -rf bar; make-4.3
>   hello
>
> [GNU Make 4.4]
>
>   $ rm -rf bar; make-4.4
>   cat: bar/../foo: No such file or directory
>   hello
>
> The 'foo' is a resursively expanded (or lazily expanded) variable.
>
> GNU Make 4.3 expands it just before running the recipe '@...o $(foo)',
> at this point, the directory 'bar' exists.
>
> GNU Make 4.4 expands it to evaluate $(shell mkdir bar) because 'foo' is
> exported. At this point, the directory 'bar' does not exit yet. The cat
> command cannot resolve the bar/../foo path, hence the error message.
>
> Let's get back to the kernel Makefile.
>
> 'KBSS_SZ' in arch/arm/boot/compressed/Makefile is a recursive variable,
> which is referenced by 'LDFLAGS_vmlinux', which is also a recursive
> variable.
>
> GNU Make 4.3 expands 'KBSS_SZ' just before running the recipes. Before
> that, $(shell mkdir -p $(obj-dirs)) in scripts/Makefile.build creates
> the output directory, arch/arm/boot/compressed.
>
> GNU Make 4.4 expands 'KBSS_SZ' in the parse stage because LDFLAGS_vmlinux
> was (accidentally) exported by commit 5d4aeffbf709 ("kbuild: rebuild
> .vmlinux.export.o when its prerequisite is updated"). $(NM) cannot
> resolve the path arch/arm/boot/compressed/../../../../vmlinux.
>
> I admit this is a bug caused by 5d4aeffbf709 (I will fix it in the next
> commit), but do not see any good reason in writing the vmlinux path in
> such an indirect way. Just say 'vmlinux'.
>
> [1]: https://git.savannah.gnu.org/cgit/make.git/commit/?id=98da874c43035a490cdca81331724f233a3d0c9a
>
> Link: https://lore.kernel.org/all/Y7i8+EjwdnhHtlrr@dev-arch.thelio-3990X/
> Fixes: 5d4aeffbf709 ("kbuild: rebuild .vmlinux.export.o when its prerequisite is updated")
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> ---



I changed my mind. I will fix 2/2 only for now,
so that backing to stable kernels gets easier.


I will send v2 with updated commit description.




-- 
Best Regards
Masahiro Yamada