linux-kernel - Re: [PATCH v6 3/4] MIPS: vmlinuz: Use generic ashldi3

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Date:   Wed, 18 Apr 2018 00:09:21 +0100
From:   James Hogan <jhogan@...nel.org>
To:     Matt Redfearn <matt.redfearn@...s.com>
Cc:     Palmer Dabbelt <palmer@...ive.com>,
        Antony Pavlov <antonynpavlov@...il.com>,
        Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...ux-mips.org,
        linux-kernel@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v6 3/4] MIPS: vmlinuz: Use generic ashldi3

On Wed, Apr 11, 2018 at 08:50:18AM +0100, Matt Redfearn wrote:
> diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile
> index adce180f3ee4..e03f522c33ac 100644
> --- a/arch/mips/boot/compressed/Makefile
> +++ b/arch/mips/boot/compressed/Makefile
> @@ -46,9 +46,12 @@ $(obj)/uart-ath79.c: $(srctree)/arch/mips/ath79/early_printk.c
>  
>  vmlinuzobjs-$(CONFIG_KERNEL_XZ) += $(obj)/ashldi3.o $(obj)/bswapsi.o
>  
> -extra-y += ashldi3.c bswapsi.c
> -$(obj)/ashldi3.o $(obj)/bswapsi.o: KBUILD_CFLAGS += -I$(srctree)/arch/mips/lib
> -$(obj)/ashldi3.c $(obj)/bswapsi.c: $(obj)/%.c: $(srctree)/arch/mips/lib/%.c
> +extra-y += ashldi3.c
> +$(obj)/ashldi3.c: $(obj)/%.c: $(srctree)/lib/%.c
> +	$(call cmd,shipped)
> +
> +extra-y += bswapsi.c
> +$(obj)/bswapsi.c: $(obj)/%.c: $(srctree)/arch/mips/lib/%.c
>  	$(call cmd,shipped)

ci20_defconfig:

arch/mips/boot/compressed/ashldi3.c:4:10: fatal error: libgcc.h: No such file or directory
 #include "libgcc.h"
           ^~~~~~~~~~

It looks like it had already copied ashldi3.c from arch/mips/lib/ when
building an older commit, and it hasn't been regenerated from lib/ since
the Makefile changed, so its still using the old version.

I think it should be using FORCE and if_changed like this:

diff --git a/arch/mips/boot/compressed/Makefile b/arch/mips/boot/compressed/Makefile
index e03f522c33ac..abe77add8789 100644
--- a/arch/mips/boot/compressed/Makefile
+++ b/arch/mips/boot/compressed/Makefile
@@ -47,12 +47,12 @@ $(obj)/uart-ath79.c: $(srctree)/arch/mips/ath79/early_printk.c
 vmlinuzobjs-$(CONFIG_KERNEL_XZ) += $(obj)/ashldi3.o $(obj)/bswapsi.o

 extra-y += ashldi3.c
-$(obj)/ashldi3.c: $(obj)/%.c: $(srctree)/lib/%.c
-	$(call cmd,shipped)
+$(obj)/ashldi3.c: $(obj)/%.c: $(srctree)/lib/%.c FORCE
+	$(call if_changed,shipped)

 extra-y += bswapsi.c
-$(obj)/bswapsi.c: $(obj)/%.c: $(srctree)/arch/mips/lib/%.c
-	$(call cmd,shipped)
+$(obj)/bswapsi.c: $(obj)/%.c: $(srctree)/arch/mips/lib/%.c FORCE
+	$(call if_changed,shipped)

 targets := $(notdir $(vmlinuzobjs-y))

That resolves the build failures when checking out old -> new without
cleaning, since the .ashldi3.c.cmd is missing so it gets rebuilt.

It should also resolve issues if the path it copies from is updated in
future since the .ashldi3.c.cmd will get updated.

If you checkout new -> old without cleaning, the now removed
arch/mips/lib/ashldi3.c will get added which will trigger regeneration,
so it won't error.

However if you do new -> old -> new then the .ashldi3.cmd file isn't
updated while at old, so you get the same error as above. I'm not sure
there's much we can practically do about that, aside perhaps avoiding
the issue in future by somehow auto-deleting stale .*.cmd files.

Cc'ing kbuild folk in case they have any bright ideas.

At least the straightforward old->new upgrade will work with the above
fixup though. If you're okay with it I'm happy to apply as a fixup.

Cheers
James

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