On Mon, Jan 09, 2023 at 04:23:17AM +0900, Masahiro Yamada wrote:
> Nathan Chancellor reports that $(NM) emits an error message when
> GNU Make 4.4 is used to build the ARM zImage.
>
> $ make-4.4 ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- O=build defconfig zImage
> [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 since 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 (i.e. lazily expanded) variable.
>
> GNU Make 4.3 expands 'foo' just before running the recipe '@echo $(foo)',
> at this point, the directory 'bar' exists.
>
> GNU Make 4.4 expands 'foo' to evaluate $(shell mkdir bar) because it 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.
>
> In arch/arm/boot/compressed/Makefile, KBSS_SZ is referenced by
> LDFLAGS_vmlinux, which is recursive and also exported by the top
> Makefile.
>
> GNU Make 4.3 expands KBSS_SZ just before running the recipes, so no
> error message.
>
> GNU Make 4.4 expands KBSS_SZ in the parse stage, where the directory
> arm/arm/boot/compressed does not exit yet. When compiled with O=,
> the output directory is created by $(shell mkdir -p $(obj-dirs))
> in scripts/Makefile.build.
>
> There are two ways to fix this particular issue:
>
> - change "$(obj)/../../../../vmlinux" in KBSS_SZ to "vmlinux"
> - unexport LDFLAGS_vmlinux
>
> This commit takes the latter course because it is what I originally
> intended.
>
> Commit 3ec8a5b33dea ("kbuild: do not export LDFLAGS_vmlinux")
> unexported LDFLAGS_vmlinux.
>
> Commit 5d4aeffbf709 ("kbuild: rebuild .vmlinux.export.o when its
> prerequisite is updated") accidentally exported it again.
>
> We can clean up arch/arm/boot/compressed/Makefile later.
>
> [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@xxxxxxxxxx>
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Reviewed-by: Nicolas Schier <nicolas@xxxxxxxxx>
Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>
Thank you again for digging into this!
> ---
>
> Changes in v3:
> - Minimize the scope of exporting.
> LDFLAGS_vmlinux is only exported to scripts/Makefile.vmlinux
>
> Changes in v2:
> - Postpone the change for arch/arm/boot/compressed/Makefile
> - Update the commit description
>
> Makefile | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index dfba294ae790..9eed3e9b3657 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -549,7 +549,7 @@ LDFLAGS_MODULE =
> CFLAGS_KERNEL =
> RUSTFLAGS_KERNEL =
> AFLAGS_KERNEL =
> -export LDFLAGS_vmlinux =
> +LDFLAGS_vmlinux =
>
> # Use USERINCLUDE when you must reference the UAPI directories only.
> USERINCLUDE := \
> @@ -1248,6 +1248,18 @@ vmlinux.o modules.builtin.modinfo modules.builtin: vmlinux_o
> @:
>
> PHONY += vmlinux
> +# LDFLAGS_vmlinux in the top Makefile defines linker flags for the top vmlinux,
> +# not for decompressors. LDFLAGS_vmlinux in arch/*/boot/compressed/Makefile is
> +# unrelated; the decompressors just happen to have the same base name,
> +# arch/*/boot/compressed/vmlinux.
> +# Export LDFLAGS_vmlinux only to scripts/Makefile.vmlinux.
> +#
> +# _LDFLAGS_vmlinux is an indirection to work around the bug:
> +# https://savannah.gnu.org/bugs/?61463
> +# For Make > 4.4, the following simple code will work:
> +# vmlinux: private export LDFLAGS_vmlinux := $(LDFLAGS_vmlinux)
> +vmlinux: private _LDFLAGS_vmlinux := $(LDFLAGS_vmlinux)
> +vmlinux: export LDFLAGS_vmlinux = $(_LDFLAGS_vmlinux)
> vmlinux: vmlinux.o $(KBUILD_LDS) modpost
> $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.vmlinux
>
> --
> 2.34.1
>
