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8debed3efe
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.
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.