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authorMasahiro Yamada <masahiroy@kernel.org>2023-01-09 04:23:17 +0900
committerMasahiro Yamada <masahiroy@kernel.org>2023-01-11 04:22:12 +0900
commit8debed3efe3a731451ad9a91a7a74eeb18a7f7eb (patch)
tree5cf8919f1b481f85c1279810392211e8da211e9e /Makefile
parentb409ea4534204d4e6da3017d8713ce338f44b489 (diff)
downloadlwn-8debed3efe3a731451ad9a91a7a74eeb18a7f7eb.tar.gz
lwn-8debed3efe3a731451ad9a91a7a74eeb18a7f7eb.zip
kbuild: export top-level LDFLAGS_vmlinux only to scripts/Makefile.vmlinux
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@kernel.org> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Reviewed-by: Nicolas Schier <nicolas@fjasle.eu> Tested-by: Nathan Chancellor <nathan@kernel.org>
Diffstat (limited to 'Makefile')
-rw-r--r--Makefile14
1 files changed, 13 insertions, 1 deletions
diff --git a/Makefile b/Makefile
index 460716314fb3..7607e20385a8 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 a workaround for the 'private export' 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