[PATCH v2 08/11] kbuild: create *.mod with full directory path and remove MODVERDIR

From: Masahiro Yamada
Date: Thu Jul 11 2019 - 01:46:25 EST

While descending directories, Kbuild produces objects for modules,
but do not link final *.ko files; it is done in the modpost.

To keep track of modules, Kbuild creates a *.mod file in $(MODVERDIR)
for every module it is building. Some post-processing steps read the
necessary information from *.mod files. This avoids descending into
directories again. This mechanism was introduced in 2003 or so.

Later, commit 551559e13af1 ("kbuild: implement modules.order") added
modules.order. So, we can simply read it out to know all the modules
with directory paths. This is easier than parsing the first line of
*.mod files.

$(MODVERDIR) has a flat directory structure, that is, *.mod files
are named only with base names. This is based on the assumption that
the module name is unique across the tree. This assumption is really
fragile.

Stephen Rothwell reported a race condition caused by a module name
conflict:

https://lkml.org/lkml/2019/5/13/991

In parallel building, two different threads could write to the same
$(MODVERDIR)/*.mod simultaneously.

Non-unique module names are the source of all kind of troubles, hence
commit 3a48a91901c5 ("kbuild: check uniqueness of module names")
introduced a new checker script.

However, it is still fragile in the build system point of view because
this race happens before scripts/modules-check.sh is invoked. If it
happens again, the modpost will emit unclear error messages.

To fix this issue completely, create *.mod in the same directory as
*.ko so that two threads never attempt to write to the same file.
$(MODVERDIR) is no longer needed.

Since modules with directory paths are listed in modules.order, Kbuild
is still able to find *.mod files without additional descending.

Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Acked-by: Nicolas Pitre <nico@xxxxxxxxxxx>
---

Changes in v2:
- Remove -r of xargs, which is a GNU extension
- Add '--' for extra safety

.gitignore | 1 +
Documentation/dontdiff | 1 +
Makefile | 20 +++-----------------
scripts/Makefile.build | 8 ++------
scripts/Makefile.modpost | 4 ++--
scripts/adjust_autoksyms.sh | 11 ++++-------
scripts/mod/sumversion.c | 16 +++-------------
scripts/package/mkspec | 2 +-
8 files changed, 17 insertions(+), 46 deletions(-)

diff --git a/.gitignore b/.gitignore
index 7587ef56b92d..8f5422cba6e2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -30,6 +30,7 @@
*.lz4
*.lzma
*.lzo
+*.mod
*.mod.c
*.o
*.o.*
diff --git a/Documentation/dontdiff b/Documentation/dontdiff
index 5eba889ea84d..9f4392876099 100644
--- a/Documentation/dontdiff
+++ b/Documentation/dontdiff
@@ -30,6 +30,7 @@
*.lzo
*.mo
*.moc
+*.mod
*.mod.c
*.o
*.o.*
diff --git a/Makefile b/Makefile
index b5e21d676ee2..4243b6daffcf 100644
--- a/Makefile
+++ b/Makefile
@@ -488,11 +488,6 @@ export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
export KBUILD_ARFLAGS

-# When compiling out-of-tree modules, put MODVERDIR in the module
-# tree rather than in the kernel tree. The kernel tree might
-# even be read-only.
-export MODVERDIR := $(if $(KBUILD_EXTMOD),$(firstword $(KBUILD_EXTMOD))/).tmp_versions
-
# Files to ignore in find ... statements

export RCS_FIND_IGNORE := \( -name SCCS -o -name BitKeeper -o -name .svn -o \
@@ -1033,7 +1028,7 @@ vmlinux-deps := $(KBUILD_LDS) $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS)

# Recurse until adjust_autoksyms.sh is satisfied
PHONY += autoksyms_recursive
-autoksyms_recursive: $(vmlinux-deps)
+autoksyms_recursive: $(vmlinux-deps) modules.order
ifdef CONFIG_TRIM_UNUSED_KSYMS
$(Q)$(CONFIG_SHELL) $(srctree)/scripts/adjust_autoksyms.sh \
"$(MAKE) -f $(srctree)/Makefile vmlinux"
@@ -1117,7 +1112,6 @@ endif

prepare1: prepare3 outputmakefile asm-generic $(version_h) $(autoksyms_h) \
include/generated/utsrelease.h
- $(cmd_crmodverdir)

archprepare: archheaders archscripts prepare1 scripts

@@ -1375,7 +1369,7 @@ endif # CONFIG_MODULES
# make distclean Remove editor backup files, patch leftover files and the like

# Directories & files removed with 'make clean'
-CLEAN_DIRS += $(MODVERDIR) include/ksym
+CLEAN_DIRS += include/ksym
CLEAN_FILES += modules.builtin.modinfo

# Directories & files removed with 'make mrproper'
@@ -1636,7 +1630,6 @@ PHONY += $(clean-dirs) clean
$(clean-dirs):
$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)

-clean: rm-dirs := $(MODVERDIR)
clean: rm-files := $(KBUILD_EXTMOD)/Module.symvers

PHONY += help
@@ -1650,8 +1643,6 @@ help:
@echo ''

PHONY += prepare
-prepare:
- $(cmd_crmodverdir)
endif # KBUILD_EXTMOD

clean: $(clean-dirs)
@@ -1662,7 +1653,7 @@ clean: $(clean-dirs)
-o -name '*.ko.*' \
-o -name '*.dtb' -o -name '*.dtb.S' -o -name '*.dt.yaml' \
-o -name '*.dwo' -o -name '*.lst' \
- -o -name '*.su' \
+ -o -name '*.su' -o -name '*.mod' \
-o -name '.*.d' -o -name '.*.tmp' -o -name '*.mod.c' \
-o -name '*.lex.c' -o -name '*.tab.[ch]' \
-o -name '*.asn1.[ch]' \
@@ -1791,11 +1782,6 @@ quiet_cmd_depmod = DEPMOD $(KERNELRELEASE)
cmd_depmod = $(CONFIG_SHELL) $(srctree)/scripts/depmod.sh $(DEPMOD) \
$(KERNELRELEASE)

-# Create temporary dir for module support files
-# clean it up only when building all modules
-cmd_crmodverdir = $(Q)mkdir -p $(MODVERDIR) \
- $(if $(KBUILD_MODULES),; rm -f $(MODVERDIR)/*)
-
# read saved command lines for existing targets
existing-targets := $(wildcard $(sort $(targets)))

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 98dede0b2ca8..9fb30633acd2 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -67,8 +67,6 @@ ifeq ($(CONFIG_MODULES)$(need-modorder),y1)
modorder-target := $(obj)/modules.order
endif

-# We keep a list of all modules in $(MODVERDIR)
-
__build: $(if $(KBUILD_BUILTIN),$(builtin-target) $(lib-target) $(extra-y)) \
$(if $(KBUILD_MODULES),$(obj-m) $(modorder-target)) \
$(subdir-ym) $(always)
@@ -278,13 +276,11 @@ $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
$(call cmd,force_checksrc)
$(call if_changed_rule,cc_o_c)

-# Single-part modules are special since we need to mark them in $(MODVERDIR)
-
$(single-used-m): $(obj)/%.o: $(src)/%.c $(recordmcount_source) $(objtool_dep) FORCE
$(call cmd,force_checksrc)
$(call if_changed_rule,cc_o_c)
@{ echo $(@:.o=.ko); echo $@; \
- $(cmd_undef_syms); } > $(MODVERDIR)/$(@F:.o=.mod)
+ $(cmd_undef_syms); } > $(patsubst %.o,%.mod,$@)

quiet_cmd_cc_lst_c = MKLST $@
cmd_cc_lst_c = $(CC) $(c_flags) -g -c -o $*.o $< && \
@@ -466,7 +462,7 @@ cmd_link_multi-m = $(LD) $(ld_flags) -r -o $@ $(filter %.o,$^) $(cmd_secanalysis
$(multi-used-m): FORCE
$(call if_changed,link_multi-m)
@{ echo $(@:.o=.ko); echo $(filter %.o,$^); \
- $(cmd_undef_syms); } > $(MODVERDIR)/$(@F:.o=.mod)
+ $(cmd_undef_syms); } > $(patsubst %.o,%.mod,$@)
$(call multi_depend, $(multi-used-m), .o, -objs -y -m)

targets += $(multi-used-m)
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 2ab1694a7df3..3e229d4f4d72 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -6,8 +6,8 @@
# Stage one of module building created the following:
# a) The individual .o files used for the module
# b) A <module>.o file which is the .o files above linked together
-# c) A <module>.mod file in $(MODVERDIR)/, listing the name of the
-# the preliminary <module>.o file, plus all .o files
+# c) A <module>.mod file, listing the name of the preliminary <module>.o file,
+# plus all .o files
# d) modules.order, which lists all the modules

# Stage 2 is handled by this file and does the following
diff --git a/scripts/adjust_autoksyms.sh b/scripts/adjust_autoksyms.sh
index aab4e299d7a2..8b44bb80a451 100755
--- a/scripts/adjust_autoksyms.sh
+++ b/scripts/adjust_autoksyms.sh
@@ -47,13 +47,10 @@ cat > "$new_ksyms_file" << EOT
*/

EOT
-[ "$(ls -A "$MODVERDIR")" ] &&
-for mod in "$MODVERDIR"/*.mod; do
- sed -n -e '3{s/ /\n/g;/^$/!p;}' "$mod"
-done | sort -u |
-while read sym; do
- echo "#define __KSYM_${sym} 1"
-done >> "$new_ksyms_file"
+sed 's/ko$/mod/' modules.order |
+xargs -n1 sed -n -e '3{s/ /\n/g;/^$/!p;}' -- |
+sort -u |
+sed -e 's/\(.*\)/#define __KSYM_\1 1/' >> "$new_ksyms_file"

# Special case for modversions (see modpost.c)
if [ -n "$CONFIG_MODVERSIONS" ]; then
diff --git a/scripts/mod/sumversion.c b/scripts/mod/sumversion.c
index 0f6dcb4011a8..166f3fa247a9 100644
--- a/scripts/mod/sumversion.c
+++ b/scripts/mod/sumversion.c
@@ -396,21 +396,11 @@ void get_src_version(const char *modname, char sum[], unsigned sumlen)
unsigned long len;
struct md4_ctx md;
char *sources, *end, *fname;
- const char *basename;
char filelist[PATH_MAX + 1];
- char *modverdir = getenv("MODVERDIR");

- if (!modverdir)
- modverdir = ".";
-
- /* Source files for module are in .tmp_versions/modname.mod,
- after the first line. */
- if (strrchr(modname, '/'))
- basename = strrchr(modname, '/') + 1;
- else
- basename = modname;
- snprintf(filelist, sizeof(filelist), "%s/%.*s.mod", modverdir,
- (int) strlen(basename) - 2, basename);
+ /* objects for a module are listed in the second line of *.mod file. */
+ snprintf(filelist, sizeof(filelist), "%.*smod",
+ (int)strlen(modname) - 1, modname);

file = grab_file(filelist, &len);
if (!file)
diff --git a/scripts/package/mkspec b/scripts/package/mkspec
index 2d29df4a0a53..8640c278f1aa 100755
--- a/scripts/package/mkspec
+++ b/scripts/package/mkspec
@@ -29,7 +29,7 @@ fi

PROVIDES="$PROVIDES kernel-$KERNELRELEASE"
__KERNELRELEASE=$(echo $KERNELRELEASE | sed -e "s/-/_/g")
-EXCLUDES="$RCS_TAR_IGNORE --exclude=.tmp_versions --exclude=*vmlinux* \
+EXCLUDES="$RCS_TAR_IGNORE --exclude=*vmlinux* --exclude=*.mod \
--exclude=*.o --exclude=*.ko --exclude=*.cmd --exclude=Documentation \
--exclude=.config.old --exclude=.missing-syscalls.d --exclude=*.s"

--
2.17.1