Commit b7dca6dd authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

kbuild: create *.mod with full directory path and remove MODVERDIR 

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 551559e1 ("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 3a48a919 ("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 with full directory path
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.

I also killed cmd_secanalysis; scripts/mod/sumversion.c computes MD4 hash
for modules with MODULE_VERSION(). When CONFIG_DEBUG_SECTION_MISMATCH=y,
it occurs not only in the modpost stage, but also during directory
descending, where sumversion.c may parse stale *.mod files. It would emit
'No such file or directory' warning when an object consisting a module is
renamed, or when a single-obj module is turned into a multi-obj module or
vice versa.

Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: default avatarNicolas Pitre <nico@fluxnic.net>
parent 7deb55f5

.gitignore

+1 −0
Original line number Diff line number Diff line
@@ -30,6 +30,7 @@ 
*.lz4

*.lzma

*.lzo

*.mod

*.mod.c

*.o

*.o.*

Documentation/dontdiff

+1 −0
Original line number Diff line number Diff line
@@ -30,6 +30,7 @@ 
*.lzo

*.mo

*.moc

*.mod

*.mod.c

*.o

*.o.*

Makefile

+3 −17
Original line number Diff line number Diff line
@@ -486,11 +486,6 @@ 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    \
@@ -1029,8 +1024,8 @@ vmlinux-deps := $(KBUILD_LDS) $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS) 


# Recurse until adjust_autoksyms.sh is satisfied

PHONY += autoksyms_recursive

autoksyms_recursive: $(vmlinux-deps)

ifdef CONFIG_TRIM_UNUSED_KSYMS

autoksyms_recursive: $(vmlinux-deps) modules.order

	$(Q)$(CONFIG_SHELL) $(srctree)/scripts/adjust_autoksyms.sh \

	  "$(MAKE) -f $(srctree)/Makefile vmlinux"

endif
@@ -1113,7 +1108,6 @@ endif 


prepare1: prepare3 outputmakefile asm-generic $(version_h) $(autoksyms_h) \

						include/generated/utsrelease.h

	$(cmd_crmodverdir)



archprepare: archheaders archscripts prepare1 scripts
@@ -1371,7 +1365,7 @@ 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'
@@ -1641,7 +1635,6 @@ PHONY += $(clean-dirs) clean 
$(clean-dirs):

	$(Q)$(MAKE) $(clean)=$(patsubst _clean_%,%,$@)



clean:	rm-dirs := $(MODVERDIR)

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



PHONY += help
@@ -1655,8 +1648,6 @@ help: 
	@echo  ''



PHONY += prepare

prepare:

	$(cmd_crmodverdir)

endif # KBUILD_EXTMOD



clean: $(clean-dirs)
@@ -1667,7 +1658,7 @@ 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]' \
@@ -1794,11 +1785,6 @@ 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)))

lib/Kconfig.debug

+1 −11
Original line number Diff line number Diff line
@@ -353,23 +353,13 @@ config DEBUG_SECTION_MISMATCH 
	  which results in the code/data being placed in specific sections.

	  The section mismatch analysis is always performed after a full

	  kernel build, and enabling this option causes the following

	  additional steps to occur:

	  additional step to occur:

	  - Add the option -fno-inline-functions-called-once to gcc commands.

	    When inlining a function annotated with __init in a non-init

	    function, we would lose the section information and thus

	    the analysis would not catch the illegal reference.

	    This option tells gcc to inline less (but it does result in

	    a larger kernel).

	  - Run the section mismatch analysis for each module/built-in.a file.

	    When we run the section mismatch analysis on vmlinux.o, we

	    lose valuable information about where the mismatch was

	    introduced.

	    Running the analysis for each module/built-in.a file

	    tells where the mismatch happens much closer to the

	    source. The drawback is that the same mismatch is

	    reported at least twice.

	  - Enable verbose reporting from modpost in order to help resolve

	    the section mismatches that are reported.



config SECTION_MISMATCH_WARN_ONLY

	bool "Make section mismatch errors non-fatal"

scripts/Makefile.build

+3 −12
Original line number Diff line number Diff line
@@ -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) $(always)
@@ -87,11 +85,6 @@ ifneq ($(KBUILD_ENABLE_EXTRA_GCC_CHECKS),) 
  cmd_checkdoc = $(srctree)/scripts/kernel-doc -none $<

endif



# Do section mismatch analysis for each module/built-in.a

ifdef CONFIG_DEBUG_SECTION_MISMATCH

  cmd_secanalysis = ; scripts/mod/modpost $@

endif



# Compile C sources (.c)

# ---------------------------------------------------------------------------
@@ -278,13 +271,11 @@ $(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 $< && \
@@ -461,12 +452,12 @@ endif 
# module is turned into a multi object module, $^ will contain header file

# dependencies recorded in the .*.cmd file.

quiet_cmd_link_multi-m = LD [M]  $@

cmd_link_multi-m = $(LD) $(ld_flags) -r -o $@ $(filter %.o,$^) $(cmd_secanalysis)

      cmd_link_multi-m = $(LD) $(ld_flags) -r -o $@ $(filter %.o,$^)



$(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)

CRA Git | Maintained and supported by SUSTech CRA and CCSE