Commit 95065ad3 authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds

[PATCH] kbuild: Improved external module support

From: Sam Ravnborg <sam@ravnborg.org>

The external module support recently introduced caused a number of problems:
- To build an external module the Module.symvers file was needed
- To create the Module.symvers file a module was required
- If Module.symvers was missing kbuild boiled out with an error
- If vmlinux was missing also the stage 2 of module build failed (make -k)
- It was not documented what was needed to actually bauild a module

The following patch addresses this by adding the following functionality:
- Always generate the Module.symvers file
- Ignore a missing Module.symvers file
- Add a new target modules_prepare, it prepares the kernel for building
  external modules, and is also usefull with O=
- And it adds some more comments to Makefile.modpost, so others may follow
  it with some luck
- .modpost.cmd is no longer generated

This should close all reports on issues with respect to building external
modules with current kernel - which has been identified as kernel problems.
parent e354a56d
......@@ -715,8 +715,12 @@ modules: $(vmlinux-dirs) $(if $(KBUILD_BUILTIN),vmlinux)
@echo ' Building modules, stage 2.';
$(Q)$(MAKE) -rR -f $(srctree)/scripts/Makefile.modpost
# Install modules
# Target to prepare building external modules
.PHONY: modules_prepare
modules_prepare: prepare-all scripts
# Target to install modules
.PHONY: modules_install
modules_install: _modinst_ _modinst_post
......
# ===========================================================================
# Module versions
# ===========================================================================
.PHONY: __modversions
__modversions:
#
# Stage one of module building created the following:
# a) The individual .o files used for the module
# b) A <module>.o file wich 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
# Stage 2 is handled by this file and does the following
# 1) Find all modules from the files listed in $(MODVERDIR)/
# 2) modpost is then used to
# 3) create one <module>.mod.c file pr. module
# 4) create one Module.symvers file with CRC for all exported symbols
# 5) compile all <module>.mod.c files
# 6) final link of the module to a <module.ko> file
# Step 3 is used to place certain information in the module's ELF
# section, including information such as:
# Version magic (see include/vermagic.h for full details)
# - Kernel release
# - SMP is CONFIG_SMP
# - PREEMPT is CONFIG_PREEMPT
# - GCC Version
# Module info
# - Module version (MODULE_VERSION)
# - Module alias'es (MODULE_ALIAS)
# - Module license (MODULE_LICENSE)
# - See include/linux/module.h for more details
# Step 4 is solely used to allow module versioning in external modules,
# where the CRC of each module is retreived from the Module.symers file.
.PHONY: _modpost
_modpost: __modpost
include .config
include scripts/Makefile.lib
#
symverfile := $(objtree)/Module.symvers
# Step 1), find all modules listed in $(MODVERDIR)/
__modules := $(shell head -q -n1 /dev/null $(wildcard $(MODVERDIR)/*.mod))
modules := $(patsubst %.o,%.ko,$(wildcard $(__modules:.ko=.o)))
modules := $(patsubst %.o,%.ko, $(wildcard $(__modules:.ko=.o)))
__modversions: $(modules)
@:
_modpost: $(modules)
# The final module link
quiet_cmd_ld_ko_o = LD [M] $@
cmd_ld_ko_o = $(LD) $(LDFLAGS) $(LDFLAGS_MODULE) -o $@ \
# Step 2), invoke modpost
# Includes step 3,4
quiet_cmd_modpost = MODPOST
cmd_modpost = scripts/modpost \
$(if $(KBUILD_EXTMOD),-i,-o) $(symverfile) \
$(filter-out FORCE,$^)
$(modules): %.ko :%.o %.mod.o FORCE
$(call if_changed,ld_ko_o)
.PHONY: __modpost
__modpost: $(wildcard vmlinux) $(modules:.ko=.o) FORCE
$(call cmd,modpost)
# Declare generated files as targets for modpost
$(symverfile): __modpost ;
$(modules:.ko=.mod.c): __modpost ;
targets += $(modules)
# Compile version info for unresolved symbols
# Step 5), compile all *.mod.c files
# modname is set to make c_flags define KBUILD_MODNAME
modname = $(*F)
quiet_cmd_cc_o_c = CC $@
......@@ -40,23 +77,16 @@ $(modules:.ko=.mod.o): %.mod.o: %.mod.c FORCE
targets += $(modules:.ko=.mod.o)
# All the .mod.c files are generated using the helper "modpost"
.PHONY: __modpost
$(modules:.ko=.mod.c): __modpost ;
# Extract all checksums for all exported symbols
quiet_cmd_modpost = MODPOST
cmd_modpost = scripts/modpost \
$(if $(filter vmlinux,$^),-o,-i) $(objtree)/Module.symvers \
# Step 6), final link of the modules
quiet_cmd_ld_ko_o = LD [M] $@
cmd_ld_ko_o = $(LD) $(LDFLAGS) $(LDFLAGS_MODULE) -o $@ \
$(filter-out FORCE,$^)
__modpost: $(if $(KBUILD_EXTMOD),,$(wildcard vmlinux)) $(modules:.ko=.o) FORCE
$(call if_changed,modpost)
$(modules): %.ko :%.o %.mod.o FORCE
$(call if_changed,ld_ko_o)
targets += $(modules)
targets += __modpost
# Add FORCE to the prequisites of a target to force it to be always rebuilt.
# ---------------------------------------------------------------------------
......
......@@ -625,10 +625,9 @@ read_dump(const char *fname)
void *file = grab_file(fname, &size);
char *line;
if (!file) {
perror(fname);
abort();
}
if (!file)
/* No symbol versions, silently ignore */
return;
while ((line = get_next_line(&pos, file, size))) {
char *symname, *modname, *d;
......
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