kbuild: improved modversioning support for external modules
With following patch a second option is enabled to obtain symbol information from a second external module when a external module is build. The recommended approach is to use a common kbuild file but that may be impractical in certain cases. With this patch one can copy over a Module.symvers from one external module to make symbols (and symbol versions) available for another external module. Updated documentation in Documentation/kbuild/modules.txt Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
This commit is contained in:
Sam Ravnborg
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@ -23,7 +23,10 @@ In this document you will find information about:
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=== 6. Module installation
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--- 6.1 INSTALL_MOD_PATH
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--- 6.2 INSTALL_MOD_DIR
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=== 7. Module versioning
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=== 7. Module versioning & Module.symvers
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--- 7.1 Symbols fron the kernel (vmlinux + modules)
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--- 7.2 Symbols and external modules
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--- 7.3 Symbols from another external module
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=== 8. Tips & Tricks
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--- 8.1 Testing for CONFIG_FOO_BAR
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@ -89,7 +92,8 @@ when building an external module.
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make -C $KDIR M=$PWD modules_install
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Install the external module(s).
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Installation default is in /lib/modules/<kernel-version>/extra,
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but may be prefixed with INSTALL_MOD_PATH - see separate chapter.
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but may be prefixed with INSTALL_MOD_PATH - see separate
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chapter.
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make -C $KDIR M=$PWD clean
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Remove all generated files for the module - the kernel
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@ -433,7 +437,7 @@ External modules are installed in the directory:
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=> Install dir: /lib/modules/$(KERNELRELEASE)/gandalf
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=== 7. Module versioning
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=== 7. Module versioning & Module.symvers
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Module versioning is enabled by the CONFIG_MODVERSIONS tag.
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@ -443,10 +447,79 @@ when a module is loaded/used then the CRC values contained in the kernel are
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compared with similar values in the module. If they are not equal then the
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kernel refuses to load the module.
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During a kernel build a file named Module.symvers will be generated. This
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file includes the symbol version of all symbols within the kernel. If the
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Module.symvers file is saved from the last full kernel compile one does not
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have to do a full kernel compile to build a module version's compatible module.
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Module.symvers contains a list of all exported symbols from a kernel build.
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--- 7.1 Symbols fron the kernel (vmlinux + modules)
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During a kernel build a file named Module.symvers will be generated.
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Module.symvers contains all exported symbols from the kernel and
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compiled modules. For each symbols the corresponding CRC value
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is stored too.
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The syntax of the Module.symvers file is:
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<CRC> <Symbol> <module>
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Sample:
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0x2d036834 scsi_remove_host drivers/scsi/scsi_mod
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For a kernel build without CONFIG_MODVERSIONING enabled the crc
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would read: 0x00000000
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Module.symvers serve two purposes.
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1) It list all exported symbols both from vmlinux and all modules
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2) It list CRC if CONFIG_MODVERSION is enabled
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--- 7.2 Symbols and external modules
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When building an external module the build system needs access to
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the symbols from the kernel to check if all external symbols are
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defined. This is done in the MODPOST step and to obtain all
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symbols modpost reads Module.symvers from the kernel.
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If a Module.symvers file is present in the directory where
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the external module is being build this file will be read too.
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During the MODPOST step a new Module.symvers file will be written
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containing all exported symbols that was not defined in the kernel.
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--- 7.3 Symbols from another external module
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Sometimes one external module uses exported symbols from another
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external module. Kbuild needs to have full knowledge on all symbols
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to avoid spitting out warnings about undefined symbols.
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Two solutions exist to let kbuild know all symbols of more than
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one external module.
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The method with a top-level kbuild file is recommended but may be
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impractical in certain situations.
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Use a top-level Kbuild file
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If you have two modules: 'foo', 'bar' and 'foo' needs symbols
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from 'bar' then one can use a common top-level kbuild file so
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both modules are compiled in same build.
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Consider following directory layout:
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./foo/ <= contains the foo module
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./bar/ <= contains the bar module
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The top-level Kbuild file would then look like:
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#./Kbuild: (this file may also be named Makefile)
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obj-y := foo/ bar/
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Executing:
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make -C $KDIR M=`pwd`
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will then do the expected and compile both modules with full
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knowledge on symbols from both modules.
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Use an extra Module.symvers file
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When an external module is build a Module.symvers file is
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generated containing all exported symbols which are not
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defined in the kernel.
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To get access to symbols from module 'bar' one can copy the
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Module.symvers file from the compilation of the 'bar' module
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to the directory where the 'foo' module is build.
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During the module build kbuild will read the Module.symvers
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file in the directory of the external module and when the
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build is finished a new Module.symvers file is created
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containing the sum of all symbols defined and not part of the
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kernel.
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=== 8. Tips & Tricks
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@ -39,7 +39,8 @@ include .config
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include scripts/Kbuild.include
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include scripts/Makefile.lib
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symverfile := $(objtree)/Module.symvers
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kernelsymfile := $(objtree)/Module.symvers
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modulesymfile := $(KBUILD_EXTMOD)/Modules.symvers
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# Step 1), find all modules listed in $(MODVERDIR)/
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__modules := $(sort $(shell grep -h '\.ko' /dev/null $(wildcard $(MODVERDIR)/*.mod)))
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@ -54,7 +55,9 @@ quiet_cmd_modpost = MODPOST
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cmd_modpost = scripts/mod/modpost \
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$(if $(CONFIG_MODVERSIONS),-m) \
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$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a,) \
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$(if $(KBUILD_EXTMOD),-i,-o) $(symverfile) \
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$(if $(KBUILD_EXTMOD),-i,-o) $(kernelsymfile) \
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$(if $(KBUILD_EXTMOD),-I $(modulesymfile)) \
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$(if $(KBUILD_EXTMOD),-o $(modulesymfile)) \
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$(filter-out FORCE,$^)
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.PHONY: __modpost
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@ -20,6 +20,8 @@ int modversions = 0;
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int have_vmlinux = 0;
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/* Is CONFIG_MODULE_SRCVERSION_ALL set? */
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static int all_versions = 0;
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/* If we are modposting external module set to 1 */
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static int external_module = 0;
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void fatal(const char *fmt, ...)
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{
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@ -45,6 +47,18 @@ void warn(const char *fmt, ...)
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va_end(arglist);
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}
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static int is_vmlinux(const char *modname)
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{
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const char *myname;
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if ((myname = strrchr(modname, '/')))
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myname++;
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else
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myname = modname;
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return strcmp(myname, "vmlinux") == 0;
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}
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void *do_nofail(void *ptr, const char *expr)
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{
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if (!ptr) {
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@ -100,6 +114,9 @@ struct symbol {
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unsigned int crc;
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int crc_valid;
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unsigned int weak:1;
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unsigned int vmlinux:1; /* 1 if symbol is defined in vmlinux */
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unsigned int kernel:1; /* 1 if symbol is from kernel
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* (only for external modules) **/
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char name[0];
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};
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@ -135,8 +152,7 @@ static struct symbol *alloc_symbol(const char *name, unsigned int weak,
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}
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/* For the hash of exported symbols */
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static void new_symbol(const char *name, struct module *module,
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unsigned int *crc)
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static struct symbol *new_symbol(const char *name, struct module *module)
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{
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unsigned int hash;
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struct symbol *new;
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@ -144,10 +160,7 @@ static void new_symbol(const char *name, struct module *module,
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hash = tdb_hash(name) % SYMBOL_HASH_SIZE;
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new = symbolhash[hash] = alloc_symbol(name, 0, symbolhash[hash]);
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new->module = module;
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if (crc) {
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new->crc = *crc;
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new->crc_valid = 1;
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}
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return new;
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}
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static struct symbol *find_symbol(const char *name)
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@ -169,20 +182,28 @@ static struct symbol *find_symbol(const char *name)
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* Add an exported symbol - it may have already been added without a
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* CRC, in this case just update the CRC
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**/
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static void add_exported_symbol(const char *name, struct module *module,
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unsigned int *crc)
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static struct symbol *sym_add_exported(const char *name, struct module *mod)
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{
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struct symbol *s = find_symbol(name);
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if (!s) {
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new_symbol(name, module, crc);
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return;
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if (!s)
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s = new_symbol(name, mod);
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s->vmlinux = is_vmlinux(mod->name);
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s->kernel = 0;
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return s;
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}
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if (crc) {
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s->crc = *crc;
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static void sym_update_crc(const char *name, struct module *mod,
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unsigned int crc)
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{
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struct symbol *s = find_symbol(name);
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if (!s)
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s = new_symbol(name, mod);
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s->crc = crc;
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s->crc_valid = 1;
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}
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}
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void *grab_file(const char *filename, unsigned long *size)
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{
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@ -332,8 +353,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
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/* CRC'd symbol */
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if (memcmp(symname, CRC_PFX, strlen(CRC_PFX)) == 0) {
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crc = (unsigned int) sym->st_value;
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add_exported_symbol(symname + strlen(CRC_PFX),
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mod, &crc);
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sym_update_crc(symname + strlen(CRC_PFX), mod, crc);
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}
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break;
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case SHN_UNDEF:
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@ -377,8 +397,7 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
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default:
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/* All exported symbols */
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if (memcmp(symname, KSYMTAB_PFX, strlen(KSYMTAB_PFX)) == 0) {
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add_exported_symbol(symname + strlen(KSYMTAB_PFX),
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mod, NULL);
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sym_add_exported(symname + strlen(KSYMTAB_PFX), mod);
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}
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if (strcmp(symname, MODULE_SYMBOL_PREFIX "init_module") == 0)
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mod->has_init = 1;
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@ -388,18 +407,6 @@ static void handle_modversions(struct module *mod, struct elf_info *info,
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}
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}
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static int is_vmlinux(const char *modname)
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{
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const char *myname;
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if ((myname = strrchr(modname, '/')))
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myname++;
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else
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myname = modname;
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return strcmp(myname, "vmlinux") == 0;
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}
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/**
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* Parse tag=value strings from .modinfo section
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**/
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@ -450,9 +457,7 @@ static void read_symbols(char *modname)
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/* When there's no vmlinux, don't print warnings about
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* unresolved symbols (since there'll be too many ;) */
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if (is_vmlinux(modname)) {
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unsigned int fake_crc = 0;
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have_vmlinux = 1;
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add_exported_symbol("struct_module", mod, &fake_crc);
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mod->skip = 1;
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}
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@ -665,7 +670,7 @@ static void write_if_changed(struct buffer *b, const char *fname)
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fclose(file);
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}
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static void read_dump(const char *fname)
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static void read_dump(const char *fname, unsigned int kernel)
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{
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unsigned long size, pos = 0;
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void *file = grab_file(fname, &size);
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@ -679,6 +684,7 @@ static void read_dump(const char *fname)
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char *symname, *modname, *d;
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unsigned int crc;
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struct module *mod;
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struct symbol *s;
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if (!(symname = strchr(line, '\t')))
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goto fail;
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@ -699,13 +705,28 @@ static void read_dump(const char *fname)
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mod = new_module(NOFAIL(strdup(modname)));
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mod->skip = 1;
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}
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add_exported_symbol(symname, mod, &crc);
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s = sym_add_exported(symname, mod);
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s->kernel = kernel;
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sym_update_crc(symname, mod, crc);
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}
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return;
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fail:
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fatal("parse error in symbol dump file\n");
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}
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/* For normal builds always dump all symbols.
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* For external modules only dump symbols
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* that are not read from kernel Module.symvers.
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**/
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static int dump_sym(struct symbol *sym)
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{
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if (!external_module)
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return 1;
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if (sym->vmlinux || sym->kernel)
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return 0;
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return 1;
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}
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static void write_dump(const char *fname)
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{
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struct buffer buf = { };
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@ -715,15 +736,10 @@ static void write_dump(const char *fname)
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for (n = 0; n < SYMBOL_HASH_SIZE ; n++) {
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symbol = symbolhash[n];
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while (symbol) {
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symbol = symbol->next;
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}
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}
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for (n = 0; n < SYMBOL_HASH_SIZE ; n++) {
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symbol = symbolhash[n];
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while (symbol) {
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buf_printf(&buf, "0x%08x\t%s\t%s\n", symbol->crc,
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symbol->name, symbol->module->name);
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if (dump_sym(symbol))
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buf_printf(&buf, "0x%08x\t%s\t%s\n",
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symbol->crc, symbol->name,
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symbol->module->name);
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symbol = symbol->next;
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}
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}
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@ -735,13 +751,18 @@ int main(int argc, char **argv)
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struct module *mod;
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struct buffer buf = { };
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char fname[SZ];
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char *dump_read = NULL, *dump_write = NULL;
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char *kernel_read = NULL, *module_read = NULL;
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char *dump_write = NULL;
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int opt;
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while ((opt = getopt(argc, argv, "i:mo:a")) != -1) {
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while ((opt = getopt(argc, argv, "i:I:mo:a")) != -1) {
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switch(opt) {
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case 'i':
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dump_read = optarg;
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kernel_read = optarg;
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break;
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case 'I':
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module_read = optarg;
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external_module = 1;
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break;
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case 'm':
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modversions = 1;
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@ -757,8 +778,10 @@ int main(int argc, char **argv)
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}
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}
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if (dump_read)
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read_dump(dump_read);
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if (kernel_read)
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read_dump(kernel_read, 1);
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if (module_read)
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read_dump(module_read, 0);
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while (optind < argc) {
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read_symbols(argv[optind++]);
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