Commit 39808e45 authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

kbuild: do not read $(KBUILD_EXTMOD)/Module.symvers 



Since commit 040fcc81 ("kbuild: improved modversioning support for
external modules"), the external module build reads Module.symvers in
the directory of the module itself, then dumps symbols back into it.
It accumulates stale symbols in the file when you build an external
module incrementally.

The idea behind it was, as the commit log explained, you can copy
Modules.symvers from one module to another when you need to pass symbol
information between two modules. However, the manual copy of the file
sounds questionable to me, and containing stale symbols is a downside.

Some time later, commit 0d96fb20 ("kbuild: Add new Kbuild variable
KBUILD_EXTRA_SYMBOLS") introduced a saner approach.

So, this commit removes the former one. Going forward, the external
module build dumps symbols into Module.symvers to be carried via
KBUILD_EXTRA_SYMBOLS, but never reads it automatically.

With the -I option removed, there is no one to set the external_module
flag unless KBUILD_EXTRA_SYMBOLS is passed. Now the -i option does it
instead.

Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
parent 1747269a

Documentation/kbuild/modules.rst

+5 −8
Original line number Diff line number Diff line
@@ -492,11 +492,8 @@ build. 
	to the symbols from the kernel to check if all external symbols

	are defined. This is done in the MODPOST step. modpost obtains

	the symbols by reading Module.symvers from the kernel source

	tree. If a Module.symvers file is present in the directory

	where the external module is being built, this file will be

	read too. During the MODPOST step, a new Module.symvers file

	will be written containing all exported symbols that were not

	defined in the kernel.

	tree. During the MODPOST step, a new Module.symvers file will be

	written containing all exported symbols from that external module.



6.3 Symbols From Another External Module

----------------------------------------
@@ -504,7 +501,7 @@ build. 
	Sometimes, an external module uses exported symbols from

	another external module. Kbuild needs to have full knowledge of

	all symbols to avoid spitting out warnings about undefined

	symbols. Three solutions exist for this situation.

	symbols. Two solutions exist for this situation.



	NOTE: The method with a top-level kbuild file is recommended

	but may be impractical in certain situations.
@@ -544,8 +541,8 @@ build. 
		all symbols defined and not part of the kernel.



	Use "make" variable KBUILD_EXTRA_SYMBOLS

		If it is impractical to copy Module.symvers from

		another module, you can assign a space separated list

		If it is impractical to add a top-level kbuild file,

		you can assign a space separated list

		of files to KBUILD_EXTRA_SYMBOLS in your build file.

		These files will be loaded by modpost during the

		initialization of its symbol tables.

scripts/Makefile.modpost

+0 −1
Original line number Diff line number Diff line
@@ -50,7 +50,6 @@ MODPOST = scripts/mod/modpost \ 
	$(if $(CONFIG_MODVERSIONS),-m)					\

	$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a)			\

	$(if $(KBUILD_EXTMOD),-i,-o) $(kernelsymfile)			\

	$(if $(KBUILD_EXTMOD),-I $(modulesymfile))			\

	$(if $(KBUILD_EXTMOD),$(addprefix -e ,$(KBUILD_EXTRA_SYMBOLS)))	\

	$(if $(KBUILD_EXTMOD),-o $(modulesymfile))			\

	$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)			\

scripts/mod/modpost.c

+2 −7
Original line number Diff line number Diff line
@@ -2561,7 +2561,7 @@ int main(int argc, char **argv) 
{

	struct module *mod;

	struct buffer buf = { };

	char *kernel_read = NULL, *module_read = NULL;

	char *kernel_read = NULL;

	char *dump_write = NULL, *files_source = NULL;

	int opt;

	int err;
@@ -2569,13 +2569,10 @@ int main(int argc, char **argv) 
	struct ext_sym_list *extsym_iter;

	struct ext_sym_list *extsym_start = NULL;



	while ((opt = getopt(argc, argv, "i:I:e:mnsT:o:awEd")) != -1) {

	while ((opt = getopt(argc, argv, "i:e:mnsT:o:awEd")) != -1) {

		switch (opt) {

		case 'i':

			kernel_read = optarg;

			break;

		case 'I':

			module_read = optarg;

			external_module = 1;

			break;

		case 'e':
@@ -2620,8 +2617,6 @@ int main(int argc, char **argv) 


	if (kernel_read)

		read_dump(kernel_read, 1);

	if (module_read)

		read_dump(module_read, 0);

	while (extsym_start) {

		read_dump(extsym_start->file, 0);

		extsym_iter = extsym_start->next;

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