Commit f292d875 authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

modpost: extract symbol versions from *.cmd files 



Currently, CONFIG_MODVERSIONS needs extra link to embed the symbol
versions into ELF objects. Then, modpost extracts the version CRCs
from them.

The following figures show how it currently works, and how I am trying
to change it.

Current implementation
======================
                                                           |----------|
                 embed CRC      -------------------------->| final    |
       $(CC)       $(LD)       /  |---------|              | link for |
       -----> *.o -------> *.o -->| modpost |              | vmlinux  |
      /              /            |         |-- *.mod.c -->| or       |
     / genksyms     /             |---------|              | module   |
  *.c ------> *.symversions                                |----------|

Genksyms outputs the calculated CRCs in the form of linker script
(*.symversions), which is used by $(LD) to update the object.

If CONFIG_LTO_CLANG=y, the build process is much more complex. Embedding
the CRCs is postponed until the LLVM bitcode is converted into ELF,
creating another intermediate *.prelink.o.

However, this complexity is unneeded. There is no reason why we must
embed version CRCs in objects so early.

There is final link stage for vmlinux (scripts/link-vmlinux.sh) and
modules (scripts/Makefile.modfinal). We can link CRCs at the very last
moment.

New implementation
==================
                                                           |----------|
                   --------------------------------------->| final    |
       $(CC)      /    |---------|                         | link for |
       -----> *.o ---->|         |                         | vmlinux  |
      /                | modpost |--- .vmlinux.export.c -->| or       |
     / genksyms        |         |--- *.mod.c ------------>| module   |
  *.c ------> *.cmd -->|---------|                         |----------|

Pass the symbol versions to modpost as separate text data, which are
available in *.cmd files.

This commit changes modpost to extract CRCs from *.cmd files instead of
from ELF objects.

Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
Reviewed-by: default avatarNicolas Schier <nicolas@fjasle.eu>
Tested-by: default avatarNathan Chancellor <nathan@kernel.org>
Reviewed-by: default avatarSami Tolvanen <samitolvanen@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # LLVM-14 (x86-64)
parent 69c4cc99

scripts/mod/modpost.c

+131 −48
Original line number Diff line number Diff line
@@ -383,19 +383,10 @@ static struct symbol *sym_add_exported(const char *name, struct module *mod, 
	return s;

}



static void sym_set_crc(const char *name, unsigned int crc)

static void sym_set_crc(struct symbol *sym, unsigned int crc)

{

	struct symbol *s = find_symbol(name);



	/*

	 * Ignore stand-alone __crc_*, which might be auto-generated symbols

	 * such as __*_veneer in ARM ELF.

	 */

	if (!s)

		return;



	s->crc = crc;

	s->crc_valid = true;

	sym->crc = crc;

	sym->crc_valid = true;

}



static void *grab_file(const char *filename, size_t *size)
@@ -618,33 +609,6 @@ static int ignore_undef_symbol(struct elf_info *info, const char *symname) 
	return 0;

}



static void handle_modversion(const struct module *mod,

			      const struct elf_info *info,

			      const Elf_Sym *sym, const char *symname)

{

	unsigned int crc;



	if (sym->st_shndx == SHN_UNDEF) {

		warn("EXPORT symbol \"%s\" [%s%s] version generation failed, symbol will not be versioned.\n"

		     "Is \"%s\" prototyped in <asm/asm-prototypes.h>?\n",

		     symname, mod->name, mod->is_vmlinux ? "" : ".ko",

		     symname);



		return;

	}



	if (sym->st_shndx == SHN_ABS) {

		crc = sym->st_value;

	} else {

		unsigned int *crcp;



		/* symbol points to the CRC in the ELF object */

		crcp = sym_get_data(info, sym);

		crc = TO_NATIVE(*crcp);

	}

	sym_set_crc(symname, crc);

}



static void handle_symbol(struct module *mod, struct elf_info *info,

			  const Elf_Sym *sym, const char *symname)

{
@@ -1952,6 +1916,104 @@ static char *remove_dot(char *s) 
	return s;

}



/*

 * The CRCs are recorded in .*.cmd files in the form of:

 * #SYMVER <name> <crc>

 */

static void extract_crcs_for_object(const char *object, struct module *mod)

{

	char cmd_file[PATH_MAX];

	char *buf, *p;

	const char *base;

	int dirlen, ret;



	base = strrchr(object, '/');

	if (base) {

		base++;

		dirlen = base - object;

	} else {

		dirlen = 0;

		base = object;

	}



	ret = snprintf(cmd_file, sizeof(cmd_file), "%.*s.%s.cmd",

		       dirlen, object, base);

	if (ret >= sizeof(cmd_file)) {

		error("%s: too long path was truncated\n", cmd_file);

		return;

	}



	buf = read_text_file(cmd_file);

	p = buf;



	while ((p = strstr(p, "\n#SYMVER "))) {

		char *name;

		size_t namelen;

		unsigned int crc;

		struct symbol *sym;



		name = p + strlen("\n#SYMVER ");



		p = strchr(name, ' ');

		if (!p)

			break;



		namelen = p - name;

		p++;



		if (!isdigit(*p))

			continue;	/* skip this line */



		crc = strtol(p, &p, 0);

		if (*p != '\n')

			continue;	/* skip this line */



		name[namelen] = '\0';



		/*

		 * sym_find_with_module() may return NULL here.

		 * It typically occurs when CONFIG_TRIM_UNUSED_KSYMS=y.

		 * Since commit e1327a127703, genksyms calculates CRCs of all

		 * symbols, including trimmed ones. Ignore orphan CRCs.

		 */

		sym = sym_find_with_module(name, mod);

		if (sym)

			sym_set_crc(sym, crc);

	}



	free(buf);

}



/*

 * The symbol versions (CRC) are recorded in the .*.cmd files.

 * Parse them to retrieve CRCs for the current module.

 */

static void mod_set_crcs(struct module *mod)

{

	char objlist[PATH_MAX];

	char *buf, *p, *obj;

	int ret;



	if (mod->is_vmlinux) {

		strcpy(objlist, ".vmlinux.objs");

	} else {

		/* objects for a module are listed in the *.mod file. */

		ret = snprintf(objlist, sizeof(objlist), "%s.mod", mod->name);

		if (ret >= sizeof(objlist)) {

			error("%s: too long path was truncated\n", objlist);

			return;

		}

	}



	buf = read_text_file(objlist);

	p = buf;



	while ((obj = strsep(&p, "\n")) && obj[0])

		extract_crcs_for_object(obj, mod);



	free(buf);

}



static void read_symbols(const char *modname)

{

	const char *symname;
@@ -2012,9 +2074,6 @@ static void read_symbols(const char *modname) 
		if (strstarts(symname, "__kstrtabns_"))

			sym_update_namespace(symname + strlen("__kstrtabns_"),

					     sym_get_data(&info, sym));

		if (strstarts(symname, "__crc_"))

			handle_modversion(mod, &info, sym,

					  symname + strlen("__crc_"));

	}



	// check for static EXPORT_SYMBOL_* functions && global vars
@@ -2042,12 +2101,17 @@ static void read_symbols(const char *modname) 


	parse_elf_finish(&info);



	/* Our trick to get versioning for module struct etc. - it's

	if (modversions) {

		/*

		 * Our trick to get versioning for module struct etc. - it's

		 * never passed as an argument to an exported function, so

		 * the automatic versioning doesn't pick it up, but it's really

	 * important anyhow */

	if (modversions)

		 * important anyhow.

		 */

		sym_add_unresolved("module_layout", mod, false);



		mod_set_crcs(mod);

	}

}



static void read_symbols_from_files(const char *filename)
@@ -2204,6 +2268,23 @@ static void add_header(struct buffer *b, struct module *mod) 
		buf_printf(b, "\nMODULE_INFO(staging, \"Y\");\n");

}



static void check_symversions(struct module *mod)

{

	struct symbol *sym;



	if (!modversions)

		return;



	list_for_each_entry(sym, &mod->exported_symbols, list) {

		if (!sym->crc_valid) {

			warn("EXPORT symbol \"%s\" [%s%s] version generation failed, symbol will not be versioned.\n"

			     "Is \"%s\" prototyped in <asm/asm-prototypes.h>?\n",

			     sym->name, mod->name, mod->is_vmlinux ? "" : ".ko",

			     sym->name);

		}

	}

}



/**

 * Record CRCs for unresolved symbols

 **/
@@ -2419,7 +2500,7 @@ static void read_dump(const char *fname) 
		}

		s = sym_add_exported(symname, mod, gpl_only);

		s->is_static = false;

		sym_set_crc(symname, crc);

		sym_set_crc(s, crc);

		sym_update_namespace(symname, namespace);

	}

	free(buf);
@@ -2545,6 +2626,8 @@ int main(int argc, char **argv) 
		if (mod->from_dump)

			continue;



		check_symversions(mod);



		if (!mod->is_vmlinux)

			write_mod_c_file(mod);

	}