[RFC PATCH] modpost: check for static EXPORT_SYMBOL* functions

[Denis Efremov]

This patch adds a check to warn about static EXPORT_SYMBOL* functions
during the modpost. In most of the cases, a static symbol marked for
exporting is an odd combination that should be fixed either by deleting
the exporting mark or by removing the static attribute and adding the
appropriate declaration to headers.

If this check will be considered useful, I will resend the patch with
review fixes.

Currently, this check emits the warnings on the following symbols, most
of which are accepted to be fixed:
1. "sas_wait_eh" [drivers/scsi/libsas/libsas]
   Patch: https://lkml.org/lkml/2019/7/8/970 (accepted)
2. "torture_onoff_cleanup" [kernel/torture]
   "torture_shuffle_cleanup" [kernel/torture]
   Patch: https://lkml.org/lkml/2019/7/4/411 (accepted)
3. "LZ4HC_setExternalDict" [lib/lz4/lz4hc_compress]
   Patch: https://lkml.org/lkml/2019/7/8/842
4. "drm_client_close" [drivers/gpu/drm/drm]
   Patch: https://lkml.org/lkml/2019/7/3/758 (accepted)
5. "gve_probe" [drivers/net/ethernet/google/gve/gve]
   Patch: https://lkml.org/lkml/2019/7/14/65
6. "i2c_new_client_device" [vmlinux]
   "i2c_new_dummy_device" [vmlinux]
   Patch: https://lkml.org/lkml/2019/7/7/226 (fixed in a different patch)
7. "ahci_em_messages" [drivers/ata/libahci]
   Patch: https://lkml.org/lkml/2019/7/10/550 (reviwed)
8. "ftrace_set_clr_event" [vmlinux]
   Patch: https://lkml.org/lkml/2019/7/4/609 (reviwed)
9. "rmi_2d_sensor_set_input_params" [drivers/input/rmi4/rmi_core]
   Patch: https://lkml.org/lkml/2019/7/8/999
10. "empty_zero_page" [vmlinux]
11. "phys_base" [vmlinux]
12. "hypercall_page" [vmlinux]

Similar commits:
1. 54638c6eaf44 ("net: phy: make exported variables non-static")
2. 98ef2046f28b ("mm: remove the exporting of totalram_pages")
3. 73df167c819e ("s390/zcrypt: remove the exporting of ap_query_configuration")
4. a57caf8c527f ("sunrpc/cache: remove the exporting of cache_seq_next")
5. e4e4730698c9 ("crypto: skcipher - remove the exporting of skcipher_walk_next")

Build time impact, allmodconfig, Dell XPS 15 9570 (measurements 3x):
$ make mrproper; make allmodconfig; time make -j12; \
  git checkout HEAD~1; \
  make mrproper; make allmodconfig; time make -j12
1.
   (with patch) 17635,94s user 1895,54s system 1085% cpu 29:59,22 total
   (w/o  patch) 17275,42s user 1803,87s system 1112% cpu 28:35,66 total
2.
   (with patch) 17369,51s user 1763,28s system 1111% cpu 28:41,47 total
   (w/o  patch) 16880,50s user 1670,93s system 1113% cpu 27:46,56 total
3.
   (with patch) 17937,88s user 1842,53s system 1109% cpu 29:42,26 total
   (w/o  patch) 17267,55s user 1725,09s system 1111% cpu 28:28,17 total

Thus, the current implementation adds approx. 1 min for allmodconfig.
However, it's possible to do the check in a more optimal way if it will
be considered useful.

Also, this kind of check could be implemented as a separate script instead.
Here is the implementation:
https://gist.github.com/evdenis/bf2322d094f0c02c0f60fe0a225848b2

Signed-off-by: Denis Efremov <efremov@xxxxxxxxx>
---
 scripts/mod/modpost.c | 35 +++++++++++++++++++++++++++++++++--
 1 file changed, 33 insertions(+), 2 deletions(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index f277e116e0eb..c51eef357721 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -169,6 +169,7 @@ struct symbol {
 	unsigned int kernel:1;     /* 1 if symbol is from kernel
 				    *  (only for external modules) **/
 	unsigned int preloaded:1;  /* 1 if symbol from Module.symvers, or crc */
+	unsigned int is_static:1;  /* 1 if symbol is not global */
 	enum export  export;       /* Type of export */
 	char name[0];
 };
@@ -199,8 +200,9 @@ static struct symbol *alloc_symbol(const char *name, unsigned int weak,
 
 	memset(s, 0, sizeof(*s));
 	strcpy(s->name, name);
-	s->weak = weak;
-	s->next = next;
+	s->weak      = weak;
+	s->next      = next;
+	s->is_static = 1;
 	return s;
 }
 
@@ -1980,6 +1982,21 @@ static void read_symbols(const char *modname)
 		handle_modversions(mod, &info, sym, symname);
 		handle_moddevtable(mod, &info, sym, symname);
 	}
+
+	// check for static EXPORT_SYMBOL_* functions && global vars
+	for (sym = info.symtab_start; sym < info.symtab_stop; sym++) {
+		unsigned char bind = ELF_ST_BIND(sym->st_info);
+		unsigned char type = ELF_ST_TYPE(sym->st_info);
+
+		if (type == STT_OBJECT || type == STT_FUNC) {
+			struct symbol *s =
+			    find_symbol(remove_dot(info.strtab + sym->st_name));
+
+			if (s && (bind == STB_GLOBAL || bind == STB_WEAK))
+				s->is_static = 0;
+		}
+	}
+
 	if (!is_vmlinux(modname) || vmlinux_section_warnings)
 		check_sec_ref(mod, modname, &info);
 
@@ -2425,6 +2442,7 @@ int main(int argc, char **argv)
 	char *dump_write = NULL, *files_source = NULL;
 	int opt;
 	int err;
+	size_t n;
 	struct ext_sym_list *extsym_iter;
 	struct ext_sym_list *extsym_start = NULL;
 
@@ -2520,6 +2538,19 @@ int main(int argc, char **argv)
 	if (sec_mismatch_count && sec_mismatch_fatal)
 		fatal("modpost: Section mismatches detected.\n"
 		      "Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.\n");
+	for (n = 0; n < SYMBOL_HASH_SIZE ; n++) {
+		struct symbol *s = symbolhash[n];
+
+		while (s) {
+			if (s->is_static)
+				warn("\"%s\" [%s] is a static %s symbol\n",
+					s->name, s->module->name,
+						export_str(s->export));
+
+			s = s->next;
+		}
+	}
+
 	free(buf.p);
 
 	return err;
-- 
2.21.0