[PATCH v5 20/21] modpost: use null string instead of NULL pointer for default namespace

Masahiro Yamada
2023-05-14T15:29:31Z

The default namespace is the null string, "".

When set, the null string "" is converted to NULL:

s->namespace = namespace[0] ? NOFAIL(strdup(namespace)) : NULL;

When printed, the NULL pointer is get back to the null string:

sym->namespace ?: ""

This saves 1 byte memory allocated for "", but loses the readability.

In kernel-space, we strive to save memory, but modpost is a userspace
tool used to build the kernel. On modern systems, such small piece of
memory is not a big deal.

Handle the namespace string as is.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
---

scripts/mod/modpost.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 7edb9a843ead..010c4f88d77b 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -298,6 +298,13 @@ static bool contains_namespace(struct list_head *head, const char *namespace)
{
struct namespace_list *list;

+ /*
+ * The default namespace is null string "", which is always implicitly
+ * contained.
+ */
+ if (!namespace[0])
+ return true;
+
list_for_each_entry(list, head, list) {
if (!strcmp(list->namespace, namespace))
return true;
@@ -367,7 +374,7 @@ static struct symbol *sym_add_exported(const char *name, struct module *mod,
s = alloc_symbol(name);
s->module = mod;
s->is_gpl_only = gpl_only;
- s->namespace = namespace[0] ? NOFAIL(strdup(namespace)) : NULL;
+ s->namespace = NOFAIL(strdup(namespace));
list_add_tail(&s->list, &mod->exported_symbols);
hash_add_symbol(s);

@@ -1784,8 +1791,7 @@ static void check_exports(struct module *mod)
else
basename = mod->name;

- if (exp->namespace &&
- !contains_namespace(&mod->imported_namespaces, exp->namespace)) {
+ if (!contains_namespace(&mod->imported_namespaces, exp->namespace)) {
modpost_log(allow_missing_ns_imports ? LOG_WARN : LOG_ERROR,
"module %s uses symbol %s from namespace %s, but does not import it.\n",
basename, exp->name, exp->namespace);
@@ -1871,8 +1877,7 @@ static void add_exported_symbols(struct buffer *buf, struct module *mod)
list_for_each_entry(sym, &mod->exported_symbols, list)
buf_printf(buf, "KSYMTAB_%s(%s, \"%s\", \"%s\");\n",
sym->is_func ? "FUNC" : "DATA", sym->name,
- sym->is_gpl_only ? "_gpl" : "",
- sym->namespace ?: "");
+ sym->is_gpl_only ? "_gpl" : "", sym->namespace);

if (!modversions)
return;
@@ -2140,7 +2145,7 @@ static void write_dump(const char *fname)
buf_printf(&buf, "0x%08x\t%s\t%s\tEXPORT_SYMBOL%s\t%s\n",
sym->crc, sym->name, mod->name,
sym->is_gpl_only ? "_GPL" : "",
- sym->namespace ?: "");
+ sym->namespace);
}
}
write_buf(&buf, fname);
--
2.39.2