RE: [PATCH v3 6/8] modpost: use null string instead of NULL pointer for default namespace

David Laight
2022-09-28T09:55:24Z

From: Masahiro Yamada
> Sent: 28 September 2022 07:40
>
> 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.

The code size changes are far larger that any data sizes.

> 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>
> ---
>
> (no changes since v1)
>
> 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 0bb5bbd176b4..29f30558a398 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -297,6 +297,13 @@ 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;
> @@ -366,7 +373,7 @@ 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);
>
> @@ -1928,8 +1935,7 @@ 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)) {

Do you still need to optimise/check for the default namespace?

David

> 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);
> @@ -2015,8 +2021,7 @@ 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;
> @@ -2284,7 +2289,7 @@ 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);
> --
> 2.34.1

-
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