linux-kernel - Re: [PATCH 7/7] modpost: use null string instead of NULL pointer for default namespace

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Date:   Mon, 25 Jul 2022 09:42:53 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Nicolas Pitre <npitre@...libre.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        linux-modules@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/7] modpost: use null string instead of NULL pointer for
 default namespace

On Fri, Jun 10, 2022 at 11:34 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> 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@...nel.org>

Sorry for the late review.  If this is still useful:
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

Feel free to ping me via mail if I'm falling behind. Otherwise you
should join us on IRC. (#clangbuiltlinux on libera)

> ---
>
>  scripts/mod/modpost.c | 16 +++++++++++-----
>  1 file changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 0db2cbb74a2a..5a1785645943 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -296,6 +296,13 @@ 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;
> @@ -371,7 +378,7 @@ 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);
>
> @@ -2117,8 +2124,7 @@ 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);
> @@ -2201,7 +2207,7 @@ static void add_exported_symbols(struct buffer *buf, struct module *mod)
>         list_for_each_entry(sym, &mod->exported_symbols, list)
>                 buf_printf(buf, "KSYMTAB_ENTRY(%s, \"%s\", \"%s\");\n",
>                            sym->name, sym->is_gpl_only ? "_gpl" : "",
> -                          sym->namespace ?: "");
> +                          sym->namespace);
>
>         if (!modversions)
>                 return;
> @@ -2471,7 +2477,7 @@ 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);
> --
> 2.32.0
>


-- 
Thanks,
~Nick Desaulniers