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

Masahiro Yamada
2022-09-28T13:53:47Z

On Wed, Sep 28, 2022 at 6:53 PM David Laight <David.Laight@aculab.com> wrote:
>
> 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?

I am not sure if I understood your comment, but
I changed the contains_namespace() body so that
contains_namespace(&mod->imported_namespaces, "")
returns true.

> 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
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>

--
Best Regards
Masahiro Yamada