linux-kernel - Re: [PATCH 10/27] modpost: traverse unresolved symbols in order

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Message-ID: <CAK7LNARmg6TipRSi8gnohPKjRgt9OB_sgR-o1LYy3beobf5WSg@mail.gmail.com>
Date:   Sun, 1 May 2022 00:24:30 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH 10/27] modpost: traverse unresolved symbols in order

On Wed, Apr 27, 2022 at 2:08 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Sun, Apr 24, 2022 at 12:09 PM Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > Currently, modpost manages unresolved in a singly liked list; it adds
>
> s/liked/linked/
>
> > a new node to the head, and traverses the list from new to old.
> >
> > Use a doubly linked list to keep the order in the symbol table in the
> > ELF file.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
> >
> >  scripts/mod/modpost.c | 20 ++++++++++++++------
> >  scripts/mod/modpost.h |  2 +-
> >  2 files changed, 15 insertions(+), 7 deletions(-)
> >
> > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> > index 1c7d2831e89d..e1eb188d6282 100644
> > --- a/scripts/mod/modpost.c
> > +++ b/scripts/mod/modpost.c
> > @@ -185,6 +185,8 @@ static struct module *new_module(const char *modname)
> >         mod = NOFAIL(malloc(sizeof(*mod) + strlen(modname) + 1));
> >         memset(mod, 0, sizeof(*mod));
> >
> > +       INIT_LIST_HEAD(&mod->unresolved_symbols);
> > +
> >         strcpy(mod->name, modname);
> >         mod->is_vmlinux = (strcmp(modname, "vmlinux") == 0);
> >         mod->gpl_compatible = true;
> > @@ -201,6 +203,7 @@ static struct module *new_module(const char *modname)
> >
> >  struct symbol {
> >         struct symbol *next;
> > +       struct list_head list;
>
> Isn't `list` meant to replace `next`?


No.  'next' is still used for the hash table.

modpost used it in various ways.
You need to read the code closely if you are interested in
how modpost works.

>
> >         struct module *module;
> >         unsigned int crc;
> >         bool crc_valid;
> > @@ -255,8 +258,12 @@ static struct symbol *new_symbol(const char *name, struct module *module,
> >
> >  static void sym_add_unresolved(const char *name, struct module *mod, bool weak)
> >  {
> > -       mod->unres = alloc_symbol(name, mod->unres);
> > -       mod->unres->weak = weak;
> > +       struct symbol *sym;
> > +
> > +       sym = alloc_symbol(name, NULL);
> > +       sym->weak = weak;
> > +
> > +       list_add_tail(&sym->list, &mod->unresolved_symbols);
>
> Because I was curious here why NULL was passed, rather than remove the
> assignment to struct symbol's next member in alloc_symbol.
> I get why you replace the `unres` member of struct module. I guess I'm
> curious then why yet another list is added to struct symbol, rather
> than replace the next member.


'next' is used for ad-hoc hash table implementation.
I will be cleaned up by a later commit.

See this patch:
https://patchwork.kernel.org/project/linux-kbuild/patch/20220424190811.1678416-20-masahiroy@kernel.org/



>
> Also, does adding a struct list_head member really not specify the
> _type_ of the next element?  I guess when I look at the definition of
> struct module, at the member unresolved symbols, I don't know whether
> it's a list of struct module* or a list of struct symbol*.


This is how include/linux/list.h works.
struct list_head is really generic, does not specify a specific type definition.



>
> <snip>
>
> > diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
> > index c3b5d2f0e2bb..6a90bfc08458 100644
> > --- a/scripts/mod/modpost.h
> > +++ b/scripts/mod/modpost.h
> > @@ -117,7 +117,7 @@ struct namespace_list {
> >  struct module {
> >         struct list_head list;
> >         int gpl_compatible;
> > -       struct symbol *unres;
> > +       struct list_head unresolved_symbols;
> >         bool from_dump;         /* true if module was loaded from *.symvers */
> >         bool is_vmlinux;
> >         bool seen;
> > --
> > 2.32.0
> >
>
>
> --
> Thanks,
> ~Nick Desaulniers



-- 
Best Regards
Masahiro Yamada