linux-kernel - Re: [PATCH v2] efi: fix -Wmissing-variable-declarations warning

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Date:   Wed, 30 Aug 2023 10:56:28 -0700
From:   Justin Stitt <justinstitt@...gle.com>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-efi@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: Re: [PATCH v2] efi: fix -Wmissing-variable-declarations warning

On Wed, Aug 30, 2023 at 10:54 AM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Wed, 30 Aug 2023 at 19:51, Justin Stitt <justinstitt@...gle.com> wrote:
> >
> > When building x86/defconfig with Clang-18 I encounter the following warnings:
> > | arch/x86/platform/efi/efi.c:934:23: warning: no previous extern declaration for non-static variable 'efi_attr_fw_vendor' [-Wmissing-variable-declarations]
> > |   934 | struct kobj_attribute efi_attr_fw_vendor = __ATTR_RO(fw_vendor);
> > | arch/x86/platform/efi/efi.c:935:23: warning: no previous extern declaration for non-static variable 'efi_attr_runtime' [-Wmissing-variable-declarations]
> > |   935 | struct kobj_attribute efi_attr_runtime = __ATTR_RO(runtime);
> > | arch/x86/platform/efi/efi.c:936:23: warning: no previous extern declaration for non-static variable 'efi_attr_config_table' [-Wmissing-variable-declarations]
> > |   936 | struct kobj_attribute efi_attr_config_table = __ATTR_RO(config_table);
> >
> > These symbols are declared extern in drivers/firmware/efi/efi.c. Move
> > the declarations to linux/efi.h to resolve these warnings.
> >
> > Also, trim a trailing space from efi_set_variable_t typedef.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1920
> > Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> > Signed-off-by: Justin Stitt <justinstitt@...gle.com>
>
> Thanks, I'll take this as a fix.
>
> > ---
> > Changes in v2:
> > - Don't use static. Instead move symbols to header file (thanks Ard)
> > - Remove duplicated warnings output from b4 (thanks Ard)
> > - Link to v1: https://lore.kernel.org/r/20230829-missingvardecl-efi-v1-1-13d055a55176@google.com
> > ---
> > Note: build-tested.
> >
> > Also, a question: Why does the compiler warn at all? The extern
> > declarations _do_ exist as Ard points out [1].
> >
> > [1]: https://lore.kernel.org/all/CAMj1kXE_xs+wWno4G4U+6CFCOwO7JWcmNv4et5=W=ZRrQatWnQ@mail.gmail.com/
>
> Those declarations are not observed by the compiler when building .c
> files other than drivers/firmware/efi/efi.c, so they essentially don't
> exist when compiling arch/x86/platform/efi/efi.c.

I see, the linker is resolving these later then?

>
>
> > ---
> >  drivers/firmware/efi/efi.c | 3 ---
> >  include/linux/efi.h        | 6 +++++-
> >  2 files changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> > index 1599f1176842..7b4e59ccf09e 100644
> > --- a/drivers/firmware/efi/efi.c
> > +++ b/drivers/firmware/efi/efi.c
> > @@ -161,9 +161,6 @@ static ssize_t fw_platform_size_show(struct kobject *kobj,
> >         return sprintf(buf, "%d\n", efi_enabled(EFI_64BIT) ? 64 : 32);
> >  }
> >
> > -extern __weak struct kobj_attribute efi_attr_fw_vendor;
> > -extern __weak struct kobj_attribute efi_attr_runtime;
> > -extern __weak struct kobj_attribute efi_attr_config_table;
> >  static struct kobj_attribute efi_attr_fw_platform_size =
> >         __ATTR_RO(fw_platform_size);
> >
> > diff --git a/include/linux/efi.h b/include/linux/efi.h
> > index ab088c662e88..32f7ca60b0e9 100644
> > --- a/include/linux/efi.h
> > +++ b/include/linux/efi.h
> > @@ -287,7 +287,7 @@ typedef efi_status_t efi_get_variable_t (efi_char16_t *name, efi_guid_t *vendor,
> >                                          unsigned long *data_size, void *data);
> >  typedef efi_status_t efi_get_next_variable_t (unsigned long *name_size, efi_char16_t *name,
> >                                               efi_guid_t *vendor);
> > -typedef efi_status_t efi_set_variable_t (efi_char16_t *name, efi_guid_t *vendor,
> > +typedef efi_status_t efi_set_variable_t (efi_char16_t *name, efi_guid_t *vendor,
> >                                          u32 attr, unsigned long data_size,
> >                                          void *data);
> >  typedef efi_status_t efi_get_next_high_mono_count_t (u32 *count);
> > @@ -632,6 +632,10 @@ typedef struct {
> >
> >  extern unsigned long __ro_after_init efi_rng_seed;             /* RNG Seed table */
> >
> > +extern __weak struct kobj_attribute efi_attr_fw_vendor;
> > +extern __weak struct kobj_attribute efi_attr_runtime;
> > +extern __weak struct kobj_attribute efi_attr_config_table;
> > +
> >  /*
> >   * All runtime access to EFI goes through this structure:
> >   */
> >
> > ---
> > base-commit: 706a741595047797872e669b3101429ab8d378ef
> > change-id: 20230829-missingvardecl-efi-59306aacfed4
> >
> > Best regards,
> > --
> > Justin Stitt <justinstitt@...gle.com>
> >