linux-kernel - Re: [PATCH v1 04/10] asm-generic: Use HAVE_DEREFERENCE_FUNCTION

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Date:   Tue, 12 Oct 2021 08:02:53 +0200
From:   Helge Deller <deller@....de>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-ia64@...r.kernel.org, linux-parisc@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 04/10] asm-generic: Use
 HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR to define associated stubs

On 10/11/21 17:25, Christophe Leroy wrote:
> Use HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR instead of 'dereference_function_descriptor'
> to know whether arch has function descriptors.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/ia64/include/asm/sections.h    | 4 ++--
>  arch/parisc/include/asm/sections.h  | 6 ++++--
>  arch/powerpc/include/asm/sections.h | 6 ++++--
>  include/asm-generic/sections.h      | 3 ++-
>  4 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/arch/ia64/include/asm/sections.h b/arch/ia64/include/asm/sections.h
> index 35f24e52149a..80f5868afb06 100644
> --- a/arch/ia64/include/asm/sections.h
> +++ b/arch/ia64/include/asm/sections.h
> @@ -7,6 +7,8 @@
>   *	David Mosberger-Tang <davidm@....hp.com>
>   */
>
> +#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> +
>  #include <linux/elf.h>
>  #include <linux/uaccess.h>
>  #include <asm-generic/sections.h>
> @@ -27,8 +29,6 @@ extern char __start_gate_brl_fsys_bubble_down_patchlist[], __end_gate_brl_fsys_b
>  extern char __start_unwind[], __end_unwind[];
>  extern char __start_ivt_text[], __end_ivt_text[];
>
> -#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> -
>  #undef dereference_function_descriptor
>  static inline void *dereference_function_descriptor(void *ptr)
>  {
> diff --git a/arch/parisc/include/asm/sections.h b/arch/parisc/include/asm/sections.h
> index bb52aea0cb21..2e781ee19b66 100644
> --- a/arch/parisc/include/asm/sections.h
> +++ b/arch/parisc/include/asm/sections.h
> @@ -2,6 +2,10 @@
>  #ifndef _PARISC_SECTIONS_H
>  #define _PARISC_SECTIONS_H
>
> +#ifdef CONFIG_64BIT
> +#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> +#endif
> +
>  /* nothing to see, move along */
>  #include <asm-generic/sections.h>
>
> @@ -9,8 +13,6 @@ extern char __alt_instructions[], __alt_instructions_end[];
>
>  #ifdef CONFIG_64BIT
>
> -#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> -
>  #undef dereference_function_descriptor
>  void *dereference_function_descriptor(void *);
>
> diff --git a/arch/powerpc/include/asm/sections.h b/arch/powerpc/include/asm/sections.h
> index 32e7035863ac..b7f1ba04e756 100644
> --- a/arch/powerpc/include/asm/sections.h
> +++ b/arch/powerpc/include/asm/sections.h
> @@ -8,6 +8,10 @@
>
>  #define arch_is_kernel_initmem_freed arch_is_kernel_initmem_freed
>
> +#ifdef PPC64_ELF_ABI_v1
> +#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> +#endif
> +
>  #include <asm-generic/sections.h>
>
>  extern bool init_mem_is_free;
> @@ -69,8 +73,6 @@ static inline int overlaps_kernel_text(unsigned long start, unsigned long end)
>
>  #ifdef PPC64_ELF_ABI_v1
>
> -#define HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR 1
> -
>  #undef dereference_function_descriptor
>  static inline void *dereference_function_descriptor(void *ptr)
>  {
> diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h
> index d16302d3eb59..1db5cfd69817 100644
> --- a/include/asm-generic/sections.h
> +++ b/include/asm-generic/sections.h
> @@ -59,7 +59,8 @@ extern char __noinstr_text_start[], __noinstr_text_end[];
>  extern __visible const void __nosave_begin, __nosave_end;
>
>  /* Function descriptor handling (if any).  Override in asm/sections.h */
> -#ifndef dereference_function_descriptor
> +#ifdef HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR
> +#else

why not
#ifndef HAVE_DEREFERENCE_FUNCTION_DESCRIPTOR
instead of #if/#else ?

>  #define dereference_function_descriptor(p) ((void *)(p))
>  #define dereference_kernel_function_descriptor(p) ((void *)(p))
>  #endif
>