[PATCH 5/7] elf: Suppress unused function clang for __ifunc_resolver

[H.J. Lu]

On Wed, Jan 1, 2025 at 2:27 AM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
> The __ifunc_resolver macro expands to:
>
>   extern __typeof (__redirect_name) name __attribute__ ((ifunc ("iname_ifunc")));
>   static __typeof (__redirect_name) *name_ifunc (void) { [...] };
>
> And although NAME_IFUNC is and alias for NAME, clang still emits
> an 'unused function 'name_ifunc' [-Werror,-Wunused-function]'

Why didn't I see it on x86-64 with non-fortify build?

> warning.  The static is used to avoid name pollution on static
> linkage.
> ---
>  elf/ifuncmain9.c           | 4 ++++
>  elf/tst-ifunc-fault-lazy.c | 4 ++++
>  include/libc-symbols.h     | 6 +++++-
>  3 files changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/elf/ifuncmain9.c b/elf/ifuncmain9.c
> index 654beeadfe..f102b140bd 100644
> --- a/elf/ifuncmain9.c
> +++ b/elf/ifuncmain9.c
> @@ -22,6 +22,7 @@
>
>  #include <stdbool.h>
>  #include <stdio.h>
> +#include <libc-diag.h>
>
>  #if __GNUC_PREREQ (5, 5)
>  /* Do not use the test framework, so that the process setup is not
> @@ -41,6 +42,8 @@ implementation (void)
>    return random_constant;
>  }
>
> +DIAG_PUSH_NEEDS_COMMENT_CLANG;
> +DIAG_IGNORE_NEEDS_COMMENT_CLANG (13, "-Wunused-function");
>  static __typeof__ (implementation) *
>  inhibit_stack_protector
>  resolver (void)
> @@ -50,6 +53,7 @@ resolver (void)
>  }
>
>  static int magic (void) __attribute__ ((ifunc ("resolver")));
> +DIAG_POP_NEEDS_COMMENT_CLANG;
>
>  int
>  main (void)
> diff --git a/elf/tst-ifunc-fault-lazy.c b/elf/tst-ifunc-fault-lazy.c
> index 5157c6cc6c..04448b2b15 100644
> --- a/elf/tst-ifunc-fault-lazy.c
> +++ b/elf/tst-ifunc-fault-lazy.c
> @@ -21,6 +21,7 @@
>     relocations.  */
>
>  #include <config.h>
> +#include <libc-diag.h>
>
>  #ifdef HAVE_GCC_IFUNC
>
> @@ -34,6 +35,8 @@ implementation (void)
>    *p = 0;
>  }
>
> +DIAG_PUSH_NEEDS_COMMENT_CLANG;
> +DIAG_IGNORE_NEEDS_COMMENT_CLANG (13, "-Wunused-function");
>  static __typeof__ (implementation) *
>  resolver (void)
>  {
> @@ -42,6 +45,7 @@ resolver (void)
>    *p = 0;
>    return implementation;
>  }
> +DIAG_POP_NEEDS_COMMENT_CLANG;
>
>  static void magic (void) __attribute__ ((ifunc ("resolver")));
>
> diff --git a/include/libc-symbols.h b/include/libc-symbols.h
> index 56ae61015d..9fe047f4d3 100644
> --- a/include/libc-symbols.h
> +++ b/include/libc-symbols.h
> @@ -86,6 +86,7 @@
>
>  /* Obtain the definition of symbol_version_reference.  */
>  #include <libc-symver.h>
> +#include <libc-diag.h>
>
>  /* When PIC is defined and SHARED isn't defined, we are building PIE
>     by default.  */
> @@ -671,7 +672,10 @@ for linking")
>  # define __ifunc_args(type_name, name, expr, init, ...)                        \
>    extern __typeof (type_name) name __attribute__                       \
>                               ((ifunc (#name "_ifunc")));               \
> -  __ifunc_resolver (type_name, name, expr, init, static, __VA_ARGS__)
> +  DIAG_PUSH_NEEDS_COMMENT_CLANG;                                       \
> +  DIAG_IGNORE_NEEDS_COMMENT_CLANG (13, "-Wunused-function");           \
> +  __ifunc_resolver (type_name, name, expr, init, static, __VA_ARGS__); \
> +  DIAG_POP_NEEDS_COMMENT_CLANG;
>
>  # define __ifunc_args_hidden(type_name, name, expr, init, ...)         \
>    __ifunc_args (type_name, name, expr, init, __VA_ARGS__)
> --
> 2.43.0
>


-- 
H.J.