Re: [PATCH] x86: Ignore protected visibility in shared libraries on Solaris

[Alan Modra <amodra@gmail.com>]

On Tue, Aug 23, 2022 at 10:34:32AM -0700, H.J. Lu via Binutils wrote:
> On x86, the PLT entry in executable may be used as function address for
> functions in shared libraries.  If functions are protected, the function
> address used in executable can be different from the function address
> used in shared library.  This will lead to incorrect run-time behavior
> if function pointer equality is needed.  By default, x86 linker issues
> an error in this case.
> 
> On Solaris, linker issued an error for
> 
> struct tm *tb = (kind == CPP_time_kind::FIXED ? gmtime : localtime) (&tt);
> 
> where gmtime is a protected function in libc.so.  Use gmtime's PLT entry
> in executable as function address is safe since function pointer equality
> isn't needed.

I'm curious as to how pointer_equality_needed came to be set for
gmtime.

>  Ignore protected visibility in shared libraries on Solaris
> to disable linker error.  If function pointer equality is needed, linker
> will silently generate executable with incorrect run-time behavior on
> Solaris.
> 
> 	PR ld/29512
> 	* elf32-i386.c (elf_i386_scan_relocs): Ignore protected
> 	visibility in shared libraries on Solaris.
> 	* elf64-x86-64.c (elf_x86_64_scan_relocs): Likewise.
> ---
>  bfd/elf32-i386.c   | 3 ++-
>  bfd/elf64-x86-64.c | 3 ++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/bfd/elf32-i386.c b/bfd/elf32-i386.c
> index 52b1db44546..9717e2c5ed6 100644
> --- a/bfd/elf32-i386.c
> +++ b/bfd/elf32-i386.c
> @@ -1808,7 +1808,8 @@ elf_i386_scan_relocs (bfd *abfd,
>  		      || (sec->flags & (SEC_CODE | SEC_READONLY)) != 0)
>  		    h->plt.refcount = 1;
>  
> -		  if (h->pointer_equality_needed
> +		  if (htab->elf.target_os != is_solaris
> +		      && h->pointer_equality_needed
>  		      && h->type == STT_FUNC
>  		      && eh->def_protected
>  		      && !SYMBOL_DEFINED_NON_SHARED_P (h)
> diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
> index 62a9a22317a..f3b54400013 100644
> --- a/bfd/elf64-x86-64.c
> +++ b/bfd/elf64-x86-64.c
> @@ -2251,7 +2251,8 @@ elf_x86_64_scan_relocs (bfd *abfd, struct bfd_link_info *info,
>  		      || (sec->flags & (SEC_CODE | SEC_READONLY)) != 0)
>  		    h->plt.refcount = 1;
>  
> -		  if (h->pointer_equality_needed
> +		  if (htab->elf.target_os != is_solaris
> +		      && h->pointer_equality_needed
>  		      && h->type == STT_FUNC
>  		      && eh->def_protected
>  		      && !SYMBOL_DEFINED_NON_SHARED_P (h)
> -- 
> 2.37.2

-- 
Alan Modra
Australia Development Lab, IBM