[PATCH 33744] Check if a section has non-zero linked_to before using it

[Jan Beulich]

On 10.01.2026 11:23, Zheng Bao wrote:
> Updated, including bugzilla ticket.

Hmm, I'm pretty sure ...

> ________________________________
> From: H.J. Lu <hjl.tools@gmail.com>
> Sent: Saturday, January 10, 2026 9:31 AM
> To: Zheng Bao <fishbaoz@hotmail.com>
> Cc: Binutils <binutils@sourceware.org>
> Subject: Re: [PATCH 33744] Check if a section has non-zero linked_to before using it
> 
> On Sat, Jan 10, 2026, 2:54 PM Zheng Bao <fishbaoz@hotmail.com<mailto:fishbaoz@hotmail.com>> wrote:
> https://sourceware.org/bugzilla/show_bug.cgi?id=33744
> 
>     gas:bfd: Check if a section has non-zero linked_to before using it
> 
>     The symbol in the section header should be assigned at
>     building stage. So it should be section like ".data".
>     The section where the symbol is defined should have output
>     section. But it is not enough. The common section has output
>     section which will not be written into any target section.
>     If the symbol is in common section, the linked_to is pointer
>     NULL and a segmentation fault comes up.
> 
>     Test suite:
>     .section __patchable_funrtion_entries,"awo",%progbits,foo
>             .dc.a   .LPFE1
>             .comm   foo,8
> 
> This test should be included in the patch.

... this was meant as "included as a new testcase", not just by extending
the description.

Jan

>     The changes in _bfd_elf_copy_special_section_fields is a similar
>     change. It also need to check before using it.
> 
>     Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33744
>     Signed-off-by: Zheng Bao <fishbaoz@hotmail.com<mailto:fishbaoz@hotmail.com>>
> 
> diff --git a/bfd/elf.c b/bfd/elf.c
> index 8b6dd3ce370..41d550205ae 100644
> --- a/bfd/elf.c
> +++ b/bfd/elf.c
> @@ -4322,7 +4322,8 @@ assign_section_numbers (bfd *abfd, struct bfd_link_info *link_info)
>                   s = kept;
>                 }
>               /* Handle objcopy. */
> -             else if (s->output_section == NULL)
> +             else if (s->output_section == NULL
> +                      || elf_section_data(s->output_section) == NULL)
>                 {
>                   _bfd_error_handler
>                     /* xgettext:c-format */
> @@ -13831,7 +13832,8 @@ _bfd_elf_copy_special_section_fields (const bfd *ibfd ATTRIBUTE_UNUSED,
> 
>    if (isection == NULL
>        || isection->bfd_section == NULL
> -      || isection->bfd_section->output_section == NULL)
> +      || isection->bfd_section->output_section == NULL
> +      || elf_section_data(isection->bfd_section->output_section) == NULL)
>      {
>        _bfd_error_handler
>         /* xgettext:c-format */
> diff --git a/gas/config/obj-elf.c b/gas/config/obj-elf.c
> index 579c1df2dc3..fb082e4c0c5 100644
> --- a/gas/config/obj-elf.c
> +++ b/gas/config/obj-elf.c
> @@ -2508,6 +2508,8 @@ set_additional_section_info (bfd *abfd,
>                 sec->map_head.linked_to_symbol_name,
>                 bfd_section_name (sec));
>        else
> +       /* TODO: If the symbol is defined in common section, it can not
> +        * be initialized at linking stage. */
>         elf_linked_to_section (sec) = S_GET_SEGMENT (linked_to_sym);
>      }
> 
> 
> Not sure if posting to bugzilla is enough. So I also send to the maillist.
> Please review.
> 
> Zheng
> 
>