[PATCH v1 1/5] ld: fix segfault caused by untagged stub sections

[Jan Beulich]

On 13.10.2025 17:22, Matthieu Longo wrote:
> On 2025-09-26 14:13, Jan Beulich wrote:
>> On 18.09.2025 17:06, Matthieu Longo wrote:
>>> --- a/bfd/bfd-in2.h
>>> +++ b/bfd/bfd-in2.h
>>> @@ -834,6 +834,12 @@ typedef struct bfd_section
>>>       const char *linked_to_symbol_name;
>>>     } map_head, map_tail;
>>>   
>>> +  /* Indicate that the section contains branch veneers.  This is used when
>>> +     support for non-contiguous memory regions is enabled.  The veneers have
>>> +     to be allocated to the same memory region as the code they are refered
>>> +     by, i.e. they cannot be moved to a subsequent memory region.  */
>>> +  bool veneer;
>>
>> Why would you put a bool between two pointer-sized fields, thus introducing
>> yet more padding, when in fact existing padding could be used. There's a set
>> of bitfields further up from here, and you could simply add a single-bit
>> field there, for example. Generic code changes are okay with that change,
>> but arch-specific ones will need arch maintainer approval.
> 
> Here is the new attribute as a flag:
> 
> diff --git a/bfd/section.c b/bfd/section.c
> index 5f0cf6e71cb..f110ed77363 100644
> --- a/bfd/section.c
> +++ b/bfd/section.c
> @@ -379,6 +379,12 @@ CODE_FRAGMENT
>   .     when memory read flag isn't set. *}
>   .#define SEC_COFF_NOREAD            0x40000000
>   .
> +.  {* Indicate that the section contains branch veneers.  This is used when
> +.     support for non-contiguous memory regions is enabled.  The 
> veneers have
> +.     to be allocated to the same memory region as the code they are 
> refered
> +.     by, i.e. they cannot be moved to a subsequent memory region.  *}
> +.#define SEC_VENEER                 0x80000000
> +.
>   .  {*  End of section flags.  *}
>   .
>   .  {* Some internal packed boolean fields.  *}
> 
> 
> With the tagging of the stub section on AArch64:
> 
> diff --git a/ld/emultempl/aarch64elf.em b/ld/emultempl/aarch64elf.em
> index 91d58d8fe5a..b00c9460da2 100644
> --- a/ld/emultempl/aarch64elf.em
> +++ b/ld/emultempl/aarch64elf.em
> @@ -193,7 +193,7 @@ elf${ELFSIZE}_aarch64_add_stub_section (const char 
> *stub_sec_name,
>     lang_output_section_statement_type *os;
>     struct hook_stub_info info;
> 
> -  flags = (SEC_ALLOC | SEC_LOAD | SEC_READONLY | SEC_CODE
> +  flags = (SEC_ALLOC | SEC_LOAD | SEC_READONLY | SEC_CODE | SEC_VENEER
>             | SEC_HAS_CONTENTS | SEC_RELOC | SEC_IN_MEMORY | SEC_KEEP);
>     stub_sec = bfd_make_section_anyway_with_flags (stub_file->the_bfd,
>                                                   stub_sec_name, flags);
> 
> Same thing on AArch32 and PowerPC.
> 
> Is this what you suggested ?

No, sorry. I said "bit field", not "section flag". I'd rather not see you
use the last available section flag. Right below where you put the new
#define is a comment "Some internal packed boolean fields" - that's where
I thought your new flag would go.

Jan