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

[Matthieu Longo]

On 2025-10-13 16:30, Jan Beulich wrote:
> 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

What about the below ?

diff --git a/bfd/section.c b/bfd/section.c
index 5f0cf6e71cb..424e53029d9 100644
--- a/bfd/section.c
+++ b/bfd/section.c
@@ -428,6 +428,12 @@ CODE_FRAGMENT
  .  {* Nonzero if section contents should not be freed.  *}
  .  unsigned int alloced:1;
  .
+.  {* 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.  *}
+.  unsigned int veneer : 1;
+.
  .  {* Bits used by various backends.  The generic code doesn't touch
  .     these fields.  *}
  .
@@ -723,11 +729,11 @@ INTERNAL
  .  {* segment_mark, sec_info_type, use_rela_p, mmapped_p, alloced, 
*}        \
  .     0,            0,             0,          0,         0,           \
  .                                                                      \
-.  {* sec_flg0, sec_flg1, sec_flg2, sec_flg3, sec_flg4, sec_flg5,    *} 
        \
+.  {* veneer, sec_flg0, sec_flg1, sec_flg2, sec_flg3, sec_flg4,      *} 
        \
  .     0,        0,        0,        0,        0,        0,             \
  .                                                                      \
-.  {* vma, lma, size, rawsize, compressed_size,                      *} 
        \
-.     0,   0,   0,    0,       0,                                      \
+.  {* sec_flg5, vma, lma, size, rawsize, compressed_size,            *} 
        \
+.     0,        0,   0,   0,    0,       0,                            \
  .                                                                      \
  .  {* output_offset, output_section, relocation, orelocation, 
*}        \
  .     0,             &SEC,           NULL,       NULL,                 \

Matthieu