[PATCH] Fix #27777 - now use a doubly-linked list for _IO_list_all

[alexandre.ferrieux@orange.com]

On 26/04/2024 20:20, FERRIEUX Alexandre INNOV/NET wrote:
> 
> 
> On 26/04/2024 19:51, Florian Weimer wrote:
>>
>> * alexandre ferrieux:
>>
>>> diff --git a/libio/bits/types/struct_FILE.h b/libio/bits/types/struct_FILE.h
>>> index 7cdaae86f8..daebd6ce0a 100644
>>> --- a/libio/bits/types/struct_FILE.h
>>> +++ b/libio/bits/types/struct_FILE.h
>>> @@ -67,7 +67,7 @@ struct _IO_FILE
>>>
>>>    struct _IO_marker *_markers;
>>>
>>> -  struct _IO_FILE *_chain;
>>> +  struct _IO_FILE *_chain,**_prevchain;
>>>
>>>    int _fileno;
>>>    int _flags2;
>>
>> Unfortunately, this struct is part of the ABI for several reasons.  For
>> example, _IO_2_1_stdin_ is a global variable exported by libc.so.6, and
>> it has a struct _IO_FILE member.  It cannot change size due to copy
>> relocations, even if nothing accesses members after _chain.

Now what about sticking the field to the end of _IO_FILE_plus ?

  struct _IO_FILE_plus
  {
    FILE file;
    const struct _IO_jump_t *vtable;
+  struct _IO_FILE_plus **_prevchain;
  };

Wouldn't that be backwards compatible with everything ?
Or do you suspect that some aircraft, dams and power plants routinely rely on 
sizeof(_IO_FILE_plus) as they allocate and fill their file pointers by hand ?
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