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

[Florian Weimer <fweimer@redhat.com>]

* alexandre ferrieux:

> 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 ?

Sorry, no, struct _IO_FILE_plus is used to define _IO_2_1_stdin_.

Florian