Re: [RFA] Ensure result of make_cleanup is never NULL.

[Doug Evans <dje at google dot com>]

On Mon, Apr 16, 2012 at 8:21 AM, Doug Evans <dje@google.com> wrote:
>
> On Apr 16, 2012 7:58 AM, "Pedro Alves" <palves@redhat.com> wrote:
>>
>> On 04/16/2012 03:40 PM, Joel Brobecker wrote:
>>
>> >> +/* A fencepost used to mark the end of a cleanup chain.
>> >> + ? The value is chosen to be non-NULL so that make_cleanup never
>> >> returns NULL,
>> >> + ? and cause a segv if dereferenced. ?*/
>> >> +#define CLEANUP_FENCEPOST ((struct cleanup *) 1)
>> >
>> > Just a tiny idea, not really important, but JIC: Could we use an enum
>> > intead of a define so that GDB prints "CLEANUP_FENCEPOST" rather than
>> > a numeric value when we print a cleanup pointer that's the fencepost?
>>
>>
>> No, because what you'll be printing will have type struct cleanup pointer,
>> not
>> whatever enum it was cast from.
>>
>> I see at least two ways to get something like that:
>>
>> - a gdb specific pretty printer for cleanups.
>>
>> - Make the sentinel a real object:
>>
>> ? static struct cleanup sentinel_cleanup;
>> ? #define CLEANUP_FENCEPOST &sentinel_cleanup
>>
>> ?And get Tromey's "set print symbol" patch in, which IIRC/IIUC, the
>> ?latest version makes GDB print the symbol name corresponding
>> ?to addresses by default. ?Then gdb would print something like:
>>
>> ? (gdb) p old_chain
>> ? $1 = 0xfoobar <sentinel_cleanup>
>>
>> --
>> Pedro Alves
>
> That was my other plan.? I can do that instead.

How about this?


2012-04-17  Doug Evans  <dje@google.com>

        * cleanups.h (struct cleanup): Move to cleanups.c.
        (make_cleanup_dtor_ftype): New typedef.
        (make_cleanup_dtor): Use it.
        (ALL_CLEANUPS): Replace with ...
        (all_cleanups): ... this.  Declare.  All uses updated.
        * cleanups.c (cleanup_sentinel): New static global.
        (CLEANUP_SENTINEL): Define.
        (cleanup_chain, final_cleanup_chain): Initialize to CLEANUP_SENTINEL.
        (make_my_cleanup2): Assert result is non-NULL.
        (all_cleanups): New function.
        (save_my_cleanups): Initialize new chain to CLEANUP_SENTINEL instead
        of NULL.

Attachment: gdb-120417-cleanups-sentinel-1.patch.txt
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