RFA: frame id enhancement

[J. Johnston]

J. Johnston wrote:
> Andrew Cagney wrote:
> 
>>>
>>>> It's the reverse of infrun.c:2383 where the inferior is falling out 
>>>> of a singnal trampoline, I think the assumptions again hold.
>>>>
>>>> infrun.c:2641:    if (!(frame_id_inner (current_frame, step_frame_id)))
>>>>
>>>> "Trust me" there's no value add.  While the comment reads:
>>>>   /* In the case where we just stepped out of a function into the
>>>>      middle of a line of the caller, continue stepping, but
>>>>      step_frame_id must be modified to current frame */
>>>> The test also updates step_frame_id when switching between frameless 
>>>> stackless leaf function.  The extra test wouldn't fix that problem. 
>>>> I'll try to remember to add some comments to that code.
>>
>>
>>
>> I've done this.
>>
>>> Ok, that simplifies things.  I have included a revised patch that 
>>> allows for the wild-card scenario.
>>
>>
>>
>> We're going to need more comments so that the next person better 
>> understands what is going on:
>>
>> +  /* The frame's special address.  This shall be constant through out 
>> the
>> +     lifetime of the frame.  This is used for architectures that may 
>> have
>> +     frames that have the same stack_addr and code_addr but are distinct
>> +     due to some other qualification (e.g. the ia64 uses a register
>> +     stack which is distinct from the memory stack).  */
>> +  CORE_ADDR special_addr;
>>
>> can you expand this definition to to note that the value isn't 
>> ordered,  and that zero is treated as a wild card (its mentioned 
>> further down but I think here, at the definition, is better).  For the 
>> ia64, is/can the second area be described as a register spill area 
>> rather than a stack? If the word "stack" can be avoided, the rationale 
>> for "special" being un-ordered is stronger.
>>
> 
> It "is" a register stack on the ia64.  Registers r32 - r127 for any 
> frame all come from this area.  It gets bumped up by a special alloc() 
> instruction.  I'm not sure I would call it unordered.  It may be better 
> to say that it is treated as unordered.  That would make the comments 
> below much simpler - i.e. the special_addr field is treated as unordered 
> so it is never used to determine order when comparing frames.
> 
> I can easily add the zero/wildcard comment.
> 
>> For:
>>
>>    NOTE: Given frameless functions A and B, where A calls B (and hence
>>    B is inner-to A).  The relationships: !eq(A,B); !eq(B,A);
>>    !inner(A,B); !inner(B,A); all hold.  This is because, while B is
>>    inner to A, B is not strictly inner to A (being frameless, they
>>    have the same .base value).  */
>>
>> an update is needed, suggest something like:
>>
>>    NOTE:
>>
>>    Given stackless functions A and B, where A calls B (and hence
>>    B is inner-to A).  The relationships: !eq(A,B); !eq(B,A);
>>    !inner(A,B); !inner(B,A); all hold.
>>
>>    This is because, while B is
>>    inner-to A, B is not strictly inner-to A.  Being stackless, they
>>    have an identical .stack_addr value, and differ only by their 
>> unordered .code_addr .special_addr values.
>>
>>    Because frame_id_inner is only used as a safety net (e.g.,
>>    detect a corrupt stack) the lack of strictness is not a problem.
>>    Code needing to determine an exact relationship between two frames
>>    must instead use frame_id_eq and frame_id_unwind.  For instance,
>>    in the above, to determine that A stepped-into B, the equation
>>    "A.id != B.id && A.id == id_unwind (B)" can be used.
>>
>>
>> and a similar update to:
>>
>> frame_id_inner (struct frame_id l, struct frame_id r)
>> {
>>   int inner;
>>   if (l.stack_addr == 0 || r.stack_addr == 0)
>>     /* Like NaN, any operation involving an invalid ID always fails.  */
>>     inner = 0;
>>   else
>>     /* Only return non-zero when strictly inner than.  Note that, per
>>        comment in "frame.h", there is some fuzz here.  Frameless
>>        functions are not strictly inner than (same .stack but
>>        different .code).  */
>>     inner = INNER_THAN (l.stack_addr, r.stack_addr);
>>
>> I can't think of a word better than "special", so I guess special it 
>> is :-)
>>

Is the revised attached patch ok?

-- Jeff J.
-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: frame_special.patch
URL: <http://sourceware.org/pipermail/gdb-patches/attachments/20031016/9d4a2fb6/attachment.ksh>