New syntax for IVMS prolog epilog size

[Douglas B Rupp]

Nick Clifton wrote:
> Hi Douglas,
> 
>>  From the HP Dwarf extensions manual:
> 
> Hmm, this makes it sound like the new directive ought to be called 
> something like:
> 
>   .dw_at_hp_prologue
> 
>> If the value of DW_AT_HP_prologue has class constant, then the integer 
>> value of the attribute gives the offset of the one and only prologue 
>> end relative to the base of reference.
>>
>> -------------
>> Note: This is the case we are discussing above,
> 
> [I am being lazy here and asking you rather than looking this up:]  Is 
> the integer value discussed above LEB128 encoded ?  

No, the single prologue is not encoded. I've been using data4 because 
that what I perceive the DEC "C" compiler to be using.

> If so then there is 
> no need to worry about having a size modifier added to the 
> .dw.at_hp_prologue directive.
> 
> Also, if this integer value is the offset of the prologue end then why 
> did your original gcc patch compute "(end - start) / 16 * 3" ?  Or did I
> misread that ?

You didn't misread and it that's the offset from the beginning of the 
function.  "Start" was the function begin label, "End" the prologue end 
label. I guess I'm not understanding your question.

> 
>> but it gets more complicated for multiple prologues (and epilogues), 
>> for which we need SLEB slot offsets, and possibly even addresses.
>> -------------
> 
> 
>> If the value of DW_AT_HP_prologue has class block, then the block 
>> contains a sequence of values. The first value is a signed non-zero 
>> LEB integer value. There are two cases:
>> 1.If the first value is positive, it is a count of the number of 
>> signed LEB integer values that follow. Each such value is an 
>> (instruction slot) offset relative to the base of reference to a 
>> prologue end location.
>>
>> This case applies when there is more than one prologue end location, 
>> but they are all in the same section as the base of reference.
>> 2.If the first value is negative, its absolute value is a count of the 
>> number of addresses that follow. Each such address is a prologue end 
>> location.
> 
> The (theoretical) advantage to calling the new directive 
> .dw_at_hp_prologue is that its syntax could be defined to handle these 
> cases as well.  Ie something like:
> 
>   .dw_at_hp_prologue <start_label>, <end_label> { , <start_label> , 
> <end_label> }
> 
> Then the code could evaluate the list of labels.  If there is only one 
> pair then the first case applies.  If there are multiple pairs and the 
> start label is the same for all of them then the last case applies, 
> otherwise the middle case applies.
> 
> Cheers
>   Nick
> 
>