New fhpd commands: ptype & plocation

New fhpd commands: ptype & plocation

[Teresa Thomas]

Two new commands have been added to fhpd:
1) ptype <VariableName/expr> :  prints the type of variable/expression
2) plocation <VariableName> : prints the location of variable, 
displaying any memory split if present.

Example (attached to hpd-c):
============================
(fhpd) ptype arr_1
[0.0]

long int [32]
(fhpd) plocation static_int
[0.0]

Address 0x8049e34 - 4 byte(s)
(fhpd) plocation int_21
[0.0]

Register eax - 4 byte(s)
============================
For multiple pieces the output of plocation will look like:
Piece 0: < location details >
Piece 1: < location details >
etc

Any suggestions on improving the output format?

Cheers,
Teresa

Re: New fhpd commands: ptype & plocation

[Phil Muldoon]

Teresa Thomas wrote:
> Two new commands have been added to fhpd:
> 1) ptype <VariableName/expr> :  prints the type of variable/expression
> 2) plocation <VariableName> : prints the location of variable, 
> displaying any memory split if present.
>

Nice bit of "just in time" here as I will soon be using this stuff for 
watchpoints (ie translating a variable to a location, or locations).

Apart from the output code, and parsing code in fhpd, is the "get the 
location" code placed in a utility class somewhere? Can you give a 
programming example of given variable foo, how to get a location or 
locations in memory of where it resides?

Regards

Phil

Re: New fhpd commands: ptype & plocation

[Teresa Thomas]

Phil Muldoon wrote:
> Apart from the output code, and parsing code in fhpd, is the "get the 
> location" code placed in a utility class somewhere? Can you give a 
> programming example of given variable foo, how to get a location or 
> locations in memory of where it resides?
Following is an example taken from /Variable.java/:

    // Get the DWARF operations that describe the variable's location 
from its DIE
    List ops = variableDie.getFormData(frame.getAdjustedAddress());
    // Create a LocationExpression from it
    LocationExpression locationExpression = new 
LocationExpression(frame, variableDie, ops);
    // Decode the expression to get the location and create a 
PieceLocation from it
    PieceLocation pieceLocation = new 
PieceLocation(locationExpression.decode(this.getType(frame).getSize()));

pieceLocation will now contain the (list of) location(s). You can print 
it by using its toPrint function, manipulate
its bytes, etc. [Refer /Location.java /and /PieceLocation.java/ (or ping 
me :-) ) for its other functions]

Re: New fhpd commands: ptype & plocation

[Phil Muldoon]

Teresa Thomas wrote:
> Following is an example taken from /Variable.java/:
>
>    // Get the DWARF operations that describe the variable's location 
> from its DIE
>    List ops = variableDie.getFormData(frame.getAdjustedAddress());
>    // Create a LocationExpression from it
>    LocationExpression locationExpression = new 
> LocationExpression(frame, variableDie, ops);
>    // Decode the expression to get the location and create a 
> PieceLocation from it
>    PieceLocation pieceLocation = new 
> PieceLocation(locationExpression.decode(this.getType(frame).getSize()));
>
> pieceLocation will now contain the (list of) location(s). You can 
> print it by using its toPrint function, manipulate
> its bytes, etc. [Refer /Location.java /and /PieceLocation.java/ (or 
> ping me :-) ) for its other functions]

Awesome. This is perfect, thanks

Regards

Phil

Re: New fhpd commands: ptype & plocation

[Andrew Cagney]

Phil Muldoon wrote:
> Apart from the output code, and parsing code in fhpd, is the "get the 
> location" code placed in a utility class somewhere? Can you give a 
> programming example of given variable foo, how to get a location or 
> locations in memory of where it resides?
>
Phil,

I wouldn't become too attached to this command's implementation as it 
currently stands; rather just view it as a a glimpse of what is to 
come.  That command reports the expression's result's location which 
isn't sufficient; instead a walk of the expression tree that generates a 
list of all referenced locations is going to be needed.

I would define the frysk.proc. object interface that you require and 
expect the location tree walk code to generate that that information; 
rather than try to have frysk.proc directly access frysk.debuginfo.

Andrew

Re: New fhpd commands: ptype & plocation

[Phil Muldoon]

Andrew Cagney wrote:
> Phil Muldoon wrote:
>> Apart from the output code, and parsing code in fhpd, is the "get the 
>> location" code placed in a utility class somewhere? Can you give a 
>> programming example of given variable foo, how to get a location or 
>> locations in memory of where it resides?
>>
> Phil,
>
> I wouldn't become too attached to this command's implementation as it 
> currently stands; rather just view it as a a glimpse of what is to 
> come.  That command reports the expression's result's location which 
> isn't sufficient; instead a walk of the expression tree that generates 
> a list of all referenced locations is going to be needed.
>
> I would define the frysk.proc. object interface that you require and 
> expect the location tree walk code to generate that that information; 
> rather than try to have frysk.proc directly access frysk.debuginfo.

That's fair enough. From the observer point of view, all that is needed 
is a memory location and range -  at the first pass. Later on as debug 
register usage is optimized to not map duplicate/overlapping ranges, it 
might be more meta-data.

Still all of the above (Teresa's work) is neat stuff indeed. Happy to 
see it in the repo.

Regards

Phil