Re: two agent expression nits (one line each)

[Stan Shebs <stanshebs at earthlink dot net>]

On 9/11/14, 10:54 AM, David Taylor wrote:
> In gdb/doc/agentexpr.texi you''ll find the text:
> 
>     @item @code{setv} (0x2d) @var{n}: @result{} @var{v}
>     Set trace state variable number @var{n} to the value found on the top
>     of the stack.  The stack is unchanged, so that the value is readily
>     available if the assignment is part of a larger expression.  The
>     handling of @var{n} is as described for @code{getv}.
> 
> The @item line and the following text do no agree with one another.  I'm
> guessing that the text is correct, in which case this line:
> 
>     @item @code{setv} (0x2d) @var{n}: @result{} @var{v}
> 
> should be changed to this:
> 
>     @item @code{setv} (0x2d) @var{n}: @var{v} @result{} @var{v}

Yes, that is correct.

> Additionally, in gdb/common/ax.def we find the line:
> 
>     DEFOP (setv, 2, 0, 0, 1, 0x2d)
> 
>>From the comment earlier in the file:
> 
>        Each line is of the form:
> 
>        DEFOP (name, size, data_size, consumed, produced, opcode)
> [...]
>        CONSUMED is the number of stack elements consumed.
>        PRODUCED is the number of stack elements produced.
> 
> which is saying that nothing is consumed and one item is produced.  Both
> should be 0 or both should be 1.  Setting them both to 1 seems better
> since if nothing is on the stack an error will occur.  So, it should be
> changed to:
> 
>     DEFOP (setv, 2, 0, 1, 1, 0x2d)

Yes to this also.  From the look of things, I cloned the getv definition
and forgot to adjust it.

Although technically an incompatible change to the bytecode language,
anybody who tried to set a state variable within a larger expression was
going to get odd behavior and/or stack overflow, while the common
case of just setting the variable and discarding the result is
unaffected.  So I think we can just make the change directly, and
perhaps add a brief note to NEWS, to make sure that target agents
get updated. (Mentor has one in-house separate from gdbserver, plus at
least two customers with their own agents.)

Stan
stan@codesourcery.com