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Re: two agent expression nits (one line each)
- From: Stan Shebs <stanshebs at earthlink dot net>
- To: David Taylor <dtaylor at emc dot com>, "gdb-patches at sourceware dot org" <gdb-patches at sourceware dot org>
- Date: Tue, 02 Dec 2014 12:45:25 -0800
- Subject: Re: two agent expression nits (one line each)
- Authentication-results: sourceware.org; auth=none
- References: <14583 dot 1410458050 at usendtaylorx2l>
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