exp/2380: change right operand, reports on left one

exp/2380: change right operand, reports on left one

[gin]

>Number:         2380
>Category:       exp
>Synopsis:       change right operand, reports on left one
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Dec 07 17:48:01 UTC 2007
>Closed-Date:
>Last-Modified:
>Originator:     gin@mo.msk.ru
>Release:        6.7.1
>Organization:
>Environment:
x86_64-unknown-linux-gnu.  Both gdb and program being debugged are
built with gcc 4.0.4.
 
>Description:
`set va' command arbitrarily refuses to evaluate expressions of the
same form.  The error message is at least misleading.  Certainly does
not point to the part of expression gdb deems incorrect.  What makes
command break is changing function in right operand of assignment.
gdb complains about left operand.

The database entry may appear related to 1799, but certainly does not
duplicate it.  That entry talks of only particular program register
represented to gdb user as `$'- variable.  This once manifests on
convenience variables as described in <(gdb) Convenience Vars>.

>How-To-Repeat:
For that particular value of user variable, `$matsp', both function
calls make perfect sense, return normally, do no non- local control
transfers.

(gdb) p Fcar
$ = {Lisp_Object (Lisp_Object)} 0x475900 <Fcar>
(gdb) p Feval
$ = {Lisp_Object (Lisp_Object)} 0x48e300 <Feval>
# completes normally
(gdb) set va $evms=Fcar($matsp)
(gdb) set va $evms=Feval($matsp)
Left operand of assignment is not a modifiable lvalue.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted:

Re: exp/2380: change right operand, reports on left one

[Ilya N. Golubev]

The following reply was made to PR exp/2380; it has been noted by GNATS.

From: "Ilya N. Golubev" <gin@mo.msk.ru>
To: Daniel Jacobowitz <drow@false.org>
Cc: gdb-gnats@sources.redhat.com
Subject: Re: exp/2380: change right operand, reports on left one
Date: Fri, 07 Dec 2007 21:15:46 +0300

 Both commands in the request complete normally consistently, and yield
 the expected results, that is, the expected value of `$evms'
 convenience variable.  This does not depend on how many times they are
 called, or on intervening commands (not changing the program state, of
 cource).

Re: exp/2380: change right operand, reports on left one

[Daniel Jacobowitz]

The following reply was made to PR exp/2380; it has been noted by GNATS.

From: Daniel Jacobowitz <drow@false.org>
To: gin@mo.msk.ru
Cc: gdb-gnats@sources.redhat.com
Subject: Re: exp/2380: change right operand, reports on left one
Date: Fri, 7 Dec 2007 12:55:02 -0500

 On Fri, Dec 07, 2007 at 05:41:59PM -0000, gin@mo.msk.ru wrote:
 > (gdb) p Fcar
 > $ = {Lisp_Object (Lisp_Object)} 0x475900 <Fcar>
 > (gdb) p Feval
 > $ = {Lisp_Object (Lisp_Object)} 0x48e300 <Feval>
 > # completes normally
 > (gdb) set va $evms=Fcar($matsp)
 > (gdb) set va $evms=Feval($matsp)
 > Left operand of assignment is not a modifiable lvalue.
 
 What does "set var $evms=Fcar($matsp)" again say at this point?
 How about "set var $evms = 1"?
 
 -- 
 Daniel Jacobowitz
 CodeSourcery