[Bug python/18175] New: gdb.parse_and_eval should un-lazy results

[Bug python/18175] New: gdb.parse_and_eval should un-lazy results

[xdje42 at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18175

            Bug ID: 18175
           Summary: gdb.parse_and_eval should un-lazy results
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: python
          Assignee: unassigned at sourceware dot org
          Reporter: xdje42 at gmail dot com

gdb.parse_and_eval should un-lazy its results.

Otherwise the following can happen.

Try 1:

(gdb) py foo = gdb.parse_and_eval ("*(char*) $sp")
(gdb) x/b $sp
0x7fffffffe1c0: 0
(gdb) py print foo
0 '\000'
(gdb) set *(char*) $sp = 42
(gdb) x/b $sp
0x7fffffffe1c0: 42
(gdb) py print foo
0 '\000' <<<<< expected result

Try 2:

(gdb) py foo = gdb.parse_and_eval ("*(char*) $sp")
(gdb) set *(char*) $sp = 43
(gdb) py print foo
43 '+' <<<<< Ugh.
(gdb) 

Note that in the first example, the "py print foo" before modifying
memory is sufficient to un-lazy the value.
I point this out to show that if we don't make this change then
debugging such things can be nasty: a simple "print" can modify
program behaviour.

Guile's parse-and-eval has the same issue.

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug python/18175] gdb.parse_and_eval should un-lazy results

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18175

Tom Tromey <tromey at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at sourceware dot org

--- Comment #1 from Tom Tromey <tromey at sourceware dot org> ---
This came up in bug #16820, but I'm inclined to disagree.
Un-lazying by default means that if parse_and_eval reads a huge
array, it will all be copied in.  But that neglects the scenario
where the code immediately uses the value to fetch just one element --
where remaining lazy would be valuable.

-- 
You are receiving this mail because:
You are on the CC list for the bug.