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* [Bug python/27141] New: [RFE] Getting a python-call result is overly complicated
@ 2021-01-02 19:12 hi-angel at yandex dot ru
2021-01-02 20:45 ` [Bug python/27141] " hi-angel at yandex dot ru
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: hi-angel at yandex dot ru @ 2021-01-02 19:12 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=27141
Bug ID: 27141
Summary: [RFE] Getting a python-call result is overly
complicated
Product: gdb
Version: 10.1
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: python
Assignee: unassigned at sourceware dot org
Reporter: hi-angel at yandex dot ru
Target Milestone: ---
Unless I'm missing something, the only way to get a return value from python is
to write a whole separate class with two methods.¹ This is unwieldy and hinders
quick scripting.
For example, right now I want to set `commands` to a breakpoint so the debugee
gets only paused when there's a certain string somewhere in the `bt` command.
Well, the check is really easy to script up:
py 'my_string' in gdb.execute('bt', to_string=True)
But then if I execute it as part of gdb "if" statement, I'll get
No symbol "py" in current context.
Having to write a whole "convenience" function means not only a redundant text,
but also a need to debug it. Also, if one has to debug it in the current
session, my experience says that unless they already know how it works, they
might screw up the current session (that's what happened to me back when I was
trying to make pretty-printers work with no experience on them)
So, it would be really helpful to either teach `py` and/or `pi` calls to return
values, so they can be executed as part of any other GDB command chain, or to
introduce a new (a `p1`?) call for that purpose.
1: https://sourceware.org/gdb/current/onlinedocs/gdb/Functions-In-Python.html
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* [Bug python/27141] [RFE] Getting a python-call result is overly complicated
2021-01-02 19:12 [Bug python/27141] New: [RFE] Getting a python-call result is overly complicated hi-angel at yandex dot ru
@ 2021-01-02 20:45 ` hi-angel at yandex dot ru
2021-01-06 18:15 ` ssbssa at sourceware dot org
2021-01-06 18:47 ` hi-angel at yandex dot ru
2 siblings, 0 replies; 4+ messages in thread
From: hi-angel at yandex dot ru @ 2021-01-02 20:45 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=27141
--- Comment #1 from Hi-Angel <hi-angel at yandex dot ru> ---
UPD: turns out, current situation is worse. Even if we only consider
workarounds such as using a convenience function, gdb does not allow returning
a value from them. To make it work one have to be really tricky, and instead
assign the value to a gdb variable, and then check value of that variable in
the command chain. Example:
class is_in_bt (gdb.Command):
"""Check if a string is in backtrace"""
def __init__ (_):
super ().__init__ ("is_in_bt", gdb.COMMAND_STATUS)
def invoke (_, args_raw, __):
args = gdb.string_to_argv(args_raw)
if len(args) != 1:
raise Exception("Wrong parameters number. Usage: is_in_bt <cmd>
<pattern>")
else:
ret = args[0] in gdb.execute('bt', to_string=True)
gdb.execute(f'set var $retval = {int(ret)}') # gdb doesn't know
what is true or True, so gotta convert it to an int
is_in_bt() # required to get it registered
And then inside gdb:
if $retval
>p 1
>end
$9 = 1
So, yeah, I feel like a number of people might not even figure out there's a
way to do that with convenience functions.
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* [Bug python/27141] [RFE] Getting a python-call result is overly complicated
2021-01-02 19:12 [Bug python/27141] New: [RFE] Getting a python-call result is overly complicated hi-angel at yandex dot ru
2021-01-02 20:45 ` [Bug python/27141] " hi-angel at yandex dot ru
@ 2021-01-06 18:15 ` ssbssa at sourceware dot org
2021-01-06 18:47 ` hi-angel at yandex dot ru
2 siblings, 0 replies; 4+ messages in thread
From: ssbssa at sourceware dot org @ 2021-01-06 18:15 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=27141
Hannes Domani <ssbssa at sourceware dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ssbssa at sourceware dot org
--- Comment #2 from Hannes Domani <ssbssa at sourceware dot org> ---
(In reply to Hi-Angel from comment #1)
> UPD: turns out, current situation is worse. Even if we only consider
> workarounds such as using a convenience function, gdb does not allow
> returning a value from them.
That's not true, you can return a value from a convenience function.
And I think this kind of situation is a perfect example where I would use it.
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* [Bug python/27141] [RFE] Getting a python-call result is overly complicated
2021-01-02 19:12 [Bug python/27141] New: [RFE] Getting a python-call result is overly complicated hi-angel at yandex dot ru
2021-01-02 20:45 ` [Bug python/27141] " hi-angel at yandex dot ru
2021-01-06 18:15 ` ssbssa at sourceware dot org
@ 2021-01-06 18:47 ` hi-angel at yandex dot ru
2 siblings, 0 replies; 4+ messages in thread
From: hi-angel at yandex dot ru @ 2021-01-06 18:47 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=27141
--- Comment #3 from Hi-Angel <hi-angel at yandex dot ru> ---
Ah, right, I stand corrected: the reason it didn't work for me is that I used
gdb.Command, whereas instead I should've used gdb.Function. The example in docs
works for example¹
1: https://sourceware.org/gdb/current/onlinedocs/gdb/Functions-In-Python.html
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2021-01-02 19:12 [Bug python/27141] New: [RFE] Getting a python-call result is overly complicated hi-angel at yandex dot ru
2021-01-02 20:45 ` [Bug python/27141] " hi-angel at yandex dot ru
2021-01-06 18:15 ` ssbssa at sourceware dot org
2021-01-06 18:47 ` hi-angel at yandex dot ru
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