[lldb-dev] How to set argument -Xxm100M for an executable?

Yin Ma yin at affinic.com
Mon Oct 7 16:42:54 PDT 2013

Hi Enrico,


This is quite complex implementation. So for this bug, 

I have reported this problem in bugzilla.

I would like to know how likely or how long this bug could be fixed 

and released to the public? This bug is reported by our client who is using 

lldb with our GUI program. This problem is blocking his work.

I would like to know more to reply him.






From: Enrico Granata [mailto:egranata at apple.com] 
Sent: Monday, October 07, 2013 4:26 PM
To: Yin Ma
Cc: lldb-dev
Subject: Re: [lldb-dev] How to set argument -Xxm100M for an executable?


Hi Yin,

the problem with your approach is that you would not simply be able to do the API equivalent of “set args” and then return.

If you are going down the SBLaunchInfo route, you will also need to launch through the API (what you do is make an SBLaunchInfo and then pass it to SBTarget::Launch, and get an SBProcess back)

Once you are in the business of launching through the API, you might also want to start listening to process events for your launched inferior

It seems like, pending a fix for the settings set bugzilla issue (thanks for filing, btw), going the API way might be your best bet, as I think others have pointed you at


A good example of how to do that is in examples/python/process_events.py, or the whole lldb-perf project if you’re more of a C++ developer


Enrico Granata
📩 egranata@.com
☎️ 27683


On Oct 7, 2013, at 4:03 PM, Yin Ma <yin at affinic.com> wrote:

Hi Enrico,


Since there is no way to work around –Xxm100M problem, I know we can define

our own command. I am wondering if it is possible to expend set command in llvm

by importing a python file, like set args  xxx, it will call my python function

to use API to do the job? If yes, could you provide me a simple example about how

to do this?






From: Enrico Granata [mailto:egranata at apple.com] 
Sent: Monday, October 07, 2013 2:55 PM
To: Yin Ma
Cc: lldb-dev
Subject: Re: [lldb-dev] How to set argument -Xxm100M for an executable?


On Oct 7, 2013, at 2:27 PM, Yin Ma < <mailto:yin at affinic.com> yin at affinic.com> wrote:



To set up a run argument, based on the document, it should be

Settings set target.run-args  , like gdb set args


However, no matter how, I cannot set my argument to –Xxm100M

I tried

Settings set target.run-args –Xxm100M

Lldb: invalid option – X


I also tried

Settings set target.run-args “-Xxm100M”

Doesn’t work.



Unfortunately you seem to be right. The only way I have been able to make this work is by saying:

(lldb) sett set target.run-args -- --Xxm100M

(lldb) r

Process 5112 launched: '/private/tmp/args' (x86_64)

argv[0] = args

argv[1] = --

argv[2] = --Xxm100M


but as you can see, this causes a spurious - - (double dash) to be passed down to your inferior process

Seems worth of a bugzilla to me. With that said, while I have not tried it, I am kinda optimistic that SBLaunchInfo (the API class) would not be subject to the same bug, since this is more of a command-line issue than anything

Could somebody let me know how to correctly set an argument.


On gdb, if we run

Set args

This means no argument

However, under lldb

Settings set target.run-args

It will report an error


Is this a good behavior?



In LLDB, you would say 

(lldb) sett set target.run-args ""


Since our settings set command is meant to set any kind of setting, it makes sense that we ask for an argument. If we were to allow setting set <foo> <end of command>, we would probably need a way to know which is the “default value” for any specific setting. Feel free to file an ER bugzilla for that too





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Enrico Granata
📩 egranata@.com
☎️ 27683


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