Re: [lldb-dev] lldb showing wrong type structure for virtual pointer type

[Jim Ingham via lldb-dev]

Yes, the code was assuming that "exact_match" would be obeyed so it explicitly 
specified returning only 1 match.  When exact doesn't work, that means you get 
the first one...  You will only have a problem with the one whose name matches 
both types, since the other way around the vtable name will have the namespace 
in it, and it won't match the bare one.  So your workaround should be good 
altogether.

Jim


> On Mar 1, 2018, at 2:11 AM, jonas echterhoff  wrote:
> 
> FWIW, I just out found that I can trivially work around this problem by 
> changing the order of object files passed to the linker.
> 
> It turns out that lldb will just pick up the first type named "Transform" in 
> the binary (regardless of namespace). Now, if I make sure that the object 
> file containing the "correct" Transform type comes first in the linker 
> command line, it will also be first in the binary, and it will be picked up 
> by lldb. Now, in theory, this might cause the same problem, just the "other 
> way around", when debugging code using the namespaced version of the type, 
> but in our case, that should not be a problem, because the latter is not a 
> virtual type, so lldb should not use dynamic lookup in that case.
> 
> jonas
> 
>> On Mar 1, 2018, at 3:59 AM, Jim Ingham  wrote:
>> 
>> 
>> 
>>> On Feb 28, 2018, at 1:09 PM, jonas echterhoff  wrote:
>>> 
>>> 
>>> 
 On Feb 28, 2018, at 9:27 PM, Jim Ingham  wrote:
 
 Interesting.  
 
 First off, you can turn off fetching dynamic values globally (including in 
 the Xcode Locals view) by putting:
 
 settings set target.prefer-dynamic-value no-dynamic-values
>>> 
 in your ~/.lldbinit file.  You can toggle this on and off in a session, 
 though Xcode won't notice you've changed the value till you cause it to 
 refresh the locals (step or whatever).
>>> 
>>> This will fix the output of "frame variable". But it does not seem to fix 
>>> the variable display in the UI.
>> 
>> They must be setting the dynamic value directly when they fetch the values.  
>> That of course overrides the general setting.  I'll go see why they do that, 
>> but that won't help you for now.
>> 
>>> 
 We do log the process of finding the dynamic type.  You can see this by 
 running the command:
 
 log enable -f /tmp/lldb-object-log.txt lldb object
 
 Probably easiest to put that in your .lldbinit.
 
 That channel also logs when we read in modules, and so it might be a 
 little chatty, but you should see:
 
 : static-type = '' has vtable symbol 'vtable 
 for '
 
 and then some more messages that trace our attempt to look up DYNAMIC 
 CLASS.  If you turn on those logs, what do you see for these classes?
>>> 
>>> 0x00010f62ecd0: static-type = 'Transform *' has vtable symbol 'vtable 
>>> for Transform'
>>> 
>>> 0x00010f62ecd0: static-type = 'Transform *' has dynamic type: 
>>> uid={0x100012d7a}, type-name='Transform'
>> 
>> Grr...  We go from the name in the vtable symbol to the class type using 
>> Module::FindTypes, passing the exact_match flag 'cause we know this is an 
>> exact match.  Turns out the Module::FindTypes only obeys its exact_match 
>> flag if either the name you pass in starts with :: or if you can dial up the 
>> exact type kind (struct, class, enum, etc...) you are looking for.  We can't 
>> do the latter here because we don't know whether the dynamic type is a class 
>> or a struct, and we were just passing the name we got from the vtable.
>> 
>> I have a small fix for the dynamic type issue in r326412.  Fixing the 
>> FindTypes behavior is more involved, and I don't know whether other places 
>> rely on this misbehavior. I filed:
>> 
>> https://bugs.llvm.org/show_bug.cgi?id=36556
>> 
>> to examine that issue further.
>> 
>> Thanks for reporting this.
>> 
>> Jim
>> 
>> 
>>> 
>>> jonas
>>> 
 
 Jim
 
 
> On Feb 28, 2018, at 12:03 PM, jonas echterhoff  wrote:
> 
> 
> 
>> On Feb 28, 2018, at 7:14 PM, Jim Ingham  wrote:
>> 
>> Jonas,
>> 
>> What are you using to inspect the this pointer?
> 
> Normally, the Xcode debugger UI.
> 
>> You can use "frame variable" (the equivalent of gdb's "info locals") 
>> which just relies on debug info or the expression evaluator e.g. 
>> "print".  Do both methods show the same problem?
> 
> (lldb) frame variable this
> (Scripting::UnityEngine::Transform *) this = 0x00010fe2eb20
> 
> That gives me the wrong namespace
> 
> (lldb) print this
> (Scripting::UnityEngine::Transform *) $4 = 0x00010fe2eb20
> 
> That also gives me the wrong namespace
> 
> But:
> 
> (lldb) print *this
> (Transform) $5 = {
> [...]
> 
> gives me the correct (global) namespace.
> 
> Also:
> 
> (lldb) 

Re: [lldb-dev] lldb showing wrong type structure for virtual pointer type

[jonas echterhoff via lldb-dev]

FWIW, I just out found that I can trivially work around this problem by 
changing the order of object files passed to the linker.

It turns out that lldb will just pick up the first type named "Transform" in 
the binary (regardless of namespace). Now, if I make sure that the object file 
containing the "correct" Transform type comes first in the linker command line, 
it will also be first in the binary, and it will be picked up by lldb. Now, in 
theory, this might cause the same problem, just the "other way around", when 
debugging code using the namespaced version of the type, but in our case, that 
should not be a problem, because the latter is not a virtual type, so lldb 
should not use dynamic lookup in that case.

jonas

> On Mar 1, 2018, at 3:59 AM, Jim Ingham  wrote:
> 
> 
> 
>> On Feb 28, 2018, at 1:09 PM, jonas echterhoff  wrote:
>> 
>> 
>> 
>>> On Feb 28, 2018, at 9:27 PM, Jim Ingham  wrote:
>>> 
>>> Interesting.  
>>> 
>>> First off, you can turn off fetching dynamic values globally (including in 
>>> the Xcode Locals view) by putting:
>>> 
>>> settings set target.prefer-dynamic-value no-dynamic-values
>> 
>>> in your ~/.lldbinit file.  You can toggle this on and off in a session, 
>>> though Xcode won't notice you've changed the value till you cause it to 
>>> refresh the locals (step or whatever).
>> 
>> This will fix the output of "frame variable". But it does not seem to fix 
>> the variable display in the UI.
> 
> They must be setting the dynamic value directly when they fetch the values.  
> That of course overrides the general setting.  I'll go see why they do that, 
> but that won't help you for now.
> 
>> 
>>> We do log the process of finding the dynamic type.  You can see this by 
>>> running the command:
>>> 
>>> log enable -f /tmp/lldb-object-log.txt lldb object
>>> 
>>> Probably easiest to put that in your .lldbinit.
>>> 
>>> That channel also logs when we read in modules, and so it might be a little 
>>> chatty, but you should see:
>>> 
>>> : static-type = '' has vtable symbol 'vtable for 
>>> '
>>> 
>>> and then some more messages that trace our attempt to look up DYNAMIC 
>>> CLASS.  If you turn on those logs, what do you see for these classes?
>> 
>> 0x00010f62ecd0: static-type = 'Transform *' has vtable symbol 'vtable 
>> for Transform'
>> 
>> 0x00010f62ecd0: static-type = 'Transform *' has dynamic type: 
>> uid={0x100012d7a}, type-name='Transform'
> 
> Grr...  We go from the name in the vtable symbol to the class type using 
> Module::FindTypes, passing the exact_match flag 'cause we know this is an 
> exact match.  Turns out the Module::FindTypes only obeys its exact_match flag 
> if either the name you pass in starts with :: or if you can dial up the exact 
> type kind (struct, class, enum, etc...) you are looking for.  We can't do the 
> latter here because we don't know whether the dynamic type is a class or a 
> struct, and we were just passing the name we got from the vtable.
> 
> I have a small fix for the dynamic type issue in r326412.  Fixing the 
> FindTypes behavior is more involved, and I don't know whether other places 
> rely on this misbehavior. I filed:
> 
> https://bugs.llvm.org/show_bug.cgi?id=36556
> 
> to examine that issue further.
> 
> Thanks for reporting this.
> 
> Jim
> 
> 
>> 
>> jonas
>> 
>>> 
>>> Jim
>>> 
>>> 
 On Feb 28, 2018, at 12:03 PM, jonas echterhoff  wrote:
 
 
 
> On Feb 28, 2018, at 7:14 PM, Jim Ingham  wrote:
> 
> Jonas,
> 
> What are you using to inspect the this pointer?
 
 Normally, the Xcode debugger UI.
 
> You can use "frame variable" (the equivalent of gdb's "info locals") 
> which just relies on debug info or the expression evaluator e.g. "print". 
>  Do both methods show the same problem?
 
 (lldb) frame variable this
 (Scripting::UnityEngine::Transform *) this = 0x00010fe2eb20
 
 That gives me the wrong namespace
 
 (lldb) print this
 (Scripting::UnityEngine::Transform *) $4 = 0x00010fe2eb20
 
 That also gives me the wrong namespace
 
 But:
 
 (lldb) print *this
 (Transform) $5 = {
 [...]
 
 gives me the correct (global) namespace.
 
 Also:
 
 (lldb) frame variable -d no-dynamic-values this
 (Transform *) this = 0x00010fe2eb20
 
 gives me the correct namespace.
 
> 
> Also note that lldb by default will try to discern the full dynamic type 
> of the variables it prints.  You can disable this by doing:
> 
> (lldb) expr -d no-dynamic-values -- this
> 
> or equivalently:
> 
> (lldb) frame variable -d no-dynamic-values this
> 
> Is it the dynamic value resolution that's causing the incorrect printing?
 
 Yes, both of those above give me the correct types!
 
 Now, this is already very helpful - Thank 

Re: [lldb-dev] lldb showing wrong type structure for virtual pointer type

[Jim Ingham via lldb-dev]

> On Feb 28, 2018, at 1:09 PM, jonas echterhoff  wrote:
> 
> 
> 
>> On Feb 28, 2018, at 9:27 PM, Jim Ingham  wrote:
>> 
>> Interesting.  
>> 
>> First off, you can turn off fetching dynamic values globally (including in 
>> the Xcode Locals view) by putting:
>> 
>> settings set target.prefer-dynamic-value no-dynamic-values
> 
>> in your ~/.lldbinit file.  You can toggle this on and off in a session, 
>> though Xcode won't notice you've changed the value till you cause it to 
>> refresh the locals (step or whatever).
> 
> This will fix the output of "frame variable". But it does not seem to fix the 
> variable display in the UI.

They must be setting the dynamic value directly when they fetch the values.  
That of course overrides the general setting.  I'll go see why they do that, 
but that won't help you for now.

> 
>> We do log the process of finding the dynamic type.  You can see this by 
>> running the command:
>> 
>> log enable -f /tmp/lldb-object-log.txt lldb object
>> 
>> Probably easiest to put that in your .lldbinit.
>> 
>> That channel also logs when we read in modules, and so it might be a little 
>> chatty, but you should see:
>> 
>> : static-type = '' has vtable symbol 'vtable for 
>> '
>> 
>> and then some more messages that trace our attempt to look up DYNAMIC CLASS. 
>>  If you turn on those logs, what do you see for these classes?
> 
> 0x00010f62ecd0: static-type = 'Transform *' has vtable symbol 'vtable for 
> Transform'
> 
> 0x00010f62ecd0: static-type = 'Transform *' has dynamic type: 
> uid={0x100012d7a}, type-name='Transform'

Grr...  We go from the name in the vtable symbol to the class type using 
Module::FindTypes, passing the exact_match flag 'cause we know this is an exact 
match.  Turns out the Module::FindTypes only obeys its exact_match flag if 
either the name you pass in starts with :: or if you can dial up the exact type 
kind (struct, class, enum, etc...) you are looking for.  We can't do the latter 
here because we don't know whether the dynamic type is a class or a struct, and 
we were just passing the name we got from the vtable.

I have a small fix for the dynamic type issue in r326412.  Fixing the FindTypes 
behavior is more involved, and I don't know whether other places rely on this 
misbehavior. I filed:

https://bugs.llvm.org/show_bug.cgi?id=36556

to examine that issue further.

Thanks for reporting this.

Jim


> 
> jonas
> 
>> 
>> Jim
>> 
>> 
>>> On Feb 28, 2018, at 12:03 PM, jonas echterhoff  wrote:
>>> 
>>> 
>>> 
 On Feb 28, 2018, at 7:14 PM, Jim Ingham  wrote:
 
 Jonas,
 
 What are you using to inspect the this pointer?
>>> 
>>> Normally, the Xcode debugger UI.
>>> 
 You can use "frame variable" (the equivalent of gdb's "info locals") which 
 just relies on debug info or the expression evaluator e.g. "print".  Do 
 both methods show the same problem?
>>> 
>>> (lldb) frame variable this
>>> (Scripting::UnityEngine::Transform *) this = 0x00010fe2eb20
>>> 
>>> That gives me the wrong namespace
>>> 
>>> (lldb) print this
>>> (Scripting::UnityEngine::Transform *) $4 = 0x00010fe2eb20
>>> 
>>> That also gives me the wrong namespace
>>> 
>>> But:
>>> 
>>> (lldb) print *this
>>> (Transform) $5 = {
>>> [...]
>>> 
>>> gives me the correct (global) namespace.
>>> 
>>> Also:
>>> 
>>> (lldb) frame variable -d no-dynamic-values this
>>> (Transform *) this = 0x00010fe2eb20
>>> 
>>> gives me the correct namespace.
>>> 
 
 Also note that lldb by default will try to discern the full dynamic type 
 of the variables it prints.  You can disable this by doing:
 
 (lldb) expr -d no-dynamic-values -- this
 
 or equivalently:
 
 (lldb) frame variable -d no-dynamic-values this
 
 Is it the dynamic value resolution that's causing the incorrect printing?
>>> 
>>> Yes, both of those above give me the correct types!
>>> 
>>> Now, this is already very helpful - Thank you! 
>>> This means I can get correct values using the lldb console. If there was 
>>> some way to make the Xcode UI show the correct values, that would be even 
>>> better.
>>> 
>>> jonas
>>> 
 
 Jim
 
 
 
 
> On Feb 28, 2018, at 3:03 AM, jonas echterhoff via lldb-dev 
>  wrote:
> 
> 
>> On Feb 28, 2018, at 11:19 AM, Dmitry Antipov  wrote:
>> 
>> On 02/28/2018 11:31 AM, jonas echterhoff via lldb-dev wrote:
>> 
>>> I'm using lldb-900.0.64.
>>   ^^
>>   ??
>> Latest official release is 5.0.1; also there are 6.0.0 (at -rc3, the 
>> next release)
>> and 7.0.0 (a.k.a SVN trunk). What's the 'version' output of your LLDB 
>> prompt?
> 
> It is what I posted:
> 
> jechter$ lldb --version
> lldb-900.0.64
> Swift-4.0
> 
> Maybe Apple uses a different versioning scheme for 

Re: [lldb-dev] lldb showing wrong type structure for virtual pointer type

[jonas echterhoff via lldb-dev]

> On Feb 28, 2018, at 9:27 PM, Jim Ingham  wrote:
> 
> Interesting.  
> 
> First off, you can turn off fetching dynamic values globally (including in 
> the Xcode Locals view) by putting:
> 
> settings set target.prefer-dynamic-value no-dynamic-values

> in your ~/.lldbinit file.  You can toggle this on and off in a session, 
> though Xcode won't notice you've changed the value till you cause it to 
> refresh the locals (step or whatever).

This will fix the output of "frame variable". But it does not seem to fix the 
variable display in the UI.

> We do log the process of finding the dynamic type.  You can see this by 
> running the command:
> 
> log enable -f /tmp/lldb-object-log.txt lldb object
> 
> Probably easiest to put that in your .lldbinit.
> 
> That channel also logs when we read in modules, and so it might be a little 
> chatty, but you should see:
> 
> : static-type = '' has vtable symbol 'vtable for 
> '
> 
> and then some more messages that trace our attempt to look up DYNAMIC CLASS.  
> If you turn on those logs, what do you see for these classes?

0x00010f62ecd0: static-type = 'Transform *' has vtable symbol 'vtable for 
Transform'

0x00010f62ecd0: static-type = 'Transform *' has dynamic type: 
uid={0x100012d7a}, type-name='Transform'

jonas

> 
> Jim
> 
> 
>> On Feb 28, 2018, at 12:03 PM, jonas echterhoff  wrote:
>> 
>> 
>> 
>>> On Feb 28, 2018, at 7:14 PM, Jim Ingham  wrote:
>>> 
>>> Jonas,
>>> 
>>> What are you using to inspect the this pointer?
>> 
>> Normally, the Xcode debugger UI.
>> 
>>> You can use "frame variable" (the equivalent of gdb's "info locals") which 
>>> just relies on debug info or the expression evaluator e.g. "print".  Do 
>>> both methods show the same problem?
>> 
>> (lldb) frame variable this
>> (Scripting::UnityEngine::Transform *) this = 0x00010fe2eb20
>> 
>> That gives me the wrong namespace
>> 
>> (lldb) print this
>> (Scripting::UnityEngine::Transform *) $4 = 0x00010fe2eb20
>> 
>> That also gives me the wrong namespace
>> 
>> But:
>> 
>> (lldb) print *this
>> (Transform) $5 = {
>> [...]
>> 
>> gives me the correct (global) namespace.
>> 
>> Also:
>> 
>> (lldb) frame variable -d no-dynamic-values this
>> (Transform *) this = 0x00010fe2eb20
>> 
>> gives me the correct namespace.
>> 
>>> 
>>> Also note that lldb by default will try to discern the full dynamic type of 
>>> the variables it prints.  You can disable this by doing:
>>> 
>>> (lldb) expr -d no-dynamic-values -- this
>>> 
>>> or equivalently:
>>> 
>>> (lldb) frame variable -d no-dynamic-values this
>>> 
>>> Is it the dynamic value resolution that's causing the incorrect printing?
>> 
>> Yes, both of those above give me the correct types!
>> 
>> Now, this is already very helpful - Thank you! 
>> This means I can get correct values using the lldb console. If there was 
>> some way to make the Xcode UI show the correct values, that would be even 
>> better.
>> 
>> jonas
>> 
>>> 
>>> Jim
>>> 
>>> 
>>> 
>>> 
 On Feb 28, 2018, at 3:03 AM, jonas echterhoff via lldb-dev 
  wrote:
 
 
> On Feb 28, 2018, at 11:19 AM, Dmitry Antipov  wrote:
> 
> On 02/28/2018 11:31 AM, jonas echterhoff via lldb-dev wrote:
> 
>> I'm using lldb-900.0.64.
>^^
>??
> Latest official release is 5.0.1; also there are 6.0.0 (at -rc3, the next 
> release)
> and 7.0.0 (a.k.a SVN trunk). What's the 'version' output of your LLDB 
> prompt?
 
 It is what I posted:
 
 jechter$ lldb --version
 lldb-900.0.64
 Swift-4.0
 
 Maybe Apple uses a different versioning scheme for lldb distributed with 
 their toolchains?
> 
>> Unfortunately, I have not yet succeeded in coming up with a small, 
>> independent repro case which shows this problem.
> 
> IIUC this is it:
 
 [...]
 
> Here 'this' is different between calls to obj2.f () and obj2.g () 
> (0x7fffdb50 vs.
> 0x7fffdb40), and objects are shown as different as well - {111, 
> 222} vs. {333, 444}.
 
 Thanks. What you are showing there seems very peculiar. 
 
 But I don't think it's the same problem as I have (and also, using the 
 same steps on my machine does not repro the problem you showed - I get the 
 same value for "this" and it's members between the calls to S::B::f and 
 S::B::g).
 
 My problem was not about showing a wrong object (My "this" pointer value 
 was correct), but about showing a wrong type representation of the correct 
 object data.
 
 jonas
 
 ___
 lldb-dev mailing list
 lldb-dev@lists.llvm.org
 http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
>>> 
>> 
> 

___
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Re: [lldb-dev] lldb showing wrong type structure for virtual pointer type

[Jim Ingham via lldb-dev]

Interesting.  

First off, you can turn off fetching dynamic values globally (including in the 
Xcode Locals view) by putting:

settings set target.prefer-dynamic-value no-dynamic-values

in your ~/.lldbinit file.  You can toggle this on and off in a session, though 
Xcode won't notice you've changed the value till you cause it to refresh the 
locals (step or whatever).

We do log the process of finding the dynamic type.  You can see this by running 
the command:

log enable -f /tmp/lldb-object-log.txt lldb object

Probably easiest to put that in your .lldbinit.

That channel also logs when we read in modules, and so it might be a little 
chatty, but you should see:

: static-type = '' has vtable symbol 'vtable for 
'

and then some more messages that trace our attempt to look up DYNAMIC CLASS.  
If you turn on those logs, what do you see for these classes?

Jim


> On Feb 28, 2018, at 12:03 PM, jonas echterhoff  wrote:
> 
> 
> 
>> On Feb 28, 2018, at 7:14 PM, Jim Ingham  wrote:
>> 
>> Jonas,
>> 
>> What are you using to inspect the this pointer?
> 
> Normally, the Xcode debugger UI.
> 
>> You can use "frame variable" (the equivalent of gdb's "info locals") which 
>> just relies on debug info or the expression evaluator e.g. "print".  Do both 
>> methods show the same problem?
> 
> (lldb) frame variable this
> (Scripting::UnityEngine::Transform *) this = 0x00010fe2eb20
> 
> That gives me the wrong namespace
> 
> (lldb) print this
> (Scripting::UnityEngine::Transform *) $4 = 0x00010fe2eb20
> 
> That also gives me the wrong namespace
> 
> But:
> 
> (lldb) print *this
> (Transform) $5 = {
> [...]
> 
> gives me the correct (global) namespace.
> 
> Also:
> 
> (lldb) frame variable -d no-dynamic-values this
> (Transform *) this = 0x00010fe2eb20
> 
> gives me the correct namespace.
> 
>> 
>> Also note that lldb by default will try to discern the full dynamic type of 
>> the variables it prints.  You can disable this by doing:
>> 
>> (lldb) expr -d no-dynamic-values -- this
>> 
>> or equivalently:
>> 
>> (lldb) frame variable -d no-dynamic-values this
>> 
>> Is it the dynamic value resolution that's causing the incorrect printing?
> 
> Yes, both of those above give me the correct types!
> 
> Now, this is already very helpful - Thank you! 
> This means I can get correct values using the lldb console. If there was some 
> way to make the Xcode UI show the correct values, that would be even better.
> 
> jonas
> 
>> 
>> Jim
>> 
>> 
>> 
>> 
>>> On Feb 28, 2018, at 3:03 AM, jonas echterhoff via lldb-dev 
>>>  wrote:
>>> 
>>> 
 On Feb 28, 2018, at 11:19 AM, Dmitry Antipov  wrote:
 
 On 02/28/2018 11:31 AM, jonas echterhoff via lldb-dev wrote:
 
> I'm using lldb-900.0.64.
 ^^
 ??
 Latest official release is 5.0.1; also there are 6.0.0 (at -rc3, the next 
 release)
 and 7.0.0 (a.k.a SVN trunk). What's the 'version' output of your LLDB 
 prompt?
>>> 
>>> It is what I posted:
>>> 
>>> jechter$ lldb --version
>>> lldb-900.0.64
>>> Swift-4.0
>>> 
>>> Maybe Apple uses a different versioning scheme for lldb distributed with 
>>> their toolchains?
 
> Unfortunately, I have not yet succeeded in coming up with a small, 
> independent repro case which shows this problem.
 
 IIUC this is it:
>>> 
>>> [...]
>>> 
 Here 'this' is different between calls to obj2.f () and obj2.g () 
 (0x7fffdb50 vs.
 0x7fffdb40), and objects are shown as different as well - {111, 
 222} vs. {333, 444}.
>>> 
>>> Thanks. What you are showing there seems very peculiar. 
>>> 
>>> But I don't think it's the same problem as I have (and also, using the same 
>>> steps on my machine does not repro the problem you showed - I get the same 
>>> value for "this" and it's members between the calls to S::B::f and S::B::g).
>>> 
>>> My problem was not about showing a wrong object (My "this" pointer value 
>>> was correct), but about showing a wrong type representation of the correct 
>>> object data.
>>> 
>>> jonas
>>> 
>>> ___
>>> lldb-dev mailing list
>>> lldb-dev@lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
>> 
> 

___
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lldb-dev@lists.llvm.org
http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev

Re: [lldb-dev] lldb showing wrong type structure for virtual pointer type

[jonas echterhoff via lldb-dev]

> On Feb 28, 2018, at 7:14 PM, Jim Ingham  wrote:
> 
> Jonas,
> 
> What are you using to inspect the this pointer?

Normally, the Xcode debugger UI.

>  You can use "frame variable" (the equivalent of gdb's "info locals") which 
> just relies on debug info or the expression evaluator e.g. "print".  Do both 
> methods show the same problem?

(lldb) frame variable this
(Scripting::UnityEngine::Transform *) this = 0x00010fe2eb20

That gives me the wrong namespace

(lldb) print this
(Scripting::UnityEngine::Transform *) $4 = 0x00010fe2eb20

That also gives me the wrong namespace

But:

(lldb) print *this
(Transform) $5 = {
[...]

gives me the correct (global) namespace.

Also:

(lldb) frame variable -d no-dynamic-values this
(Transform *) this = 0x00010fe2eb20

gives me the correct namespace.

> 
> Also note that lldb by default will try to discern the full dynamic type of 
> the variables it prints.  You can disable this by doing:
> 
> (lldb) expr -d no-dynamic-values -- this
> 
> or equivalently:
> 
> (lldb) frame variable -d no-dynamic-values this
> 
> Is it the dynamic value resolution that's causing the incorrect printing?

Yes, both of those above give me the correct types!

Now, this is already very helpful - Thank you! 
This means I can get correct values using the lldb console. If there was some 
way to make the Xcode UI show the correct values, that would be even better.

jonas

> 
> Jim
> 
> 
> 
> 
>> On Feb 28, 2018, at 3:03 AM, jonas echterhoff via lldb-dev 
>>  wrote:
>> 
>> 
>>> On Feb 28, 2018, at 11:19 AM, Dmitry Antipov  wrote:
>>> 
>>> On 02/28/2018 11:31 AM, jonas echterhoff via lldb-dev wrote:
>>> 
 I'm using lldb-900.0.64.
>>>  ^^
>>>  ??
>>> Latest official release is 5.0.1; also there are 6.0.0 (at -rc3, the next 
>>> release)
>>> and 7.0.0 (a.k.a SVN trunk). What's the 'version' output of your LLDB 
>>> prompt?
>> 
>> It is what I posted:
>> 
>> jechter$ lldb --version
>> lldb-900.0.64
>> Swift-4.0
>> 
>> Maybe Apple uses a different versioning scheme for lldb distributed with 
>> their toolchains?
>>> 
 Unfortunately, I have not yet succeeded in coming up with a small, 
 independent repro case which shows this problem.
>>> 
>>> IIUC this is it:
>> 
>> [...]
>> 
>>> Here 'this' is different between calls to obj2.f () and obj2.g () 
>>> (0x7fffdb50 vs.
>>> 0x7fffdb40), and objects are shown as different as well - {111, 
>>> 222} vs. {333, 444}.
>> 
>> Thanks. What you are showing there seems very peculiar. 
>> 
>> But I don't think it's the same problem as I have (and also, using the same 
>> steps on my machine does not repro the problem you showed - I get the same 
>> value for "this" and it's members between the calls to S::B::f and S::B::g).
>> 
>> My problem was not about showing a wrong object (My "this" pointer value was 
>> correct), but about showing a wrong type representation of the correct 
>> object data.
>> 
>> jonas
>> 
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> 

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Re: [lldb-dev] lldb showing wrong type structure for virtual pointer type

[Jim Ingham via lldb-dev]

Jonas,

What are you using to inspect the this pointer?  You can use "frame variable" 
(the equivalent of gdb's "info locals") which just relies on debug info or the 
expression evaluator e.g. "print".  Do both methods show the same problem?

Also note that lldb by default will try to discern the full dynamic type of the 
variables it prints.  You can disable this by doing:

(lldb) expr -d no-dynamic-values -- this

or equivalently:

(lldb) frame variable -d no-dynamic-values this

Is it the dynamic value resolution that's causing the incorrect printing?

Jim




> On Feb 28, 2018, at 3:03 AM, jonas echterhoff via lldb-dev 
>  wrote:
> 
> 
>> On Feb 28, 2018, at 11:19 AM, Dmitry Antipov  wrote:
>> 
>> On 02/28/2018 11:31 AM, jonas echterhoff via lldb-dev wrote:
>> 
>>> I'm using lldb-900.0.64.
>>   ^^
>>   ??
>> Latest official release is 5.0.1; also there are 6.0.0 (at -rc3, the next 
>> release)
>> and 7.0.0 (a.k.a SVN trunk). What's the 'version' output of your LLDB prompt?
> 
> It is what I posted:
> 
> jechter$ lldb --version
> lldb-900.0.64
>  Swift-4.0
> 
> Maybe Apple uses a different versioning scheme for lldb distributed with 
> their toolchains?
>> 
>>> Unfortunately, I have not yet succeeded in coming up with a small, 
>>> independent repro case which shows this problem.
>> 
>> IIUC this is it:
> 
> [...]
> 
>> Here 'this' is different between calls to obj2.f () and obj2.g () 
>> (0x7fffdb50 vs.
>> 0x7fffdb40), and objects are shown as different as well - {111, 222} 
>> vs. {333, 444}.
> 
> Thanks. What you are showing there seems very peculiar. 
> 
> But I don't think it's the same problem as I have (and also, using the same 
> steps on my machine does not repro the problem you showed - I get the same 
> value for "this" and it's members between the calls to S::B::f and S::B::g).
> 
> My problem was not about showing a wrong object (My "this" pointer value was 
> correct), but about showing a wrong type representation of the correct object 
> data.
> 
> jonas
> 
> ___
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> lldb-dev@lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev

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Re: [lldb-dev] lldb showing wrong type structure for virtual pointer type

[jonas echterhoff via lldb-dev]

> On Feb 28, 2018, at 11:19 AM, Dmitry Antipov  wrote:
> 
> On 02/28/2018 11:31 AM, jonas echterhoff via lldb-dev wrote:
> 
>> I'm using lldb-900.0.64.
>^^
>??
> Latest official release is 5.0.1; also there are 6.0.0 (at -rc3, the next 
> release)
> and 7.0.0 (a.k.a SVN trunk). What's the 'version' output of your LLDB prompt?

It is what I posted:

jechter$ lldb --version
lldb-900.0.64
  Swift-4.0

Maybe Apple uses a different versioning scheme for lldb distributed with their 
toolchains?
> 
>> Unfortunately, I have not yet succeeded in coming up with a small, 
>> independent repro case which shows this problem.
> 
> IIUC this is it:

[...]

> Here 'this' is different between calls to obj2.f () and obj2.g () 
> (0x7fffdb50 vs.
> 0x7fffdb40), and objects are shown as different as well - {111, 222} 
> vs. {333, 444}.

Thanks. What you are showing there seems very peculiar. 

But I don't think it's the same problem as I have (and also, using the same 
steps on my machine does not repro the problem you showed - I get the same 
value for "this" and it's members between the calls to S::B::f and S::B::g).

My problem was not about showing a wrong object (My "this" pointer value was 
correct), but about showing a wrong type representation of the correct object 
data.

jonas

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Re: [lldb-dev] lldb showing wrong type structure for virtual pointer type

[Dmitry Antipov via lldb-dev]

On 02/28/2018 11:31 AM, jonas echterhoff via lldb-dev wrote:


I'm using lldb-900.0.64.

^^
??
Latest official release is 5.0.1; also there are 6.0.0 (at -rc3, the next 
release)
and 7.0.0 (a.k.a SVN trunk). What's the 'version' output of your LLDB prompt?


Unfortunately, I have not yet succeeded in coming up with a small, independent 
repro case which shows this problem.


IIUC this is it:

struct A {
  int id0;
  A () { id0 = 111; }
  virtual int f (int x) { return x + 1; }
  int g (int x) { return x + 11; }
};

struct B: A {
  int id1;
  B () { id1 = 222; }
  virtual int f (int x) { return x + 2; }
  int g (int x) { return x + 12; }
};

namespace S {
  struct AS {
int id0;
AS () { id0 = 333; }
virtual int f (int x) { return x + 3; }
int g (int x) { return x + 13; }
  };
  struct B: AS {
int id1;
B () { id1 = 444; }
virtual int f (int x) { return x + 4; }
int g (int x) { return x + 14; }
  };
}

int main (int argc, char *argv[])
{
  B obj1;
  S::B obj2;
  return
obj1.f (argc) +
obj2.f (argc) +
obj1.g (argc) +
obj2.g (argc);
}

And in gdb, it is:

$ gdb -q t-class2
Reading symbols from t-class2...done.
(gdb) b S::B::f
Breakpoint 1 at 0x400775: file t-class2.cc, line 25.
(gdb) b S::B::g
Breakpoint 2 at 0x400789: file t-class2.cc, line 26.
(gdb) r
Starting program: /home/dantipov/tmp/t-class2

Breakpoint 1, S::B::f (this=0x7fffdb50, x=1) at t-class2.cc:25
25  virtual int f (int x) { return x + 4; }
(gdb) bt
#0  S::B::f (this=0x7fffdb50, x=1) at t-class2.cc:25
#1  0x00400643 in main (argc=1, argv=0x7fffdc68) at t-class2.cc:36
(gdb) p this
$1 = (S::B * const) 0x7fffdb50
(gdb) p *this
$2 = { = {_vptr.AS = 0x400840 , id0 = 333}, id1 = 
444}
(gdb) c
Continuing.

Breakpoint 2, S::B::g (this=0x7fffdb50, x=1) at t-class2.cc:26
26  int g (int x) { return x + 14; }
(gdb) bt
#0  S::B::g (this=0x7fffdb50, x=1) at t-class2.cc:26
#1  0x00400669 in main (argc=1, argv=0x7fffdc68) at t-class2.cc:38
(gdb) p this
$3 = (S::B * const) 0x7fffdb50
(gdb) p *this
$4 = { = {_vptr.AS = 0x400840 , id0 = 333}, id1 = 
444}

E.g. in calls to obj2.f () and obj2.g (), 'this' is 0x7fffdb50, and the 
object
itself is {333, 444}.

With lldb, it is:

$ /home/dantipov/.local/llvm-6.0.0/bin/lldb t-class2
(lldb) target create "t-class2"
Current executable set to 't-class2' (x86_64).
(lldb) breakpoint set -n S::B::f
Breakpoint 1: where = t-class2`S::B::f(int) at t-class2.cc:25, address = 
0x0040076a
(lldb) breakpoint set -n S::B::g
Breakpoint 2: where = t-class2`S::B::g(int) + 11 at t-class2.cc:26, address = 
0x00400789
(lldb) run
Process 5180 launched: '/home/dantipov/tmp/t-class2' (x86_64)
Process 5180 stopped
* thread #1, name = 't-class2', stop reason = breakpoint 1.1
frame #0: 0x0040076a t-class2`S::B::f(this=0x7fffdb50, x=1) 
at t-class2.cc:25
   22 struct B: AS {
   23   int id1;
   24   B () { id1 = 444; }
-> 25virtual int f (int x) { return x + 4; }
   26   int g (int x) { return x + 14; }
   27 };
   28   }
(lldb) bt
* thread #1, name = 't-class2', stop reason = breakpoint 1.1
  * frame #0: 0x0040076a t-class2`S::B::f(this=0x7fffdb50, x=1) 
at t-class2.cc:25
frame #1: 0x00400643 t-class2`main(argc=1, argv=0x7fffdc58) 
at t-class2.cc:36
frame #2: 0x7712000a libc.so.6`__libc_start_main(main=(t-class2`main at t-class2.cc:31), argc=1, argv=0x7fffdc58, init=, fini=, rtld_fini=, 
stack_end=0x7fffdc48) at libc-start.c:308

frame #3: 0x0040054a t-class2`_start + 42
(lldb) p this
(S::B *) $0 = 0x7fffdb50
(lldb) p *this
(S::B) $1 = {
  S::AS = (id0 = 111)
  id1 = 222
}
(lldb) c
Process 5180 resuming
Process 5180 stopped
* thread #1, name = 't-class2', stop reason = breakpoint 2.1
frame #0: 0x00400789 t-class2`S::B::g(this=0x7fffdb40, x=1) 
at t-class2.cc:26
   23   int id1;
   24   B () { id1 = 444; }
   25   virtual int f (int x) { return x + 4; }
-> 26int g (int x) { return x + 14; }
   27 };
   28   }
   29   
(lldb) bt
* thread #1, name = 't-class2', stop reason = breakpoint 2.1
  * frame #0: 0x00400789 t-class2`S::B::g(this=0x7fffdb40, x=1) 
at t-class2.cc:26
frame #1: 0x00400669 t-class2`main(argc=1, argv=0x7fffdc58) 
at t-class2.cc:38
frame #2: 0x7712000a libc.so.6`__libc_start_main(main=(t-class2`main at t-class2.cc:31), argc=1, argv=0x7fffdc58, init=, fini=, rtld_fini=, 
stack_end=0x7fffdc48) at libc-start.c:308

frame #3: 0x0040054a t-class2`_start + 42
(lldb) p this
(S::B *) $2 = 0x7fffdb40
(lldb) p *this
(S::B) $3 = {
  S::AS = (id0 = 333)
  id1 = 444
}

Here 'this' is different between calls to obj2.f () and obj2.g () 
(0x7fffdb50 vs.
0x7fffdb40), and objects are shown as 

[lldb-dev] lldb showing wrong type structure for virtual pointer type

[jonas echterhoff via lldb-dev]

Hi,

I'm having a problem where lldb will resolve the wrong type for virtual 
pointers, showing incorrect data for variables. This makes debugging our 
project very hard.

In our project, we commonly have the following structure:

class Transform : SomeParentClass
{
   virtual foo();
   void bar();
   /*...*/
}

namespace Scripting {
class Transform : SomeScriptingParentClass
{
   /*...*/
}
}

ie, we have native internal classes (like "Transform" in this case), and 
wrapper classes with identical names (but in a different namespace). (These are 
used to link the native class to a user facing API of the same name).

Now, when I put a breakpoint into "Transform::bar" and try to inspect the 
"this" variable, lldb shows "this" as a pointer to "Scripting::Transform" 
instead of as a pointer to "::Transform", thus showing the wrong data and 
making it impossible to inspect it's member variables. Since this is a common 
structure in our code, it makes debugging very hard.

Now, it seems that this is caused by Transform being a virtual class. So lldb 
will try to derive it's type at runtime by looking at the symbol name of the 
vtable (which is "__ZTV9Transform"). Then it will incorrectly map that to 
"Scripting::Transform" instead of "::Transform", which seems to be a bug in 
lldb.

I can work around the problem by patching the mach-o binary to remove the name 
of the vtable ("__ZTV9Transform") from the symbol table. Then lldb will be 
unable to look up the type dynamically at runtime, and use the dwarf info of 
the "bar" function, which specifies "this" to be a pointer to "::Transform". 
Obviously, this is a rather inconvenient workaround.

I guess I could rename the scripting representations of all our classes to use 
a different naming scheme (like "Scripting::_Transform"), but I'd only like to 
do that as a last resort.

I'm using lldb-900.0.64.
Unfortunately, I have not yet succeeded in coming up with a small, independent 
repro case which shows this problem.

So I'm wondering:
-Is this a known issue?
-Is there a fix?
-Any ideas for a better workaround?

Thanks for any help!

jonas
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