llvm dev - Apr 2018 - [Dwarf] Register a local variable in DIBuilder and locate it later with a DwarfContext

Hi Paul,
How can i make this call to intrinsic from the c++ code ?
I'm not working with the IR language, but directly in C++ with
IRBuilder::CreateAlloca.
My goal is that one :
- Generate machine code with an instance of the class 'IRBuilder'
- Emit 'ObjFile' class instance with MCJIT
- Create a DwarfContext instance directly from the emitted ObjFile object
(DwarfContextInMemory) (on JitEventListener::NotifyObjectEmitted)
- Use this DwarfContext to step into my home made runtime debugger.

Now I can perform step over/into/out in my debugger using the DwarfContext
instance without problem, but I'm still stuck on how
to watch my local variables in my debugger (i can't figure out how to
locate them in registers/stack from that DwarfContext)

Thanks for your help

2018-04-01 20:17 GMT+02:00 <paul.robinson at sony.com>:
> Binding the alloca to the debug-info metadata is not automatic.  You need
> to emit an intrinsic function call to llvm.dbg.declare to bind the two
> together.
>
> If you are simply trying to emit DWARF for your program, the rest of the
> processing should already be in place for that.  If you are trying to do
> something else, you would need to describe that so we understand what you
> need.
>
> --paulr
>
>
>
> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of
*Vivien
> Millet via llvm-dev
> *Sent:* Saturday, March 31, 2018 7:33 AM
> *To:* llvm-dev
> *Subject:* [llvm-dev] [Dwarf] Register a local variable in DIBuilder and
> locate it later with a DwarfContext
>
>
>
> Hi,
>
> First, considering I'm using an IRBuilder and a DIBuilder to build my
> program, how can I automatically bind the CreateAlloca with my named local
> variable inside the DIBuilder ? Is it automatic with the Twine name of
> CreateAlloca ? And/Or should I use DIBuilder::createAutoVariable and how ?
>
>
> Then, I'm wondering how to locate back my local variable in memory
> (register or stack) once i have a DwarfContext ready.
>
> I'm a bit lost with all this pipeline, sorry If my question seem
trivial.
>
> Thanks !
>
> Vivien
>
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"IR" often refers to the general concept/semantics, not only the
textual
format in .ll files (there are 3 main forms - bitcode, textual IR, and the
in-memory representation (llvm::Module, etc - constructed using IRBuilder)).

A great place to start is to look at what Clang does to produce debug info
- it uses IRBuilder, for instance. So you could look at how Clang uses the
IRBuilder when compiling a small source file containing a local variable.
You'll find it calls into DIBuilder (the debug info equivalent of
IRBuilder) for constructing types and the location descriptions (see
"insertDeclare"/insertDbgValueIntrinsic", etc.).

On Sun, Apr 1, 2018 at 2:17 PM Vivien Millet via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi Paul,
> How can i make this call to intrinsic from the c++ code ?
> I'm not working with the IR language, but directly in C++ with
> IRBuilder::CreateAlloca.
> My goal is that one :
> - Generate machine code with an instance of the class 'IRBuilder'
> - Emit 'ObjFile' class instance with MCJIT
> - Create a DwarfContext instance directly from the emitted ObjFile object
> (DwarfContextInMemory) (on JitEventListener::NotifyObjectEmitted)
> - Use this DwarfContext to step into my home made runtime debugger.
>
> Now I can perform step over/into/out in my debugger using the DwarfContext
> instance without problem, but I'm still stuck on how
> to watch my local variables in my debugger (i can't figure out how to
> locate them in registers/stack from that DwarfContext)
>
> Thanks for your help
>
> 2018-04-01 20:17 GMT+02:00 <paul.robinson at sony.com>:
>
>> Binding the alloca to the debug-info metadata is not automatic.  You
need
>> to emit an intrinsic function call to llvm.dbg.declare to bind the two
>> together.
>>
>> If you are simply trying to emit DWARF for your program, the rest of
the
>> processing should already be in place for that.  If you are trying to
do
>> something else, you would need to describe that so we understand what
you
>> need.
>>
>> --paulr
>>
>>
>>
>> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf
Of *Vivien
>> Millet via llvm-dev
>> *Sent:* Saturday, March 31, 2018 7:33 AM
>> *To:* llvm-dev
>> *Subject:* [llvm-dev] [Dwarf] Register a local variable in DIBuilder
and
>> locate it later with a DwarfContext
>>
>>
>>
>> Hi,
>>
>> First, considering I'm using an IRBuilder and a DIBuilder to build
my
>> program, how can I automatically bind the CreateAlloca with my named
local
>> variable inside the DIBuilder ? Is it automatic with the Twine name of
>> CreateAlloca ? And/Or should I use DIBuilder::createAutoVariable and
how ?
>>
>>
>> Then, I'm wondering how to locate back my local variable in memory
>> (register or stack) once i have a DwarfContext ready.
>>
>> I'm a bit lost with all this pipeline, sorry If my question seem
trivial.
>>
>> Thanks !
>>
>> Vivien
>>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Thanks I will try that, it seems to be exactly what I need for the IR<->DI
binding part !

Once i have done this, do you have an idea on how I can extract the
information back from my DwarfContext ?
I assume it should start with a call to DwarfContext::getDebugFrame(), but
I'm not really sure, I'm really lost with that format...
What i would like is to be able to provide my function address and get,
from a string "myLocalVar",  the information of the register/stack
where
the variable is.
I m still digging the llvm source code to find...
Thanks !

2018-04-02 17:18 GMT+02:00 David Blaikie <dblaikie at gmail.com>:
> "IR" often refers to the general concept/semantics, not only the
textual
> format in .ll files (there are 3 main forms - bitcode, textual IR, and the
> in-memory representation (llvm::Module, etc - constructed using
IRBuilder)).
>
> A great place to start is to look at what Clang does to produce debug info
> - it uses IRBuilder, for instance. So you could look at how Clang uses the
> IRBuilder when compiling a small source file containing a local variable.
> You'll find it calls into DIBuilder (the debug info equivalent of
> IRBuilder) for constructing types and the location descriptions (see
> "insertDeclare"/insertDbgValueIntrinsic", etc.).
>
> On Sun, Apr 1, 2018 at 2:17 PM Vivien Millet via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi Paul,
>> How can i make this call to intrinsic from the c++ code ?
>> I'm not working with the IR language, but directly in C++ with
>> IRBuilder::CreateAlloca.
>> My goal is that one :
>> - Generate machine code with an instance of the class
'IRBuilder'
>> - Emit 'ObjFile' class instance with MCJIT
>> - Create a DwarfContext instance directly from the emitted ObjFile
object
>> (DwarfContextInMemory) (on JitEventListener::NotifyObjectEmitted)
>> - Use this DwarfContext to step into my home made runtime debugger.
>>
>> Now I can perform step over/into/out in my debugger using the
>> DwarfContext instance without problem, but I'm still stuck on how
>> to watch my local variables in my debugger (i can't figure out how
to
>> locate them in registers/stack from that DwarfContext)
>>
>> Thanks for your help
>>
>> 2018-04-01 20:17 GMT+02:00 <paul.robinson at sony.com>:
>>
>>> Binding the alloca to the debug-info metadata is not automatic. 
You
>>> need to emit an intrinsic function call to llvm.dbg.declare to bind
the two
>>> together.
>>>
>>> If you are simply trying to emit DWARF for your program, the rest
of the
>>> processing should already be in place for that.  If you are trying
to do
>>> something else, you would need to describe that so we understand
what you
>>> need.
>>>
>>> --paulr
>>>
>>>
>>>
>>> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On
Behalf Of
>>> *Vivien Millet via llvm-dev
>>> *Sent:* Saturday, March 31, 2018 7:33 AM
>>> *To:* llvm-dev
>>> *Subject:* [llvm-dev] [Dwarf] Register a local variable in
DIBuilder
>>> and locate it later with a DwarfContext
>>>
>>>
>>>
>>> Hi,
>>>
>>> First, considering I'm using an IRBuilder and a DIBuilder to
build my
>>> program, how can I automatically bind the CreateAlloca with my
named local
>>> variable inside the DIBuilder ? Is it automatic with the Twine name
of
>>> CreateAlloca ? And/Or should I use DIBuilder::createAutoVariable
and how ?
>>>
>>>
>>> Then, I'm wondering how to locate back my local variable in
memory
>>> (register or stack) once i have a DwarfContext ready.
>>>
>>> I'm a bit lost with all this pipeline, sorry If my question
seem trivial.
>>>
>>> Thanks !
>>>
>>> Vivien
>>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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