llvm dev - Jan 2019 - [llvm-pdbutil] : merge not working properly

Well, that’s certainly possible, but improving llvm-pdbutil is another
possibility. Doing it directly in your jit compiler will probably save you
time though, since you won’t have to worry about writing tests and going
through code review
On Wed, Jan 16, 2019 at 1:01 PM Vivien Millet <vivien.millet at gmail.com>
wrote:
> Thanks for the tips !
> When you talk about doing all of this I suppose you think about using
> llvm/debuginfo/pdb, pick code here and there to generate the pdb in memory,
> read the executable one and perform the merge directly in my jit compiler,
> right ? Not using pdbutil ?
>
>
>
> Le mar. 15 janv. 2019 à 22:49, Zachary Turner <zturner at google.com>
a
> écrit :
>
>>
>>
>> On Tue, Jan 15, 2019 at 2:50 AM Vivien Millet <vivien.millet at
gmail.com>
>> wrote:
>>
>>> Hello Zachary !
>>> Thanks for your time !
>>> So you are one of the happy guys who suffered from the lack of PDB
>>> format information :)
>>>
>> Yes, that would be me :)
>>
>>
>>> To be honest I'm really a beginner in the PDB stuff, I just
read some
>>> llvm documentation to understand what went wrong when merging my
PDBs.
>>> In my case, what I do with my team and try to achieve is this :
>>> - Run our application under a visual studio debugger
>>> - Generate JIT code ( using llvm MCJIT  )
>>> - Then, either :
>>>    - export as COFF obj file with dwarf information and then
convert it
>>> with cv2pdb to obtain a pdb of my JIT symbols (what I do now)
>>>    - export directly to PDB my JIT debug info (what i would like to
do,
>>> if you have an idea how..)
>>> - Detach the visual studio debugger
>>> - Merge my JIT pdb into a copy of the executable pdb (where things
start
>>> to go bad..)
>>> - Replace original executable by the copy (creating a backup of
original)
>>> - Reattach  the visual studio debugger to my executable (loading
the new
>>> pdb version)
>>> - Debug JIT code with visual studio.
>>> - On each JIT rebuild, restart these steps from the original native
>>> executable PDB to avoid merge conflict between the multiple JIT
iterations
>>>
>> Yea, it's an interesting use case.  It makes me think it would be
nice if
>> the PDB format supported some way of having a symbol which simply
refers to
>> another PDB file, that way you could re-write that PDB file at runtime
once
>> all your code is jitted, and when the debugger tries to look up that
>> symbol, it finds a record that tells it to go check the other PDB file.
>>
>> So, here are the things I think you would need to do:
>>
>> 1) Create a JIT module in the module list with a unique name.  All
>> symbols will go here.  llvm-pdbutil dump -modules shows you the list. 
Be
>> careful about putting it at the end though, because there's already
one at
>> the end called * LINKER * that is kind of special.  On the other hand,
you
>> don't want to put it first because it means you will have to do
lots of
>> fixups on the EXE PDB.  It's probably best to add it right before
the
>> linker module, this has the least chance of breaking anything.
>>
>> 2) In the debug stream for this module, add all symbols.  You will need
>> to fix up their type indices.  As you noticed, llvm-pdbutil already
merges
>> type information from the JIT PDB, so after merging the type indices in
the
>> EXE PDB will be different than they were in the JIT PDB, but the symbol
>> records will refer to the JIT PDB type indices.  So these need to be
fixed
>> up.  LLD already has code to do this, you can probably borrow a similar
>> algorithm with some slight modifications (lldb/COFF/PDB.cpp, search for
>> mergeSymbolRecords)
>>
>> 3) Merge in the new section contributions and section map.  See LLD
again
>> for how to modify these.  Hopefully the object file you exported
contains
>> relocated symbol addresses so you don't have to do any fixups here.
>>
>> 4) Merge in the publics and globals.  This shouldn't be too hard, I
think
>> you can just iterate over them in the JIT PDB and add them to the new
EXE
>> PDB.
>>
>> You're kind of in uncharted territory here, so this is just a rough
idea
>> of what needs to be done.  There may be other issues that you don't
>> encounter until you actually try it out.
>>
>> Unfortunately I don't personally have the time to work on this, but
it
>> sounds neat, and I'm happy to help if you run into questions or
problems
>> along the way.
>>
>>
>>
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I would be up to improve pdbutil but I doubt I have enough knowledge or
time to provide the complete merge feature, it would still be a very
specific kind of merge as you describe it. Anyway I could start trying to
do it in my jit compiler and then, once I get something working (if that
happens :)), i can come back to you with the piece of code and see if it is
worth integrating it to pdbutil and how ?

Le mer. 16 janv. 2019 à 22:12, Zachary Turner <zturner at google.com> a
écrit :
> Well, that’s certainly possible, but improving llvm-pdbutil is another
> possibility. Doing it directly in your jit compiler will probably save you
> time though, since you won’t have to worry about writing tests and going
> through code review
> On Wed, Jan 16, 2019 at 1:01 PM Vivien Millet <vivien.millet at
gmail.com>
> wrote:
>
>> Thanks for the tips !
>> When you talk about doing all of this I suppose you think about using
>> llvm/debuginfo/pdb, pick code here and there to generate the pdb in
memory,
>> read the executable one and perform the merge directly in my jit
compiler,
>> right ? Not using pdbutil ?
>>
>>
>>
>> Le mar. 15 janv. 2019 à 22:49, Zachary Turner <zturner at
google.com> a
>> écrit :
>>
>>>
>>>
>>> On Tue, Jan 15, 2019 at 2:50 AM Vivien Millet <vivien.millet at
gmail.com>
>>> wrote:
>>>
>>>> Hello Zachary !
>>>> Thanks for your time !
>>>> So you are one of the happy guys who suffered from the lack of
PDB
>>>> format information :)
>>>>
>>> Yes, that would be me :)
>>>
>>>
>>>> To be honest I'm really a beginner in the PDB stuff, I just
read some
>>>> llvm documentation to understand what went wrong when merging
my PDBs.
>>>> In my case, what I do with my team and try to achieve is this :
>>>> - Run our application under a visual studio debugger
>>>> - Generate JIT code ( using llvm MCJIT  )
>>>> - Then, either :
>>>>    - export as COFF obj file with dwarf information and then
convert it
>>>> with cv2pdb to obtain a pdb of my JIT symbols (what I do now)
>>>>    - export directly to PDB my JIT debug info (what i would
like to do,
>>>> if you have an idea how..)
>>>> - Detach the visual studio debugger
>>>> - Merge my JIT pdb into a copy of the executable pdb (where
things
>>>> start to go bad..)
>>>> - Replace original executable by the copy (creating a backup of
>>>> original)
>>>> - Reattach  the visual studio debugger to my executable
(loading the
>>>> new pdb version)
>>>> - Debug JIT code with visual studio.
>>>> - On each JIT rebuild, restart these steps from the original
native
>>>> executable PDB to avoid merge conflict between the multiple JIT
iterations
>>>>
>>> Yea, it's an interesting use case.  It makes me think it would
be nice
>>> if the PDB format supported some way of having a symbol which
simply refers
>>> to another PDB file, that way you could re-write that PDB file at
runtime
>>> once all your code is jitted, and when the debugger tries to look
up that
>>> symbol, it finds a record that tells it to go check the other PDB
file.
>>>
>>> So, here are the things I think you would need to do:
>>>
>>> 1) Create a JIT module in the module list with a unique name.  All
>>> symbols will go here.  llvm-pdbutil dump -modules shows you the
list.  Be
>>> careful about putting it at the end though, because there's
already one at
>>> the end called * LINKER * that is kind of special.  On the other
hand, you
>>> don't want to put it first because it means you will have to do
lots of
>>> fixups on the EXE PDB.  It's probably best to add it right
before the
>>> linker module, this has the least chance of breaking anything.
>>>
>>> 2) In the debug stream for this module, add all symbols.  You will
need
>>> to fix up their type indices.  As you noticed, llvm-pdbutil already
merges
>>> type information from the JIT PDB, so after merging the type
indices in the
>>> EXE PDB will be different than they were in the JIT PDB, but the
symbol
>>> records will refer to the JIT PDB type indices.  So these need to
be fixed
>>> up.  LLD already has code to do this, you can probably borrow a
similar
>>> algorithm with some slight modifications (lldb/COFF/PDB.cpp, search
for
>>> mergeSymbolRecords)
>>>
>>> 3) Merge in the new section contributions and section map.  See LLD
>>> again for how to modify these.  Hopefully the object file you
exported
>>> contains relocated symbol addresses so you don't have to do any
fixups here.
>>>
>>> 4) Merge in the publics and globals.  This shouldn't be too
hard, I
>>> think you can just iterate over them in the JIT PDB and add them to
the new
>>> EXE PDB.
>>>
>>> You're kind of in uncharted territory here, so this is just a
rough idea
>>> of what needs to be done.  There may be other issues that you
don't
>>> encounter until you actually try it out.
>>>
>>> Unfortunately I don't personally have the time to work on this,
but it
>>> sounds neat, and I'm happy to help if you run into questions or
problems
>>> along the way.
>>>
>>>
>>>
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Sure. Along the way I’m happy to answer any specific questions you might
have too even if it’s for your downstream project
On Wed, Jan 16, 2019 at 1:38 PM Vivien Millet <vivien.millet at gmail.com>
wrote:
> I would be up to improve pdbutil but I doubt I have enough knowledge or
> time to provide the complete merge feature, it would still be a very
> specific kind of merge as you describe it. Anyway I could start trying to
> do it in my jit compiler and then, once I get something working (if that
> happens :)), i can come back to you with the piece of code and see if it is
> worth integrating it to pdbutil and how ?
>
> Le mer. 16 janv. 2019 à 22:12, Zachary Turner <zturner at google.com>
a
> écrit :
>
>> Well, that’s certainly possible, but improving llvm-pdbutil is another
>> possibility. Doing it directly in your jit compiler will probably save
you
>> time though, since you won’t have to worry about writing tests and
going
>> through code review
>> On Wed, Jan 16, 2019 at 1:01 PM Vivien Millet <vivien.millet at
gmail.com>
>> wrote:
>>
>>> Thanks for the tips !
>>> When you talk about doing all of this I suppose you think about
using
>>> llvm/debuginfo/pdb, pick code here and there to generate the pdb in
memory,
>>> read the executable one and perform the merge directly in my jit
compiler,
>>> right ? Not using pdbutil ?
>>>
>>>
>>>
>>> Le mar. 15 janv. 2019 à 22:49, Zachary Turner <zturner at
google.com> a
>>> écrit :
>>>
>>>>
>>>>
>>>> On Tue, Jan 15, 2019 at 2:50 AM Vivien Millet <vivien.millet
at gmail.com>
>>>> wrote:
>>>>
>>>>> Hello Zachary !
>>>>> Thanks for your time !
>>>>> So you are one of the happy guys who suffered from the lack
of PDB
>>>>> format information :)
>>>>>
>>>> Yes, that would be me :)
>>>>
>>>>
>>>>> To be honest I'm really a beginner in the PDB stuff, I
just read some
>>>>> llvm documentation to understand what went wrong when
merging my PDBs.
>>>>> In my case, what I do with my team and try to achieve is
this :
>>>>> - Run our application under a visual studio debugger
>>>>> - Generate JIT code ( using llvm MCJIT  )
>>>>> - Then, either :
>>>>>    - export as COFF obj file with dwarf information and
then convert
>>>>> it with cv2pdb to obtain a pdb of my JIT symbols (what I do
now)
>>>>>    - export directly to PDB my JIT debug info (what i would
like to
>>>>> do, if you have an idea how..)
>>>>> - Detach the visual studio debugger
>>>>> - Merge my JIT pdb into a copy of the executable pdb (where
things
>>>>> start to go bad..)
>>>>> - Replace original executable by the copy (creating a
backup of
>>>>> original)
>>>>> - Reattach  the visual studio debugger to my executable
(loading the
>>>>> new pdb version)
>>>>> - Debug JIT code with visual studio.
>>>>> - On each JIT rebuild, restart these steps from the
original native
>>>>> executable PDB to avoid merge conflict between the multiple
JIT iterations
>>>>>
>>>> Yea, it's an interesting use case.  It makes me think it
would be nice
>>>> if the PDB format supported some way of having a symbol which
simply refers
>>>> to another PDB file, that way you could re-write that PDB file
at runtime
>>>> once all your code is jitted, and when the debugger tries to
look up that
>>>> symbol, it finds a record that tells it to go check the other
PDB file.
>>>>
>>>> So, here are the things I think you would need to do:
>>>>
>>>> 1) Create a JIT module in the module list with a unique name. 
All
>>>> symbols will go here.  llvm-pdbutil dump -modules shows you the
list.  Be
>>>> careful about putting it at the end though, because there's
already one at
>>>> the end called * LINKER * that is kind of special.  On the
other hand, you
>>>> don't want to put it first because it means you will have
to do lots of
>>>> fixups on the EXE PDB.  It's probably best to add it right
before the
>>>> linker module, this has the least chance of breaking anything.
>>>>
>>>> 2) In the debug stream for this module, add all symbols.  You
will need
>>>> to fix up their type indices.  As you noticed, llvm-pdbutil
already merges
>>>> type information from the JIT PDB, so after merging the type
indices in the
>>>> EXE PDB will be different than they were in the JIT PDB, but
the symbol
>>>> records will refer to the JIT PDB type indices.  So these need
to be fixed
>>>> up.  LLD already has code to do this, you can probably borrow a
similar
>>>> algorithm with some slight modifications (lldb/COFF/PDB.cpp,
search for
>>>> mergeSymbolRecords)
>>>>
>>>> 3) Merge in the new section contributions and section map.  See
LLD
>>>> again for how to modify these.  Hopefully the object file you
exported
>>>> contains relocated symbol addresses so you don't have to do
any fixups here.
>>>>
>>>> 4) Merge in the publics and globals.  This shouldn't be too
hard, I
>>>> think you can just iterate over them in the JIT PDB and add
them to the new
>>>> EXE PDB.
>>>>
>>>> You're kind of in uncharted territory here, so this is just
a rough
>>>> idea of what needs to be done.  There may be other issues that
you don't
>>>> encounter until you actually try it out.
>>>>
>>>> Unfortunately I don't personally have the time to work on
this, but it
>>>> sounds neat, and I'm happy to help if you run into
questions or problems
>>>> along the way.
>>>>
>>>>
>>>>
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