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

Hi Zachary !
If there a way to easily create a new PDBFileBuilder from an existing
PDBFile or can/should I do the translation myself ?
I would like to start from a builder filled with the EXE PDB data and then
complete its DBI stream with the JIT module/symbols.

Thanks !


Le mer. 16 janv. 2019 à 23:41, Vivien Millet <vivien.millet at gmail.com>
a
écrit :
> Thank you Zachary !
> I will have some soon I think ..
> I first need to explore the llvmpdb-util code more because I don't even
> know where to start with the PDB api..
>
> Le mer. 16 janv. 2019 à 22:51, Zachary Turner <zturner at google.com>
a
> écrit :
>
>> 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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It's possible in theory to support incremental updates to a PDB (the file
format is designed specifically with that in mind).  But this functionality
was never added to the PDB library since lld doesn't support incremental
linking, we never really needed it.

The "dumb" way would be to just create a new PDB file, build it using
the
old contents and the new contents (making sure to de-duplicate records as
necessary).

Supporting incremental updates should be possible, but most of LLVM's File
I/O abstractions are based around mmapping a file and writing to it, which
doesn't work when you don't know the file size in advance.  So there
would
be some interesting problems to solve here.

On Thu, Jan 17, 2019 at 10:03 AM Vivien Millet <vivien.millet at
gmail.com>
wrote:
> Hi Zachary !
> If there a way to easily create a new PDBFileBuilder from an existing
> PDBFile or can/should I do the translation myself ?
> I would like to start from a builder filled with the EXE PDB data and then
> complete its DBI stream with the JIT module/symbols.
>
> Thanks !
>
>
> Le mer. 16 janv. 2019 à 23:41, Vivien Millet <vivien.millet at
gmail.com> a
> écrit :
>
>> Thank you Zachary !
>> I will have some soon I think ..
>> I first need to explore the llvmpdb-util code more because I don't
even
>> know where to start with the PDB api..
>>
>> Le mer. 16 janv. 2019 à 22:51, Zachary Turner <zturner at
google.com> a
>> écrit :
>>
>>> 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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Ok I see..
what do you mean by “making sure to de-duplicate records as necessary” ?

Le jeu. 17 janv. 2019 à 19:09, Zachary Turner <zturner at google.com> a
écrit :
> It's possible in theory to support incremental updates to a PDB (the
file
> format is designed specifically with that in mind).  But this functionality
> was never added to the PDB library since lld doesn't support
incremental
> linking, we never really needed it.
>
> The "dumb" way would be to just create a new PDB file, build it
using the
> old contents and the new contents (making sure to de-duplicate records as
> necessary).
>
> Supporting incremental updates should be possible, but most of LLVM's
File
> I/O abstractions are based around mmapping a file and writing to it, which
> doesn't work when you don't know the file size in advance.  So
there would
> be some interesting problems to solve here.
>
> On Thu, Jan 17, 2019 at 10:03 AM Vivien Millet <vivien.millet at
gmail.com>
> wrote:
>
>> Hi Zachary !
>> If there a way to easily create a new PDBFileBuilder from an existing
>> PDBFile or can/should I do the translation myself ?
>> I would like to start from a builder filled with the EXE PDB data and
>> then complete its DBI stream with the JIT module/symbols.
>>
>> Thanks !
>>
>>
>> Le mer. 16 janv. 2019 à 23:41, Vivien Millet <vivien.millet at
gmail.com> a
>> écrit :
>>
>>> Thank you Zachary !
>>> I will have some soon I think ..
>>> I first need to explore the llvmpdb-util code more because I
don't even
>>> know where to start with the PDB api..
>>>
>>> Le mer. 16 janv. 2019 à 22:51, Zachary Turner <zturner at
google.com> a
>>> écrit :
>>>
>>>> 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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