[llvm-dev] [lldb-dev] Trying out lld to link windows binaries (using msvc as a compiler)

[Zachary Turner via llvm-dev]

Yea as long as you compare clang-cl object file with automatically
generated .debug$H section against clang-cl object file without .debug$H
but added after the fact with llvm-objcopy, that should expose the problem
I think when you run obj2yaml on them.

On Thu, Jan 25, 2018 at 9:49 AM Leonardo Santagada <santagada at gmail.com>
wrote:

> I did reorder my sections, so that .debug$H is in the correct place, but
> now I get some errors on dubplicate symbols, I created a folder with
> examples:
>
> https://www.dropbox.com/sh/nmvzi44pi0boe76/AAA0f47O5PCJ9JiUc6wVuwBra?dl=0
>
> t.obj is generated by vs 2015 and it links fine with lld-link.exe, but
> tout.obj gives this errors:
>
> lld-link.exe /DEBUG:GHASH tout.obj
> LLD-LINK.EXE: error: duplicate symbol: __local_stdio_printf_options in
> tout.obj and in LIBCMT.lib(default_local_stdio_options.obj)
> LLD-LINK.EXE: error: duplicate symbol: __local_stdio_printf_options in
> tout.obj and in libvcruntime.lib(undname.obj)
>
> I'm using PEView from http://wjradburn.com/software/ to look at the files
> and can't see anything wrong, except some valid differences in the offsets
> being used for the data (so pointer to data is different between them).
>
> I will look into yaml2obj now to see if I see anything else weird going on.
>
>
> On Thu, Jan 25, 2018 at 6:41 PM, Zachary Turner <zturner at google.com>
> wrote:
>
>> I'm pretty confident that cl is not putting anything strange in the
>> .debug$T sections.  We've done a lot of testing and never seen anything
>> except CodeView type records in a .debug$T.  My hunch is that your objcopy
>> patch is probably not doing the right thing in one or more of the section
>> headers, and this is confusing the linker.
>>
>> One idea might be to build a simple object file with clang-cl but without
>> the magic -mllvm -emit-codeview-ghash-section, then run your llvm-objcopy
>> on it.  Then build the same object file passing -mllvm
>> -emit-codeview-ghash-section.  Then run obj2yaml on both and diff the
>> results.  They should be byte-for-byte identical.  That should give you a
>> clue about if objcopy is doing something wrong.
>>
>> On Thu, Jan 25, 2018 at 2:21 AM Leonardo Santagada <santagada at gmail.com>
>> wrote:
>>
>>> Don't worry, I definetly want to perfect this to generate legal obj
>>> files, this is just to speed up testing.
>>>
>>> Now after patching all the obj files I get this errors when linking a
>>> small part of our code base (msvc 2017 15.5.3, lld and llvm-objcopy 7.0.0):
>>> lld-link.exe : error : relocation against symbol in discarded section:
>>> $LN8
>>> lld-link.exe : error : relocation against symbol in discarded section:
>>> $LN43
>>> lld-link.exe : error : relocation against symbol in discarded section:
>>> $LN37
>>>
>>> I'm starting to guess that cl.exe might be putting some random comdat or
>>> other discardable symbols in the .debug$T and clang doesn't? I will try to
>>> debug this and see what more I can uncover.
>>>
>>> Linking works perfectly without my llvm-objcopy pass to add .debug$H?
>>>
>>>
>>> On Thu, Jan 25, 2018 at 1:53 AM, Zachary Turner <zturner at google.com>
>>> wrote:
>>>
>>>> It might not influence LLD, but at the same time we don't want to
>>>> upstream something that is producing technically illegal COFF files.  Also
>>>> good to hear about the planned changes to your header files.  Looking
>>>> forward to hearing about your experiences with clang-cl.
>>>>
>>>> On Wed, Jan 24, 2018 at 10:41 AM Leonardo Santagada <
>>>> santagada at gmail.com> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> I finally got my first .obj file patched with .debug$H to look
>>>>> somewhat right. I added the new section at the end of the file so I don't
>>>>> have to recalculate all sections (although now I probably could position it
>>>>> in the middle, knowing that each section is: SizeOfRawData +
>>>>> (last.Header.NumberOfRelocations * (4+4+2)) and the $H needs to come right
>>>>> after $T in the file). That although illegal based on the coff specs
>>>>> doesn't seem its going to influence lld.
>>>>>
>>>>> Also we talked and we are probably going to do something similar to a
>>>>> bunch of windows defines and a check for our own define (to guarantee that
>>>>> no one imported windows.h before win32.h) and drop the namespace and the
>>>>> conflicting names.
>>>>>
>>>>>
>>>>> On Tue, Jan 23, 2018 at 12:46 AM, Zachary Turner <zturner at google.com>
>>>>> wrote:
>>>>>
>>>>>> That's very possible that a 3rd party indirect header include is
>>>>>> involved.  One idea might be like I suggested where you #define _WINDOWS_
>>>>>> in win32.h and guarantee that it's always included first.  Then those other
>>>>>> headers won't be able to #include <windows.h>.  but it will probably
>>>>>> greatly expand the amount of stuff you have to add to win32.h, as you will
>>>>>> probably find some callers of functions that aren't yet in your win32.h
>>>>>> that you'd have to add.
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Mon, Jan 22, 2018 at 3:28 PM Leonardo Santagada <
>>>>>> santagada at gmail.com> wrote:
>>>>>>
>>>>>>> Ok some information was lost on getting this example to you, I'm
>>>>>>> sorry for not being clear.
>>>>>>>
>>>>>>> We have a huge code base, let's say 90% of it doesn't include either
>>>>>>> header, 9% include win32.h and 1% includes both, I will try to discover
>>>>>>> why, but my guess is they include both a third party that includes
>>>>>>> windows.h and some of our libs that use win32.h.
>>>>>>>
>>>>>>> I will try to fully understand this tomorrow.
>>>>>>>
>>>>>>> I guess clang will not implement this ever so finishing the object
>>>>>>> copier is the best solution until all code is ported to clang.
>>>>>>>
>>>>>>> On 23 Jan 2018 00:02, "Zachary Turner" <zturner at google.com> wrote:
>>>>>>>
>>>>>>>> You said win32.h doesn't include windows.h, but main.cpp does.  So
>>>>>>>> what's the disadvantage of just including it in win32.h anyway, since it's
>>>>>>>> already going to be in every translation unit?  (Unless you didn't mean to
>>>>>>>> #include it in main.cpp)
>>>>>>>>
>>>>>>>>
>>>>>>>> I guess all I can do is warn you how bad of an idea this is.  For
>>>>>>>> starters, I already found a bug in your code ;-)
>>>>>>>>
>>>>>>>> // stdint.h
>>>>>>>> typedef int                int32_t;
>>>>>>>>
>>>>>>>> // winnt.h
>>>>>>>> typedef long LONG;
>>>>>>>>
>>>>>>>> // windef.h
>>>>>>>> typedef struct tagPOINT
>>>>>>>> {
>>>>>>>>     LONG  x;   // long x
>>>>>>>>     LONG  y;   // long y
>>>>>>>> } POINT, *PPOINT, NEAR *NPPOINT, FAR *LPPOINT;
>>>>>>>>
>>>>>>>> // win32.h
>>>>>>>> typedef int32_t LONG;
>>>>>>>>
>>>>>>>> struct POINT
>>>>>>>> {
>>>>>>>> LONG x;   // int x
>>>>>>>> LONG y;   // int y
>>>>>>>> };
>>>>>>>>
>>>>>>>> So POINT is defined two different ways.  In your minimal interface,
>>>>>>>> it's declared as 2 int32's, which are int.  In the actual Windows header
>>>>>>>> files, it's declared as 2 longs.
>>>>>>>>
>>>>>>>> This might seem like a unimportant bug since int and long are the
>>>>>>>> same size, but int and long also mangle differently and affect overload
>>>>>>>> resolution, so you could have weird linker errors or call the wrong
>>>>>>>> function overload.
>>>>>>>>
>>>>>>>> Plus, it illustrates the fact that this struct *actually is* a
>>>>>>>> different type from the one in the windows header.
>>>>>>>>
>>>>>>>> You said at the end that you never intentionally import win32.h and
>>>>>>>> windows.h from the same translation unit.  But then in this example you
>>>>>>>> did.  I wonder if you could enforce that by doing this:
>>>>>>>>
>>>>>>>> // win32.h
>>>>>>>> #pragma once
>>>>>>>>
>>>>>>>> // Error if windows.h was included before us.
>>>>>>>> #if defined(_WINDOWS_)
>>>>>>>> #error "You're including win32.h after having already included
>>>>>>>> windows.h.  Don't do this!"
>>>>>>>> #endif
>>>>>>>>
>>>>>>>> // And also make sure windows.h can't get included after us
>>>>>>>> #define _WINDOWS_
>>>>>>>>
>>>>>>>> For the record, I tried the test case you linked when windows.h is
>>>>>>>> not included in main.cpp and it works (but still has the bug about int and
>>>>>>>> long).
>>>>>>>>
>>>>>>>> On Mon, Jan 22, 2018 at 2:23 PM Leonardo Santagada <
>>>>>>>> santagada at gmail.com> wrote:
>>>>>>>>
>>>>>>>>> It is super gross, but we copy parts of windows.h because having
>>>>>>>>> all of it if both gigantic and very very messy. So our win32.h has a couple
>>>>>>>>> thousands of lines and not 30k+ for windows.h and we try to have zero
>>>>>>>>> macros. Win32.h doesn't include windows.h so using ::BOOL wouldn't work. We
>>>>>>>>> don't want to create a namespace, we just want a cleaner interface to
>>>>>>>>> windows api. The namespace with c linkage is the way to trick cl into
>>>>>>>>> allowing us to in some files have both windows.h and Win32.h. I really
>>>>>>>>> don't see any way for us to have this Win32.h without this cl support, so
>>>>>>>>> maybe we should either put windows.h in a compiled header somewhere and not
>>>>>>>>> care that it is infecting everything or just have one place we can call to
>>>>>>>>> clean up after including windows.h (a massive set of undefs).
>>>>>>>>>
>>>>>>>>> So using can't work, because we never intentionally import
>>>>>>>>> windows.h and win32.h on the same translation unit.
>>>>>>>>>
>>>>>>>>> On Mon, Jan 22, 2018 at 7:08 PM, Zachary Turner <
>>>>>>>>> zturner at google.com> wrote:
>>>>>>>>>
>>>>>>>>>> This is pretty gross, honestly :)
>>>>>>>>>>
>>>>>>>>>> Can't you just use using declarations?
>>>>>>>>>>
>>>>>>>>>> namespace Win32 {
>>>>>>>>>> extern "C" {
>>>>>>>>>>
>>>>>>>>>> using ::BOOL;
>>>>>>>>>> using ::LONG;
>>>>>>>>>> using ::POINT;
>>>>>>>>>> using ::LPPOINT;
>>>>>>>>>>
>>>>>>>>>> using ::GetCursorPos;
>>>>>>>>>> }
>>>>>>>>>> }
>>>>>>>>>>
>>>>>>>>>> This works with clang-cl.
>>>>>>>>>>
>>>>>>>>>> On Mon, Jan 22, 2018 at 5:39 AM Leonardo Santagada <
>>>>>>>>>> santagada at gmail.com> wrote:
>>>>>>>>>>
>>>>>>>>>>> Here it is a minimal example, we do this so we don't have to
>>>>>>>>>>> import the whole windows api everywhere.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> https://gist.github.com/santagada/7977e929d31c629c4bf18ebb987f6be3
>>>>>>>>>>>
>>>>>>>>>>> On Sun, Jan 21, 2018 at 2:31 AM, Zachary Turner <
>>>>>>>>>>> zturner at google.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Clang-cl maintains compatibility with msvc even in cases where
>>>>>>>>>>>> it’s non standards compliant (eg 2 phase name lookup), but we try to keep
>>>>>>>>>>>> these cases few and far between.
>>>>>>>>>>>>
>>>>>>>>>>>> To help me understand your case, do you mean you copy windows.h
>>>>>>>>>>>> and modify it? How does this lead to the same struct being defined twice?
>>>>>>>>>>>> If i were to write this:
>>>>>>>>>>>>
>>>>>>>>>>>> struct Foo {};
>>>>>>>>>>>> struct Foo {};
>>>>>>>>>>>>
>>>>>>>>>>>> Is this a small repro of the issue you’re talking about?
>>>>>>>>>>>>
>>>>>>>>>>>> On Sat, Jan 20, 2018 at 3:44 PM Leonardo Santagada <
>>>>>>>>>>>> santagada at gmail.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> I can totally see something like incremental linking with a
>>>>>>>>>>>>> simple padding between obj and a mapping file (which can also help with
>>>>>>>>>>>>> edit and continue, something we also would love to have).
>>>>>>>>>>>>>
>>>>>>>>>>>>> We have another developer doing the port to support clang-cl,
>>>>>>>>>>>>> but although most of our code also goes trough a version of clang,
>>>>>>>>>>>>> migrating the rest to clang-cl has been a fight. From what I heard the main
>>>>>>>>>>>>> problem is that we have a copy of parts of windows.h (so not to bring the
>>>>>>>>>>>>> awful parts of it like lower case macros) and that totally works on cl, but
>>>>>>>>>>>>> clang (at least 6.0) complains about two struct/vars with the same name,
>>>>>>>>>>>>> even though they are exactly the same. Making clang-cl as broken as cl.exe
>>>>>>>>>>>>> is not an option I suppose? I would love to turn on a flag
>>>>>>>>>>>>> --accept-that-cl-made-bad-decisions-and-live-with-it and have this at least
>>>>>>>>>>>>> until this is completely fixed in our code base.
>>>>>>>>>>>>>
>>>>>>>>>>>>> the biggest win with moving to cl would be a better more
>>>>>>>>>>>>> standards compliant compiler, no 1 minute compiles on heavily templated
>>>>>>>>>>>>> files and maybe the holy grail of ThinLTO.
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Sat, Jan 20, 2018 at 10:56 PM, Zachary Turner <
>>>>>>>>>>>>> zturner at google.com> wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>> 10-15s will be hard without true incremental linking.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> At some point that's going to be the only way to get any
>>>>>>>>>>>>>> faster, but incremental linking is hard (putting it lightly), and since our
>>>>>>>>>>>>>> full links are already really fast we think we can get reasonably close to
>>>>>>>>>>>>>> link.exe incremental speeds with full links.  But it's never enough and I
>>>>>>>>>>>>>> will always want it to be faster, so you may see incremental linking in the
>>>>>>>>>>>>>> future after we hit a performance wall with full link speed :)
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> In any case, I'm definitely interested in seeing what kind of
>>>>>>>>>>>>>> numbers you get with /debug:ghash after you get this llvm-objcopy feature
>>>>>>>>>>>>>> implemented.  So keep me updated :)
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> As an aside, have you tried building with clang instead of
>>>>>>>>>>>>>> cl?  If you build with clang you wouldn't even have to do this llvm-objcopy
>>>>>>>>>>>>>> work, because it would "just work".  If you've tried but ran into issues
>>>>>>>>>>>>>> I'm interested in hearing about those too.  On the other hand, it's also
>>>>>>>>>>>>>> reasonable to only switch one thing at a time.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Sat, Jan 20, 2018 at 1:34 PM Leonardo Santagada <
>>>>>>>>>>>>>> santagada at gmail.com> wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> if we get to < 30s I think most users would prefer it to
>>>>>>>>>>>>>>> link.exe, just hopping there is still some more optimizations to get closer
>>>>>>>>>>>>>>> to ELF linking times (around 10-15s here).
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> On Sat, Jan 20, 2018 at 9:50 PM, Zachary Turner <
>>>>>>>>>>>>>>> zturner at google.com> wrote:
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>> Generally speaking a good rule of thumb is that
>>>>>>>>>>>>>>>> /debug:ghash will be close to or faster than /debug:fastlink, but with none
>>>>>>>>>>>>>>>> of the penalties like slow debug time
>>>>>>>>>>>>>>>> On Sat, Jan 20, 2018 at 12:44 PM Zachary Turner <
>>>>>>>>>>>>>>>> zturner at google.com> wrote:
>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> Chrome is actually one of my exact benchmark cases. When
>>>>>>>>>>>>>>>>> building blink_core.dll and browser_tests.exe, i get anywhere from a 20-40%
>>>>>>>>>>>>>>>>> reduction in link time. We have some other optimizations in the pipeline
>>>>>>>>>>>>>>>>> but not upstream yet.
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>> My best time so far (including other optimizations not yet
>>>>>>>>>>>>>>>>> upstream) is 28s on blink_core.dll, compared to 110s with /debug
>>>>>>>>>>>>>>>>> On Sat, Jan 20, 2018 at 12:28 PM Leonardo Santagada <
>>>>>>>>>>>>>>>>> santagada at gmail.com> wrote:
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> On Sat, Jan 20, 2018 at 9:05 PM, Zachary Turner <
>>>>>>>>>>>>>>>>>> zturner at google.com> wrote:
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> You probably don't want to go down the same route that
>>>>>>>>>>>>>>>>>>> clang goes through to write the object file.  If you think yaml2coff is
>>>>>>>>>>>>>>>>>>> convoluted, the way clang does it will just give you a headache.  There are
>>>>>>>>>>>>>>>>>>> multiple abstractions involved to account for different object file formats
>>>>>>>>>>>>>>>>>>> (ELF, COFF, MachO) and output formats (Assembly, binary file).  At least
>>>>>>>>>>>>>>>>>>> with yaml2coff
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> I think your phrase got cut there, but yeah I just found
>>>>>>>>>>>>>>>>>> AsmPrinter.cpp and it is convoluted.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> It's true that yaml2coff is using the COFFParser
>>>>>>>>>>>>>>>>>>> structure, but if you look at the writeCOFF function in
>>>>>>>>>>>>>>>>>>> yaml2coff it's pretty bare-metal.  The logic you need will be almost
>>>>>>>>>>>>>>>>>>> identical, except that instead of checking the COFFParser for the various
>>>>>>>>>>>>>>>>>>> fields, you'll check the existing COFFObjectFile, which should have similar
>>>>>>>>>>>>>>>>>>> fields.
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> The only thing you need to different is when writing the
>>>>>>>>>>>>>>>>>>> section table and section contents, to insert a new entry.  Since
>>>>>>>>>>>>>>>>>>> you're injecting a section into the middle, you'll also probably need to
>>>>>>>>>>>>>>>>>>> push back the file pointer of all subsequent sections so that they don't
>>>>>>>>>>>>>>>>>>> overlap.  (e.g. if the original sections are 1, 2, 3, 4, 5 and you insert
>>>>>>>>>>>>>>>>>>> between 2 and 3, then the original sections 3, 4, and 5 would need to have
>>>>>>>>>>>>>>>>>>> their FilePointerToRawData offset by the size of the new section).
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> I have the PE/COFF spec open here and I'm happy that I
>>>>>>>>>>>>>>>>>> read a bit of it so I actually know what you are talking about... yeah it
>>>>>>>>>>>>>>>>>> doesn't seem too complicated.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> If you need to know what values to put for the other
>>>>>>>>>>>>>>>>>>> fields in a section header, run `dumpbin /headers foo.obj` on a
>>>>>>>>>>>>>>>>>>> clang-generated object file that has a .debug$H section already (e.g. run
>>>>>>>>>>>>>>>>>>> clang with -emit-codeview-ghash-section, and look at the properties of the
>>>>>>>>>>>>>>>>>>> .debug$H section and use the same values).
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Thanks I will do that and then also look at how the
>>>>>>>>>>>>>>>>>> CodeView part of the code does it if I can't understand some of it.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> The only invariant that needs to be maintained is that
>>>>>>>>>>>>>>>>>>> Section[N]->FilePointerOfRawData == Section[N-1]->FilePointerOfRawData +
>>>>>>>>>>>>>>>>>>> Section[N-1]->SizeOfRawData
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Well, that and all the sections need to be on the final
>>>>>>>>>>>>>>>>>> file... But I'm hopeful.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Anyone has times on linking a big project like chrome
>>>>>>>>>>>>>>>>>> with this so that at least I know what kind of performance to expect?
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> My numbers are something like:
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> 1 pdb per obj file: link.exe takes ~15 minutes and 16GB
>>>>>>>>>>>>>>>>>> of ram, lld-link.exe takes 2:30 minutes and ~8GB of ram
>>>>>>>>>>>>>>>>>> around 10 pdbs per folder: link.exe takes 1 minute and
>>>>>>>>>>>>>>>>>> 2-3GB of ram, lld-link.exe takes 1:30 minutes and ~6GB of ram
>>>>>>>>>>>>>>>>>> faslink: link.exe takes 40 seconds, but then 20 seconds
>>>>>>>>>>>>>>>>>> of loading at the first break point in the debugger and we lost DIA support
>>>>>>>>>>>>>>>>>> for listing symbols.
>>>>>>>>>>>>>>>>>> incremental: link.exe takes 8 seconds, but it only
>>>>>>>>>>>>>>>>>> happens when very minor changes happen.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> We have an non negligible number of symbols used on some
>>>>>>>>>>>>>>>>>> runtime systems.
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>> On Sat, Jan 20, 2018 at 11:52 AM Leonardo Santagada <
>>>>>>>>>>>>>>>>>>> santagada at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> Thanks for the tips, I now have something that reads
>>>>>>>>>>>>>>>>>>>> the obj file, finds .debug$T sections and global hashes it (proof of
>>>>>>>>>>>>>>>>>>>> concept kind of code). What I can't find is: how does clang itself writes
>>>>>>>>>>>>>>>>>>>> the coff files with global hashes, as that might help me understand how to
>>>>>>>>>>>>>>>>>>>> create the .debug$H section, how to update the file section count and how
>>>>>>>>>>>>>>>>>>>> to properly write this back.
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> The code on yaml2coff is expecting to be working on the
>>>>>>>>>>>>>>>>>>>> yaml COFFParser struct and I'm having quite a bit of a headache turning the
>>>>>>>>>>>>>>>>>>>> COFFObjectFile into a COFFParser object or compatible... Tomorrow I might
>>>>>>>>>>>>>>>>>>>> try the very non efficient path of coff2yaml and then yaml2coff with the
>>>>>>>>>>>>>>>>>>>> hashes header... but it seems way too inefficient and convoluted.
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> On Fri, Jan 19, 2018 at 10:38 PM, Zachary Turner <
>>>>>>>>>>>>>>>>>>>> zturner at google.com> wrote:
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> On Fri, Jan 19, 2018 at 1:02 PM Leonardo Santagada <
>>>>>>>>>>>>>>>>>>>>> santagada at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> On Fri, Jan 19, 2018 at 9:44 PM, Zachary Turner <
>>>>>>>>>>>>>>>>>>>>>> zturner at google.com> wrote:
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> On Fri, Jan 19, 2018 at 12:29 PM Leonardo Santagada <
>>>>>>>>>>>>>>>>>>>>>>> santagada at gmail.com> wrote:
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>> Hi,
>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>> No I didn't, I used cl.exe from the visual studio
>>>>>>>>>>>>>>>>>>>>>>>> toolchain. What I'm proposing is a tool for processing .obj files in COFF
>>>>>>>>>>>>>>>>>>>>>>>> format, reading them and generating the GHASH part.
>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>> To make our build faster we use hundreds of unity
>>>>>>>>>>>>>>>>>>>>>>>> build files (.cpp's with a lot of other .cpp's in them aka munch files) but
>>>>>>>>>>>>>>>>>>>>>>>> still have a lot of single .cpp's as well (in total something like 3.4k
>>>>>>>>>>>>>>>>>>>>>>>> .obj files).
>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>> ps: sorry for sending to the wrong list, I was
>>>>>>>>>>>>>>>>>>>>>>>> reading about llvm mailing lists and jumped when I saw what I thought was a
>>>>>>>>>>>>>>>>>>>>>>>> lld exclusive list.
>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> A tool like this would be useful, yes.  We've talked
>>>>>>>>>>>>>>>>>>>>>>> about it internally as well and agreed it would be useful, we just haven't
>>>>>>>>>>>>>>>>>>>>>>> prioritized it.  If you're interested in submitting a patch along those
>>>>>>>>>>>>>>>>>>>>>>> lines though, I think it would be a good addition.
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> I'm not sure what the best place for it would be.
>>>>>>>>>>>>>>>>>>>>>>> llvm-readobj and llvm-objdump seem like obvious choices, but they are
>>>>>>>>>>>>>>>>>>>>>>> intended to be read-only, so perhaps they wouldn't be a good fit.
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> llvm-pdbutil is kind of a hodgepodge of everything
>>>>>>>>>>>>>>>>>>>>>>> else related to PDBs and symbols, so I wouldn't be opposed to making a new
>>>>>>>>>>>>>>>>>>>>>>> subcommand there called "ghash" or something that could process an object
>>>>>>>>>>>>>>>>>>>>>>> file and output a new object file with a .debug$H section.
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> A third option would be to make a new tool for it.
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>> I don't htink it would be that hard to write.  If
>>>>>>>>>>>>>>>>>>>>>>> you're interested in trying to make a patch for this, I can offer some
>>>>>>>>>>>>>>>>>>>>>>> guidance on where to look in the code.  Otherwise it's something that we'll
>>>>>>>>>>>>>>>>>>>>>>> probably get to, I'm just not sure when.
>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>> I would love to write it and contribute it back,
>>>>>>>>>>>>>>>>>>>>>> please do tell, I did find some of the code of ghash in lld, but in fuzzy
>>>>>>>>>>>>>>>>>>>>>> on the llvm codeview part of it and never seen llvm-readobj/objdump or
>>>>>>>>>>>>>>>>>>>>>> llvm-pdbutil, but I'm not afraid to look :)
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>  Luckily all of the important code is hidden behind
>>>>>>>>>>>>>>>>>>>>> library calls, and it should already just do the right thing, so I suspect
>>>>>>>>>>>>>>>>>>>>> you won't need to know much about CodeView to do this.
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> I think Peter has the right idea about putting this in
>>>>>>>>>>>>>>>>>>>>> llvm-objcopy.
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> You can look at one of the existing CopyBinary
>>>>>>>>>>>>>>>>>>>>> functions there, which currently only work for ELF, but you can just make a
>>>>>>>>>>>>>>>>>>>>> new overload that accepts a COFFObjectFile.
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> I would probably start by iterating over each of the
>>>>>>>>>>>>>>>>>>>>> sections (getNumberOfSections / getSectionName) looking for .debug$T and
>>>>>>>>>>>>>>>>>>>>> .debug$H sections.
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> If you find a .debug$H section then you can just skip
>>>>>>>>>>>>>>>>>>>>> that object file.
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> If you find a .debug$T but not a .debug$H, then
>>>>>>>>>>>>>>>>>>>>> basically do the same thing that LLD does in PDBLinker::mergeDebugT
>>>>>>>>>>>>>>>>>>>>> (create a CVTypeArray, and pass it to GloballyHashedType::hashTypes.  That
>>>>>>>>>>>>>>>>>>>>> will return an array of hash values.  (the format of .debug$H is the
>>>>>>>>>>>>>>>>>>>>> header, followed by the hash values).  Then when you're writing the list of
>>>>>>>>>>>>>>>>>>>>> sections, just add in the .debug$H section right after the .debug$T section.
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> Currently llvm-objcopy only writes ELF files, so it
>>>>>>>>>>>>>>>>>>>>> would need to be taught to write COFF files.  We have code to do this in
>>>>>>>>>>>>>>>>>>>>> the yaml2obj utility (specifically, in yaml2coff.cpp in the function
>>>>>>>>>>>>>>>>>>>>> writeCOFF).  There may be a way to move this code to somewhere else
>>>>>>>>>>>>>>>>>>>>> (llvm/Object/COFF.h?) so that it can be re-used by both yaml2coff and
>>>>>>>>>>>>>>>>>>>>> llvm-objcopy, but in the worst case scenario you could copy the code and
>>>>>>>>>>>>>>>>>>>>> re-write it to work with these new structures.
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>> Lastly, you'll probably want to put all of this behind
>>>>>>>>>>>>>>>>>>>>> an option in llvm-objcopy such as -add-codeview-ghash-section
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>> Leonardo Santagada
>>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>> Leonardo Santagada
>>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> --
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>> Leonardo Santagada
>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>> --
>>>>>>>>>>>>>
>>>>>>>>>>>>> Leonardo Santagada
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>>
>>>>>>>>>>> Leonardo Santagada
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> --
>>>>>>>>>
>>>>>>>>> Leonardo Santagada
>>>>>>>>>
>>>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>>
>>>>> Leonardo Santagada
>>>>>
>>>>
>>>
>>>
>>> --
>>>
>>> Leonardo Santagada
>>>
>>
>
>
> --
>
> Leonardo Santagada
>
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