[lldb-dev] PDB symbol reader supports C++ only?

[Zachary Turner via lldb-dev]

I think Aaron added that code for when the language is not set, but he can
clarify.

Off the top of my head I guess it helps with demangling symbols. Eg you
can’t demangle symbols from a TU without knowing what the language is.
There could be other reasons though. For example each language is going to
have an ABI with respect to the generated code. This is used for unwinding,
stepping, jitting code to run in the target, etc. all of those could be
affected by the language.

Maybe someone else can chime in with more reasons
On Tue, Aug 21, 2018 at 7:10 PM Vadim Chugunov <vadimcn at gmail.com> wrote:

> Would you mind going into a bit more detail on what sort of problems an
> unknown language could cause?   I'd like to understand the issue before
> jumping in to fix anything.  AFAIK, in the case of DWARF symbols, debug
> info for unknown languages is still used, so it wouldn't be the first for
> LLDB...
>
> Also, the second fragment
> <https://github.com/llvm-mirror/llvm/blob/baa88cf6cb85d4256bb0f806e1b4dc87b29ea98e/lib/DebugInfo/PDB/PDBSymbolCompiland.cpp#L104>
> checks for specific file extensions, which is an unreliable method, IMO,
> since there's more extensions in use for c++ alone.  Code could also be
> generated by a template engine, which will probably use a different
> extension, etc.   I'd rather not just hardcode '.rs' for Rust.
> I was hoping Aaron could commend on why this is necessary (i.e. why not
> just trust the language flag?)
>
> Thanks!
>
> On Mon, Aug 20, 2018 at 7:35 PM Zachary Turner <zturner at google.com> wrote:
>
>> Various parts of lldb require knowing the source language. It’s possible
>> that things will mostly work if you report that the language is c++, but
>> you’ll probably get errors in other areas. It goes all the way down to the
>> CodeView level, where certain cv records indicate the original source
>> language. Can you check cvconst.h (ships with DIA SDK) and look for the
>> enumeration corresponding to source language? Does it have a value for
>> Rust? I’m guessing it doesn’t. When you generate PDBs for Rust you probably
>> need to put something unique value there, then we could properly set the
>> language in lldb
>> On Mon, Aug 20, 2018 at 7:15 PM Vadim Chugunov <vadimcn at gmail.com> wrote:
>>
>>> Hi!
>>> I've been investigating why LLDB refuses to set breakpoints in Rust
>>> source files when using PDB debug info on Windows...  This seems to stem
>>> from a couple of checks here
>>> <https://github.com/llvm-mirror/lldb/blob/f6f930a3608daf81441d3c9051fd9cff84eb6d58/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp#L1509>
>>> and here
>>> <https://github.com/llvm-mirror/llvm/blob/baa88cf6cb85d4256bb0f806e1b4dc87b29ea98e/lib/DebugInfo/PDB/PDBSymbolCompiland.cpp#L104>.
>>>
>>> I am wondering, what is the backstory there?  Are those still
>>> necessary?  I tried disabling them and Rust debugging worked just fine...
>>>
>>>
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