[cfe-dev] [PATCH] Wrap clang modules inside Mach-O/ELF/COFF containers

[Richard Smith]

On Thu, Dec 11, 2014 at 2:40 PM, Argyrios Kyrtzidis <kyrtzidis at apple.com>
wrote:

> The .pcm file is currently independent of debug info, meaning the compiler
> invocation will be able to use the same .pcm file regardless of whether the
> invocation had enabled debug info or not;


We can't use the same .pcm file for -DNDEBUG vs -UNDEBUG builds. Do we ever
get to reuse a .pcm file like this in practice?

with this change if an invocation had built a module file with debug info
> disabled, it would be inapplicable to the same invocation that had debug
> info enabled and would have to rebuild it; essentially we are tying module
> building with debug info. The module file as the “collection of semantic
> info” is conceptually independent from debug info.
>
> Did you consider having the debug info container being another file (e.g.
> besides the .pcm) that will reference the .pcm file ? This way, instead of
> having to update all users of module files, regardless if they care about
> debug info or not, you’d just make debug info another user of .pcm files,
> no more special than the others.
>
> > On Dec 10, 2014, at 2:27 PM, Adrian Prantl <aprantl at apple.com> wrote:
> >
> > Hi everyone,
> >
> > As the first step in preparation for module debugging (see
> http://lists.cs.uiuc.edu/pipermail/cfe-dev/2014-November/040076.html)
> this patch turns the *.pcm files that are used to store clang modules and
> precompiled headers in a platform-dependent Mach-O/ELF/COFF container, so
> that eventually we will be able to store debug information alongside the
> module in the same file.
> >
> > This is implemented by using the standard LLVM code generation
> machinery. Instead of directly writing to the output file, the serialized
> AST blob is attached to an empty llvm::Module as a ModuleFlag. The module
> is passed to the backend which emits the AST blob into a special
> “__clang_pch" section in TargetLoweringObjectFile*.
> > On the ASTReader side, any object file is transparently unwrapped and
> the BitstreamReader is pointed directly to the AST section.
> >
> > Other than the .pcm files having an extra header inside, this patch is
> not meant to have any user-visible effects.
> >
> > Known bugs: I still need to figure out how to make c-index-test link
> against and register the available targets (check-all passes, but the
> modules created by c-index-test currently are plain old .pcm files).
> > Open questions: I made up the name of the new __clang_pch section and
> the various flags on the different platforms on the spot. I’m open to
> better suggestions.
> >
> > Let me know what you think!
> >
> > -- adrian
> > <clang.diff><llvm.diff>_______________________________________________
> > cfe-dev mailing list
> > cfe-dev at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>
>
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