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

[Richard Smith]

On Wed, Dec 10, 2014 at 2:36 PM, David Majnemer <david.majnemer at gmail.com>
wrote:

> Can we use _cfepch instead?  MSVC linker will silently truncate section
> names longer than 8 characters.
>

I don't like "cfe"; we should indicate which compiler is involved here. I
don't like "pch"; this is used for all kinds of AST files, not just PCH
files.

Can we use "ClangAST", or do we need the leading underscore?


> On Wed, 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
>>
>>
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>>
>>
>
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