[cfe-dev] Relocatable modules?

[Andrew Gallagher via cfe-dev]

> You can also diff the output of "llvm-bcanalyzer -dump" to investigate
how modules built on different machines differ.

Ah thanks, this is super useful!

>From the dump, it appears the CWD path is embedded in the
`MODULE_DIRECTORY` and `ORIGINAL_PCH_DIR`.  I'm using a pretty simple repro
with just an empty header and a module.modulemap in the current working dir
and compiling the module via `clang++ -fmodules -x c++-header -Xclang
-emit-module -c -o a.pcm module.modulemap -fmodule-name=a`, so I don't
think I'm passing the absolute paths (but I'm not confident that I'm not
doing something wrong).

Interestingly, if I pass `-Xclang -fmodule-map-file-home-is-cwd``, the
`MODULE_DIRECTORY` field is no longer set -- but then it appears that
headers listed in the module map must be found relative to this location
(as opposed to the module map directory -- which makes sense).

Anywho, thanks for the tips -- it give me a good place to start digging.

Andrew

On Fri, Aug 17, 2018 at 7:19 PM Richard Smith <richard at metafoo.co.uk> wrote:

> On Fri, 17 Aug 2018 at 18:15, Andrew Gallagher via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> I was looking into getting a build system to cache/share module files
>> (i.e. *.pcm files) between different users to speed up builds.  One problem
>> is that it appears clang is embedding absolute paths into the module file,
>> which causes issues when users build from different locations (e.g. their
>> home directories).  From the output of `clang -fmodule-file-info ...` it
>> looks like this absolute path is the location of the various
>> `module.modulemap` files the build uses.  Anyone know of a way to get clang
>> to these absolute path (e.g. using relative paths instead, or something
>> similar to `$ORIGIN`)?
>>
>
> The paths to module.modulemap files found implicitly by clang will be
> based on the -I / -isystem paths that Clang is using: if those paths are
> relative, Clang should use relative paths to the module map files, and if
> those paths are absolute, Clang will use absolute paths to the module map.
> (The paths to module.modulemap files found by explicit -fmodule-map-file=
> arguments should match the form used in said argument.)
>
> You can also diff the output of "llvm-bcanalyzer -dump" to investigate how
> modules built on different machines differ.
>
>
>> Thanks!
>> Andrew
>> _______________________________________________
>> cfe-dev mailing list
>> cfe-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>
>
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