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Re: Meeting on February 4th at 9AM Pacific

From: Tom Honermann <tom_at_[hidden]>
Date: Fri, 4 Feb 2022 13:20:33 -0500
On 2/4/22 1:10 PM, Gabriel Dos Reis wrote:
>
> [Tom]
>
> * Because those module artifacts may be present in multiple such
> artifacts or also be present in a .bmi or .ifc file specified on
> the command line or present in a search path. Which one wins?
>
> I am not sure I understand.
>
> Consider that today, you have libA.a and A.h for a component A.† That
> component gets modularized into a module M, where libA.a now contains
> the BMI for module M.† Where are the multiple artifacts coming from?
>
As I mentioned, a .ifc for module M may be passed on the command line or
be present in a search path (one that might be present in order to find
other module BMIs).

Additionally, if there are transitive dependencies, BMIs for those
transitive dependencies would presumably also be included. If so, they
would likely be present in other libraries as well.

Tom.

> -- Gaby
>
> *From:* Tom Honermann <tom_at_[hidden]>
> *Sent:* Friday, February 4, 2022 9:58 AM
> *To:* sg15_at_[hidden]; Olga Arkhipova <olgaark_at_[hidden]>
> *Cc:* Gabriel Dos Reis <gdr_at_[hidden]>
> *Subject:* Re: [SG15] Meeting on February 4th at 9AM Pacific
>
> On 2/4/22 12:08 PM, Gabriel Dos Reis via SG15 wrote:
>
> [Tom]
>
> 1. I'm struggling with this one though. Modules are needed at
> parse time. Placing them in link-time artifacts seems too late
> in the tooling pipeline; a compiler may not know how to
> extract them from archives or shared objects.
>
> I donít follow.† At install time (or when the modules is built and
> distributed), exactly why putting the needed information in the
> distributed artifact matters where its use it at compile-time?†
> All you need is that the toolset gives you the mean to extract the
> information you need.† For example, GCC already provides some of
> that.† MSVC has always been planned to be doing that too.
>
> My (possibly incorrect) understanding of your statement was that the
> compiler would have the ability to extract module artifacts directly
> from the link-time artifacts. That would create friction with other
> tools by imposing on them a requirement to be able to do such
> extraction themselves, or to use an implementor specific tool to
> extract the information. In either case, that imposes implementation
> specific requirements on such tools. I'd prefer a solution that allows
> tools to perform module artifact discovery without having to be
> customized for every implementation.
>
> 2. It also complicates the search for module artifacts by adding
> more sources;
>
> Why is that an additional source if the information is embedded in
> the needed artifact (.a or .so or whatever)?
>
> Because those module artifacts may be present in multiple such
> artifacts or also be present in a .bmi or .ifc file specified on the
> command line or present in a search path. Which one wins?
>
> Is the .d.json the additional source youíre worried about?
>
> No.
>
> Tom.
>
> -- Gaby
>
> *From:* Tom Honermann <tom_at_[hidden]> <mailto:tom_at_[hidden]>
> *Sent:* Friday, February 4, 2022 9:03 AM
> *To:* sg15_at_[hidden] <mailto:sg15_at_[hidden]>; Olga
> Arkhipova <olgaark_at_[hidden]> <mailto:olgaark_at_[hidden]>
> *Cc:* Gabriel Dos Reis <gdr_at_[hidden]> <mailto:gdr_at_[hidden]>
> *Subject:* Re: [SG15] Meeting on February 4th at 9AM Pacific
>
> On 2/4/22 11:39 AM, Gabriel Dos Reis via SG15 wrote:
>
> We also need to account for scenarios where one single
> container hosts several BMIs (for several modules),
>
> That seems reasonable.
>
>
> or where the BMI is embedded either in the .a or the .so (or
> equivalent) to provide self-describing artifacts less
> disconnected (your header units arenít out-of-sync with the
> object files anymore).† I donít think that does violence to
> the unixy world.
>
> I'm struggling with this one though. Modules are needed at parse
> time. Placing them in link-time artifacts seems too late in the
> tooling pipeline; a compiler may not know how to extract them from
> archives or shared objects. It also complicates the search for
> module artifacts by adding more sources; do you search for
> matching modules by BMIs named on the command line first, then in
> linker artifacts? Or perhaps in the order that they appear on the
> command line? If so, that has implications for '-lmylib' vs
> '-Wl,-lmylib'.
>
> Tom.
>
> -- Gaby
>
> *From:* SG15 <sg15-bounces_at_[hidden]>
> <mailto:sg15-bounces_at_[hidden]> *On Behalf Of *Steve
> Downey via SG15
> *Sent:* Thursday, February 3, 2022 5:44 PM
> *To:* Olga Arkhipova <olgaark_at_[hidden]>
> <mailto:olgaark_at_[hidden]>
> *Cc:* Steve Downey <sdowney_at_[hidden]>
> <mailto:sdowney_at_[hidden]>; ISO C++ Tooling Study Group
> <sg15_at_[hidden]> <mailto:sg15_at_[hidden]>
> *Subject:* Re: [SG15] Meeting on February 4th at 9AM Pacific
>
> On Thu, Feb 3, 2022 at 8:07 PM Olga Arkhipova
> <olgaark_at_[hidden] <mailto:olgaark_at_[hidden]>> wrote:
>
> The compiler will have to find all BMIs so their locations
> should be defined by some command line options.
>
> My point is that the same options can be used to find the
> .d.json files.
>
> Thanks,
>
> Olga
>
> I agree that if the build system can figure out how to do one,
> it can do the other, as long as there is some discernible
> relationship between the bmi and the .d.json file. But in a
> typical unixy environment, libraries and other artifacts to be
> consumed are not separated out. Perhaps, though the bmi and
> .d.json both live together in an isolated filesystem-like
> thing based on the module name? E.g. a directory or zip file,
> or some such. On the other hand, since .d.json is intended to
> be portable, I would expect to find it in something like
> /usr/share/module_${name} in an FHS style system? Or if a
> library provides multiple modules, underneath
> /usr/share/lib${name}/?
>
> Replace /usr with /usr/local/, ~, ${etcetera}, etc above.
>
> (sorry I sent this only to Olga, now replying on list, Olga if
> you reply, either here or add the list back?)
>
>
>
>
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Received on 2022-02-04 18:20:35