[cfe-dev] [llvm-dev] [RFC] Open sourcing and contributing TAPI back to the LLVM community

John Ericson via cfe-dev cfe-dev at lists.llvm.org
Tue Apr 10 14:39:44 PDT 2018

Seems like there are a few of us interested in this then. I new around 
here and don't really know how decisions are made, so what's next? Just 
open a diff with the entire library??


On 04/10/2018 05:33 PM, Jake Ehrlich wrote:
> Benifits of TBD:
> 1) It's human readable and diffs on TBDs correspond to changes in the 
> ABI. Diffs can be automatically added to review processes to ensure 
> that changes to the ABI are reviewed. The TBDs also document your 
> precise ABI.
> 2) The size is smaller which means they can be shipped in an SDK 
> instead of binaries to reduce the size of an SDK
> 3) Stubs are producible from TBDs (or should be) which means stubs for 
> linking can be produced even if we don't directly support them in LLD. 
> This lets you ship the smaller TBD files in place of larger binaries 
> and still link things without direct linker support (assuming you 
> already ship a toolchain with your SDK or expect your users to have 
> this tool)
> Since stubs are producible from TBDs I don't really see a downside. I 
> think we need both, I was going to propose a yaml based representation 
> for ELF for the above reasons anyhow.
> On Tue, Apr 10, 2018 at 1:14 PM Andrew Kelley via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>     On Mon, Apr 9, 2018 at 10:11 PM, John Ericson via llvm-dev
>     <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>         > Regardless of any of that, given that TBD files _are_ an integral part
>         of the apple platform, supporting them is certainly a
>         necessity in order to have a working apple linker. So, if
>         making LLD work for Apple/MachO is the justification for
>         adding TBD support to LLVM, that seems self-evidently a
>         reasonable thing to do. On the other hand, it looks like the
>         LLD mach-o code is unmaintained and nobody seems to be much
>         interested in it. And having code for reading TBD files in
>         LLVM seems not terribly interesting, unless it is as part of a
>         project to make the LLD MachO linker actually functional and
>         supported.
>         Yes. I hope this can be reason enough. Hobbyists could push
>         for LLD support for Mach-O besides Apple, and if LLD is to
>         displace other linkers this is a necessary component as you
>         say. Better to upstream now before the code diverges than more
>         work later? Conversely if nothing happens, I doubt libtapi
>         would be a greater drag on the codebase than the MachO LLD
>         code, so whatever cost/benefit analysis exists for keeping
>         that around could also apply to this.
>     Speaking for the Zig project here, our goal is to support
>     cross-compilation for any target, on any target, without requiring
>     installation of any target-specific SDK. So, for example, these
>     use cases:
>      * on linux, compile & link a binary targeting macos
>      * on windows, compile & link a binary targeting macos
>     This works today, although it depends on a patch to LLD to fix the
>     MACH-O linker that is not high enough quality to upstream.
>     So we have a vested interest in improving the MACH-O linker, and
>     in fact a Zig community member has fixed at least one bug in
>     MACH-O LLD: reviews.llvm.org/D35387 <http://reviews.llvm.org/D35387>
>     I don't fully understand how TBD or TAPI works, but I hope that it
>     results in improvements to the MACH-O linker.
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