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   mcc (mcc@mastodon.social)'s status on Sunday, 12-Jan-2025 10:01:59 JST mcc

   Say I'm talking to someone who believes the clang libunwind and gcc libunwind are API incompatible.

   I'm fairly certain this is incorrect. But I can't *prove* it.

   The GCC libunwind docs are here. It lists all these unw_ functions. https://www.nongnu.org/libunwind/docs.html

   The clang libunwind docs are here https://bcain-llvm.readthedocs.io/projects/libunwind/en/latest/ and they are… build instructions. Nothing else. It describes itself as implementing "the HP libunwind interface". Google doesn't find such a thing and I don't think HP-UX is supported.

   • Embed this notice
     mcc (mcc@mastodon.social)'s status on Sunday, 12-Jan-2025 10:01:57 JST mcc

     in reply to

     • ✧✦Catherine✦✧

     Okay. I've talked to some people and some things have been explained to me. I now understand the origin of the linker error.

     First, let me clarify something: it was incorrect or imprecise to refer to "gcc libunwind" in the top post. I think it is probably clearest to refer to this library (Debian "libunwind-dev", with no numbers) as "Savannah libunwind". According to @whitequark, this *is* "HP Libunwind" (through some former open source release, I guess?)

     GreenSkyOverMe (Monika) repeated this.
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     mcc (mcc@mastodon.social)'s status on Sunday, 12-Jan-2025 10:01:57 JST mcc

     in reply to

     So, with that out of the way, the answers to my top of thread questions:

     - Savannah/HP libunwind and Clang/LLVM libunwind are C/C++ source compatible. The developer-facing function interfaces are the same.

     - However, the *set of exported symbols in the libraries* are totally different. C/C++ source compatibility is only possible because both(?) libraries implement the functions as macros.

     - Therefore, if you access these libraries from a non C language like Rust, they're fully incompatible.

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     mcc (mcc@mastodon.social)'s status on Sunday, 12-Jan-2025 10:01:58 JST mcc

     in reply to

     Googling about the hp libunwind, it sounds like it's a series of unw_ functions. Which sounds like the GCC libunwind interface. But that is vibes; if someone *believes* the two are API incompatible, *what could I tell them to convince them otherwise*?

     Also, is it weird that llvm libunwind seems to literally has no usage documentation at all? Did I miss something? Is Google simply cooked?

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     mcc (mcc@mastodon.social)'s status on Sunday, 12-Jan-2025 10:01:58 JST mcc

     in reply to

     Update: Building Rust on a local computer against llvm libunwind I get these linker errors which makes me think maybe it's not api compatible

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     mcc (mcc@mastodon.social)'s status on Sunday, 12-Jan-2025 10:01:58 JST mcc

     in reply to

     I lose https://mastodon.social/@mcc/113807871925781727

     This is the limit of my ability to debug. I cannot work out why an undocumented function, whose name begins with an underscore, from library A is not being provided by a library B which has no documentation at all, when building someone else's code that I do not know the purpose of. I lose! I thought I could just keep powering through build errors but no.

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     mcc (mcc@mastodon.social)'s status on Sunday, 12-Jan-2025 10:01:58 JST mcc

     in reply to

     Now I get to uninstall the libc++ from my computer completely and replace it with a different one. Because it's the only remaining way to fix this linker error.

     This post has been edited.

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     ✧✦Catherine✦✧ (whitequark@mastodon.social)'s status on Sunday, 12-Jan-2025 12:04:26 JST ✧✦Catherine✦✧

     in reply to

     @mcc llvm libunwind is essentially an internal component of the platform runtime. it is documented in the Itanium (EH)ABI.

     the other libunwind you're dealing with is some other thing with the same name that's unrelated except for its purpose

     libgcc_s and llvm libunwind implement the same interface and are mutually exclusive; the other libunwind could be used together with each

     does this clarify

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     argv minus one (argv_minus_one@mastodon.sdf.org)'s status on Sunday, 12-Jan-2025 12:04:26 JST argv minus one

     in reply to

     • ✧✦Catherine✦✧

     @whitequark @mcc

     #Intel : goes through hell to design an entirely new instruction set architecture and calls it #Itanium

     Everyone: “We'll just take the #C++ #ABI, thanks. We're going with #AMD for everything else. Toodles.”