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faq: adds section about linkers errors when using linkers incompatibl… #163

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Aug 30, 2022
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faq: adds section about linkers errors when using linkers incompatibl… #163

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faq: adds section about linkers errors when using linkers incompatibl…
hbobenicio Aug 29, 2022
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Merge branch 'master' into faq-troubleshooting-lto-linking-error
bmoffatt Aug 29, 2022
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2 changes: 2 additions & 0 deletions README.md
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Expand Up @@ -214,6 +214,8 @@ curl_easy_setopt(curl_handle, CURLOPT_CAINFO, "/etc/pki/tls/certs/ca-bundle.crt"
- You can try hitting the non-TLS version of the endpoint if available. (Not Recommended).
1. **No known conversion between `std::string` and `Aws::String`**
- Either turn off custom memory management in the AWS C++ SDK or build it as a static library (`-DBUILD_SHARED_LIBS=OFF`)
1. **I'm getting wierd linking errors like `/usr/bin/ld: /home/<...>bin/lib/libaws-lambda-runtime.a: error adding symbols: file format not recognized clang: error: linker command failed with exit code 1 (use -v to see invocation)`**
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@marcomagdy marcomagdy Aug 30, 2022 •
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@hbobenicio can you fix this typo wierd -> weird.

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Woops :)
Nice catch!

- By default this project enables _link-time optimization (LTO)_ (configurable with `ENABLE_LTO` _cmake_ option). This tells compilers to delay optimizations until the linking phase. For some compilers (like _clang_) this means that each compilation unit should be compiled down only to intermediate representations (_e.g._ _clang_ uses _LLVM IR_) instead of directly to native object files. As a side-effect, library archives (like _aws-lambda-runtime_) would also contain only _IR_ code. This may result in linker errors like the above if you use a linker incompatible with the _IR_ code generated by your compiler (e.g. _GNU ld_ linker doesn't support _LLVM IR_). In order for the linking step to succeed with _LTO_ you must either use an appropriate linker with something like `-DCMAKE_CXX_FLAGS="-fuse-ld=lld"` (_GNU ld_ for _gcc_ and _lld_ for _clang_ are known to work) or disable _LTO_ (`-DENABLE_LTO=OFF`).
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this means that each compilation unit should be compiled down only to intermediate representations (e.g. clang uses LLVM IR) instead of directly to native object files.

Moreover, I'd rather avoid making such claims on how the linker/compiler works because:

  • I'm not an expert so I really don't know.
  • If that information gets outdated in the future, we don't end up with stale or wrong claims.

I think it's better to suggest turning off LTO and keep it succinct. That's assuming the problem exists, which I'm not yet sure is that case.

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@hbobenicio hbobenicio Aug 30, 2022 •
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Totally agreeded. You're right. I'm gonna try to rephrase that tomorrow. This became too assertive.

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Thank you!
Also, it would be nice if you can provide me with steps on triggering this problem. I can't reproduce it.

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@hbobenicio hbobenicio Sep 3, 2022 •
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Sure. Working on it

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@hbobenicio hbobenicio Sep 3, 2022 •
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Done. The dockerfile is on the issue #151


## License

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