talksik
40 lines
1.9 KiB
Markdown
40 lines
1.9 KiB
Markdown
# Overview
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This repository serves as a complex example of how C++ tooling and cross-compilation works.
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## The challenge
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The variables at play:
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* Protoc used to generate C++ files
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* Compilation of the generated C++ files & other library/source files.
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* Linking the correct protobuf runtime library for the target machine.
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`protoc` from any host machine can generate portable C++ files (.cpp and .h). However, the version of protoc that is used must match the _protobuf runtime library_ that is used.
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For example, the generated header will have something like this:
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```cpp
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#include "google/protobuf/runtime_version.h"
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#if PROTOBUF_VERSION != 5029003
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#error "Protobuf C++ gencode is built with an incompatible version of"
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#error "Protobuf C++ headers/runtime. See"
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#error "https://protobuf.dev/support/cross-version-runtime-guarantee/#cpp"
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#endif
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```
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If we are trying to build an application for arm64 from a x86_64 machine, the protobuf runtime library that we use _must_ be for that target (AND still match the protoc version that we used to generate the C++ files from `.proto`). This is why we use vcpkg.
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See [here](https://claude.ai/share/c6c6394d-b9b4-41b4-9146-265682223174) for in-depth conversation with claude.
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## The solution
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```sh
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./build.sh # build for applications meant only for the host machine
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./cross-compile-for-ios.sh # uses ios/arm64 toolchain to compile all protoc generated C++ as well as other library files. More importantly, it also ensures that it compiles (or pulls from vcpkg cache) the correct protobuf runtime version for arm64.
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```
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Please look into the scripts to see how it all comes together.
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## Troubleshooting
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I had an issue with vcpkg whereby the protobuf was conflicting between host machine one and the target machine one. So I had to add the cmake flag `-DVCPKG_BINARY_SOURCES=clear`.
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See [this issue](https://github.com/microsoft/vcpkg/issues/44517#issuecomment-2816462459) that I posted.
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