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Add a note about unintended _main symbol generation. #160

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merged 2 commits into from
Jul 3, 2025
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Add a note about unintended _main symbol generation. #160

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ba1c7ee
Add a note about unintended _main symbol generation.
andre-richter Jun 25, 2025
c86e8c8
Differentiate between main symbols by target
andre-richter Jul 2, 2025
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2 changes: 2 additions & 0 deletions Sources/EmbeddedSwift/Documentation.docc/UsingEmbeddedSwift/Basics.md
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Expand Up @@ -52,6 +52,8 @@ $ swiftc -target armv7-none-none-eabi -enable-experimental-feature Embedded -wmo
input1.swift input2.swift ... -c -o output.o
```

> Note: Passing only a single `.swift` file to swiftc results in the generation of a `_main` (Mach-O targets) or `main` (ELF) symbol. During linking, this symbol could potentially clash with other objects that also define one. To avoid this, compile multiple Swift files together or use the `-parse-as-library` flag.

Additionally, you probably want to specify additional Clang and/or LLVM flags to get the compiler to produce code for the exact ISA and ABI you need for your target.

For example, a Raspberry Pi Pico / Pico W should target the ARMv6-M architecture via the `armv6m-*` target triple, but the `-mfloat-abi=soft` Clang option should also be used, and if you want to match ABI with libraries built with the GNU toolchain, you might also need `-fshort-enums`. To pass those to Swift, use the `-Xcc` prefix:
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