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docs(secp256k1): document local build loading and submodule init #123

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36 changes: 36 additions & 0 deletions secp256k1/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,11 @@ git clone --recursive https://github.com/diybitcoinhardware/embit.git

This will automatically pull in the `libsecp256k1-zkp` repo and checkout the correct commit within that repo.

Alternatively, if you already have `embit` cloned, run:
```sh
git submodule update --recursive --init
```


## Building the library
This directory (`secp256k1/` in the `embit` root) already has a fully-configured Makefile to run the compilation for you.
Expand All @@ -22,6 +27,37 @@ On your target platform run:
make
```

This creates a platform-specific shared library under `secp256k1/build/`, for
example:

```sh
secp256k1/build/libsecp256k1_linux_x86_64.so
```

## Loading the local build in Python

`embit` looks for local libsecp256k1 artifacts in
`secp256k1/secp256k1-zkp/.libs/` before falling back to system library paths.
After running `make`, expose the helper Makefile output at that lookup path:

```sh
mkdir -p secp256k1-zkp/.libs
ln -sf ../../build/libsecp256k1_$(uname -s | tr A-Z a-z)_$(uname -m).so \
secp256k1-zkp/.libs/libsecp256k1.so
Comment on lines +45 to +46

@qlrd qlrd May 14, 2026 •
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These files are dynamically generated, right? maybe using find could work too, with less references to .so or .dylib.

Suggested change
ln -sf ../../build/libsecp256k1_$(uname -s | tr A-Z a-z)_$(uname -m).so \
secp256k1-zkp/.libs/libsecp256k1.so
src=$(find build -maxdepth 1 -name 'libsecp256k1_*' -print -quit)
ln -sf "../../$src" "secp256k1-zkp/.libs/libsecp256k1.${src##*.}"

Some output on my mac running this:

 lrwxr-xr-x@ 1 qlrd  staff  43 May 14 XX:XX secp256k1-zkp/.libs/libsecp256k1.dylib -> ../../build/libsecp256k1_darwin_arm64.dylib

```

Run those commands from the `secp256k1/` directory. On macOS, replace the
`.so` suffix with `.dylib`.
Comment on lines +49 to +50

You can verify that Python loaded the native backend from the repository root:

```sh
PYTHONPATH=src python -c "from embit.ec import secp256k1; print(hasattr(secp256k1, 'ecdh'), hasattr(secp256k1, 'rangeproof_rewind'))"
```

Both values should print `True`. If they do, the optional ECDH and Liquid/ZKP
tests can run instead of being skipped.

Install the resulting library into a standard system library location so the dynamic loader can find it (for example `/usr/local/lib` on Unix-like systems), then refresh your linker environment as needed for your platform.

Note: runtime lookup prefers local `secp256k1/secp256k1-zkp/.libs` and system library paths.
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