build(docker): add armv7l cross-compilation support

- Add Dockerfile.linux-armv7l for ARMv7l cross-compilation environment
- Create build-linux-armv7l.sh script to automate the build process
- Update .dockerignore to exclude more build artifacts and temporary files
- Extend README.md with ARMv7l build instructions and target details

docker-build/.dockerignore

@@ -1,16 +1,153 @@
+# Version Control
 .git
 .gitignore
-docker-build
+.gitattributes
+
+# Build directories and artifacts
 build
+build-aux/config.guess
+build-aux/config.sub
+build-aux/depcomp
+build-aux/install-sh
+build-aux/ltmain.sh
+build-aux/missing
+build-aux/compile
+build-aux/test-driver
+build-aux/m4/libtool.m4
+build-aux/m4/lt~obsolete.m4
+build-aux/m4/ltoptions.m4
+build-aux/m4/ltsugar.m4
+build-aux/m4/ltversion.m4
 dist*
 out
+releases
+db4/
+linux-coverage-build
+linux-build
+win32-build
+
+# Docker build system (avoid recursion)
+docker-build
+
+# Compiled binaries and libraries
 *.o
 *.a
 *.so
 *.dylib
 *.exe
 *.app
+*.pdb
+*.lo
+*.la
+
+# Build configuration and cache
+config.cache
+config.log
+config.status
+configure
+libtool
+autom4te.cache/
+Makefile
+Makefile.in
+aclocal.m4
+.deps
+.dirstamp
+.libs
+src/config/
+src/obj
+src/univalue/gen
+
+# Qt specific
+src/qt/*.moc
+src/qt/moc_*.cpp
+src/qt/forms/ui_*.h
+src/qt/test/moc*.cpp
+src/qt/palladium-qt.config
+src/qt/palladium-qt.creator
+src/qt/palladium-qt.creator.user
+src/qt/palladium-qt.files
+src/qt/palladium-qt.includes
+*.qm
+qrc_*.cpp
+Palladium-Qt.app
+
+# Test files and coverage
+test/config.ini
+test/cache/
+*.trs
+test_palladium.coverage/
+total.coverage/
+coverage_percent.txt
+*.gcno
+*.gcda
+*.info
+Makefile.test
+palladium-qt_test
+
+# Logs and temporary files
 *.log
+*.tmp
+*.temp
+*.bak
+*.swp
+*.swo
+*.orig
+*.rej
+*.patch
+!depends/patches/**/*.patch
+*.*~*
+*~
+
+# Python
 __pycache__
+*.pyc
+.python-version
+
+# Archives and packages
 *.tar*
 *.zip
+*.gz
+*.dmg
+
+# IDE and editor files
+.vscode/
+.idea/
+*.sublime-*
+.DS_Store
+Thumbs.db
+desktop.ini
+
+# CI/CD and development tools
+.travis.yml
+.appveyor.yml
+.cirrus.yml
+.github/
+ci/
+.tx/
+.style.yapf
+
+# Documentation generation
+doc/doxygen/
+/doc/doxygen/
+
+# macOS specific
+*.background.tiff
+background.tiff*
+osx_volname
+
+# Windows specific build
+build_msvc/
+
+# Clang tools
+*.plist
+
+# Generated files
+*.json.h
+*.raw.h
+*.pb.cc
+*.pb.h
+*.dat
+share/setup.nsi
+share/qt/Info.plist
+libpalladiumconsensus.pc
+contrib/devtools/split-debug.sh

docker-build/Dockerfile.linux-armv7l

@@ -0,0 +1,16 @@
+FROM ubuntu:20.04
+
+ENV DEBIAN_FRONTEND=noninteractive TZ=UTC
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    build-essential libtool autotools-dev automake autoconf pkg-config \
+    bsdmainutils python3 curl ca-certificates git unzip zip file rsync \
+    make cmake patch \
+    g++-arm-linux-gnueabihf binutils-arm-linux-gnueabihf \
+ && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /src
+
+COPY . /src
+
+CMD ["/bin/bash"]

docker-build/README.md

@@ -10,6 +10,13 @@ All builds use:
 - **Host Architecture**: x86_64 (AMD64)
 - **Build Method**: Cross-compilation for target platforms
 
+## Supported Target Architectures
+
+- **Linux x86_64**: Native Linux 64-bit binaries
+- **Linux aarch64**: ARM64 binaries for Raspberry Pi 4+ and modern ARM devices
+- **Linux ARMv7l**: 32-bit ARM binaries for Raspberry Pi 2/3, Pi Zero, and older ARM devices
+- **Windows x86_64**: Windows executables via MinGW-w64 cross-compilation
+
 ## Linux x86_64 Build
 
 ### Overview
@@ -135,6 +142,81 @@ docker run --rm -it -v "$(pwd)/../build/linux-aarch64":/out palladium-builder:li
 
 **Docker build issues:** Ensure Docker has sufficient resources and the daemon is running
 
+## Linux ARMv7l Build
+
+### Overview
+
+This build creates Linux ARMv7l (32-bit ARM) binaries specifically designed for older ARM-based devices and single board computers. The build process uses cross-compilation in a Docker container:
+
+1. **Builds a Docker image** (`palladium-builder:linux-armv7l-ubuntu20.04`) containing ARMv7l cross-compilation toolchain
+2. **Copies the entire repository** into the container during image build
+3. **Cross-compiles for ARMv7l** using the `depends` system with `arm-linux-gnueabihf` target
+4. **Outputs binaries** to a mounted volume for host access
+
+### Quick Start
+
+```bash
+cd docker-build
+chmod +x build-linux-armv7l.sh
+./build-linux-armv7l.sh
+```
+
+ARMv7l binaries will be available in `../build/armv7l/` directory.
+
+### Prerequisites
+
+- Docker installed and running ([installation guide](https://docs.docker.com/get-docker/))
+- Sufficient disk space for the build process (at least 12 GB free)
+- Internet connection for downloading dependencies and ARMv7l cross-compilation toolchain
+
+### Target Devices
+
+This build is optimized for:
+- **Raspberry Pi 2** and **Raspberry Pi 3** (32-bit mode)
+- **Raspberry Pi Zero** and **Zero W**
+- Older ARM-based single board computers (BeagleBone, etc.)
+- ARMv7l Linux embedded devices
+- 32-bit ARM servers and workstations
+
+### Produced Binaries
+
+The following ARMv7l binaries are built and copied to the output directory:
+
+- `palladiumd`: Main daemon
+- `palladium-cli`: Command-line client
+- `palladium-tx`: Transaction utility
+- `palladium-wallet`: Wallet utility
+- `palladium-qt`: GUI application (if Qt dependencies are available)
+
+### Output Directory
+
+Binaries are placed in: `../build/armv7l/` (relative to the docker-build directory)
+
+### Cross-Compilation Details
+
+- **Target Triple**: `arm-linux-gnueabihf`
+- **Toolchain**: GCC ARM cross-compiler with hard-float ABI
+- **Dependencies**: Built using the `depends` system for ARMv7l target
+- **Configuration**: Uses `CONFIG_SITE` for proper cross-compilation setup
+- **ABI**: Hard-float (gnueabihf) for better performance on modern ARM devices
+
+### Troubleshooting
+
+**Permission errors:** The build script automatically handles file permissions using host UID/GID
+
+**Build failed:** Run interactive container for debugging:
+```bash
+docker run --rm -it -v "$(pwd)/../build/armv7l":/out palladium-builder:linux-armv7l-ubuntu20.04 bash
+```
+
+**Cross-compilation issues:** Ensure the ARM cross-compilation toolchain is properly installed in the container
+
+**Missing binaries:** Check that the configure script detected the ARMv7l target correctly
+
+**Docker build issues:** Ensure Docker has sufficient resources and the daemon is running
+
+**Performance considerations:** ARMv7l builds may take longer to execute on target devices compared to ARM64 builds
+
 ## Windows x86_64 Build
 
 ### Overview

docker-build/build-linux-armv7l.sh

@@ -0,0 +1,60 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+IMAGE_NAME="palladium-builder:linux-armv7l-ubuntu20.04"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+REPO_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
+OUT_DIR="${REPO_DIR}/build/armv7l"
+HOST_TRIPLE="arm-linux-gnueabihf"
+
+HOST_UID="$(id -u)"
+HOST_GID="$(id -g)"
+
+echo "[*] Building Docker image including the ENTIRE repository (COPY . /src)..."
+docker build --platform=linux/amd64 \
+  -t "$IMAGE_NAME" \
+  -f "${SCRIPT_DIR}/Dockerfile.linux-armv7l" \
+  "${REPO_DIR}"
+
+mkdir -p "${OUT_DIR}"
+
+echo "[*] Starting container: build COMPLETED in container; mounting ONLY the output..."
+docker run --rm --platform=linux/amd64 \
+  -e HOST_UID="${HOST_UID}" -e HOST_GID="${HOST_GID}" \
+  -v "${OUT_DIR}":/out \
+  "$IMAGE_NAME" \
+  bash -c "
+    set -euo pipefail
+    cd /src
+
+    echo '[*] depends (HOST=${HOST_TRIPLE})...'
+    cd depends && make HOST=${HOST_TRIPLE} -j\$(nproc) && cd ..
+
+    echo '[*] autogen/configure...'
+    [[ -x ./autogen.sh ]] && ./autogen.sh
+    [[ -f ./configure ]] || { echo 'configure not found: autogen failed'; exit 1; }
+
+    ./configure --prefix=\$PWD/depends/${HOST_TRIPLE} \
+                --host=${HOST_TRIPLE} \
+                --enable-glibc-back-compat \
+                --enable-reduce-exports \
+                CC=${HOST_TRIPLE}-gcc CXX=${HOST_TRIPLE}-g++ \
+                AR=${HOST_TRIPLE}-ar RANLIB=${HOST_TRIPLE}-ranlib STRIP=${HOST_TRIPLE}-strip \
+                LDFLAGS='-static-libstdc++'
+
+    echo '[*] make...'
+    make -j\$(nproc)
+
+    echo '[*] copy binaries to /out...'
+    mkdir -p /out
+    for b in src/palladiumd src/palladium-cli src/palladium-tx src/palladium-wallet src/qt/palladium-qt; do
+      [[ -f \"\$b\" ]] && install -m 0755 \"\$b\" /out/
+    done
+
+    # Add permissions to host user
+    chown -R \${HOST_UID:-0}:\${HOST_GID:-0} /out
+
+    echo '[*] build COMPLETED (all binaries in container) → /out'
+  "
+
+echo "[*] ARMv7l binaries available in: ${OUT_DIR}"