openwrt/docs/flint1-sdk-research.md

GL-AX1800 (Flint1) SDK Research and Cross-Compilation Strategy

Date: 2026-01-11
Device: GL-AX1800 (Flint 1)
SoC: Qualcomm IPQ6000 (Quad-core ARM @ 1.2GHz)

Architecture Confirmation (CORRECTED)

Important

Confirmed from actual hardware:

• Flint1 (GL-AX1800): ARMv7 rev 4 (v7l) - 32-bit ARM
• Flint2 (GL-MT6000): ARMv8 rev 4 (v8l) - 64-bit ARM (aarch64)

These are different architectures and require separate binaries.

Architecture Details

GL-AX1800 (Flint1):

• CPU: ARMv7 Processor rev 4 (v7l)
• Instruction set: 32-bit ARM
• Typical target triplet: arm-linux-musleabihf or armv7l-linux-musleabihf

GL-MT6000 (Flint2):

• CPU: ARMv8 Processor rev 4 (v8l)
• Instruction set: 64-bit ARM (aarch64)
• Typical target triplet: aarch64-linux-musl

---

SDK Options for GL-AX1800 (ARMv7)

Option 1: Pre-built musl.cc Toolchain (RECOMMENDED for Quick Start)

Source: https://musl.cc/

Relevant Toolchains

• armv7l-linux-musleabihf-cross.tgz (ARMv7, hard-float)
• arm-linux-musleabihf-cross.tgz (Generic ARM, hard-float)

Download:

wget https://musl.cc/armv7l-linux-musleabihf-cross.tgz
tar -xzf armv7l-linux-musleabihf-cross.tgz
export PATH=$PWD/armv7l-linux-musleabihf-cross/bin:$PATH

Advantages

• Quick setup (download and extract)
• Modern GCC (13.2+) with C++23 support
• Proven for static binary compilation
• Small download (~40-50MB compressed)

Disadvantages

• Not optimized for IPQ6000 specifically
• Generic ARMv7 (not Cortex-A7 specific)

---

Option 2: musl-cross-make (Build Your Own)

Source: https://github.com/richfelker/musl-cross-make

Configuration for ARMv7

TARGET = armv7l-linux-musleabihf
# or: arm-linux-musleabihf
GCC_VER = 14.2.0
MUSL_VER = 1.2.5
LINUX_VER = 6.6.y
GCC_CONFIG += --with-arch=armv7-a --with-fpu=vfpv3-d16 --with-float=hard

Advantages

• Full control over toolchain versions
• Can build latest GCC 14+ for C++23
• Optimize for Cortex-A7 specifically
• Creates musl-based static-friendly toolchain

Disadvantages

• Time-consuming build (30-60 minutes)
• Requires build dependencies
• More complex setup

---

Option 3: GL.iNet SDK (NOT RECOMMENDED)

SDK: ipq807x-2102
GCC: 5.5.0 (Too old)
Architecture: arm_cortex-a7 (32-bit)

Why Not Use This?

• ❌ GCC 5.5.0 cannot compile C++23 (btop)
• ❌ Outdated toolchain from ~2017
• ❌ Build failures documented in agent-notes/glax1800-build-results.md
• ✅ Correct architecture (ARMv7), but toolchain too old

---

Compilation Requirements

btop Requirements

Language: C++23
Minimum GCC: 11 (experimental), 14+ recommended (full support)
Dependencies: None (headers only)
Build System: Make or CMake
Static Linking: Fully supported with musl

Build Strategy

# With OpenWrt SDK
make STATIC=true VERBOSE=true CXX=aarch64-openwrt-linux-musl-g++ \
     CXXFLAGS="-static -std=c++23 -O3" LDFLAGS="-static"

---

mosh Requirements

Language: C++14
Build System: Autotools (./configure)
Dependencies (must be cross-compiled):

• protobuf 3.x (C++ library, requires host protoc)
• ncurses 6.x (terminfo)
• OpenSSL 1.1.x (or omit with --without-crypto)
• zlib (compression)

Build Strategy (Multi-Stage)

1. Build host protoc (x86_64)

   cd protobuf-3.17.3
   ./configure --prefix=/usr/local
   make && sudo make install
   

2. Cross-compile protobuf libraries

   ./configure --host=aarch64-linux-musl --prefix=$PWD/sysroot \
               --with-protoc=/usr/local/bin/protoc \
               CXXFLAGS="-static" LDFLAGS="-static"
   make && make install
   

3. Cross-compile ncurses

   ./configure --host=aarch64-linux-musl --prefix=$PWD/sysroot \
               --without-shared --with-normal --without-debug
   make && make install
   

4. Build mosh (static)

   ./configure --host=aarch64-linux-musl \
               PKG_CONFIG_PATH=$PWD/sysroot/lib/pkgconfig \
               CXXFLAGS="-static" LDFLAGS="-static -pthread" \
               --without-crypto  # Optional: skip OpenSSL
   make
   

Existing Build Environment

The src/mosh/ directory already has:

• env.sh - Cross-compilation environment
• sysroot/ - Custom libraries
• host_protoc/ - Host protobuf compiler
• Built static binaries (for aarch64)

✅ This can likely be reused or adapted!

---

Recommended Approach (CORRECTED)

Phase 1: Toolchain Setup

Use musl.cc pre-built ARMv7 toolchain for fastest results:

cd /home/user/Public/Projects/OpenWRT/sdk/

# Download ARMv7 hard-float toolchain
wget https://musl.cc/armv7l-linux-musleabihf-cross.tgz
tar -xzf armv7l-linux-musleabihf-cross.tgz

# Add to PATH
export PATH=$PWD/armv7l-linux-musleabihf-cross/bin:$PATH

# Verify
armv7l-linux-musleabihf-gcc --version

---

Phase 2: Build btop for ARMv7

cd /home/user/Public/Projects/OpenWRT/src/btop

# Clean previous builds
make clean

# Build static for ARMv7
make STATIC=true \
     CXX=armv7l-linux-musleabihf-g++ \
     CXXFLAGS="-static -std=c++23 -O3 -march=armv7-a -mfpu=vfpv3-d16 -mfloat-abi=hard" \
     LDFLAGS="-static"

# Verify architecture
file bin/btop
# Should show: ELF 32-bit LSB executable, ARM, EABI5

# Copy to flint1 binaries
cp bin/btop /home/user/Public/Projects/OpenWRT/binaries/flint1/btop/

---

Phase 3: Build mosh for ARMv7

Mosh requires cross-compiling dependencies. Two options:

Option A: Adapt Existing Environment

The src/mosh/ directory has a working setup for aarch64. Update it for ARMv7:

cd /home/user/Public/Projects/OpenWRT/src/mosh

# Update environment
export PATH=/path/to/armv7l-linux-musleabihf-cross/bin:$PATH
export CC=armv7l-linux-musleabihf-gcc
export CXX=armv7l-linux-musleabihf-g++
export AR=armv7l-linux-musleabihf-ar
export RANLIB=armv7l-linux-musleabihf-ranlib

# Rebuild protobuf for ARMv7
# (Host protoc already built)

# Configure mosh
./configure --host=armv7l-linux-musleabihf \
            CXXFLAGS="-static" \
            LDFLAGS="-static -pthread" \
            --without-crypto

make clean && make

Option B: Fresh Build

Follow multi-stage process from research document (protobuf → ncurses → mosh).

---

Next Steps

1. ✅ Verify architecture - Confirmed ARMv7 (32-bit ARM) vs ARMv8 (aarch64)
2. ⏭️ Download ARMv7 toolchain - Use musl.cc armv7l-linux-musleabihf
3. ⏭️ Build btop - Static ARMv7 binary with modern GCC
4. ⏭️ Build mosh - Cross-compile dependencies + static linking
5. ⏭️ Create .ipk packages - Package for opkg installation
6. ⏭️ Test on hardware - Verify on actual GL-AX1800