A cross compilation setup by Claude for loongarch64 to check that things build.

cmake/Toolchains/loongarch64-linux-gnu.cmake

@@ -0,0 +1,40 @@
+set(CMAKE_SYSTEM_NAME Linux)
+set(CMAKE_SYSTEM_PROCESSOR loongarch64)
+
+set(CMAKE_C_COMPILER loongarch64-linux-gnu-gcc-14)
+set(CMAKE_CXX_COMPILER loongarch64-linux-gnu-g++-14)
+set(CMAKE_ASM_COMPILER loongarch64-linux-gnu-gcc-14)
+
+set(CMAKE_FIND_ROOT_PATH /usr/loongarch64-linux-gnu)
+set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
+
+# No X11 in the sysroot; disable the X11 Vulkan path to avoid include-dir errors.
+set(USING_X11_VULKAN OFF CACHE BOOL "" FORCE)
+
+# Bypass find_package(OpenGL REQUIRED).  A stub libGL.so is required so that
+# GLEW's static archive can be linked via PLT entries (direct B26 branches to
+# address 0 would overflow on LoongArch).
+#
+# Primary: run cmake/scripts/setup-loongarch64-cross.sh (sudo) once — it
+#          installs the stub + GL headers into the sysroot.
+# Fallback: the stub can also sit in <build-dir>/stublibs/libGL.so;
+#           b.sh --loongarch64 creates this automatically on first run.
+set(OPENGL_LIBRARIES GL CACHE STRING "" FORCE)
+set(CMAKE_EXE_LINKER_FLAGS
+    "${CMAKE_EXE_LINKER_FLAGS} -L${CMAKE_BINARY_DIR}/stublibs"
+    CACHE STRING "" FORCE)
+
+# Allow CMake's compile-check programs to run via QEMU.
+# The /lib64 symlink is created by the setup script; without it, pass -L
+# explicitly so QEMU can find the loongarch64 dynamic linker.
+if(EXISTS "/lib64/ld-linux-loongarch-lp64d.so.1")
+    set(CMAKE_CROSSCOMPILING_EMULATOR "qemu-loongarch64-static"
+        CACHE STRING "" FORCE)
+else()
+    set(CMAKE_CROSSCOMPILING_EMULATOR
+        "qemu-loongarch64-static;-L;/usr/loongarch64-linux-gnu"
+        CACHE STRING "" FORCE)
+endif()

cmake/scripts/setup-loongarch64-cross.sh

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+#!/bin/bash
+# Sets up the loongarch64 cross-compilation environment.
+# Run once with sudo.  After this, ./b.sh --loongarch64 works on a fresh checkout.
+
+set -e
+
+SYSROOT=/usr/loongarch64-linux-gnu
+CROSS_GCC=loongarch64-linux-gnu-gcc-14
+
+if ! command -v $CROSS_GCC &>/dev/null; then
+    echo "Error: $CROSS_GCC not found. Install it first:"
+    echo "  sudo apt install gcc-14-loongarch64-linux-gnu g++-14-loongarch64-linux-gnu binutils-loongarch64-linux-gnu"
+    exit 1
+fi
+
+if [ "$(id -u)" -ne 0 ]; then
+    echo "This script must be run with sudo."
+    exit 1
+fi
+
+# ── OpenGL headers ───────────────────────────────────────────────────────────
+# GL headers are platform-independent C headers; copy from the host.
+echo "Installing GL headers into sysroot..."
+mkdir -p $SYSROOT/include/GL
+for h in gl.h glext.h glcorearb.h; do
+    [ -f /usr/include/GL/$h ] && cp /usr/include/GL/$h $SYSROOT/include/GL/ && echo "  $h"
+done
+
+# ── GL stub library ──────────────────────────────────────────────────────────
+# Generate a loongarch64 libGL.so that exports all symbols from the host
+# libGL so that GLEW's static archive can be linked via PLT entries (a direct
+# B26 branch to address 0 would overflow on LoongArch).
+echo "Generating libGL.so stub..."
+
+HOST_GL=""
+for candidate in \
+        /usr/lib/x86_64-linux-gnu/libGL.so.1 \
+        /usr/lib/x86_64-linux-gnu/libGL.so \
+        /usr/lib/libGL.so.1 ; do
+    [ -f "$candidate" ] && HOST_GL="$candidate" && break
+done
+
+STUB_C=$(mktemp /tmp/gl_stub_XXXXXX.c)
+echo "/* Loongarch64 GL/GLX stub - for cross-compilation only */" > "$STUB_C"
+echo "void __loongarch64_gl_placeholder(void) {}" >> "$STUB_C"
+
+if [ -n "$HOST_GL" ]; then
+    nm -D "$HOST_GL" 2>/dev/null | awk '/^[0-9a-f]+ T /{ print "void "$3"(void){}" }' >> "$STUB_C"
+    echo "  Extracted symbols from $HOST_GL"
+fi
+# Always include the minimal set GLEW needs (in case host GL wasn't found)
+for sym in glXGetProcAddressARB glXGetClientString glXQueryVersion \
+           glBindTexture glGetString glGetIntegerv glGetError; do
+    grep -q "void ${sym}(" "$STUB_C" || echo "void ${sym}(void){}" >> "$STUB_C"
+done
+
+$CROSS_GCC -shared -fPIC -Wno-implicit-function-declaration \
+    -o $SYSROOT/lib/libGL.so "$STUB_C"
+rm "$STUB_C"
+echo "  Installed to $SYSROOT/lib/libGL.so"
+
+# ── Dynamic linker symlink ───────────────────────────────────────────────────
+# Without this, binfmt_misc can't find the loongarch64 dynamic linker.
+LD_LINUX=$SYSROOT/lib/ld-linux-loongarch-lp64d.so.1
+if [ -f "$LD_LINUX" ]; then
+    mkdir -p /lib64
+    ln -sf "$LD_LINUX" /lib64/ld-linux-loongarch-lp64d.so.1
+    echo "Created /lib64/ld-linux-loongarch-lp64d.so.1 -> $LD_LINUX"
+fi
+
+echo ""
+echo "Setup complete."
+echo "Build:  ./b.sh --loongarch64"
+echo "Run:    qemu-loongarch64-static -L $SYSROOT <binary>"
+echo "  (after setup the /lib64 symlink lets you run loongarch64 binaries directly)"