fix the fPIC issue in library build

Author: gaelforget

lib/build_mitgcm_lib.sh

@@ -132,8 +132,24 @@ if ! grep -q '_BYTESWAPIO' "$BUILD_DIR/Makefile" 2>/dev/null; then
     make depend 2>&1 | tail -3
 fi
 
-echo "  Compiling MITgcm..."
-make -j$(sysctl -n hw.ncpu 2>/dev/null || nproc 2>/dev/null || echo 4) 2>&1 | tail -5
+# For shared library mode, compile everything with -fPIC
+echo "  Compiling MITgcm with -fPIC for shared library..."
+
+# Clean previous builds to force recompilation with new flags
+make clean 2>&1 | tail -2
+make depend 2>&1 | tail -3
+
+# Build with -fPIC appended to all compiler flags
+# Extract existing flags first
+EXISTING_FFLAGS=$(grep '^FFLAGS = ' "$BUILD_DIR/Makefile" | sed 's/^FFLAGS = //' | head -1)
+EXISTING_FOPTIM=$(grep '^FOPTIM = ' "$BUILD_DIR/Makefile" | sed 's/^FOPTIM = //' | head -1)
+EXISTING_CFLAGS=$(grep '^CFLAGS = ' "$BUILD_DIR/Makefile" | sed 's/^CFLAGS = //' | head -1)
+
+make -j$(sysctl -n hw.ncpu 2>/dev/null || nproc 2>/dev/null || echo 4) \
+    FFLAGS="${EXISTING_FFLAGS} -fPIC" \
+    FOPTIM="${EXISTING_FOPTIM} -fPIC" \
+    CFLAGS="${EXISTING_CFLAGS} -fPIC" \
+    2>&1 | tail -5
 
 echo "  MITgcm build complete."
 echo ""
@@ -216,6 +232,15 @@ else
     done
 fi
 
+echo ">> $FC"
+echo ">> $SHLIB_FLAGS"
+echo ">> $OUTPUT_DIR"
+echo ">> $OBJ_FILES"
+echo ">> $SHLIB_NAME"
+echo ">> $LIBS"
+
+#echo "$FC $SHLIB_FLAGS -o $OUTPUT_DIR/$SHLIB_NAME $OBJ_FILES $LIBS"
+
 $FC $SHLIB_FLAGS -o "$OUTPUT_DIR/$SHLIB_NAME" $OBJ_FILES $LIBS
 
 echo "  Created: $OUTPUT_DIR/$SHLIB_NAME"