build: default CROSS=riscv64-elf + document toolchain variants in README

Makefile

@@ -1,4 +1,15 @@
-CROSS ?= riscv64-unknown-elf
+# Default cross-compiler prefix. We prefer `riscv64-elf-` because that's
+# what the mainstream bare-metal toolchain (xpack-riscv-none-elf-gcc,
+# riscv-collaborations/riscv-gnu-toolchain) installs on most distros.
+#
+# If you have the `riscv64-unknown-elf-` variant instead (Debian's
+# `gcc-riscv64-unknown-elf` package), override with:
+#   make CROSS=riscv64-unknown-elf
+#
+# If you have the Linux-targeted `riscv64-linux-gnu-` (Arch's
+# `riscv64-linux-gnu-gcc`), bare-metal OnyxBoot won't link correctly —
+# install a bare-metal variant instead.
+CROSS ?= riscv64-elf
 CC = $(CROSS)-gcc
 OBJCOPY = $(CROSS)-objcopy
 
@@ -16,18 +27,18 @@ SRCS = src/boot_entry.c src/boot_main.c src/string.c fs/fat.c fs/ext4.c
 all: bootloader.bin
 
 bootloader.elf: $(SRCS)
-	$(CC) $(CFLAGS) $^ $(LDFLAGS) -o $@
+        $(CC) $(CFLAGS) $^ $(LDFLAGS) -o $@
 
 bootloader.bin: bootloader.elf
-	$(OBJCOPY) -O binary $< $@
+        $(OBJCOPY) -O binary $< $@
 
 clean:
-	rm -f bootloader.elf bootloader.bin
+        rm -f bootloader.elf bootloader.bin
 
 test:
-	./test/run_qemu.sh
+        ./test/run_qemu.sh
 
 test-all:
-	./test/test_all.sh
+        ./test/test_all.sh
 
 .PHONY: all clean test test-all

README.md

@@ -48,7 +48,7 @@ First-stage loader for [OnyxOS](https://github.com/anomalyco/OnyxOS).
 ## Quick start
 
 ```console
-$ make CROSS=riscv64-elf
+$ make                                          # default: CROSS=riscv64-elf
 $ qemu-system-riscv64 -M virt -m 256M -bios bootloader.bin \
     -drive file=disk.img,format=raw,if=none,id=drive0 \
     -device virtio-blk-device,drive=drive0 \
@@ -67,17 +67,22 @@ $ bash test/run_qemu.sh
 
 | Tool | Purpose |
 |------|---------|
-| `riscv64-elf-g++` or `riscv64-unknown-elf-g++` | Cross-compiler |
+| `riscv64-elf-g++` (preferred) or `riscv64-unknown-elf-g++` | Cross-compiler |
 | `riscv64-elf-objcopy` | Binary extraction |
 | `make` | Build |
 | `qemu-system-riscv64` | Test (optional) |
 
-Override toolchain:
+Override toolchain (if you have the `riscv64-unknown-elf-` variant):
 
 ```console
 make CROSS=riscv64-unknown-elf
 ```
 
+The Makefile's default is `CROSS ?= riscv64-elf` — this matches the
+mainstream bare-metal toolchain (xpack-riscv-none-elf-gcc, RISC-V
+collaborations/riscv-gnu-toolchain). If you have Debian's
+`gcc-riscv64-unknown-elf` package instead, override as shown above.
+
 ----
 
 ## How it works

README.ru.md

@@ -22,7 +22,7 @@ OnyxBoot - крошечный bare-metal загрузчик для RISC-V 64-bit
 ## Быстрый старт
 
 ```console
-$ make CROSS=riscv64-elf
+$ make                                          # по умолчанию CROSS=riscv64-elf
 $ qemu-system-riscv64 -M virt -m 256M -bios bootloader.bin \
     -drive file=disk.img,format=raw,if=none,id=drive0 \
     -device virtio-blk-device,drive=drive0 \
@@ -41,17 +41,22 @@ $ bash test/run_qemu.sh
 
 | Инструмент | Назначение |
 |-----------|-----------|
-| `riscv64-elf-g++` или `riscv64-unknown-elf-g++` | Кросс-компилятор |
+| `riscv64-elf-g++` (предпочтительно) или `riscv64-unknown-elf-g++` | Кросс-компилятор |
 | `riscv64-elf-objcopy` | Извлечение бинарника |
 | `make` | Сборка |
 | `qemu-system-riscv64` | Тестирование (опционально) |
 
-Сменить тулчейн:
+Сменить тулчейн (если у вас вариант `riscv64-unknown-elf-`):
 
 ```console
 make CROSS=riscv64-unknown-elf
 ```
 
+В Makefile по умолчанию `CROSS ?= riscv64-elf` — это соответствует
+основному bare-metal тулчейну (xpack-riscv-none-elf-gcc, RISC-V
+collaborations/riscv-gnu-toolchain). Если у вас установлен Debian-пакет
+`gcc-riscv64-unknown-elf`, переопределите как показано выше.
+
 ----
 
 ## Как это работает