Customize bootargs for system emulation

.gitignore

@@ -20,6 +20,8 @@ build/linux-x86-softfp/
 build/riscv32/
 build/sail_cSim/
 build/sha1sum-*
+build/bin2c
+build/minimal.dtb
 *.a
 *.o
 *.o.d
@@ -29,3 +31,4 @@ tests/arch-test-target/sail_cSim/riscv_sim_RV32
 tests/scimark2/
 __pycache__/
 src/rv32_jit.c
+src/minimal_dtb.h

.gitmodules

@@ -31,3 +31,7 @@
 	path = tests/quake
 	url = https://github.com/sysprog21/quake-embedded
 	shallow = true
+[submodule "src/dtc"]
+	path = src/dtc
+	url = https://git.kernel.org/pub/scm/utils/dtc/dtc.git
+	shallow = true

LICENSE

@@ -1,4 +1,4 @@
-Copyright (c) 2020-2024 National Cheng Kung University, Taiwan
+Copyright (c) 2020-2025 National Cheng Kung University, Taiwan
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

Makefile

@@ -241,7 +241,7 @@ include mk/artifact.mk
 include mk/wasm.mk
 include mk/system.mk
 
-all: config $(BUILD_DTB) $(BIN)
+all: config $(BUILD_DTB) $(BUILD_DTB2C) $(BIN)
 
 OBJS := \
 	map.o \
@@ -269,6 +269,7 @@ $(OBJS): $(GDBSTUB_LIB)
 endif
 
 $(OUT)/%.o: src/%.c $(deps_emcc)
+	$(Q)mkdir -p $(shell dirname $@)
 	$(VECHO) "  CC\t$@\n"
 	$(Q)$(CC) -o $@ $(CFLAGS) $(CFLAGS_emcc) -c -MMD -MF $@.d $<
 
@@ -369,7 +370,7 @@ endif
 endif
 
 clean:
-	$(RM) $(BIN) $(OBJS) $(DEV_OBJS) $(BUILD_DTB) $(HIST_BIN) $(HIST_OBJS) $(deps) $(WEB_FILES) $(CACHE_OUT) src/rv32_jit.c
+	$(RM) $(BIN) $(OBJS) $(DEV_OBJS) $(BUILD_DTB) $(BUILD_DTB2C) $(HIST_BIN) $(HIST_OBJS) $(deps) $(WEB_FILES) $(CACHE_OUT) src/rv32_jit.c
 distclean: clean
 	-$(RM) $(DOOM_DATA) $(QUAKE_DATA) $(BUILDROOT_DATA) $(LINUX_DATA)
 	$(RM) -r $(OUT)/linux-image

README.md

@@ -77,7 +77,7 @@ $ make ENABLE_SYSTEM=1 system
 Build using run using specified images:
 ```shell
 $ make ENABLE_SYSTEM=1
-$ build/rv32emu -k <kernel_img_path> -i <rootfs_img_path> -b <dtb_path>
+$ build/rv32emu -k <kernel_img_path> -i <rootfs_img_path>
 ```
 
 #### Build Linux image

mk/system.mk

@@ -1,13 +1,24 @@
 # Peripherals for system emulation
 ifeq ($(call has, SYSTEM), 1)
 
+CFLAGS += -Isrc/dtc/libfdt
+LIBFDT_HACK := $(shell git submodule update --init src/dtc)
+
 DEV_SRC := src/devices
 
 DTC ?= dtc
-$(OUT)/minimal.dtb: $(DEV_SRC)/minimal.dts
+BUILD_DTB := $(OUT)/minimal.dtb
+$(BUILD_DTB): $(DEV_SRC)/minimal.dts
 	$(VECHO) " DTC\t$@\n"
 	$(Q)$(DTC) $^ -o $@
-BUILD_DTB := $(OUT)/minimal.dtb
+
+BIN_TO_C := $(OUT)/bin2c
+$(BIN_TO_C): tools/bin2c.c
+	$(Q)$(CC) -Wall -o $@ $^
+
+BUILD_DTB2C := src/minimal_dtb.h
+$(BUILD_DTB2C): $(BIN_TO_C) $(BUILD_DTB)
+	$(BIN_TO_C) $(BUILD_DTB) > $(BUILD_DTB2C)
 
 $(DEV_OUT)/%.o: $(DEV_SRC)/%.c $(deps_emcc)
 	$(Q)mkdir -p $(DEV_OUT)
@@ -17,11 +28,12 @@ DEV_OBJS := $(patsubst $(DEV_SRC)/%.c, $(DEV_OUT)/%.o, $(wildcard $(DEV_SRC)/*.c
 deps := $(DEV_OBJS:%.o=%.o.d)
 
 OBJS_EXT += system.o
+OBJS_EXT += dtc/libfdt/fdt.o dtc/libfdt/fdt_ro.o dtc/libfdt/fdt_rw.o
 
 # system target execution by using default dependencies
 LINUX_IMAGE_DIR := linux-image
-system_action := ($(BIN) -k $(OUT)/$(LINUX_IMAGE_DIR)/Image -i $(OUT)/$(LINUX_IMAGE_DIR)/rootfs.cpio -b $(OUT)/minimal.dtb)
-system_deps += artifact $(BUILD_DTB) $(BIN)
+system_action := ($(BIN) -k $(OUT)/$(LINUX_IMAGE_DIR)/Image -i $(OUT)/$(LINUX_IMAGE_DIR)/rootfs.cpio)
+system_deps += artifact $(BUILD_DTB) $(BUILD_DTB2C) $(BIN)
 system: $(system_deps)
 	$(system_action)
 

src/main.c

@@ -55,7 +55,7 @@ static char *prof_out_file;
 /* Linux kernel data */
 static char *opt_kernel_img;
 static char *opt_rootfs_img;
-static char *opt_dtb;
+static char *opt_bootargs;
 #endif
 
 static void print_usage(const char *filename)
@@ -73,7 +73,7 @@ static void print_usage(const char *filename)
 #if RV32_HAS(SYSTEM) && !RV32_HAS(ELF_LOADER)
             "  -k <image> : use <image> as kernel image\n"
             "  -i <image> : use <image> as rootfs\n"
-            "  -b <dtb> : use <dtb> as device tree blob\n"
+            "  -b <bootargs> : use customized <bootargs> for the kernel\n"
 #endif
             "  -d [filename]: dump registers as JSON to the "
             "given file or `-` (STDOUT)\n"
@@ -115,7 +115,7 @@ static bool parse_args(int argc, char **args)
             emu_argc++;
             break;
         case 'b':
-            opt_dtb = optarg;
+            opt_bootargs = optarg;
             emu_argc++;
             break;
 #endif
@@ -263,7 +263,7 @@ int main(int argc, char **args)
 #if RV32_HAS(SYSTEM) && !RV32_HAS(ELF_LOADER)
     attr.data.system.kernel = opt_kernel_img;
     attr.data.system.initrd = opt_rootfs_img;
-    attr.data.system.dtb = opt_dtb;
+    attr.data.system.bootargs = opt_bootargs;
 #else
     attr.data.user.elf_program = opt_prog_name;
 #endif

src/riscv.c

@@ -14,6 +14,7 @@
 
 #if RV32_HAS(SYSTEM) && !RV32_HAS(ELF_LOADER)
 #include <termios.h>
+#include "dtc/libfdt/libfdt.h"
 #endif
 
 #if !defined(_WIN32) && !defined(_WIN64)
@@ -259,6 +260,64 @@ static void map_file(char **ram_loc, const char *name)
     exit(EXIT_FAILURE);
 }
 
+#define ALIGN_FDT(x) (((x) + (FDT_TAGSIZE) - 1) & ~((FDT_TAGSIZE) - 1))
+static char *realloc_property(char *fdt,
+                              int nodeoffset,
+                              const char *name,
+                              int newlen)
+{
+    int delta = 0;
+    int oldlen = 0;
+
+    if (!fdt_get_property(fdt, nodeoffset, name, &oldlen))
+        /* strings + property header */
+        delta = sizeof(struct fdt_property) + strlen(name) + 1;
+
+    if (newlen > oldlen)
+        /* actual value in off_struct */
+        delta += ALIGN_FDT(newlen) - ALIGN_FDT(oldlen);
+
+    int new_sz = fdt_totalsize(fdt) + delta;
+    /* Assume the pre-allocated RAM is enough here, so we
+     * don't realloc any memory for fdt */
+    fdt_open_into(fdt, fdt, new_sz);
+    return fdt;
+}
+
+static void load_dtb(char **ram_loc, char *bootargs)
+{
+#include "minimal_dtb.h"
+    char *blob = *ram_loc;
+    char *buf;
+    size_t len;
+    int node, err;
+    int totalsize;
+
+    memcpy(blob, minimal, sizeof(minimal));
+
+    if (bootargs) {
+        node = fdt_path_offset(blob, "/chosen");
+        assert(node > 0);
+
+        len = strlen(bootargs) + 1;
+        buf = malloc(len);
+        assert(buf);
+        memcpy(buf, bootargs, len - 1);
+        buf[len] = 0;
+        err = fdt_setprop(blob, node, "bootargs", buf, len + 1);
+        if (err == -FDT_ERR_NOSPACE) {
+            blob = realloc_property(blob, node, "bootargs", len);
+            err = fdt_setprop(blob, node, "bootargs", buf, len);
+        }
+        free(buf);
+        assert(!err);
+    }
+
+    totalsize = fdt_totalsize(blob);
+    *ram_loc += totalsize;
+    return;
+}
+
 /*
  * The control mode flag for keyboard.
  *
@@ -294,6 +353,7 @@ static void capture_keyboard_input()
     term.c_lflag &= ~TERMIOS_C_CFLAG;
     tcsetattr(0, TCSANOW, &term);
 }
+
 #endif
 
 /*
@@ -409,7 +469,7 @@ riscv_t *rv_create(riscv_user_t rv_attr)
 
     uint32_t dtb_addr = attr->mem->mem_size - (1 * 1024 * 1024);
     ram_loc = ((char *) attr->mem->mem_base) + dtb_addr;
-    map_file(&ram_loc, attr->data.system.dtb);
+    load_dtb(&ram_loc, attr->data.system.bootargs);
     /*
      * Load optional initrd image at last 8 MiB before the dtb region to
      * prevent kernel from overwritting it
@@ -517,8 +577,7 @@ void rv_run(riscv_t *rv)
     vm_attr_t *attr = PRIV(rv);
     assert(attr &&
 #if RV32_HAS(SYSTEM) && !RV32_HAS(ELF_LOADER)
-           attr->data.system.kernel && attr->data.system.initrd &&
-           attr->data.system.dtb
+           attr->data.system.kernel && attr->data.system.initrd
 #else
            attr->data.user.elf_program
 #endif

src/riscv.h

@@ -551,7 +551,7 @@ typedef struct {
 typedef struct {
     char *kernel;
     char *initrd;
-    char *dtb;
+    char *bootargs;
 } vm_system_t;
 #endif /* RV32_HAS(SYSTEM) */