Refine hard-coded memory layout for system emulation

During the enhancement of guestOS to run SDL-based applications like
Doom, the Doom artifacts (DOOM1.wad) occupy 4.0MiB, and the default
rootfs.cpio also uses 4.0MiB, totaling 8MiB. When additional
applications are added to rootfs.cpio, the hard-coded 8MiB limit for
rootfs.cpio in map_file becomes insufficient. This commit refines the
hard-coded memory layout variables and makes them configurable during
the build.

The user can now define MEM_SIZE, DTB_SIZE, and INITRD_SIZE in MiB,
while other memory offsets are calculated dynamically based on these
values.

Related: #510

Author: ChinYikMing

Makefile

@@ -30,6 +30,34 @@ $(call set-feature, BLOCK_CHAINING)
 ENABLE_SYSTEM ?= 0
 $(call set-feature, SYSTEM)
 
+# Definition that bridges:
+#   Device Tree(initrd, memory range)
+#   src/io.c(memory init)
+#   src/riscv.c(system emulation layout init)
+ifeq ($(call has, SYSTEM), 1)
+ifeq ($(call has, ELF_LOADER), 0)
+MiB = 1024*1024
+MEM_START ?= 0
+MEM_SIZE ?= 512 # unit in MiB
+DTB_SIZE ?= 1 # unit in MiB
+INITRD_SIZE ?= 8 # unit in MiB
+
+compute_size = $(shell echo "obase=16; ibase=10; $(1)*$(MiB)" | bc)
+REAL_MEM_SIZE = $(call compute_size, $(MEM_SIZE))
+REAL_DTB_SIZE = $(call compute_size, $(DTB_SIZE))
+REAL_INITRD_SIZE = $(call compute_size, $(INITRD_SIZE))
+
+CFLAGS_dt += -DMEM_START=0x$(MEM_START) \
+             -DMEM_END=0x$(shell echo "obase=16; ibase=16; $(MEM_START)+$(REAL_MEM_SIZE)" | bc) \
+             -DINITRD_START=0x$(shell echo "obase=16; ibase=16; \
+                              $(REAL_MEM_SIZE) - $(call compute_size, ($(INITRD_SIZE)+$(DTB_SIZE)))" | bc) \
+             -DINITRD_END=0x$(shell echo "obase=16; ibase=16; \
+                            $(REAL_MEM_SIZE) - $(call compute_size, $(DTB_SIZE)) - 1" | bc)
+
+CFLAGS += -DMEM_SIZE=0x$(REAL_MEM_SIZE) -DDTB_SIZE=0x$(REAL_DTB_SIZE) -DINITRD_SIZE=0x$(REAL_INITRD_SIZE)
+endif
+endif
+
 # Enable link-time optimization (LTO)
 ENABLE_LTO ?= 1
 ifeq ($(call has, LTO), 1)
@@ -149,6 +177,14 @@ LDFLAGS += $(shell pkg-config --libs SDL2_mixer)
 endif
 endif
 
+# If SYSTEM is enabled and ELF_LOADER is not, then skip FULL4G bacause guestOS
+# has dedicated memory mapping range.
+ifeq ($(call has, SYSTEM), 1)
+ifeq ($(call has, ELF_LOADER), 0)
+override ENABLE_FULL4G := 0
+endif
+endif
+
 # Full access to a 4 GiB address space, necessitating more memory mapping
 # during emulator initialization.
 $(call set-feature, FULL4G)

mk/system.mk

@@ -10,7 +10,7 @@ DTC ?= dtc
 BUILD_DTB := $(OUT)/minimal.dtb
 $(BUILD_DTB): $(DEV_SRC)/minimal.dts
 	$(VECHO) " DTC\t$@\n"
-	$(Q)$(DTC) $^ -o $@
+	$(Q)$(CC) -nostdinc -E -P -x assembler-with-cpp -undef $(CFLAGS_dt) $^ | $(DTC) - > $@
 
 BIN_TO_C := $(OUT)/bin2c
 $(BIN_TO_C): tools/bin2c.c

src/devices/minimal.dts

@@ -12,8 +12,8 @@
     chosen {
         bootargs = "earlycon console=ttyS0";
         stdout-path = "serial0";
-        linux,initrd-start = <0x1f700000>; /* @403 MiB (503 * 1024 * 1024)     */
-        linux,initrd-end = <0x1fefffff>;   /* @511 MiB (511 * 1024 * 1024 - 1) */
+        linux,initrd-start = <INITRD_START>;
+        linux,initrd-end = <INITRD_END>;
     };
 
     cpus {
@@ -37,7 +37,7 @@
 
     sram: memory@0 {
         device_type = "memory";
-        reg = <0x00000000 0x20000000>;
+        reg = <MEM_START MEM_END>;
         reg-names = "sram0";
     };
 

src/main.c

@@ -226,12 +226,6 @@ void indirect_rv_halt()
 }
 #endif
 
-#if RV32_HAS(SYSTEM) && !RV32_HAS(ELF_LOADER)
-/* forcely undefine MEM_SIZE to prevent any define in Makefile */
-#undef MEM_SIZE
-#define MEM_SIZE 512 * 1024 * 1024
-#endif
-
 int main(int argc, char **args)
 {
     if (argc == 1 || !parse_args(argc, args)) {

src/riscv.c

@@ -467,15 +467,15 @@ riscv_t *rv_create(riscv_user_t rv_attr)
     char *ram_loc = (char *) attr->mem->mem_base;
     map_file(&ram_loc, attr->data.system.kernel);
 
-    uint32_t dtb_addr = attr->mem->mem_size - (1 * 1024 * 1024);
+    uint32_t dtb_addr = attr->mem->mem_size - DTB_SIZE;
     ram_loc = ((char *) attr->mem->mem_base) + dtb_addr;
     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
      */
     if (attr->data.system.initrd) {
-        uint32_t initrd_addr = dtb_addr - (8 * 1024 * 1024);
+        uint32_t initrd_addr = dtb_addr - INITRD_SIZE;
         ram_loc = ((char *) attr->mem->mem_base) + initrd_addr;
         map_file(&ram_loc, attr->data.system.initrd);
     }