Fetch the initrd address from the DTB blob

The kernel entry has a pointer to the DTB blob as a parameter. From this pointer we can parse the the DTB blob to find the properties "chosen->linux,initrd-start" and "chosen->linux,initrd-start". These properties are guaranteed to have 64-bit addresses which point where the initrd is in memory, which we need to fetch the binaries to be loaded. Signed-off-by: Miquel Sabaté Solà <[email protected]>
mssola · Nov 20, 2024 · fb9627c · fb9627c
1 parent d3afdd9
commit fb9627c
Show file tree

Hide file tree

Showing 14 changed files with 285 additions and 52 deletions.
diff --git a/.gitignore b/.gitignore
@@ -2,8 +2,12 @@
 kernel/fbos.ld
 /fbos
 .cache
+
 usr/bin/*
 usr/initramfs.cpio
 
+test/*.o
+test/test_dt
+
 # You can generate it with Bear: `$ bear -- make`.
 compile_commands.json
diff --git a/Makefile b/Makefile
@@ -17,19 +17,20 @@ endif
 # I did not go too much into the rabbit hole of platform-specific flags. Hence
 # no `-mcpu`, no `-mtune`, no funny business.
 
-CC    = $(CROSS_COMPILE)gcc$(CC_SUFFIX)
-LD    = $(CROSS_COMPILE)ld
+CC     = $(CROSS_COMPILE)gcc$(CC_SUFFIX)
+LD     = $(CROSS_COMPILE)ld
+HOSTCC = gcc
 QEMU ?= qemu-system-riscv64
 
-ISA     ?= rv64imafdc_zicntr_zicsr_zifencei_zihpm_zca_zcd_zba_zbb
-ASFLAGS  = -march=$(ISA) -mabi=lp64d -mcmodel=medany
-CCFLAGS  = $(ASFLAGS) -Iinclude/
-CCFLAGS += -Werror -Wpedantic -Wall -Wextra -Wcast-align -Wcast-qual -Winit-self \
-           -Wmissing-include-dirs -Wredundant-decls -Wshadow -Wsign-conversion \
-           -Wswitch-default -Wundef -Wunreachable-code \
-           -nostdinc -nostdlib -std=gnu17
-LDFLAGS  = -Iinclude/ -static -melf64lriscv -z noexecstack
-USRFLAGS = -static -melf64lriscv
+ISA      ?= rv64imafdc_zicntr_zicsr_zifencei_zihpm_zca_zcd_zba_zbb
+ASFLAGS   = -march=$(ISA) -mabi=lp64d -mcmodel=medany
+CCFLAGS   = $(ASFLAGS) -Iinclude/ -D__KERNEL__ -std=gnu17 -nostdinc -nostdlib
+WARNINGS  = -Werror -Wpedantic -Wall -Wextra -Wcast-align -Wcast-qual -Winit-self \
+            -Wmissing-include-dirs -Wredundant-decls -Wshadow -Wsign-conversion \
+            -Wswitch-default -Wundef -Wunreachable-code
+CCFLAGS  += $(WARNINGS)
+LDFLAGS   = -Iinclude/ -static -melf64lriscv -z noexecstack
+USRFLAGS  = -static -melf64lriscv
 
 ##
 # Optional parameters for QEMU and gdb.
@@ -55,20 +56,21 @@ endif
 ##
 # Paths
 
-SRC    = $(filter-out kernel/fbos.ld.S, $(wildcard kernel/*.S kernel/*.c))
+SRC    = $(filter-out kernel/fbos.ld.S, $(wildcard kernel/*.S kernel/*.c lib/*.c))
 OBJ    = $(patsubst %.c,%.o,$(patsubst %.S,%.o,$(SRC)))
 LINKER = kernel/fbos.ld
 KRNL   = fbos
 USR    = usr/bin/foo
 INIT   = usr/initramfs.cpio
+TESTS  = test/test_dt
 
 LDFLAGS += -T $(LINKER)
 
 ##
 # Kernel
 
 .PHONY: all
-all: clean $(KRNL) usr
+all: clean $(KRNL) usr test
 
 .PHONY: $(KRNL)
 $(KRNL): $(OBJ) $(LINKER).S
@@ -78,12 +80,12 @@ $(KRNL): $(OBJ) $(LINKER).S
 	$(Q) $(LD) $(LDFLAGS) $(OBJ) -o $(KRNL)
 
 .c.o:
-	$(E) "	CC	" $(*F)
-	$(Q) $(CC) $(CCFLAGS) -c $< -o $@
+	$(E) "	CC	" $(basename $@)
+	$(Q) $(CC) $(CCFLAGS) $(KRNLFLAGS) -c $< -o $@
 
 .S.o:
-	$(E) "	CC	" $(*F)
-	$(Q) $(CC) $(CCFLAGS) -D__ASSEMBLY__ -c $< -o $@
+	$(E) "	CC	" $(basename $@)
+	$(Q) $(CC) $(CCFLAGS) -D__ASSEMBLY__ -D__KERNEL__ -c $< -o $@
 
 ##
 # User space
@@ -95,7 +97,7 @@ usr: $(USR)
 
 usr/src/%.o: usr/src/%.S
 	$(E) "	CC	" $(basename $@)
-	$(Q) $(CC) $(ASFLAGS) -D__ASSEMBLY__ -c $< -o $@
+	$(Q) $(CC) $(ASFLAGS) -D__ASSEMBLY__ -D__KERNEL__ -c $< -o $@
 
 usr/bin/%: usr/src/%.o
 	$(Q) mkdir -p usr/bin/
@@ -105,6 +107,24 @@ usr/bin/%: usr/src/%.o
 # HACK: do not remove object files from usr/src/.
 .SECONDARY:
 
+##
+# Tests
+
+.PHONY: test
+test: host_lib $(TESTS)
+	$(Q) ./test/test_dt
+
+host_lib:
+	$(Q) $(HOSTCC) $(WARNINGS) -Iinclude/ -g -c lib/dt.c -o lib/dt.o
+
+test/%.o: test/%.c
+	$(E) "	HOSTCC	" $(basename $@)
+	$(Q) $(HOSTCC) $(WARNINGS) -g -Iinclude/ -c $< -o $@
+
+test/%: test/%.o
+	$(E) "	HOSTLD	" $@
+	$(Q) $(HOSTCC) -Iinclude/ $< lib/dt.o -o $@
+
 ##
 # Hacking
 
@@ -122,7 +142,7 @@ gdb:
 
 .PHONY: clean
 clean:
-	$(Q) rm -f $(OBJ) $(KRNL) $(LINKER) $(USR) usr/src/*.o $(INIT)
+	$(Q) rm -f $(OBJ) $(KRNL) $(LINKER) $(USR) usr/src/*.o $(INIT) test/*.o $(TESTS)
 
 .PHONY: lint
 lint:

diff --git a/include/fbos/compiler.h b/include/fbos/compiler.h
@@ -11,25 +11,35 @@
  * Compiler attributes specific to linker sections.
  */
 
+#ifdef __KERNEL__
 #define __section(s) __attribute__((__section__(s)))
 #define __kernel __section(".kernel.text")
+#else
+#define __kernel
+#endif /* __KERNEL__ */
 
 /*
- * Multiple aliases for 64-bit integers which have their definition on the
+ * Multiple aliases for 32/64-bit integers which have their definition on the
  * standard library.
  */
 
+typedef int int32_t;
 typedef long ssize_t;
+typedef long int64_t;
+
 typedef unsigned long size_t;
+typedef unsigned int uint32_t;
 typedef unsigned long uint64_t;
 typedef unsigned long uintptr_t;
 
 /*
  * NULL
  */
 
+#ifdef __KERNEL__
 #define NULL (void *)0
 #define nullptr NULL
+#endif /* __KERNEL__ */
 
 // Helpful macro when prototyping.
 #define __unused(x) (void)x

diff --git a/include/fbos/dt.h b/include/fbos/dt.h
@@ -3,6 +3,13 @@
 
 #include <fbos/compiler.h>
 
-void parse_dtb(uint64_t *dtb);
+// Pair of addresses where the initrd is located in memory.
+struct initrd_addr {
+	uintptr_t start;
+	uintptr_t end;
+};
+
+// Returns the `initrd` addresses as parsed from the given DTB blob.
+struct initrd_addr find_dt_initrd_addr(uint32_t *dtb);
 
 #endif // __FBOS_DT_H_
diff --git a/include/fbos/init.h b/include/fbos/init.h
@@ -6,6 +6,6 @@
 extern struct task_struct init_task;
 
 // The entry point for the kernel.
-__noreturn __kernel void start_kernel(uintptr_t *dtb);
+__noreturn __kernel void start_kernel(void *dtb);
 
 #endif /* __FBOS_INIT_H */
diff --git a/include/fbos/printk.h b/include/fbos/printk.h
@@ -1,7 +1,24 @@
 #ifndef __FBOS_PRINTK_H_
 #define __FBOS_PRINTK_H_
 
+/*
+ * This file might be pulled from user space tests. Hence, define alternatives
+ * for this functions from glibc.
+ */
+
+#ifdef __KERNEL__
 extern void die(const char *const message);
 extern void printk(const char *const message);
+#else
+#include <stdio.h>
+#include <stdlib.h>
+
+#define die(x)     \
+	do {           \
+		printf(x); \
+		exit(1);   \
+	} while (0)
+#define printk(x) printf(x)
+#endif /* __KERNEL */
 
 #endif // __FBOS_PRINTK_H_
diff --git a/include/fbos/string.h b/include/fbos/string.h
@@ -4,5 +4,6 @@
 #include <fbos/compiler.h>
 
 extern size_t strlen(const char *);
+extern int strcmp(const char *, const char *);
 
 #endif // __FBOS_STRING_H_
diff --git a/kernel/dt.c b/kernel/dt.c
diff --git a/kernel/main.c b/kernel/main.c
@@ -13,13 +13,14 @@ struct task_struct init_task = { .stack = init_stack };
  * function can (and will) assume that everything has been reset and that we can
  * start the whole thing.
  */
-__noreturn __kernel void start_kernel(uintptr_t *dtb)
+__noreturn __kernel void start_kernel(void *dtb)
 {
 	// TODO: disable irqs, etc.
 
 	printk("Welcome to FizzBuzz OS!\n");
 
-	parse_dtb(dtb);
+	struct initrd_addr addr = find_dt_initrd_addr(dtb);
+	__unused(addr); // TODO
 
 	// TODO: reenable stuff
 

diff --git a/kernel/string.S b/kernel/string.S
@@ -0,0 +1,46 @@
+/*
+ * Defined in include/fbos/string.h
+ *
+ *     size_t strlen(const char *str)
+ *
+ * Returns (a0): string length.
+ * Parameter (a0): string to measure.
+ * Clobbers: t0, t1.
+ */
+.globl strlen
+.type strlen, @function
+strlen:
+	mv t1, a0
+1:
+	lbu t0, 0(t1)
+	beqz t0, 2f
+	addi t1, t1, 1
+	j 1b
+2:
+	sub a0, t1, a0
+	ret
+
+/*
+ * Defined in include/fbos/string.h
+ *
+ *     int strcmp(const char *s1, const char *s2)
+ *
+ * Returns (a0): comparison result as in stdlib.
+ * Parameter (a0, a1): strings to compare.
+ * Clobbers: t0, t1.
+ */
+.globl strcmp
+.type strcmp, @function
+strcmp:
+1:
+	lbu t0, 0(a0)
+	lbu	t1, 0(a1)
+	bne	t0, t1, 2f
+	addi a0, a0, 1
+	addi a1, a1, 1
+	bnez t0, 1b
+	li a0, 0
+	ret
+2:
+	sub	a0, t0, t1
+	ret
diff --git a/kernel/strlen.S b/kernel/strlen.S