Merge pull request #258 from cksystemsteaching/machine

ckirsch · web-flow · commit 8e6553f0ad5f · 2021-02-19T19:14:30.000+01:00
Add Bachelor's Thesis "RISC-V Bare-Metal Library Operating System for Selfie"
diff --git a/machine/Makefile b/machine/Makefile
@@ -2,15 +2,14 @@ HOSTCC:=$(CC)
 
 PREFIX=riscv64-linux-gnu-
 CC=$(PREFIX)gcc
-LD=$(PREFIX)ld
 AS=$(CC)
 OBJCOPY=$(PREFIX)objcopy
 QEMU=qemu-system-riscv64
 
 # Our ABI, architecture and memory model must match with OpenSBI
-CFLAGS=-g3 -mabi=lp64 -march=rv64imafdc -mcmodel=medany -ffreestanding -nostdlib -Iinclude -Iopensbi/include -Wl,--build-id=none -Wall -Wextra -MMD -MP
+CFLAGS=-mabi=lp64d -march=rv64imafdc -mcmodel=medany -ffreestanding -Iinclude -Wall -Wextra -MMD -MP -O3
 ASFLAGS=$(CFLAGS)
-LDFLAGS=-r -b elf64-littleriscv -m elf64lriscv
+LDFLAGS=-nostdlib -lgcc -Wl,--build-id=none
 QEMUFLAGS=-M virt -m 128M -nographic -bios none
 # for debugging, add '-gdb tcp::9000 -S' to the QEMUFLAGS
 
@@ -22,7 +21,7 @@ OPENSBI_RELEASE=v0.7
 OPENSBI_VERSION_FILE=opensbi/opensbi_version
 
 SBI_WRAPPER_SRCS_COMMON = bootstrap.c tinycstd.c console.c filesystem.c files_package.c syscalls.c asm/crt.S diag.c sbi_ecall.c
-SBI_WRAPPER_SRCS_LIBRARY = bootstrap_library.c selfie.c glue_libraryos.c
+SBI_WRAPPER_SRCS_LIBRARY = bootstrap_library.c selfie.c glue_libraryos.c asm/mem.S
 SBI_WRAPPER_SRCS_KERNEL =  bootstrap_kernel.c mmu.c context.c trap.c elf.c asm/trap.S
 
 SBI_WRAPPER_FILES_PACKAGE = $(SELFIE_PATH)/selfie.m $(SELFIE_PATH)/selfie.c $(SELFIE_PATH)/examples/hello-world.c $(SELFIE_PATH)/hello-world.m
@@ -51,7 +50,7 @@ $(eval $(call add-all-target-aliases))
 all: all-selfie-elf all-selfie-opensbi-elf
 
 include/asm_offsets.h: $(ASM_STRUCT_HEADERS)
-	$(HOSTCC) -I. tools/asm_struct_macro_generator.c -o tools/asm_struct_macro_generator
+	$(HOSTCC) -Iinclude tools/asm_struct_macro_generator.c -o tools/asm_struct_macro_generator
 	tools/asm_struct_macro_generator > "$@"
 
 
@@ -87,7 +86,7 @@ opensbi:
 
 .PHONY: debug
 debug:
-	$(eval CFLAGS += -DDEBUG)
+	$(eval CFLAGS += -O0 -g3 -DDEBUG)
 	@echo "Enabled debug macro"
 
 
diff --git a/machine/asm/crt.S b/machine/asm/crt.S
@@ -12,7 +12,7 @@
 .text
 
   .section .entry, "ax", %progbits
-  .p2align 3
+  .p2align 2
   .global _start
 _start:
   /* Set up the Global Pointer */
@@ -37,7 +37,7 @@ _start_warm:
   csrw sip, zero
 
   /* Setup exception vectors */
-  la a3, _start_hang
+  la a3, hang_machine
   csrw stvec, a3
 
   /* Setup stack */
@@ -48,14 +48,14 @@ _start_warm:
   call bootstrap
 
   /* We don't expect to reach here hence just hang */
-  j _start_hang
+  j hang_machine
 
   .section .entry, "ax", %progbits
-  .p2align 3
-  .global _start_hang
-_start_hang:
+  .p2align 2
+  .global hang_machine
+hang_machine:
   wfi
-  j _start_hang
+  j hang_machine
 
   .global initial_stack_start
 initial_stack_start:
diff --git a/machine/asm/mem.S b/machine/asm/mem.S
@@ -0,0 +1,67 @@
+// a0: address
+// a1: size, in bytes
+.global zero_mem
+zero_mem:
+    // Check whether we are 8 byte aligned
+    addi t0, zero, 8
+    remu t1, a0, t0
+    beqz t1, after_align_addr
+
+    // Align if we are not
+    sub t1, t0, t1
+align_addr:
+    beqz t1, after_align_addr
+    sb zero, 0(a0)
+    addi a0, a0, 1
+    addi a1, a1, -1
+    addi t1, t1, -1
+    j align_addr
+    
+
+after_align_addr:
+
+    // Now that the address is 8 byte aligned, do the actual zeroing
+    // using decreasing granularity: sd(8) -> sw(4) -> sh(2) -> sb(1)
+    addi t0, zero, 8
+
+zero_sd_loop:
+    beqz a1, zero_done
+    blt a1, t0, zero_sw
+    sd zero, 0(a0)
+    add a0, a0, t0
+    sub a1, a1, t0
+    j zero_sd_loop
+
+zero_sw:
+    addi t0, zero, 4
+zero_sw_loop:
+    beqz a1, zero_done
+    blt a1, t0, zero_sh
+    sw zero, 0(a0)
+    add a0, a0, t0
+    sub a1, a1, t0
+    j zero_sw_loop
+
+zero_sh:
+    addi t0, zero, 2
+zero_sh_loop:
+    beqz a1, zero_done
+    blt a1, t0, zero_sb
+    sh zero, 0(a0)
+    add a0, a0, t0
+    sub a1, a1, t0
+    j zero_sh_loop
+
+zero_sb:
+    addi t0, zero, 1
+zero_sb_loop:
+    blt a1, t0, zero_done
+    sb zero, 0(a0)
+    add a0, a0, t0
+    sub a1, a1, t0
+    j zero_sb_loop
+
+zero_done:
+    ret
+
+
diff --git a/machine/bootstrap.c b/machine/bootstrap.c
@@ -1,6 +1,7 @@
 #include "bootstrap.h"
 #include "config.h"
 #include "console.h"
+#include "diag.h"
 #include "tinycstd.h"
 
 int main(int argc, char** argv);
@@ -36,5 +37,8 @@ void bootstrap() {
   }
   printf("    <END>\n\n");
 
-  start_init_process(argc, args);
+  uint64_t result = start_init_process(argc, args);
+
+  printf("\nInit process terminated with exit code %d\n", result);
+  shutdown();
 }
diff --git a/machine/defines.mk b/machine/defines.mk
@@ -44,7 +44,6 @@ endef
 define add-target
 $(call generate-target-vars,$(1),$(2))
 $(call generate-target-obj-rules,$(1),$(2))
-$(call generate-target-combine-rule,$(1),$(2))
 $(call generate-target-elf-bin,$(1),$(2))
 $(call generate-target-sbi-elf,$(1),$(2))
 endef
@@ -127,19 +126,6 @@ $$(TARGET_$(1)_$(2)_DIR)/selfie.o: $$(SELFIE_PATH)/selfie.c
 
 endef
 
-###############################################################################
-# $(call generate-target-combine-rule,board,profile)
-#
-# - board         : The board
-# - profile       : The build profile
-#
-define generate-target-combine-rule
-
-$$(TARGET_$(1)_$(2)_DIR)/selfie_bare_metal.o: $$(TARGET_$(1)_$(2)_OBJS)
-	$$(LD) $$(LDFLAGS) $$^ -o $$@
-
-endef
-
 ###############################################################################
 # $(call generate-target-elf-bin,board,profile)
 #
@@ -152,8 +138,8 @@ $$(TARGET_$(1)_$(2)_DIR)/selfie.ld:
 	SBI_START=$$(BOARD_$(1)_PAYLOAD_START) PAYLOAD_OFFSET=$$(BOARD_$(1)_PAYLOAD_OFFSET) envsubst '$$$$SBI_START$$$$PAYLOAD_OFFSET' <payload_template.ld >$$@
 
 
-$$(TARGET_$(1)_$(2)_DIR)/selfie.elf: $$(TARGET_$(1)_$(2)_DIR)/selfie_bare_metal.o | $$(TARGET_$(1)_$(2)_DIR)/selfie.ld
-	$$(CC) $$(CFLAGS) -static-libgcc -lgcc $$^ -o $$@ -T $$(TARGET_$(1)_$(2)_DIR)/selfie.ld
+$$(TARGET_$(1)_$(2)_DIR)/selfie.elf: $$(TARGET_$(1)_$(2)_OBJS) | $$(TARGET_$(1)_$(2)_DIR)/selfie.ld
+	$$(CC) $$(CFLAGS) $$(LDFLAGS) $$^ -o $$@ -T $$(TARGET_$(1)_$(2)_DIR)/selfie.ld
 
 $$(TARGET_$(1)_$(2)_DIR)/selfie.bin: $$(TARGET_$(1)_$(2)_DIR)/selfie.elf
 	$$(OBJCOPY) -S -O binary $$< $$@
diff --git a/machine/diag.c b/machine/diag.c
@@ -21,4 +21,7 @@ void panic(const char* diagnostic_message, ...) {
 
 void shutdown() {
   sbi_ecall_sbi_shutdown();
+
+  printf("shutdown failed - hanging machine...\n");
+  hang_machine();
 }
diff --git a/machine/filesystem.mk b/machine/filesystem.mk
@@ -13,7 +13,7 @@ files_package.c: $(SBI_WRAPPER_FILES_PACKAGE)
 	done;
 
 	@# Create a mapping to all packaged files
-	@echo "static const KFILE file_defs[] = {" >>$@;
+	@echo "const KFILE files[] = {" >>$@;
 	@for file in $^;\
 	do \
 		BASENAME=`basename $$file` ;\
@@ -23,7 +23,6 @@ files_package.c: $(SBI_WRAPPER_FILES_PACKAGE)
 	done;
 	@echo "  {\"\", (const char*) NULL, 0}," >>$@;
 	@echo "};" >>$@;
-	@echo "const KFILE* files = file_defs;" >>$@;
 
 $(SELFIE_PATH)/selfie.m: $(SELFIE_PATH)/selfie.c
 	$(MAKE) -C$(SELFIE_PATH) selfie.m
diff --git a/machine/glue_libraryos.c b/machine/glue_libraryos.c
@@ -24,7 +24,7 @@ uint64_t open(char* filename, uint64_t flags, uint64_t mode) {
 }
 
 
-
+extern void zero_mem(uint64_t* addr, uint64_t size);
 void* malloc(unsigned long long size) {
   void* return_ptr;
 
@@ -35,6 +35,8 @@ void* malloc(unsigned long long size) {
   printf("-- malloc: allocated 0x%x bytes at addr %p-%p\n", size, return_ptr, heap_head);
 #endif /* DEBUG */
 
+  zero_mem(return_ptr, size);
+
   return return_ptr;
 }
 
diff --git a/machine/include/diag.h b/machine/include/diag.h
@@ -4,7 +4,9 @@
 #include <stdarg.h>
 
 void panic(const char* diagnostic_message, ...);
-void shutdown();
+void shutdown() __attribute__((noreturn));
+
+extern void hang_machine() __attribute__((noreturn));
 
 #ifdef DEBUG
 #define assert(x) if (!(x)) panic("Assertion failed: " __FILE__ ":%u: " #x, __LINE__)
diff --git a/machine/include/filesystem.h b/machine/include/filesystem.h
@@ -16,7 +16,7 @@ typedef struct FILEDESC {
   size_t pos;
 } FILEDESC;
 
-extern const KFILE* files;
+extern const KFILE files[];
 
 const KFILE* find_file(const char* filename);
 
diff --git a/machine/syscalls.c b/machine/syscalls.c
@@ -40,7 +40,7 @@ bool fd_is_opened(int fd, FILEDESC* open_files, size_t num_fds) {
 }
 
 
-ssize_t kread(int fd, char* buf, size_t count, FILEDESC* open_files, size_t num_fds) {
+ssize_t kread(int fd, char* buf, size_t nbytes, FILEDESC* open_files, size_t num_fds) {
   if (!fd_is_valid(fd, num_fds))
     return -1;
 
@@ -52,17 +52,16 @@ ssize_t kread(int fd, char* buf, size_t count, FILEDESC* open_files, size_t num_
     if (!fd_entry_is_opened(desc))
       return -1;
 
-    uint64_t num_read = 0;
-    while (count) {
-      if (desc->pos >= desc->file->length)
-          break;
+    uint64_t num_read = nbytes;
+    uint64_t max_readable = desc->file->length - desc->pos;
+    if (num_read > max_readable)
+      num_read = max_readable;
 
-      *(buf++) = desc->file->data[desc->pos];
+    const char* fileDataOffset = desc->file->data + desc->pos;
+
+    memcpy(buf, fileDataOffset, num_read);
+    desc->pos += num_read;
 
-      --count;
-      num_read++;
-      desc->pos++;
-    }
     return num_read;
   }
 }
diff --git a/machine/tools/asm_struct_macro_generator.c b/machine/tools/asm_struct_macro_generator.c
@@ -1,6 +1,6 @@
 
 #include <stdio.h>
-#include "include/context.h"
+#include "context.h"
 
 #define PRINT_SIZE_DEF(prefix, name, stru) printf("#define %s%s %lu\n", #prefix, #name, sizeof(stru))
 #define PRINT_OFFSET_DEF(prefix, name, stru, memb) printf("#define %s%s %lu\n", #prefix, #name, offsetof(stru, memb))
diff --git a/theses/README.md b/theses/README.md
@@ -1,6 +1,10 @@
 # Bachelor Theses on Selfie
 
 
+## RISC-V Bare-Metal Library Operating System for Selfie by Marcell Haritopoulos, University of Salzburg, Austria, 2021 ([PDF](https://github.com/cksystemsteaching/selfie/releases/download/bachelor_thesis_haritopoulos/bachelor_thesis_haritopoulos.pdf), [Release](https://github.com/cksystemsteaching/selfie/releases/tag/bachelor_thesis_haritopoulos))
+
+Despite its young age, the field of Computer Science is multifaceted and complex, at the expense of the entry barrier. Selfie, an educational project, aims to close the gap on the fundamentals. It runs on a hosted environment, but was not able to run on bare metal RISC-V hardware. We introduce a simple library operating system for RISC-V that implements the system call interface of Selfie and supports (nearly) all applications, that are written in Selfie's tiny C subset C* and are using its syscall interface, without any modifications, including Selfie itself. The OS is linked to the application as a static library and is responsible for maintaining a C environment. System calls are performed as mere function invocations instead of raising an exception using ecall. Files are stored in a static read-only file system. I/O system calls are implemented in a general way so that related projects may share the same semantics.
+
 ## RISC-V S-Mode-Hosted Bare-Metal Selfie by Martin Fischer, University of Salzburg, Austria, 2020 ([PDF](https://github.com/cksystemsteaching/selfie/releases/download/bachelor_thesis_fischer/bachelor_thesis_fischer.pdf), [Release](https://github.com/cksystemsteaching/selfie/releases/tag/bachelor_thesis_fischer))
 
 Modern operating systems like Linux run on a great variety of different machine architectures and have complicated mechanisms for process and resource management. Since this makes understanding their internals a tedious task, we present a simple preemptive multitasking kernel that targets a 64-bit RISC-V platform and which is tailored to run binaries compiled by selfie through the implementation of its Application Binary Interface. It runs in supervisor-mode, executes spatially isolated processes in user-mode, and communicates through the Supervisor Binary Interface with OpenSBI, a hardware abstraction layer, running in machine-mode; all while sharing core parts of its code base with a library operating system that is described in another bachelor thesis. The main difficulties that arise through the use of memory virtualization are discussed and solutions for them are presented. The kernel is able to execute on top of real RISC-V hardware in the form of a SiFive HiFive Unleashed.
diff --git a/theses/bachelor_thesis_haritopoulos.pdf b/theses/bachelor_thesis_haritopoulos.pdf

Original file line number	Diff line number	Diff line change
`@@ -21,4 +21,7 @@ void panic(const char* diagnostic_message, ...) {`
`21`	`21`
`22`	`22`	`void shutdown() {`
`23`	`23`	`sbi_ecall_sbi_shutdown();`
	`24`	`+`
	`25`	`+ printf("shutdown failed - hanging machine...\n");`
	`26`	`+ hang_machine();`
`24`	`27`	`}`
Original file line number	Diff line number	Diff line change
`@@ -24,7 +24,7 @@ uint64_t open(char* filename, uint64_t flags, uint64_t mode) {`
`24`	`24`	`}`
`25`	`25`
`26`	`26`
`27`		`-`
	`27`	`+extern void zero_mem(uint64_t* addr, uint64_t size);`
`28`	`28`	`void* malloc(unsigned long long size) {`
`29`	`29`	`void* return_ptr;`
`30`	`30`
`@@ -35,6 +35,8 @@ void* malloc(unsigned long long size) {`
`35`	`35`	`printf("-- malloc: allocated 0x%x bytes at addr %p-%p\n", size, return_ptr, heap_head);`
`36`	`36`	`#endif /* DEBUG */`
`37`	`37`
	`38`	`+ zero_mem(return_ptr, size);`
	`39`	`+`
`38`	`40`	`return return_ptr;`
`39`	`41`	`}`
`40`	`42`