Makefile

@@ -21,10 +21,6 @@ CC_FLAGS=-Wall -Wextra -std=gnu99 -nostdlib -ffreestanding -fstack-protector -fn
 LD := x86_64-elf-ld
 
 $(ELFFILE): $(BUILDDIR) $(OBJFILES)
-	nasm -f bin user/hello.S -o $(BUILDDIR)/hello
-	nasm -f bin user/pedicel.S -o $(BUILDDIR)/pedicel
-	tar cvf $(BUILDDIR)/initfs.tar -C $(BUILDDIR) hello pedicel
-
 	nasm -f elf64 src/arch/x86/idt.S -o $(BUILDDIR)/idt_stub.o
 	$(LD) -o $(ELFFILE) -T linker.ld $(OBJFILES) $(BUILDDIR)/idt_stub.o
 	# Get the symbols for debugging
@@ -45,7 +41,11 @@ limine/limine:
 	git clone https://github.com/limine-bootloader/limine.git --branch=v9.x-binary --depth=1
 	$(MAKE) -C limine
 
-initfs:
+.PHONY: user
+user:
+	nasm -f bin user/hello.S -o $(BUILDDIR)/hello
+	nasm -f bin user/pedicel.S -o $(BUILDDIR)/pedicel
+	tar cvf $(BUILDDIR)/initfs.tar -C $(BUILDDIR) hello pedicel -C ../user wow.txt
 
 build-iso: limine/limine $(ELFFILE)
 	rm -rf iso_root

docs/MANUAL.md

@@ -41,8 +41,12 @@ The recommended hardware to run PepperOS is the following:
 ## III. Syscall table
 
 The syscall interface in the Pepper kernel uses the System V ABI convention for argument order.
+It vaguely mimics Unix-like systems.
 
 Name | Number (%rax) | arg0 (%rdi) | arg1 (%rsi) | arg2 (%rdx) |
 |---|---|---|---|---|
-| sys_write | 1 | unsigned int fd | const char* buf | size_t count | | 
+| sys_read | 0 | unsigned int fd | char* buf | size_t count |
-| sys_exit | 60 | int error_code | | | |
+| sys_write | 1 | unsigned int fd | const char* buf | size_t count |
+| sys_open | 2 | const char* filename | int flags | |
+| sys_close | 3 | unsigned int fd | | |
+| sys_exit | 60 | int error_code | | |

include/fs/initfs.h

@@ -11,7 +11,7 @@
 
 int initfs_init(struct limine_file* tar_file);
 int tar_lookup(unsigned char* archive, char* filename, char** out);
-int tar_read(char* filename, char** buf);
 int tar_exists(const char* filename);
+int tar_read(char* filename, char* out, int count, int offset);
 
 #endif

include/kernel.h

@@ -14,7 +14,8 @@ enum ErrorCodes {
 	EIO,    // Input/output error
 	ENOENT, // No entry
 	EBADFD,  // Bad file descriptor
-	EMFILE  // Too many open files
+	EMFILE,  // Too many open files
+	EINVAL  // Invalid argument
 };
 
 #define CLEAR_INTERRUPTS __asm__ volatile("cli")

src/arch/x86/syscall.c

@@ -70,10 +70,12 @@ int sys_read(unsigned int fd, char* buf, size_t count)
                 return -EBADFD; // File descriptor wasn't open
             }
             // Here fd refers to a valid opened file..
-            int sz = tar_read(current_process->fdt[fd].filename,&buf);
+            int sz = tar_read(current_process->fdt[fd].filename, buf, count,
+                            current_process->fdt[fd].cursor);
             if (sz == 0) {
                 return -ENOENT;
             } else {
+                current_process->fdt[fd].cursor += sz;
                 return sz;
             }
     }
@@ -82,27 +84,25 @@ int sys_read(unsigned int fd, char* buf, size_t count)
 }
 
 // TODO: Should have a return value: number of bytes written on success, -1 on error (errno set) 
-void sys_write(unsigned int fd, const char* buf, size_t count)
+int sys_write(unsigned int fd, const char* buf, size_t count)
 {
     switch (fd) {
         case 1: //stdout
-            for (size_t i=0; i<count; i++) {
-                internal_putc(buf[i], NULL);
-            }
-            break;
-
         case 2: //stderr
             for (size_t i=0; i<count; i++) {
                 internal_putc(buf[i], NULL);
             }
-            break;
+            return count;
+        default:
+            return -EBADFD;
     }
 }
 
-void sys_exit(int error_code)
+int sys_exit(int error_code)
 {
     current_process->status = DEAD;
-    DEBUG("exiting process PID=%u name=%s", current_process->pid, current_process->name);
+    DEBUG("(pid=%u, name=%s)", current_process->pid, current_process->name);
+    return error_code;
 }
 
 /*
@@ -125,29 +125,36 @@ void sys_exit(int error_code)
  */
 struct cpu_status* syscall_handler(struct cpu_status* regs)
 {
-    DEBUG("Syscall %lx with (arg0=%lx arg1=%lx)", regs->rax, regs->rdi, regs->rsi);
-
     switch (regs->rax)
     {
-        case 0: //sys_read
+        case 0:
+            DEBUG("sys_read(fd=%u, buf=%p, count=%u)", regs->rdi, regs->rsi, regs->rdx);
             regs->rax = sys_read(regs->rdi, (char*)regs->rsi, regs->rdx);
             break;
-        case 1: //sys_write
+        case 1:
-            sys_write(regs->rdi, (char*)regs->rsi, regs->rdx);
+            DEBUG("sys_write(fd=%u, buf=%p, count=%u)", regs->rdi, regs->rsi, regs->rdx);
+            regs->rax = sys_write(regs->rdi, (char*)regs->rsi, regs->rdx);
             break;
         case 2:
+            DEBUG("sys_open(filename=%s, flags=%u)", regs->rdi, regs->rsi);
             regs->rax = sys_open((const char*)regs->rdi, regs->rsi);
             break;
         case 3:
+            DEBUG("sys_close(fd=%u)", regs->rdi);
             regs->rax = sys_close(regs->rdi);
             break;
-        case 60: //sys_exit
+        case 60:
-            sys_exit(regs->rdi);
+            DEBUG("sys_exit(error_code=%d)", regs->rdi);
+            regs->rax = sys_exit(regs->rdi);
             break;
-        default: // bad syscall
+        default:
+            DEBUG("Bad syscall! (rax=%p, rdi=%p, rsi=%p, rdx=%p)",
+                    regs->rax, regs->rdi, regs->rsi, regs->rdx);
             regs->rax = 0xbad515ca11;
             break;
     }
 
+    DEBUG("returned rax=%p (%u)", regs->rax, regs->rax);
+
     return regs;
 }

src/fs/initfs.c

@@ -42,7 +42,7 @@ int tar_oct2bin(unsigned char* str, int size)
  *
  * Return:
  * $filesize - size of the file, if found 
- * $0        - file not found
+ * $-ENOENT  - file not found
  */
 int tar_lookup(unsigned char* archive, char* filename, char** out)
 {
@@ -56,21 +56,39 @@ int tar_lookup(unsigned char* archive, char* filename, char** out)
         }
         ptr += (((filesize + 511) / 512) + 1) * 512;
     }
-    return 0;
+    return -ENOENT;
 }
 
 /*
- * tar_read - read a file in the TAR file
+ * tar_read - read a file in the TAR archive
  * @filename: file to read (absolute path)
- * @out:      out buffer (if file is found)
+ * @out:      where to store file data if found
+ * @count:    amount of bytes to read
+ * @offset:   read from byte offset (0 for none)
  *
  * Return:
  * $filesize - size of the file, if found 
- * $0        - file not found
+ * $-ENOENT  - file not found
  */
-int tar_read(char* filename, char** buf)
+int tar_read(char* filename, char* out, int count, int offset)
 {
-    return tar_lookup(archive_start_addr, filename, buf);
+    char* file_data;
+    int filesize = tar_lookup(archive_start_addr, filename, &file_data);
+
+    if (filesize <= 0) {
+        return filesize;
+    }
+
+    if (offset >= filesize) {
+        return -EINVAL;
+    }
+
+    int remaining = filesize - offset;
+    int to_read = remaining < count ? remaining : count;
+
+    memcpy(out, file_data + offset, to_read);
+
+    return to_read;
 }
 
 /*

user/pedicel.S

@@ -1,7 +1,8 @@
 bits 64
 
 section .data
-hello db 0x0A, 0x0D, "User program 2 speaking", 0x0A, 0x0D, 0
+hello db 0x0A, 0x0D, "TEST PROGRAM...", 0x0A, 0x0D, 0
+filename db "wow.txt", 0
 
 section .text
 
@@ -9,7 +10,29 @@ _start:
     mov rax, 0x1    ;sys_write
     mov rdi, 0x1    ;stdout
     lea rsi, [rel hello]
-    mov rdx, 27     ;count
+    mov rdx, 19     ;count
+    int 0x80
+
+    ; Open a file
+    mov rax, 0x2            ;sys_open
+    lea rdi, [rel filename] ;filename
+    mov rsi, 0x0            ;flags
+    int 0x80
+
+    mov rdi, rax            ;fd
+    mov rax, 0x0            ;sys_read
+    lea rsi, [rel buf]      ;buf
+    mov rdx, 33             ;count
+    int 0x80
+
+    mov rax, 0x1        ;sys_write
+    mov rdi, 0x1        ;stdout
+    lea rsi, [rel buf]  ;buf
+    mov rdx, 33         ;count
+    int 0x80
+
+    mov rax, 0x3        ;sys_close
+    mov rdi, 0x3        ;fd
     int 0x80
 
 ; when we are ready to have an os specific toolchain,
@@ -23,3 +46,6 @@ _start:
 
 .loop:
     jmp .loop
+
+section .bss
+buf resb 10

user/wow.txt

@@ -0,0 +1 @@
+hi from a file opened in usermode