feat(userspace): add ring-3 runtime startup and syscall wrappers

user/crt.S

@@ -0,0 +1,12 @@
+.section .text
+.global _start
+_start:
+    xorq %rbp, %rbp
+    call main
+    movq %rax, %rdi
+    movq $0, %rax
+    int $0x80
+1:
+    jmp 1b
+
+.section .note.GNU-stack, "", @progbits

user/ulib.c

@@ -0,0 +1,123 @@
+#include "ulib.h"
+
+static long syscall3(long number, long a1, long a2, long a3)
+{
+    long ret;
+    __asm__ volatile(
+        "int $0x80"
+        : "=a"(ret)
+        : "a"(number), "D"(a1), "S"(a2), "d"(a3)
+        : "memory", "rcx", "r11");
+    return ret;
+}
+
+long userWrite(int fd, const char* buffer, unsigned long length)
+{
+    return syscall3(sysWrite, fd, (long)buffer, (long)length);
+}
+
+long userRead(int fd, char* buffer, unsigned long length)
+{
+    return syscall3(sysRead, fd, (long)buffer, (long)length);
+}
+
+void userExit(int code)
+{
+    syscall3(sysExit, code, 0, 0);
+}
+
+long userYield(void)
+{
+    return syscall3(sysYield, 0, 0, 0);
+}
+
+long userGetpid(void)
+{
+    return syscall3(sysGetpid, 0, 0, 0);
+}
+
+void* userSbrk(long increment)
+{
+    return (void*)syscall3(sysSbrk, increment, 0, 0);
+}
+
+void userSleep(unsigned long milliseconds)
+{
+    syscall3(sysSleep, (long)milliseconds, 0, 0);
+}
+
+long userOpen(const char* path, unsigned int flags)
+{
+    return syscall3(sysOpen, (long)path, (long)flags, 0);
+}
+
+long userClose(int fd)
+{
+    return syscall3(sysClose, fd, 0, 0);
+}
+
+long userLseek(int fd, long offset, int whence)
+{
+    return syscall3(sysLseek, fd, offset, whence);
+}
+
+long userStat(const char* path, FbStat* out)
+{
+    return syscall3(sysStat, (long)path, (long)out, 0);
+}
+
+long userGetdents(int fd, FbDirent* out, unsigned long length)
+{
+    return syscall3(sysGetdents, fd, (long)out, (long)length);
+}
+
+long userMkdir(const char* path)
+{
+    return syscall3(sysMkdir, (long)path, 0, 0);
+}
+
+long userUnlink(const char* path)
+{
+    return syscall3(sysUnlink, (long)path, 0, 0);
+}
+
+unsigned long stringLength(const char* text)
+{
+    unsigned long length = 0;
+    while (text[length])
+        length++;
+    return length;
+}
+
+void print(const char* text)
+{
+    userWrite(1, text, stringLength(text));
+}
+
+void printDec(long value)
+{
+    unsigned long magnitude;
+    if (value < 0) {
+        userWrite(1, "-", 1);
+        magnitude = (unsigned long)(-value);
+    } else {
+        magnitude = (unsigned long)value;
+    }
+
+    if (magnitude == 0) {
+        userWrite(1, "0", 1);
+        return;
+    }
+
+    char reversed[24];
+    int length = 0;
+    while (magnitude > 0) {
+        reversed[length++] = (char)('0' + (magnitude % 10));
+        magnitude /= 10;
+    }
+
+    char ordered[24];
+    for (int i = 0; i < length; i++)
+        ordered[i] = reversed[length - 1 - i];
+    userWrite(1, ordered, (unsigned long)length);
+}

user/ulib.h

@@ -0,0 +1,27 @@
+#ifndef FROSTBYTE_ULIB_H
+#define FROSTBYTE_ULIB_H
+
+#include "syscall.h"
+#include "fs.h"
+
+long userWrite(int fd, const char* buffer, unsigned long length);
+long userRead(int fd, char* buffer, unsigned long length);
+void userExit(int code);
+long userYield(void);
+long userGetpid(void);
+void* userSbrk(long increment);
+void userSleep(unsigned long milliseconds);
+
+long userOpen(const char* path, unsigned int flags);
+long userClose(int fd);
+long userLseek(int fd, long offset, int whence);
+long userStat(const char* path, FbStat* out);
+long userGetdents(int fd, FbDirent* out, unsigned long length);
+long userMkdir(const char* path);
+long userUnlink(const char* path);
+
+void print(const char* text);
+void printDec(long value);
+unsigned long stringLength(const char* text);
+
+#endif

user/user.ld

@@ -0,0 +1,24 @@
+ENTRY(_start)
+
+PHDRS
+{
+    load PT_LOAD FILEHDR PHDRS FLAGS(7);
+}
+
+SECTIONS
+{
+    . = USER_BASE + SIZEOF_HEADERS;
+
+    .text   : { *(.text .text.*) }         :load
+    .rodata : { *(.rodata .rodata.*) }      :load
+    .data   : { *(.data .data.*) }          :load
+    .bss    : { *(.bss .bss.*) *(COMMON) }  :load
+
+    /DISCARD/ :
+    {
+        *(.comment)
+        *(.note .note.*)
+        *(.eh_frame)
+        *(.eh_frame_hdr)
+    }
+}