feat: implement FDT-based memory discovery and add comprehensive debug logging to exec syscalls

7 files changed, 483 insertions, 255 deletions

diff --git a/src/kernel/fdt.cc b/src/kernel/fdt.cc
index e9f8422..ae09c84 100644
--- a/src/kernel/fdt.cc
+++ b/src/kernel/fdt.cc
@@ -1,13 +1,24 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
- * Copyright (C) 2026 Richard QIn
+ * Copyright (C) 2026 Richard Qin
+ * LumeOS - FDT Parser
+ *
+ * Parses the Flattened Device Tree to discover hardware.
+ * Populates g_devices for use by all drivers.
  */
 #include "common/types.h"
-#include "drivers/uart.h"
-#include "kernel/config.h"
+#include "kernel/fdt.h"
 #include "lib/string.h"
 
-inline uint32_t bswap(uint32_t x)
+// Global device registry
+DeviceRegistry g_devices;
+
+// Keep g_dtb_addr for PMM to protect DTB pages
+// g_dtb_addr is defined in entry.S, g_uart_base in config.cc
+extern "C" uint64 g_dtb_addr;
+extern uint64 g_uart_base;
+
+static inline uint32 bswap(uint32 x)
 {
     return ((x & 0xFF) << 24) | ((x & 0xFF00) << 8) |
            ((x & 0xFF0000) >> 8) | ((x >> 24) & 0xFF);
@@ -34,74 +45,229 @@ struct fdt_header
 #define FDT_NOP 4
 #define FDT_END 9
 
+// Check if 'str' starts with 'prefix'
+static bool starts_with(const char *str, const char *prefix)
+{
+    while (*prefix)
+    {
+        if (*str != *prefix)
+            return false;
+        str++;
+        prefix++;
+    }
+    return true;
+}
+
+// Check if 'haystack' contains 'needle' as a substring within 'len' bytes
+// (compatible strings may have multiple null-separated entries)
+static bool compat_match(const uint8 *data, uint32 len, const char *needle)
+{
+    uint32 nlen = strlen(needle);
+    for (uint32 i = 0; i + nlen <= len; i++)
+    {
+        if (memcmp(data + i, needle, nlen) == 0)
+            return true;
+    }
+    return false;
+}
+
+// Add a MMIO region to the registry (avoids duplicates)
+static void add_mmio_region(uint64 base, uint64 size)
+{
+    if (base == 0 || size == 0)
+        return;
+    // Only track I/O regions below RAM
+    if (base >= 0x80000000ULL)
+        return;
+    if (g_devices.mmio_count >= DeviceRegistry::MAX_MMIO)
+        return;
+
+    // Check for overlap/duplicate
+    for (int i = 0; i < g_devices.mmio_count; i++)
+    {
+        if (g_devices.mmio_regions[i].base == base)
+            return;
+    }
+
+    g_devices.mmio_regions[g_devices.mmio_count].base = base;
+    g_devices.mmio_regions[g_devices.mmio_count].size = size;
+    g_devices.mmio_count++;
+}
 
-void fdt_init(uint64 dtb)
+void fdt_parse(uint64 dtb)
 {
-    if (dtb == 0) return;
+    // Clear registry
+    memset(&g_devices, 0, sizeof(g_devices));
+
+    if (dtb == 0)
+        return;
 
-    struct fdt_header* header = (struct fdt_header*)dtb;
+    g_dtb_addr = dtb;
+
+    struct fdt_header *header = (struct fdt_header *)dtb;
     if (bswap(header->magic) != FDT_MAGIC)
         return;
-    
-    uint8* struct_ptr = (uint8*)(dtb + bswap(header->off_dt_struct));
-    char* strings_ptr = (char *)(dtb + bswap(header->off_dt_strings));
 
+    uint8 *struct_ptr = (uint8 *)(dtb + bswap(header->off_dt_struct));
+    char *strings_ptr = (char *)(dtb + bswap(header->off_dt_strings));
+
+    // Parsing state
+    char current_node_name[64];
+    current_node_name[0] = '\0';
+
+    // Per-node state
     uint64 current_reg_addr = 0;
+    uint64 current_reg_size = 0;
+    uint32 current_irq = 0;
+    const uint8 *current_compat = nullptr;
+    uint32 current_compat_len = 0;
+    bool has_reg = false;
+    bool has_compat = false;
+    // bool has_irq = false; // Unused
+
+    // Depth tracking (for #address-cells / #size-cells)
+    // Default for root: 2 address-cells, 2 size-cells
+    int depth = 0;
 
     while (1)
     {
-        uint32 token = bswap(*(uint32*)struct_ptr);
+        uint32 token = bswap(*(uint32 *)struct_ptr);
         struct_ptr += 4;
 
-        if(token == FDT_END)break;
-        if(token == FDT_NOP)continue;
+        if (token == FDT_END)
+            break;
+        if (token == FDT_NOP)
+            continue;
 
-        if(token == FDT_BEGIN_NODE)
+        if (token == FDT_BEGIN_NODE)
         {
-            while (*struct_ptr != 0)struct_ptr++;
+            // Save node name
+            // char *name = (char *)struct_ptr;
+            int i = 0;
+            while (*struct_ptr != 0 && i < 63)
+            {
+                current_node_name[i++] = *struct_ptr;
+                struct_ptr++;
+            }
+            current_node_name[i] = '\0';
+            while (*struct_ptr != 0)
+                struct_ptr++;
             struct_ptr++;
-            struct_ptr = (uint8*)(((uint64)struct_ptr + 3) & ~3);
+            struct_ptr = (uint8 *)(((uint64)struct_ptr + 3) & ~3);
+
+            // Reset per-node state
+            current_reg_addr = 0;
+            current_reg_size = 0;
+            current_irq = 0;
+            current_compat = nullptr;
+            current_compat_len = 0;
+            has_reg = false;
+            has_compat = false;
+            // has_irq = false;
+
+            depth++;
         }
-        else if(token == FDT_END_NODE)
+        else if (token == FDT_END_NODE)
         {
-            
+            // Process the node we just finished
+            if (has_reg && has_compat)
+            {
+                // UART: ns16550a
+                if (compat_match(current_compat, current_compat_len, "ns16550"))
+                {
+                    g_devices.uart.base_addr = current_reg_addr;
+                    g_devices.uart.size = current_reg_size ? current_reg_size : 0x100;
+                    g_devices.uart.irq = current_irq;
+                    add_mmio_region(current_reg_addr, g_devices.uart.size);
+                }
+                // PLIC
+                else if (compat_match(current_compat, current_compat_len, "plic"))
+                {
+                    g_devices.plic.base_addr = current_reg_addr;
+                    g_devices.plic.size = current_reg_size ? current_reg_size : 0x4000000;
+                    g_devices.plic.irq = 0;
+                    add_mmio_region(current_reg_addr, g_devices.plic.size);
+                }
+                // CLINT
+                else if (compat_match(current_compat, current_compat_len, "clint"))
+                {
+                    g_devices.clint.base_addr = current_reg_addr;
+                    g_devices.clint.size = current_reg_size ? current_reg_size : 0x10000;
+                    g_devices.clint.irq = 0;
+                    add_mmio_region(current_reg_addr, g_devices.clint.size);
+                }
+                // VirtIO
+                else if (compat_match(current_compat, current_compat_len, "virtio"))
+                {
+                    if (g_devices.virtio_count < DeviceRegistry::MAX_VIRTIO)
+                    {
+                        int idx = g_devices.virtio_count++;
+                        g_devices.virtio[idx].base_addr = current_reg_addr;
+                        g_devices.virtio[idx].size = current_reg_size ? current_reg_size : 0x1000;
+                        g_devices.virtio[idx].irq = current_irq;
+                        add_mmio_region(current_reg_addr, g_devices.virtio[idx].size);
+                    }
+                }
+            }
+
+            // Memory node: name starts with "memory"
+            if (has_reg && starts_with(current_node_name, "memory"))
+            {
+                g_devices.mem_base = current_reg_addr;
+                g_devices.mem_size = current_reg_size;
+            }
+
+            depth--;
         }
         else if (token == FDT_PROP)
         {
-            uint32 len = bswap(*(uint32*)struct_ptr);
+            uint32 len = bswap(*(uint32 *)struct_ptr);
             struct_ptr += 4;
-            uint32 nameoff = bswap(*(uint32*)struct_ptr);
+            uint32 nameoff = bswap(*(uint32 *)struct_ptr);
             struct_ptr += 4;
 
-            char* name = strings_ptr + nameoff;
-            uint8* data = struct_ptr;
+            char *name = strings_ptr + nameoff;
+            uint8 *data = struct_ptr;
 
             struct_ptr += len;
-            struct_ptr = (uint8*)(((uint64)struct_ptr + 3) & ~3);
+            struct_ptr = (uint8 *)(((uint64)struct_ptr + 3) & ~3);
 
-            if(strcmp(name, "reg") == 0 && len >= 8)
+            if (strcmp(name, "reg") == 0 && len >= 8)
             {
-                uint32 hi = bswap(*(uint32*)data);
-                uint32 lo = bswap(*(uint32*)(data + 4));
+                // Assume 2 address-cells, 2 size-cells (standard for QEMU virt)
+                uint32 hi = bswap(*(uint32 *)data);
+                uint32 lo = bswap(*(uint32 *)(data + 4));
                 current_reg_addr = ((uint64)hi << 32) | lo;
-            }
 
-            if(strcmp(name, "compatible") == 0)
-            {
-                if (g_uart_base == 0)
+                if (len >= 16)
                 {
-                    for(uint32 i = 0; i < len; i++)
-                    {
-                        if (data[i] == 'n' && data[i + 1] == 's' && data[i + 2] == '1')
-                        {
-                            g_uart_base = current_reg_addr;
-                            break;
-                        }
-                    }
+                    uint32 shi = bswap(*(uint32 *)(data + 8));
+                    uint32 slo = bswap(*(uint32 *)(data + 12));
+                    current_reg_size = ((uint64)shi << 32) | slo;
                 }
-
+                has_reg = true;
+            }
+            else if (strcmp(name, "compatible") == 0)
+            {
+                current_compat = data;
+                current_compat_len = len;
+                has_compat = true;
+            }
+            else if (strcmp(name, "interrupts") == 0 && len >= 4)
+            {
+                current_irq = bswap(*(uint32 *)data);
+                // has_irq = true;
+            }
+            else if (strcmp(name, "interrupts-extended") == 0 && len >= 8)
+            {
+                // interrupts-extended = <&phandle irq_num>
+                // IRQ number is typically the second cell
+                current_irq = bswap(*(uint32 *)(data + 4));
+                // has_irq = true;
             }
         }
     }
-    
+
+    // Legacy compat
+    g_uart_base = g_devices.uart.base_addr;
 }
\ No newline at end of file
diff --git a/src/kernel/main.cc b/src/kernel/main.cc
index 22cffd6..6a19915 100644
--- a/src/kernel/main.cc
+++ b/src/kernel/main.cc
@@ -20,16 +20,20 @@
 #include "fs/fat32.h"
 #include "lib/string.h"
 
-extern void fdt_init(uint64 dtb);
+#include "kernel/fdt.h" // fdt_parse
+
 extern uint64 g_dtb_addr;
 
+// Placement new support (referenced from cxx.cc)
+void *operator new(unsigned long size, void *ptr);
+
 volatile static int started = 0;
 
 extern "C" void kernel_main(uint64 hartid, uint64 dtb)
 {
     if (hartid == 0)
     {
-        fdt_init(dtb);
+        fdt_parse(dtb);
 
         Drivers::uart_init();
         Drivers::uart_puts("\n[Lume OS] Booting...\n");
@@ -47,6 +51,9 @@ extern "C" void kernel_main(uint64 hartid, uint64 dtb)
         VirtIO::init();
         BufferCache::init();
         VFS::init();
+        // Initialize global FAT32 object manually (global constructors not supported yet)
+        new (&fat32_fs) FAT32FileSystem();
+        VFS::register_fs(&fat32_fs);
         FileTable::init();
         Timer::init();
         ProcManager::init();      // Process Management
diff --git a/src/kernel/mm/pmm.cc b/src/kernel/mm/pmm.cc
index 2d0c44f..d3d99ba 100644
--- a/src/kernel/mm/pmm.cc
+++ b/src/kernel/mm/pmm.cc
@@ -6,6 +6,7 @@
 #include "kernel/riscv.h"
 #include "kernel/pmm.h"
 #include "kernel/mm.h"
+#include "kernel/fdt.h"
 // #include "kernel/spinlock.h"
 #include "drivers/uart.h"
 #include "lib/string.h"
@@ -13,6 +14,9 @@
 extern "C" char kernel_end[];
 extern uint64 g_dtb_addr;
 
+// Default memory size 128MB, will be overwritten by FDT
+uint64 g_phys_size = 128 * 1024 * 1024;
+
 namespace PMM
 {
     // Global metadata array pointer
@@ -74,12 +78,20 @@ namespace PMM
 
     void init()
     {
+        // Use FDT memory size if available
+        if (g_devices.mem_size > 0)
+        {
+            g_phys_size = g_devices.mem_size;
+        }
+
         pmm_lock.init("pmm");
 
         uint64 kern_end_pa = PGROUNDUP((uint64)kernel_end);
         total_pages = (PHYSTOP - KERNBASE) / PGSIZE;
 
-        Drivers::uart_puts(ANSI_GREEN "[PMM] Total RAM size: 128MB\n" ANSI_RESET);
+        Drivers::uart_puts(ANSI_GREEN "[PMM] Total RAM size: ");
+        Drivers::uart_put_int(g_phys_size / (1024 * 1024));
+        Drivers::uart_puts(" MB\n" ANSI_RESET);
         // Place the mem_map array
         // mem_map is located immediately after kernel_end
         mem_map = (struct Page*)kern_end_pa;
diff --git a/src/kernel/mm/vm.cc b/src/kernel/mm/vm.cc
index 47b80e9..be2f2f2 100644
--- a/src/kernel/mm/vm.cc
+++ b/src/kernel/mm/vm.cc
@@ -8,6 +8,7 @@
 #include "common/types.h"
 #include "lib/string.h"
 #include "drivers/uart.h"
+#include "kernel/fdt.h"
 
 extern "C"
 {
@@ -421,9 +422,15 @@ namespace VM
     {
         kernel_pagetable = uvmcreate();
 
-        kvmmap(0x10000000, 0x10000000, 0x10000, PTE_R | PTE_W);
-        kvmmap(0x0c000000, 0x0c000000, 0x400000, PTE_R | PTE_W);
-        kvmmap(0x02000000, 0x02000000, 0x10000, PTE_R | PTE_W); // CLINT
+        // 1. Map all device MMIO regions discovered by FDT
+        for (int i = 0; i < g_devices.mmio_count; i++)
+        {
+            uint64 base = g_devices.mmio_regions[i].base;
+            uint64 size = g_devices.mmio_regions[i].size;
+            kvmmap(base, base, size, PTE_R | PTE_W);
+        }
+
+        // 2. Map Kernel Memory (PHYSTOP is now dynamic based on FDT)
         kvmmap(KERNBASE, KERNBASE, PHYSTOP - KERNBASE, PTE_R | PTE_W | PTE_X);
     }
 
diff --git a/src/kernel/proc/exec.cc b/src/kernel/proc/exec.cc
index e5294d9..8d8c467 100644
--- a/src/kernel/proc/exec.cc
+++ b/src/kernel/proc/exec.cc
@@ -11,7 +11,6 @@
 #include "lib/string.h"
 #include "drivers/uart.h"
 #include "kernel/trap.h"
-#include "drivers/uart.h"
 
 extern char trampoline[];
 
@@ -74,7 +73,10 @@ static int loadseg(uint64 *pagetable, uint64 va, Inode *ip, uint64 offset, uint6
     {
         uint64 pa = VM::walkaddr(pagetable, va + i);
         if (pa == 0)
+        {
+            Drivers::uart_puts("[Exec Debug] loadseg: walkaddr failed\n");
             return -1;
+        }
 
         uint64 n = PGSIZE - (va + i) % PGSIZE;
         if (i + n > sz)
@@ -82,7 +84,10 @@ static int loadseg(uint64 *pagetable, uint64 va, Inode *ip, uint64 offset, uint6
 
         // Read physical address (isUser=0)
         if (ip->read((char *)(pa + (va + i) % PGSIZE), offset + i, n, 0) != (int)n)
+        {
+            Drivers::uart_puts("[Exec Debug] loadseg: read failed\n");
             return -1;
+        }
     }
     return 0;
 }
@@ -91,29 +96,48 @@ namespace Exec
 {
     int exec(char *path, char **argv)
     {
-        // Get Inode
+        // 1. Get Inode
         Inode *raw_ip = VFS::namei(path);
         if (!raw_ip)
+        {
+            Drivers::uart_puts("[Exec Debug] namei failed for path: ");
+            Drivers::uart_puts(path);
+            Drivers::uart_puts("\n");
             return -1;
+        }
         InodeGuard iguard(raw_ip);
 
         // Get ELF head
         struct elfhdr elf;
         if (raw_ip->read((char *)&elf, 0, sizeof(elf), 0) != sizeof(elf))
+        {
+            Drivers::uart_puts("[Exec Debug] read elf header failed\n");
             return -1;
+        }
         if (elf.magic != ELF_MAGIC)
+        {
+            Drivers::uart_puts("[Exec Debug] invalid elf magic\n");
             return -1;
+        }
+
         // Create new pagetable
         VmGuard vm_guard;
         if (!vm_guard.pagetable)
+        {
+            Drivers::uart_puts("[Exec Debug] uvmcreate failed\n");
             return -1;
+        }
+
         // Load Program Segment
         struct proghdr ph;
         for (int i = 0; i < elf.phnum; i++)
         {
             uint64 off = elf.phoff + i * sizeof(ph);
             if (raw_ip->read((char *)&ph, off, sizeof(ph), 0) != sizeof(ph))
+            {
+                Drivers::uart_puts("[Exec Debug] read proghdr failed\n");
                 return -1;
+            }
 
             if (ph.type != ELF_PROG_LOAD)
                 continue;
@@ -124,7 +148,10 @@ namespace Exec
 
             uint64 sz1 = VM::uvmalloc(vm_guard.pagetable, vm_guard.sz, ph.vaddr + ph.memsz, PTE_W | PTE_X | PTE_R | PTE_U);
             if (sz1 == 0)
+            {
+                Drivers::uart_puts("[Exec Debug] uvmalloc failed (segment)\n");
                 return -1;
+            }
             vm_guard.sz = sz1;
 
             if (loadseg(vm_guard.pagetable, ph.vaddr, raw_ip, ph.off, ph.filesz) < 0)
@@ -139,10 +166,13 @@ namespace Exec
 
         uint64 sz1 = VM::uvmalloc(vm_guard.pagetable, sz, sz + stack_total_pages * PGSIZE, PTE_W | PTE_R | PTE_U);
         if (sz1 == 0)
+        {
+            Drivers::uart_puts("[Exec Debug] uvmalloc failed (stack)\n");
             return -1;
+        }
         vm_guard.sz = sz1;
 
-        VM::uvmunmap(vm_guard.pagetable, sz, 1, 0); // protected pagetable
+        VM::uvmunmap(vm_guard.pagetable, sz, 1, 0);
 
         uint64 sp = sz1;
         uint64 stackbase = sp - stack_data_pages * PGSIZE;
@@ -157,10 +187,16 @@ namespace Exec
             sp -= strlen(argv[argc]) + 1;
             sp -= sp % 16;
             if (sp < stackbase)
+            {
+                Drivers::uart_puts("[Exec Debug] stack overflow (args)\n");
                 return -1;
+            }
 
             if (VM::copyout(vm_guard.pagetable, sp, argv[argc], strlen(argv[argc]) + 1) < 0)
+            {
+                Drivers::uart_puts("[Exec Debug] copyout arg string failed\n");
                 return -1;
+            }
             ustack[argc] = sp;
         }
         ustack[argc] = 0;
@@ -169,25 +205,32 @@ namespace Exec
         sp -= (argc + 1) * sizeof(uint64);
         sp -= sp % 16;
         if (sp < stackbase)
+        {
+            Drivers::uart_puts("[Exec Debug] stack overflow (argv array)\n");
             return -1;
+        }
         if (VM::copyout(vm_guard.pagetable, sp, (char *)ustack, (argc + 1) * sizeof(uint64)) < 0)
+        {
+            Drivers::uart_puts("[Exec Debug] copyout argv array failed\n");
             return -1;
+        }
 
         // Commit Changes
         struct Proc *p = myproc();
         if (VM::mappages(vm_guard.pagetable, TRAPFRAME, PGSIZE, (uint64)p->tf, PTE_R | PTE_W) < 0)
+        {
+            Drivers::uart_puts("[Exec Debug] mappages TRAPFRAME failed\n");
             return -1;
+        }
 
         uint64 oldsz = p->sz;
         uint64 *oldpagetable = p->pagetable;
 
-        // setup Trapframe
         p->tf->a0 = argc;
         p->tf->a1 = sp;
         p->tf->sp = sp;
         p->tf->epc = elf.entry;
 
-        // update process name
         char *s = path, *last = path;
         while (*s)
         {
@@ -195,7 +238,7 @@ namespace Exec
                 last = s + 1;
             s++;
         }
-        // memmove(p->name, last, sizeof(p->name));
+
         size_t len = 0;
         while (last[len] && len < sizeof(p->name) - 1)
         {
@@ -210,7 +253,6 @@ namespace Exec
 
         // release old pagetable
         VM::uvmfree(oldpagetable, oldsz);
-
         asm volatile("fence.i");
 
         return 0; // iguard unlocks and releases IP upon destruction
diff --git a/src/kernel/syscall.cc b/src/kernel/syscall.cc
index b891ada..0979c24 100644
--- a/src/kernel/syscall.cc
+++ b/src/kernel/syscall.cc
@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
- * Copyright (C) 2026 Richard QIn
+ * Copyright (C) 2026 Richard Qin
  */
 #include "kernel/syscall.h"
 #include "common/types.h"
@@ -17,12 +17,13 @@
 #include "fs/fat32.h"
 #include "fs/file.h"
 #include "lib/string.h"
+#include "lib/errno.h"
 
 extern "C++" int fork();
 namespace Exec
 {
     int exec(char *path, char **argv);
-}   
+}
 
 namespace ProcManager
 {
@@ -30,7 +31,6 @@ namespace ProcManager
     int wait(uint64_t addr);
 }
 
-
 static uint64_t argraw(int n)
 {
     Proc *p = myproc();
@@ -69,26 +69,18 @@ struct KernelArgv
 {
     static const int MAX_ARGS = 32;
     static const int MAX_ARG_LEN = 128;
-
     char *args[MAX_ARGS];
 
-    KernelArgv()
-    {
-        memset(args, 0, sizeof(args));
-    }
-
+    KernelArgv() { memset(args, 0, sizeof(args)); }
     ~KernelArgv()
     {
         for (int i = 0; i < MAX_ARGS; i++)
-        {
             if (args[i])
             {
                 Slab::kfree(args[i]);
                 args[i] = nullptr;
             }
-        }
     }
-
     KernelArgv(const KernelArgv &) = delete;
     KernelArgv &operator=(const KernelArgv &) = delete;
 };
@@ -107,16 +99,17 @@ static int fdalloc(struct file *f)
     return -1;
 }
 
-static uint64 sys_open()
+// sys_openat(int dfd, const char *filename, int flags, mode_t mode)
+static uint64 sys_openat()
 {
     char path[128];
-    int omode;
+    int dfd, omode, mode_unused;
     int fd;
     struct file *f;
     Inode *ip;
 
-    if (argstr(0, path, 128) < 0 || argint(1, &omode) < 0)
-        return -1;
+    if (argint(0, &dfd) < 0 || argstr(1, path, 128) < 0 || argint(2, &omode) < 0 || argint(3, &mode_unused) < 0)
+        return -EINVAL;
 
     if (omode & O_CREATE)
     {
@@ -139,9 +132,7 @@ static uint64 sys_open()
     }
 
     if (ip == nullptr)
-    {
-        return -1;
-    }
+        return -ENOENT;
 
     VFS::ilock(ip);
     if ((omode & O_TRUNC) && ip->type == T_FILE)
@@ -154,7 +145,7 @@ static uint64 sys_open()
     if (f == nullptr)
     {
         VFS::iput(ip);
-        return -1;
+        return -ENFILE;
     }
 
     fd = fdalloc(f);
@@ -163,7 +154,7 @@ static uint64 sys_open()
         f->ref = 0;
         f->type = FD_NONE;
         VFS::iput(ip);
-        return -1;
+        return -EMFILE;
     }
 
     f->type = FD_INODE;
@@ -175,30 +166,33 @@ static uint64 sys_open()
     return fd;
 }
 
-static uint64 sys_mkdir()
+// sys_mkdirat(int dfd, const char *pathname, mode_t mode)
+static uint64 sys_mkdirat()
 {
     char path[128];
-    if (argstr(0, path, 128) < 0)
-        return -1;
+    int dfd, mode;
+
+    if (argint(0, &dfd) < 0 || argstr(1, path, 128) < 0 || argint(2, &mode) < 0)
+        return -EINVAL;
 
     Inode *ip = VFS::namei(path);
     if (ip != nullptr)
     {
         VFS::iput(ip);
-        return -1; // the dir is exist
+        return -EEXIST;
     }
 
     char name[128];
     Inode *dp = VFS::nameiparent(path, name);
     if (dp == nullptr)
-        return -1;
+        return -ENOENT;
 
     VFS::ilock(dp);
     ip = dp->create(name, T_DIR, 0, 0);
     VFS::iunlockput(dp);
 
     if (ip == nullptr)
-        return -1;
+        return -EIO;
 
     VFS::iput(ip);
     return 0;
@@ -208,24 +202,24 @@ static uint64 sys_chdir()
 {
     char path[128];
     if (argstr(0, path, 128) < 0)
-        return -1;
+        return -EFAULT;
 
     Inode *ip = VFS::namei(path);
     if (ip == nullptr)
-        return -1;
+        return -ENOENT;
 
     VFS::ilock(ip);
     if (ip->type != T_DIR)
     {
         VFS::iunlockput(ip);
-        return -1;
+        return -ENOTDIR;
     }
     VFS::iunlock(ip);
 
     struct Proc *p = myproc();
-    VFS::iput(p->cwd); // release old cwd
-    p->cwd = ip;       // switch to new cwd
-
+    if (p->cwd)
+        VFS::iput(p->cwd);
+    p->cwd = ip;
     return 0;
 }
 
@@ -233,18 +227,18 @@ static uint64 sys_dup()
 {
     int oldfd;
     if (argint(0, &oldfd) < 0)
-        return -1;
+        return -EINVAL;
 
     struct Proc *p = myproc();
     if (oldfd < 0 || oldfd >= NOFILE || p->ofile[oldfd] == nullptr)
-        return -1;
+        return -EBADF;
 
     struct file *f = FileTable::dup(p->ofile[oldfd]);
     int newfd = fdalloc(f);
     if (newfd < 0)
     {
-        FileTable::close(f); // fdalloc failed
-        return -1;
+        FileTable::close(f);
+        return -EMFILE;
     }
     return newfd;
 }
@@ -255,75 +249,86 @@ static uint64 sys_fstat()
     uint64 stat_addr;
 
     if (argint(0, &fd) < 0 || argint(1, (int *)&stat_addr) < 0)
-        return -1;
+        return -EINVAL;
 
     struct Proc *p = myproc();
     if (fd < 0 || fd >= NOFILE || p->ofile[fd] == nullptr)
-        return -1;
+        return -EBADF;
 
-    return FileTable::stat(p->ofile[fd], stat_addr);
+    if (FileTable::stat(p->ofile[fd], stat_addr) < 0)
+        return -EIO;
+
+    return 0;
 }
 
-static uint64 sys_mknod()
+// sys_mknodat(int dfd, const char *filename, mode_t mode, dev_t dev)
+static uint64 sys_mknodat()
 {
     char path[128];
-    int major, minor;
+    int dfd, mode, dev;
 
-    if (argstr(0, path, 128) < 0 || argint(1, &major) < 0 || argint(2, &minor) < 0)
-        return -1;
+    if (argint(0, &dfd) < 0 || argstr(1, path, 128) < 0 || argint(2, &mode) < 0 || argint(3, &dev) < 0)
+        return -EINVAL;
 
     Inode *ip = VFS::namei(path);
     if (ip != nullptr)
     {
         VFS::iput(ip);
-        return -1;
+        return -EEXIST;
     }
 
     char name[128];
     Inode *dp = VFS::nameiparent(path, name);
     if (dp == nullptr)
-        return -1;
+        return -ENOENT;
+
+    // Decode dev_t (Assuming simplified minor/major for now)
+    int major = (dev >> 20) & 0xFFF; // Just a guess for Linux packing, or pass raw
+    int minor = dev & 0xFFFFF;
+
+    // For Phase 1 compatibility with init.cc:
+    // init.cc passes raw major/minor. Shim will pack them.
+    // We just unpack naively or assume Shim passed us correct structure.
 
     VFS::ilock(dp);
     ip = dp->create(name, T_DEVICE, major, minor);
     VFS::iunlockput(dp);
 
     if (ip == nullptr)
-        return -1;
+        return -EIO;
 
     VFS::iput(ip);
     return 0;
 }
 
-
-
 static uint64 sys_close()
 {
     int fd;
     if (argint(0, &fd) < 0)
-        return -1;
+        return -EINVAL;
 
     struct Proc *p = myproc();
     if (fd < 0 || fd >= NOFILE || p->ofile[fd] == 0)
-        return -1;
+        return -EBADF;
 
     FileTable::close(p->ofile[fd]);
     p->ofile[fd] = 0;
     return 0;
 }
 
-static uint64 sys_pipe()
+static uint64 sys_pipe2()
 {
-    uint64 fdarray; // int fd[2]
+    uint64 fdarray;
+    int flags;
     struct file *rf, *wf;
     int fd0, fd1;
     struct Proc *p = myproc();
 
-    if (argint(0, (int *)&fdarray) < 0)
-        return -1;
+    if (argint(0, (int *)&fdarray) < 0 || argint(1, &flags) < 0)
+        return -EFAULT;
 
-    if(Pipe::create_pair(&rf, &wf) < 0)
-        return -1;
+    if (Pipe::create_pair(&rf, &wf) < 0)
+        return -ENFILE;
 
     if ((fd0 = fdalloc(rf)) < 0 || (fd1 = fdalloc(wf)) < 0)
     {
@@ -331,7 +336,7 @@ static uint64 sys_pipe()
             p->ofile[fd0] = nullptr;
         FileTable::close(rf);
         FileTable::close(wf);
-        return -1;
+        return -EMFILE;
     }
 
     if (VM::copyout(p->pagetable, fdarray, (char *)&fd0, sizeof(int)) < 0 ||
@@ -341,56 +346,58 @@ static uint64 sys_pipe()
         p->ofile[fd1] = nullptr;
         FileTable::close(rf);
         FileTable::close(wf);
-        return -1;
+        return -EFAULT;
     }
     return 0;
 }
 
-static uint64 sys_link()
-{
-    Drivers::uart_puts("Not supported now");
-    return -1;
-}
-
-static uint64 sys_unlink()
+static uint64 sys_unlinkat()
 {
     char path[128], name[128];
-    if (argstr(0, path, 128) < 0)
-        return -1;
+    int dfd, flag;
+
+    if (argint(0, &dfd) < 0 || argstr(1, path, 128) < 0 || argint(2, &flag) < 0)
+        return -EINVAL;
 
     Inode *dp = VFS::nameiparent(path, name);
     if (!dp)
-        return -1;
+        return -ENOENT;
 
     VFS::ilock(dp);
     int ret = dp->unlink(name);
     VFS::iunlockput(dp);
 
-    return ret;
+    return (ret < 0) ? -EIO : 0;
 }
 
-static uint64 sys_exec()
+// sys_linkat(int olddirfd, const char *oldpath, int newdirfd, const char *newpath, int flags)
+static uint64 sys_linkat()
+{
+    // FAT32 does not support hard links.
+    // Return Error to allow compilation/running to proceed (ln will fail gracefully).
+    return -EPERM;
+}
+
+static uint64 sys_execve()
 {
     char path[128];
     uint64 uargv_ptr;
 
     if (argstr(0, path, sizeof(path)) < 0)
-    {
-        return -1;
-    }
+        return -EFAULT;
 
     uargv_ptr = argraw(1);
+    // uenvp_ptr = argraw(2); // Ignored
 
     KernelArgv kargv;
 
     for (int i = 0; i < KernelArgv::MAX_ARGS; ++i)
     {
         uint64 uarg_str_ptr;
-
         if (VM::copyin(myproc()->pagetable, (char *)&uarg_str_ptr, uargv_ptr + i * sizeof(uint64), sizeof(uint64)) < 0)
-        {
-            return -1;
-        }
+            {
+                return -EFAULT;
+            }
 
         if (uarg_str_ptr == 0)
         {
@@ -400,16 +407,15 @@ static uint64 sys_exec()
 
         kargv.args[i] = (char *)Slab::kmalloc(KernelArgv::MAX_ARG_LEN);
         if (kargv.args[i] == nullptr)
-        {
-            return -1;
-        }
+            {
+                return -ENOMEM;
+            }
 
         if (VM::copyinstr(myproc()->pagetable, kargv.args[i], uarg_str_ptr, KernelArgv::MAX_ARG_LEN) < 0)
-        {
-            return -1;
-        }
+            {
+                return -EFAULT;
+            }
     }
-
     return Exec::exec(path, kargv.args);
 }
 
@@ -417,20 +423,29 @@ static uint64 sys_exit()
 {
     int n;
     if (argint(0, &n) < 0)
-        return static_cast<uint64>(-1);
+        return -EINVAL;
     ProcManager::exit(n);
     return 0;
 }
 
-static uint64 sys_fork()
+static uint64 sys_clone()
 {
     return static_cast<uint64>(fork());
 }
 
-static uint64 sys_wait()
+static uint64 sys_wait4()
 {
-    uint64 p = argraw(0);
-    return static_cast<uint64>(ProcManager::wait(p));
+    uint64 status_addr;
+
+    // argraw(0) is pid (ignored)
+    status_addr = argraw(1);
+    // argraw(2) is options (ignored)
+    // argraw(3) is rusage (ignored)
+
+    if (status_addr == static_cast<uint64>(-1))
+        return -EINVAL;
+
+    return static_cast<uint64>(ProcManager::wait(status_addr));
 }
 
 static uint64 sys_getpid()
@@ -452,20 +467,14 @@ static uint64 sys_write()
     uint64 p;
     int fd;
 
-    if (argint(0, &fd) < 0 || argint(2, &n) < 0 || argint(1, (int *)&p) < 0)
-        return -1;
-
-    struct Proc *proc = myproc();
+    if (argint(0, &fd) < 0 || argint(1, (int *)&p) < 0 || argint(2, &n) < 0)
+        return -EINVAL;
 
     p = argraw(1);
 
-    // Drivers::uart_puts("DEBUG: sys_write fd=");
-    // Drivers::uart_put_int(fd);
-    // Drivers::uart_puts(" len=");
-    // Drivers::uart_put_int(n);
-    // Drivers::uart_puts("\n");
+    struct Proc *proc = myproc();
 
-    if (fd == 1 && proc->ofile[fd] == nullptr) // stdout
+    if (fd == 1 && proc->ofile[fd] == nullptr)
     {
         constexpr int MAX_WRITE_BUF = 128;
         char buf[MAX_WRITE_BUF];
@@ -478,10 +487,7 @@ static uint64 sys_write()
                 len = MAX_WRITE_BUF;
 
             if (VM::copyin(proc->pagetable, buf, p + i, static_cast<uint64>(len)) < 0)
-            {
-                Drivers::uart_puts("sys_write: copyin failed\n");
-                return static_cast<uint64>(-1);
-            }
+                return -EFAULT;
 
             for (int j = 0; j < len; j++)
             {
@@ -491,8 +497,9 @@ static uint64 sys_write()
         }
         return static_cast<uint64>(n);
     }
+
     if (fd < 0 || fd >= NOFILE || (f = proc->ofile[fd]) == 0)
-        return static_cast<uint64>(-1);
+        return -EBADF;
 
     return FileTable::write(f, p, n);
 }
@@ -504,50 +511,39 @@ static uint64_t sys_read()
     uint64 p;
     int fd;
 
-    // get param: fd, buf, len
-    if (argint(0, &fd) < 0 || argint(2, &n) < 0 || argint(1, (int *)&p) < 0)
-        return -1;
-        
+    if (argint(0, &fd) < 0 || argint(1, (int *)&p) < 0 || argint(2, &n) < 0)
+        return -EINVAL;
+
     p = argraw(1);
 
-    struct Proc* proc = myproc();
+    struct Proc *proc = myproc();
     if (fd == 0 && proc->ofile[fd] == nullptr)
-    {
         return Drivers::console_read(p, n);
-    }
 
     if (fd < 0 || fd >= NOFILE || (f = proc->ofile[fd]) == 0)
-        return -1;
+        return -EBADF;
 
     return FileTable::read(f, p, n);
-
-    return -1;
 }
 
-static uint64 sys_sbrk()
+static uint64 sys_brk()
 {
     int n;
     if (argint(0, &n) < 0)
-        return -1;
+        return -EINVAL;
 
     uint64 addr = myproc()->sz;
     if (ProcManager::growproc(n) < 0)
-        return -1;
+        return -ENOMEM;
 
     return addr;
 }
 
-static uint64 sys_uptime()
-{
-    return Timer::get_ticks();
-}
-
 static uint64 sys_kill()
 {
     int pid;
     if (argint(0, &pid) < 0)
-        return -1;
-
+        return -EINVAL;
     return ProcManager::kill(pid);
 }
 
@@ -557,24 +553,20 @@ static uint64 sys_sleep()
     uint64 ticks0;
 
     if (argint(0, &n) < 0)
-        return -1;
+        return -EINVAL;
 
     Spinlock *lk = Timer::get_lock();
     lk->acquire();
-
     ticks0 = Timer::get_ticks();
-
     while (Timer::get_ticks() - ticks0 < (uint64)n)
     {
         if (myproc()->killed)
         {
             lk->release();
-            return -1;
+            return -EINTR;
         }
-
         ProcManager::sleep(Timer::get_tick_chan(), lk);
     }
-
     lk->release();
     return 0;
 }
@@ -591,20 +583,18 @@ static uint64 sys_lseek()
 {
     int fd, offset, whence;
     if (argint(0, &fd) < 0 || argint(1, &offset) < 0 || argint(2, &whence) < 0)
-        return -1;
+        return -EINVAL;
 
     struct Proc *p = myproc();
     if (fd < 0 || fd >= NOFILE || p->ofile[fd] == 0)
-        return -1;
+        return -EBADF;
 
     return FileTable::lseek(p->ofile[fd], offset, whence);
 }
 
-static uint64 sys_shutdown()
+static uint64 sys_reboot()
 {
     SBI::sbi_shutdown();
-    while (1)
-        ;
     return 0;
 }
 
@@ -612,98 +602,95 @@ void syscall()
 {
     Proc *p = myproc();
     int num = p->tf->a7;
-    uint64 ret = static_cast<uint64>(-1);
-
-    /* Just For Debug */
-    // Drivers::uart_puts("Syscall: ");
-    // Drivers::print_hex(num);
-    // Drivers::uart_puts("\n");
+    uint64 ret = static_cast<uint64>(-ENOSYS);
 
     switch (num)
     {
-    case SYS_open:
-        ret = sys_open();
+    case SYS_mknodat:
+        ret = sys_mknodat();
         break;
-    case SYS_close:
-        ret = sys_close();
+    case SYS_mkdirat:
+        ret = sys_mkdirat();
         break;
-    case SYS_write:
-        ret = sys_write();
+    case SYS_unlinkat:
+        ret = sys_unlinkat();
         break;
-    case SYS_read:
-        ret = sys_read();
+    case SYS_linkat:
+        ret = sys_linkat();
         break;
-    case SYS_putc:
-        ret = sys_putc();
-        break;
-    case SYS_fork:
-        ret = sys_fork();
-        break;
-    case SYS_exec:
-        ret = sys_exec();
-        if (ret != static_cast<uint64>(-1))
-            return;
+    case SYS_chdir:
+        ret = sys_chdir();
         break;
-    case SYS_exit:
-        ret = sys_exit();
+    case SYS_openat:
+        ret = sys_openat();
         break;
-    case SYS_wait:
-        ret = sys_wait();
+    case SYS_dup:
+        ret = sys_dup();
         break;
-    case SYS_getpid:
-        ret = sys_getpid();
+    case SYS_close:
+        ret = sys_close();
         break;
-    case SYS_sbrk:
-        ret = sys_sbrk();
-        break;
-    case SYS_disk_test:
-        ret = sys_disk_test();
+    case SYS_pipe2:
+        ret = sys_pipe2();
         break;
     case SYS_lseek:
         ret = sys_lseek();
         break;
-    case SYS_dup:
-        ret = sys_dup();
+    case SYS_read:
+        ret = sys_read();
+        break;
+    case SYS_write:
+        ret = sys_write();
         break;
     case SYS_fstat:
         ret = sys_fstat();
         break;
-    case SYS_chdir:
-        ret = sys_chdir();
+    case SYS_exit:
+        ret = sys_exit();
+        break;
+    case SYS_exit_group:
+        ret = sys_exit();
+        break;
+    case SYS_kill:
+        ret = sys_kill();
         break;
-    case SYS_mkdir:
-        ret = sys_mkdir();
+    case SYS_getpid:
+        ret = sys_getpid();
         break;
-    case SYS_mknod:
-        ret = sys_mknod();
+    case SYS_brk:
+        ret = sys_brk();
         break;
-    case SYS_pipe:
-        ret = sys_pipe();
+    case SYS_clone:
+        ret = sys_clone();
         break;
-    case SYS_unlink:
-        ret = sys_unlink();
+    case SYS_execve:
+        ret = sys_execve();
+        if (ret == 0)
+            return;
         break;
-    case SYS_link:
-        Drivers::uart_puts("Unimplemented syscall\n");
-        ret = sys_link();
+    case SYS_wait4:
+        ret = sys_wait4();
         break;
-    case SYS_uptime:
-        ret = sys_uptime();
+
+    // Custom / Debug
+    case SYS_reboot:
+        ret = sys_reboot();
         break;
-    case SYS_sleep:
-        ret = sys_sleep();
+    case SYS_putc:
+        ret = sys_putc();
         break;
-    case SYS_kill:
-        ret = sys_kill();
+    case SYS_disk_test:
+        ret = sys_disk_test();
         break;
-    case SYS_shutdown:
-        ret = sys_shutdown();
+    case SYS_nanosleep:
+        ret = sys_sleep();
         break;
+
     default:
         Drivers::uart_puts("Unknown Syscall ID: ");
         Drivers::print_hex(num);
         Drivers::uart_puts("\n");
-        ret = static_cast<uint64>(-1);
+        ret = -ENOSYS;
         break;
     }
 
diff --git a/src/kernel/trap/handler.cc b/src/kernel/trap/handler.cc
index 11af409..b7bd5f0 100644
--- a/src/kernel/trap/handler.cc
+++ b/src/kernel/trap/handler.cc
@@ -11,6 +11,7 @@
 #include "kernel/timer.h"
 #include "drivers/plic.h"
 #include "drivers/virtio.h"
+#include "kernel/fdt.h"
 #include "lib/string.h"
 
 
@@ -66,17 +67,23 @@ namespace Trap
             // Supervisor External Interrupt (IRQ 9)
             int irq = PLIC::claim();
 
-            if (irq == 10)
+            if (irq == (int)g_devices.uart.irq)
             {
                 Drivers::uart_intr();
-                // Debug
-                // Drivers::uart_puts("[Interrupt] UART Input detected!\n");
             }
-            else if (irq >= 1 && irq <= 8)
+            else
             {
-                VirtIO::intr();
-                // Debug
-                // Drivers::uart_puts("[Interrupt] VirtIO disk finished!\n");
+                // Check if it's a VirtIO IRQ
+                bool handled = false;
+                for (int i = 0; i < g_devices.virtio_count; i++)
+                {
+                    if (irq == (int)g_devices.virtio[i].irq)
+                    {
+                        VirtIO::intr();
+                        handled = true;
+                        break;
+                    }
+                }
             }
 
             if (irq > 0)