syscalls: implement basic execve syscall, no argc, argv, envp support yet

src/tasking/syscalls.c

@@ -247,6 +247,89 @@ int sys_close(TrapFrame *tf)
     return -1;
 }
 
+#include "../include/exec_from_file.h"
+
+extern void execve_return(TrapFrame *tf);
+
+int sys_execve(TrapFrame *tf) {
+    const char* filename = (const char*)tf->ebx;
+
+    uint8_t* file_buffer;
+    int err = vsf_read_file_by_path(filename, &file_buffer, root_dir);
+    if (err != 0) {
+        debug_log("execve: failed to read file '%s'\n", filename);
+        return -1;
+    }
+
+    Elf32_Ehdr *elf_header = (Elf32_Ehdr*)file_buffer;
+    if (memcmp(elf_header->e_ident, "\x7F" "ELF", 4) != 0) {
+        debug_log("execve: '%s' is not a valid ELF file\n", filename);
+        free(file_buffer);
+        return -1;
+    }
+
+    uint32_t* new_page_dir = create_page_dir();
+    if (!new_page_dir) {
+        free(file_buffer);
+        return -1;
+    }
+    uint32_t new_page_dir_phys = (uint32_t)get_physaddr((void*)new_page_dir);
+    uint32_t* old_page_dir_to_free = current->pagedir;
+
+    set_page_dir(new_page_dir_phys);
+    current->pagedir = new_page_dir;
+
+    void* kstack_phys = get_physaddr(current->kstack);
+    map_page(kstack_phys, current->kstack, PAGE_PRESENT | PAGE_RW);
+
+    uint32_t highest_vaddr = 0;
+    for (int i = 0; i < elf_header->e_phnum; i++) {
+        Elf32_Phdr *p_header = (Elf32_Phdr *)(file_buffer + elf_header->e_phoff + i * elf_header->e_phentsize);
+        if (p_header->p_type == PT_LOAD) {
+            for (uint32_t vaddr = p_header->p_vaddr; vaddr < p_header->p_vaddr + p_header->p_memsz; vaddr += PAGE_SIZE) {
+                void* phys_addr = alloc_page();
+                map_page(phys_addr, (void*)(vaddr & ~0xFFF), PAGE_PRESENT | PAGE_RW | PAGE_USER);
+            }
+            memcpy((void*)p_header->p_vaddr, file_buffer + p_header->p_offset, p_header->p_filesz);
+            if (p_header->p_memsz > p_header->p_filesz) {
+                memset((void*)(p_header->p_vaddr + p_header->p_filesz), 0, p_header->p_memsz - p_header->p_filesz);
+            }
+            if (p_header->p_vaddr + p_header->p_memsz > highest_vaddr) {
+                highest_vaddr = p_header->p_vaddr + p_header->p_memsz;
+            }
+        }
+    }
+
+    for (uint32_t vaddr = USER_STACK_BOTTOM; vaddr <= USER_STACK_TOP; vaddr += PAGE_SIZE) {
+        void* phys_addr = alloc_page();
+        map_page(phys_addr, (void*)(vaddr & ~0xFFF), PAGE_PRESENT | PAGE_RW | PAGE_USER);
+    }
+    uint32_t user_esp = USER_STACK_TOP;
+    user_esp -= 4; *(uint32_t*)user_esp = 0; // envp
+    user_esp -= 4; *(uint32_t*)user_esp = 0; // argv
+    user_esp -= 4; *(uint32_t*)user_esp = 0; // argc
+
+    current->brk = (void*)(DivRoundUp(highest_vaddr, PAGE_SIZE) * PAGE_SIZE);
+    free(file_buffer);
+    destroy_page_dir(old_page_dir_to_free);
+
+    tf->gs = SEG_UDATA | DPL_USER;
+    tf->fs = SEG_UDATA | DPL_USER;
+    tf->es = SEG_UDATA | DPL_USER;
+    tf->ds = SEG_UDATA | DPL_USER;
+    tf->eax = 0; tf->ecx = 0; tf->edx = 0; tf->ebx = 0;
+    tf->ebp = 0; tf->esi = 0; tf->edi = 0;
+    tf->eip = elf_header->e_entry;
+    tf->cs = SEG_UCODE | DPL_USER;
+    tf->eflags = FL_IF;
+    tf->usermode_esp = user_esp;
+    tf->usermode_ss = SEG_UDATA | DPL_USER;
+
+    execve_return(tf);
+
+    return 0;
+}
+
 int sys_chdir(TrapFrame *tf)
 {
     //strcat(current->cwd->fat->path, "/");
@@ -355,6 +438,10 @@ void handle_syscall(TrapFrame *tf)
         case 6://close
             tf->eax = sys_close(tf);
             break;
+
+        case 11://execve
+            tf->eax = sys_execve(tf);
+            break;
         
         case 12://chdir
             tf->eax = sys_chdir(tf);