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

grubshit/callee.c

@@ -0,0 +1,22 @@
+// callee.c
+#include <stdio.h>
+#include <unistd.h>
+
+int main(int argc, char *argv[], char *envp[]) {
+    printf("--- In callee.c ---\n");
+    printf("This program has taken over the process.\n");
+
+    printf("argc: %d\n", argc);
+
+    printf("\nArguments (argv):\n");
+    for (int i = 0; argv[i] != NULL; i++) {
+        printf("  argv[%d]: %s\n", i, argv[i]);
+    }
+
+    printf("\nEnvironment Variables (envp):\n");
+    for (int i = 0; envp[i] != NULL; i++) {
+        printf("  %s\n", envp[i]);
+    }
+
+    return 0;
+}

grubshit/caller.c

@@ -0,0 +1,26 @@
+// caller.c
+#include <stdio.h>
+#include <unistd.h>
+
+int main() {
+    printf("--- In caller.c ---\n");
+    printf("This message is from the original program.\n");
+    printf("Calling execve to run './callee'...\n\n");
+
+    // Arguments for the new program
+    // The first argument is conventionally the program name
+    char *argv[] = {NULL}; //{ "./callee", "first_arg", "second_arg", NULL };
+
+    // Environment variables for the new program
+    char *envp[] = {NULL}; //{ "CUSTOM_VAR=Hello from caller!", "ANOTHER_VAR=123", NULL };
+
+    // The execve system call
+    // The first argument is the path to the executable
+    // The second is the array of arguments
+    // The third is the array of environment variables
+    execve("callee.", argv, envp);
+
+    // This part of the code will only be reached if execve fails
+    perror("execve failed");
+    return 1;
+}

include/exec_from_file.h

@@ -3,4 +3,10 @@
 #include "../include/vfs.h"
 #include "../include/lib9660.h"
 
+#define DivRoundUp(number, divisor) ((number + divisor - 1) / divisor)
+
+#define USER_STACK_TOP            0xBFFFFFF0 // Top of user space memory
+#define USER_STACK_SIZE         0x4000         // 16KB stack (4 pages)
+#define USER_STACK_BOTTOM     (USER_STACK_TOP - USER_STACK_SIZE)
+
 void exec_from_file(const char* filename, const char* dirname);

include/vfs.h

@@ -19,4 +19,6 @@ size_t vfs_read_file_length(l9660_file *file, uint8_t* buffer, size_t length);
 
 void test_iso9660();
 
+int vsf_read_file_by_path(const char* path, uint8_t** buffer, l9660_dir* dir);
+
 #endif

src/fs/vfs.c

@@ -189,4 +189,36 @@ void test_iso9660()
         printf("Total bytes read: ");
         printf("0x%X\n", total_bytes);
     }
+}
+
+int vsf_read_file_by_path(const char* path, uint8_t** buffer, l9660_dir* dir)
+{
+    l9660_file* file = (l9660_file*)malloc(sizeof(l9660_file));
+
+    l9660_status err;
+
+    err = l9660_openat(file, dir, path);
+    if (err != L9660_OK)
+    {
+        debug_log("read_file: err: 0x%X\n", err);
+        return err;
+    }
+
+    debug_log("HEHE %s\n", path);
+
+    l9660_seek(file, L9660_SEEK_END, 0);
+    uint32_t file_size = l9660_tell(file);
+    debug_log("file_size: %X\n", file_size);
+    l9660_seek(file, L9660_SEEK_SET, 0);
+
+    *buffer = (uint8_t*)malloc(file_size);
+    debug_log("eeee\n");
+
+    size_t read;
+
+    read = vfs_read_file(file, *buffer);
+    free(file);
+    debug_log("bytes read: 0x%X\n", read);
+    
+    return 0;
 }

src/kernel/kernel.c

@@ -131,7 +131,7 @@ void kmain(unsigned int magic, unsigned int info)
 
 	mount_fs();
 
-	exec_from_file("main.", ".");
+	exec_from_file("caller.", ".");
 
 	while(1)
 	{

src/tasking/exec_from_file.c

@@ -6,42 +6,6 @@
 #include "../include/paging.h"
 #include "../include/task.h"
 
-#define DivRoundUp(number, divisor) ((number + divisor - 1) / divisor)
-
-#define USER_STACK_TOP            0xBFFFFFF0 // Top of user space memory
-#define USER_STACK_SIZE         0x4000         // 16KB stack (4 pages)
-#define USER_STACK_BOTTOM     (USER_STACK_TOP - USER_STACK_SIZE)
-
-int read_file(const char* path, uint8_t** buffer, l9660_dir* dir)
-{
-    l9660_file* file = (l9660_file*)malloc(sizeof(l9660_file));
-
-    l9660_status err;
-
-    err = l9660_openat(file, dir, path);
-    if (err != L9660_OK)
-    {
-        debug_log("read_file: err: 0x%X\n", err);
-        return err;
-    }
-
-    l9660_seek(file, L9660_SEEK_END, 0);
-    uint32_t file_size = l9660_tell(file);
-    debug_log("file_size: %X\n", file_size);
-    l9660_seek(file, L9660_SEEK_SET, 0);
-
-    *buffer = (uint8_t*)malloc(file_size);
-    debug_log("eeee\n");
-
-    size_t read;
-
-    read = vfs_read_file(file, *buffer);
-    free(file);
-    debug_log("bytes read: 0x%X\n", read);
-    
-    return 0;
-}
-
 void exec_from_file(const char* filename, const char* dirname)
 {
     asm volatile("cli");
@@ -58,7 +22,7 @@ void exec_from_file(const char* filename, const char* dirname)
 
     uint32_t bss_start, bss_end;
 
-    err = read_file(filename, &file, &dir);
+    err = vsf_read_file_by_path(filename, &file, &dir);
 
     if(err != 0)
     {

src/tasking/sys_exit.asm

@@ -31,5 +31,20 @@ sys_exit_handler:
     ; Возвращаемся в Ring 3
     iret
 
+global execve_return
+
+execve_return:
+    mov esp, [esp+4]
+
+    pop gs
+    pop fs
+    pop es
+    pop ds
+    popa
+
+    add esp, 8
+
+    iret
+
 section .data
 sys_exit_msg: db "Returned from Ring 3", 0

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);