From 2c8b5d4752e2c325f2699f82102bce4369b22ec6 Mon Sep 17 00:00:00 2001
From: Ruslan Isaev <ubijca16@gmail.com>
Date: Tue, 16 Sep 2025 22:41:32 +0300
Subject: [PATCH] syscalls: implement argv and envp handling in execve

---
 grubshit/caller.c      |  4 +--
 src/tasking/syscalls.c | 73 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 72 insertions(+), 5 deletions(-)

diff --git a/grubshit/caller.c b/grubshit/caller.c
index bc6a312..0cbb593 100644
--- a/grubshit/caller.c
+++ b/grubshit/caller.c
@@ -9,10 +9,10 @@ int main() {
 
     // Arguments for the new program
     // The first argument is conventionally the program name
-    char *argv[] = {NULL}; //{ "./callee", "first_arg", "second_arg", NULL };
+    char *argv[] = { "./callee", "first_arg", "second_arg", NULL };
 
     // Environment variables for the new program
-    char *envp[] = {NULL}; //{ "CUSTOM_VAR=Hello from caller!", "ANOTHER_VAR=123", NULL };
+    char *envp[] = { "CUSTOM_VAR=Hello from caller!", "ANOTHER_VAR=123", NULL };
 
     // The execve system call
     // The first argument is the path to the executable
diff --git a/src/tasking/syscalls.c b/src/tasking/syscalls.c
index 6f81440..c270350 100644
--- a/src/tasking/syscalls.c
+++ b/src/tasking/syscalls.c
@@ -18,6 +18,8 @@ extern void switchProcess(Process* next);
 
 #define EBADF 9
 
+#define EXECVE_MAX_ARGUMENT_SIZE 255
+
 const char* flags_to_mode_str(int flags) {
     static char mode[4] = {0};
     int accmode = flags & 3;
@@ -251,9 +253,44 @@ int sys_close(TrapFrame *tf)
 
 extern void execve_return(TrapFrame *tf);
 
+/**
+ * this might be a not really good implementation as it only supports
+ * up to EXECVE_MAX_ARGUMENT_SIZE characters in each argument or environment
+ * string and for some reason I was unable to use malloc for kernel_argv and
+ * kernel_envp
+*/
 int sys_execve(TrapFrame *tf) {
     const char* filename = (const char*)tf->ebx;
 
+    char **argv = (char**)tf->ecx;
+    char **envp = (char**)tf->edx;
+
+    int argc = 0;
+    int envc = 0;
+
+    while(argv[argc] != NULL)
+    {
+        argc++;
+    }
+    while(envp[envc] != NULL)
+    {
+        envc++;
+    }
+
+    //TODO: check why was there a triple fault when I tried using malloc
+    char kernel_argv[argc][EXECVE_MAX_ARGUMENT_SIZE];
+    char kernel_envp[envc][EXECVE_MAX_ARGUMENT_SIZE];
+
+    for(int i = 0; i < argc; i++)
+    {
+        strcpy(kernel_argv[i], argv[i]);
+    }
+
+    for(int i = 0; i < envc; i++)
+    {
+        strcpy(kernel_envp[i], envp[i]);
+    }
+
     uint8_t* file_buffer;
     int err = vsf_read_file_by_path(filename, &file_buffer, root_dir);
     if (err != 0) {
@@ -304,10 +341,40 @@ int sys_execve(TrapFrame *tf) {
         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
+    
+    //push environment strings
+    uint32_t envp_pointers[envc + 1];
+    for (int i = envc - 1; i >= 0; i--) {
+        size_t len = strlen(kernel_envp[i]) + 1;
+        user_esp -= len;
+        memcpy((void*)user_esp, kernel_envp[i], len);
+        envp_pointers[i] = user_esp;
+    }
+    envp_pointers[envc] = 0;//null terminator
+    
+    //push argument strings
+    uint32_t argv_pointers[argc + 1];
+    for (int i = argc - 1; i >= 0; i--) {
+        size_t len = strlen(kernel_argv[i]) + 1;
+        user_esp -= len;
+        memcpy((void*)user_esp, kernel_argv[i], len);
+        argv_pointers[i] = user_esp;
+    }
+    argv_pointers[argc] = 0;//null terminator
+
+    //push envp pointers
+    user_esp -= (envc + 1) * sizeof(uint32_t);
+    memcpy((void*)user_esp, envp_pointers, (envc + 1) * sizeof(uint32_t));
+    
+    //push argv pointers
+    user_esp -= (argc + 1) * sizeof(uint32_t);
+    memcpy((void*)user_esp, argv_pointers, (argc + 1) * sizeof(uint32_t));
+    
+    //push argc
+    user_esp -= sizeof(uint32_t);
+    *((uint32_t*)user_esp) = argc;
 
     current->brk = (void*)(DivRoundUp(highest_vaddr, PAGE_SIZE) * PAGE_SIZE);
     free(file_buffer);