From ab61b49aca271de66a049959620766c1938e2234 Mon Sep 17 00:00:00 2001
From: Bananymous <bananymousosq@gmail.com>
Date: Wed, 31 May 2023 20:57:33 +0300
Subject: [PATCH] Kernel: Add SYS_EXEC syscall

---
 kernel/kernel/Syscall.cpp  | 11 +++++++++++
 libc/include/sys/syscall.h |  1 +
 libc/unistd.cpp            | 16 +++++++++++++++-
 userspace/test/test.cpp    | 24 ++++++++----------------
 4 files changed, 35 insertions(+), 17 deletions(-)

diff --git a/kernel/kernel/Syscall.cpp b/kernel/kernel/Syscall.cpp
index 8030512ea..f7fd4012d 100644
--- a/kernel/kernel/Syscall.cpp
+++ b/kernel/kernel/Syscall.cpp
@@ -112,6 +112,14 @@ namespace Kernel
 		return 0;
 	}
 
+	long sys_exec(const char* pathname, const char* const* argv, const char* const* envp)
+	{
+		auto ret = Process::current().exec(pathname, argv, envp);
+		if (ret.is_error())
+			return -ret.error().get_error_code();
+		ASSERT_NOT_REACHED();
+	}
+
 	extern "C" long sys_fork_trampoline();
 
 	extern "C" long cpp_syscall_handler(int syscall, uintptr_t arg1, uintptr_t arg2, uintptr_t arg3, uintptr_t arg4, uintptr_t arg5)
@@ -171,6 +179,9 @@ namespace Kernel
 		case SYS_SLEEP:
 			ret = sys_sleep((unsigned int)arg1);
 			break;
+		case SYS_EXEC:
+			ret = sys_exec((const char*)arg1, (const char* const*)arg2, (const char* const*)arg3);
+			break;
 		default:
 			Kernel::panic("Unknown syscall {}", syscall);
 		}
diff --git a/libc/include/sys/syscall.h b/libc/include/sys/syscall.h
index 1d9e67e68..a253b2141 100644
--- a/libc/include/sys/syscall.h
+++ b/libc/include/sys/syscall.h
@@ -19,6 +19,7 @@ __BEGIN_DECLS
 #define SYS_SET_TERMIOS 12
 #define SYS_FORK 13
 #define SYS_SLEEP 14
+#define SYS_EXEC 15
 
 __END_DECLS
 
diff --git a/libc/unistd.cpp b/libc/unistd.cpp
index b1d3eec64..9c7918e54 100644
--- a/libc/unistd.cpp
+++ b/libc/unistd.cpp
@@ -2,8 +2,9 @@
 #include <kernel/Syscall.h>
 #include <errno.h>
 #include <stdarg.h>
-#include <stddef.h>
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <sys/syscall.h>
 #include <unistd.h>
 
@@ -121,6 +122,14 @@ long syscall(long syscall, ...)
 			ret = Kernel::syscall(SYS_SLEEP, seconds);
 			break;
 		}
+		case SYS_EXEC:
+		{
+			const char* pathname = va_arg(args, const char*);
+			const char* const* argv = va_arg(args, const char* const*);
+			const char* const* envp = va_arg(args, const char* const*);
+			ret = Kernel::syscall(SYS_EXEC, (uintptr_t)pathname, (uintptr_t)argv, (uintptr_t)envp);
+			break;
+		}
 		default:
 			puts("LibC: Unhandeled syscall");
 			ret = -ENOSYS;
@@ -138,6 +147,11 @@ long syscall(long syscall, ...)
 	return ret;
 }
 
+int execv(const char* pathname, char* const argv[])
+{
+	return syscall(SYS_EXEC, pathname, argv, nullptr);
+}
+
 pid_t fork(void)
 {
 	return syscall(SYS_FORK);
diff --git a/userspace/test/test.cpp b/userspace/test/test.cpp
index 2361135cb..47253ca69 100644
--- a/userspace/test/test.cpp
+++ b/userspace/test/test.cpp
@@ -10,25 +10,17 @@ int main()
 {
 	printf("userspace\n");
 
-	FILE* fp = fopen("/usr/include/kernel/kprint.h", "r");
-	if (fp == NULL)
-		ERROR("fopen");
-
-	char* buffer = (char*)malloc(128);
-	fread(buffer, 1, 100, fp);
-
-	pid_t pid = fork();
-	if (pid == 0)
+	if (fork() == 0)
 	{
-		while (size_t n_read = fread(buffer, 1, 127, fp))
-			fwrite(buffer, 1, n_read, stdout);
-		free(buffer);
-		fclose(fp);
+		char* argv[3];
+		argv[0] = (char*)malloc(100); strcpy(argv[0], "/usr/bin/cat");
+		argv[1] = (char*)malloc(100); strcpy(argv[1], "/usr/include/kernel/kprint.h");
+		argv[2] = NULL;
+		execv("/usr/bin/cat", (char**)argv);
+		ERROR("execl");
 		return 0;
 	}
 
-	free(buffer);
-	fclose(fp);
-
+	printf("parent\n");
 	return 0;
 }