syscalls: implement execbuf

i have been planning to implement something like this for a while now.
it should be faster when doing consecutive syscalls (to be tested).

it will also be helpful in writing the elf loader

1 files changed, 38 insertions, 0 deletions

diff --git a/src/kernel/execbuf.c b/src/kernel/execbuf.c
new file mode 100644
index 0000000..6136d0e
--- /dev/null
+++ b/src/kernel/execbuf.c
@@ -0,0 +1,38 @@
+#include <kernel/execbuf.h>
+#include <kernel/mem/alloc.h>
+#include <kernel/panic.h>
+#include <shared/execbuf.h>
+#include <shared/mem.h>
+
+_Noreturn static void halt(struct process *proc) {
+	kfree(proc->execbuf.buf);
+	proc->execbuf.buf = NULL;
+	process_switch_any();
+}
+
+static void try_fetch(struct process *proc, uint64_t *buf, size_t amt) {
+	size_t bytes = amt * sizeof(uint64_t);
+	if (proc->execbuf.pos + bytes > proc->execbuf.len)
+		halt(proc);
+	memcpy(buf, proc->execbuf.buf + proc->execbuf.pos, bytes);
+	proc->execbuf.pos += bytes;
+}
+
+_Noreturn void execbuf_run(struct process *proc) {
+	uint64_t buf[5];
+	assert(proc == process_current); // idiotic, but needed because of _syscall.
+	assert(proc->state == PS_RUNNING);
+	assert(proc->execbuf.buf);
+
+	for (;;) {
+		try_fetch(proc, buf, 1);
+		switch (buf[0]) {
+			case EXECBUF_SYSCALL:
+				try_fetch(proc, buf, 5);
+				_syscall(buf[0], buf[1], buf[2], buf[3], buf[4]);
+				break;
+			default:
+				halt(proc);
+		}
+	}
+}