user/libc: don't access the old stack from the new thread at all

3 files changed, 46 insertions, 20 deletions

diff --git a/src/user/lib/thread.S b/src/user/lib/thread.S
index 3cd3500..1a27c30 100644
--- a/src/user/lib/thread.S
+++ b/src/user/lib/thread.S
@@ -1,8 +1,40 @@
+#define ASM_FILE 1
+#include <camellia/syscalls.h>
+#include <camellia/flags.h>
+
 .section .text
-.global chstack
-.type chstack, @function
-// _Noreturn void chstack(void *arg, void (*fn)(void*), void *esp);
-chstack:
-	mov %rdx, %rsp
-	call *%rsi
-	jmp 0 // "exit"
+.global thread_creates
+.type thread_creates, @function
+// void thread_creates(int flags, void (*fn)(void*), void *arg, void *stack);
+thread_creates:
+	push %r12
+	push %r13
+	push %r14
+
+	/* save fn, arg, stack */
+	mov %rsi, %r12
+	mov %rdx, %r13
+	mov %rcx, %r14
+
+	mov %rdi, %rsi
+	or $(FORK_SHAREMEM | FORK_SHAREHANDLE), %rsi
+	mov $_SYSCALL_FORK, %rdi
+	xor %rdx, %rdx
+	syscall
+
+	test %rax, %rax
+	jz 1f
+	/* in parent, return normally */
+	pop %r14
+	pop %r13
+	pop %r12
+	ret
+1:	/* in child */
+	mov %r14, %rsp
+	mov %r13, %rdi
+	call *%r12
+
+	mov $_SYSCALL_EXIT, %rdi
+	xor %rsi, %rsi
+	syscall
+	hlt /* if all else fails... */
diff --git a/src/user/lib/thread.c b/src/user/lib/thread.c
deleted file mode 100644
index f7353ad..0000000
--- a/src/user/lib/thread.c
+++ /dev/null
@@ -1,11 +0,0 @@
-#include <camellia/flags.h>
-#include <camellia/syscalls.h>
-#include <stdlib.h>
-#include <user/lib/thread.h>
-
-void thread_create(int flags, void (*fn)(void*), void *arg) {
-	if (!_syscall_fork(flags | FORK_SHAREMEM | FORK_SHAREHANDLE, NULL)) {
-		void *stack = malloc(4096);
-		chstack(arg, fn, stack + 4096);
-	}
-}
diff --git a/src/user/lib/thread.h b/src/user/lib/thread.h
index 0d7376a..5a5ddc0 100644
--- a/src/user/lib/thread.h
+++ b/src/user/lib/thread.h
@@ -1,4 +1,9 @@
 #pragma once
+#include <stdlib.h>
 
-void thread_create(int flags, void (*fn)(void*), void *arg);
-_Noreturn void chstack(void *arg, void (*fn)(void*), void *esp);
+void thread_creates(int flags, void (*fn)(void*), void *arg, void *stack);
+
+static inline void thread_create(int flags, void (*fn)(void*), void *arg) {
+	/* error checking is for WIMPS. */
+	thread_creates(flags, fn, arg, malloc(4096) + 4096);
+}