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

1 files changed, 39 insertions, 7 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... */