From 6a9e57741328dcae97b7966a6df69c2962f4ca2f Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sun, 28 Aug 2016 00:26:06 +0000
Subject: [PATCH] Follow ABI when calling __error from the ptrace(2) wrapper.

In particular, preserve syscall arguments on stack, since callee is
not required to preserve arg-passing registers.  Align stack.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
---
 lib/libc/amd64/sys/ptrace.S | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/lib/libc/amd64/sys/ptrace.S b/lib/libc/amd64/sys/ptrace.S
index c367a4ea12d..c65a51ba2ef 100644
--- a/lib/libc/amd64/sys/ptrace.S
+++ b/lib/libc/amd64/sys/ptrace.S
@@ -42,11 +42,21 @@ __FBSDID("$FreeBSD$");
 	.type	CNAME(__error),@function
 
 ENTRY(ptrace)
+	pushq	%rdi	/* align stack */
+	pushq	%rdi
+	pushq	%rsi
+	pushq	%rdx
+	pushq	%rcx
 #ifdef PIC
 	callq	PIC_PLT(CNAME(__error))
 #else
 	callq	CNAME(__error)
 #endif
+	popq	%rcx
+	popq	%rdx
+	popq	%rsi
+	popq	%rdi
+	popq	%rdi
 	movl	$0,(%rax)
 	mov	$SYS_ptrace,%eax
 	KERNCALL