From cc595c7c9908c33e644a41e2d96004c647e25c84 Mon Sep 17 00:00:00 2001
From: Giacomo Tesio <giacomo@tesio.it>
Date: Sun, 21 May 2017 00:15:51 +0200
Subject: [PATCH] kernel: save and restore all registers on syscall

---
 sys/src/kern/amd64/dat.h         |  2 ++
 sys/src/kern/amd64/l64vsyscall.S | 14 +++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/sys/src/kern/amd64/dat.h b/sys/src/kern/amd64/dat.h
index 7ae0376..a8bb4f4 100644
--- a/sys/src/kern/amd64/dat.h
+++ b/sys/src/kern/amd64/dat.h
@@ -198,6 +198,8 @@ struct Mach
 	uint64_t	machno;		/* physical id of processor */
 	uint64_t	splpc;		/* pc of last caller to splhi */
 	Proc*		proc;		/* current process on this processor */
+	uint64_t	tmp0;		/* for syscallentry */
+	uint64_t	tmp1;		/* for syscallentry */
 
 	int		apicno;
 	int		online;
diff --git a/sys/src/kern/amd64/l64vsyscall.S b/sys/src/kern/amd64/l64vsyscall.S
index 500715c..a6fc8a4 100644
--- a/sys/src/kern/amd64/l64vsyscall.S
+++ b/sys/src/kern/amd64/l64vsyscall.S
@@ -28,10 +28,14 @@ touser:
 syscallentry:
 	swapgs
 
-	movq	%gs:0, %r15			/* m-> (movq GS:0x0, R15) */
+	xchgq	%gs:0, %r15
+	movq	%r14, 24(%r15)			/* save %r14 to m->tmp0 */
 	movq	16(%r15), %r14			/* m->proc (set up->) */
+	movq	%r13, 32(%r15)			/* save %r13 to m->tmp1 */
 	movq	16*8(%r14), %r13		/* m->proc->kstack (after the Label) */
 	xchgq	%r13, %rsp
+	movq	24(%r15), %r14			/* restore %r14 */
+
 	addq	$KSTACK, %rsp
 
 	/* build Ureg */
@@ -41,6 +45,10 @@ syscallentry:
 	pushq	$SSEL(SiUCS, SsRPL3)		/* old code segment */
 	pushq	%rcx				/* old ip */
 
+	movq	%r14, 24(%r15)			/* restore %r14 from m->tmp0 */
+	movq	%r13, 32(%r15)			/* restore %r13 from m->tmp1 */
+	xchgq	%gs:0, %r15			/* restore %r15 */
+
 	subq	$(17*8), %rsp
 
 	movq	%rax, (0*8)(%rsp)	// ureg.ax
@@ -61,6 +69,10 @@ syscallentry:
 	// (15*8)(%rsp)	// ureg.type
 	// (16*8)(%rsp) // ureg.error
 
+	/* prepare m-> and up-> for the kernel */
+	movq	%gs:0, %r15
+	movq	16(%r15), %r14
+
 	movq	%rsp, %rsi 				/* Ureg* */
 	// system call number is in %rax, as per linux.
 	movq	%rax, %rdi