From 04e6ae6bc3ac9739568b0f1225ee5e2d53cba919 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Thu, 8 Feb 2018 16:59:17 +0100
Subject: [PATCH] runtime: use Android O friendly syscalls on 64-bit machines

Android O disallows open on 64-bit, so let's use openat with AT_FDCWD to
achieve the same behavior.

Android O disallows epoll_wait on 64-bit, so let's use epoll_pwait with
the last argument as NULL to achieve the same behavior.

See here:
https://android.googlesource.com/platform/bionic/+/master/libc/seccomp/arm64_app_policy.cpp
https://android.googlesource.com/platform/bionic/+/master/libc/seccomp/mips64_app_policy.cpp
https://android.googlesource.com/platform/bionic/+/master/libc/seccomp/x86_64_app_policy.cpp

Fixes #23750

Change-Id: If8d5a663357471e5d2c1f516151344a9d05b188a
Reviewed-on: https://go-review.googlesource.com/92895
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
---
 src/runtime/sys_linux_amd64.s   | 18 +++++++++++-------
 src/runtime/sys_linux_mips64x.s | 18 +++++++++++-------
 2 files changed, 22 insertions(+), 14 deletions(-)

diff --git a/src/runtime/sys_linux_amd64.s b/src/runtime/sys_linux_amd64.s
index 5a94bda7c2..017e7dcaef 100644
--- a/src/runtime/sys_linux_amd64.s
+++ b/src/runtime/sys_linux_amd64.s
@@ -12,7 +12,6 @@
 
 #define SYS_read		0
 #define SYS_write		1
-#define SYS_open		2
 #define SYS_close		3
 #define SYS_mmap		9
 #define SYS_munmap		11
@@ -41,9 +40,10 @@
 #define SYS_sched_getaffinity	204
 #define SYS_epoll_create	213
 #define SYS_exit_group		231
-#define SYS_epoll_wait		232
 #define SYS_epoll_ctl		233
+#define SYS_openat		257
 #define SYS_pselect6		270
+#define SYS_epoll_pwait		281
 #define SYS_epoll_create1	291
 
 TEXT runtime·exit(SB),NOSPLIT,$0-4
@@ -65,10 +65,12 @@ TEXT runtime·exitThread(SB),NOSPLIT,$0-8
 	JMP	0(PC)
 
 TEXT runtime·open(SB),NOSPLIT,$0-20
-	MOVQ	name+0(FP), DI
-	MOVL	mode+8(FP), SI
-	MOVL	perm+12(FP), DX
-	MOVL	$SYS_open, AX
+	// This uses openat instead of open, because Android O blocks open.
+	MOVL	$-100, DI // AT_FDCWD, so this acts like open
+	MOVQ	name+0(FP), SI
+	MOVL	mode+8(FP), DX
+	MOVL	perm+12(FP), R10
+	MOVL	$SYS_openat, AX
 	SYSCALL
 	CMPQ	AX, $0xfffffffffffff001
 	JLS	2(PC)
@@ -655,11 +657,13 @@ TEXT runtime·epollctl(SB),NOSPLIT,$0
 
 // int32 runtime·epollwait(int32 epfd, EpollEvent *ev, int32 nev, int32 timeout);
 TEXT runtime·epollwait(SB),NOSPLIT,$0
+	// This uses pwait instead of wait, because Android O blocks wait.
 	MOVL	epfd+0(FP), DI
 	MOVQ	ev+8(FP), SI
 	MOVL	nev+16(FP), DX
 	MOVL	timeout+20(FP), R10
-	MOVL	$SYS_epoll_wait, AX
+	MOVQ	$0, R8
+	MOVL	$SYS_epoll_pwait, AX
 	SYSCALL
 	MOVL	AX, ret+24(FP)
 	RET
diff --git a/src/runtime/sys_linux_mips64x.s b/src/runtime/sys_linux_mips64x.s
index 784e187e73..50e103bb63 100644
--- a/src/runtime/sys_linux_mips64x.s
+++ b/src/runtime/sys_linux_mips64x.s
@@ -16,7 +16,7 @@
 #define SYS_exit		5058
 #define SYS_read		5000
 #define SYS_write		5001
-#define SYS_open		5002
+#define SYS_openat		5247
 #define SYS_close		5003
 #define SYS_getpid		5038
 #define SYS_kill		5060
@@ -42,7 +42,7 @@
 #define SYS_exit_group		5205
 #define SYS_epoll_create	5207
 #define SYS_epoll_ctl		5208
-#define SYS_epoll_wait		5209
+#define SYS_epoll_pwait		5272
 #define SYS_clock_gettime	5222
 #define SYS_epoll_create1	5285
 #define SYS_brk			5012
@@ -67,10 +67,12 @@ TEXT runtime·exitThread(SB),NOSPLIT|NOFRAME,$0-8
 	JMP	0(PC)
 
 TEXT runtime·open(SB),NOSPLIT|NOFRAME,$0-20
-	MOVV	name+0(FP), R4
-	MOVW	mode+8(FP), R5
-	MOVW	perm+12(FP), R6
-	MOVV	$SYS_open, R2
+	// This uses openat instead of open, because Android O blocks open.
+	MOVW	$-100, R4 // AT_FDCWD, so this acts like open
+	MOVV	name+0(FP), R5
+	MOVW	mode+8(FP), R6
+	MOVW	perm+12(FP), R7
+	MOVV	$SYS_openat, R2
 	SYSCALL
 	BEQ	R7, 2(PC)
 	MOVW	$-1, R2
@@ -423,11 +425,13 @@ TEXT runtime·epollctl(SB),NOSPLIT|NOFRAME,$0
 
 // int32 runtime·epollwait(int32 epfd, EpollEvent *ev, int32 nev, int32 timeout);
 TEXT runtime·epollwait(SB),NOSPLIT|NOFRAME,$0
+	// This uses pwait instead of wait, because Android O blocks wait.
 	MOVW	epfd+0(FP), R4
 	MOVV	ev+8(FP), R5
 	MOVW	nev+16(FP), R6
 	MOVW	timeout+20(FP), R7
-	MOVV	$SYS_epoll_wait, R2
+	MOVV	$0, R8
+	MOVV	$SYS_epoll_pwait, R2
 	SYSCALL
 	MOVW	R2, ret+24(FP)
 	RET