[dev.link] all: merge branch 'master' into dev.linkdev.link

Clean merge.

Change-Id: Ia7b2808bc649790198d34c226a61d9e569084dc5

19 files changed, 286 insertions, 113 deletions

diff --git a/src/runtime/cgo/asm_386.s b/src/runtime/cgo/asm_386.s
index 7293c20bf8..2e7e9512e2 100644
--- a/src/runtime/cgo/asm_386.s
+++ b/src/runtime/cgo/asm_386.s
@@ -5,8 +5,9 @@
 #include "textflag.h"
 
 // Called by C code generated by cmd/cgo.
-// func crosscall2(fn func(a unsafe.Pointer, n int32, ctxt uintptr), a unsafe.Pointer, n int32, ctxt uintptr)
-// Saves C callee-saved registers and calls fn with three arguments.
+// func crosscall2(fn, a unsafe.Pointer, n int32, ctxt uintptr)
+// Saves C callee-saved registers and calls cgocallback with three arguments.
+// fn is the PC of a func(a unsafe.Pointer) function.
 TEXT crosscall2(SB),NOSPLIT,$28-16
 	MOVL BP, 24(SP)
 	MOVL BX, 20(SP)
@@ -15,12 +16,11 @@ TEXT crosscall2(SB),NOSPLIT,$28-16
 
 	MOVL	ctxt+12(FP), AX
 	MOVL	AX, 8(SP)
-	MOVL	n+8(FP), AX
-	MOVL	AX, 4(SP)
 	MOVL	a+4(FP), AX
-	MOVL	AX, 0(SP)
+	MOVL	AX, 4(SP)
 	MOVL	fn+0(FP), AX
-	CALL	AX
+	MOVL	AX, 0(SP)
+	CALL	runtime·cgocallback(SB)
 
 	MOVL 12(SP), DI
 	MOVL 16(SP), SI
diff --git a/src/runtime/cgo/asm_amd64.s b/src/runtime/cgo/asm_amd64.s
index 06c538b9bc..5dc8e2d235 100644
--- a/src/runtime/cgo/asm_amd64.s
+++ b/src/runtime/cgo/asm_amd64.s
@@ -5,8 +5,10 @@
 #include "textflag.h"
 
 // Called by C code generated by cmd/cgo.
-// func crosscall2(fn func(a unsafe.Pointer, n int32, ctxt uintptr), a unsafe.Pointer, n int32, ctxt uintptr)
-// Saves C callee-saved registers and calls fn with three arguments.
+// func crosscall2(fn, a unsafe.Pointer, n int32, ctxt uintptr)
+// Saves C callee-saved registers and calls cgocallback with three arguments.
+// fn is the PC of a func(a unsafe.Pointer) function.
+// This signature is known to SWIG, so we can't change it.
 #ifndef GOOS_windows
 TEXT crosscall2(SB),NOSPLIT,$0x50-0 /* keeps stack pointer 32-byte aligned */
 #else
@@ -33,11 +35,12 @@ TEXT crosscall2(SB),NOSPLIT,$0x110-0 /* also need to save xmm6 - xmm15 */
 	MOVUPS	X14, 0xe0(SP)
 	MOVUPS	X15, 0xf0(SP)
 
-	MOVQ	DX, 0x0(SP)	/* arg */
-	MOVQ	R8, 0x8(SP)	/* argsize (includes padding) */
+	MOVQ	CX, 0x0(SP)	/* fn */
+	MOVQ	DX, 0x8(SP)	/* arg */
+	// Skip n in R8.
 	MOVQ	R9, 0x10(SP)	/* ctxt */
 
-	CALL	CX	/* fn */
+	CALL	runtime·cgocallback(SB)
 
 	MOVQ	0x48(SP), DI
 	MOVQ	0x50(SP), SI
@@ -52,11 +55,12 @@ TEXT crosscall2(SB),NOSPLIT,$0x110-0 /* also need to save xmm6 - xmm15 */
 	MOVUPS	0xe0(SP), X14
 	MOVUPS	0xf0(SP), X15
 #else
-	MOVQ	SI, 0x0(SP)	/* arg */
-	MOVQ	DX, 0x8(SP)	/* argsize (includes padding) */
+	MOVQ	DI, 0x0(SP)	/* fn */
+	MOVQ	SI, 0x8(SP)	/* arg */
+	// Skip n in DX.
 	MOVQ	CX, 0x10(SP)	/* ctxt */
 
-	CALL	DI	/* fn */
+	CALL	runtime·cgocallback(SB)
 #endif
 
 	MOVQ	0x18(SP), BX
diff --git a/src/runtime/cgo/asm_arm.s b/src/runtime/cgo/asm_arm.s
index 60132c14a8..ea55e173c1 100644
--- a/src/runtime/cgo/asm_arm.s
+++ b/src/runtime/cgo/asm_arm.s
@@ -5,51 +5,52 @@
 #include "textflag.h"
 
 // Called by C code generated by cmd/cgo.
-// func crosscall2(fn func(a unsafe.Pointer, n int32, ctxt uintptr), a unsafe.Pointer, n int32, ctxt uintptr)
-// Saves C callee-saved registers and calls fn with three arguments.
+// func crosscall2(fn, a unsafe.Pointer, n int32, ctxt uintptr)
+// Saves C callee-saved registers and calls cgocallback with three arguments.
+// fn is the PC of a func(a unsafe.Pointer) function.
 TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
-	/*
-	 * We still need to save all callee save register as before, and then
-	 *  push 3 args for fn (R1, R2, R3).
-	 * Also note that at procedure entry in gc world, 4(R13) will be the
-	 *  first arg, so we must push another dummy reg (R0) for 0(R13).
-	 *  Additionally, runtime·load_g will clobber R0, so we need to save R0
-	 *  nevertheless.
-	 */
 	SUB	$(8*9), R13 // Reserve space for the floating point registers.
-	MOVM.WP	[R0, R1, R2, R3, R4, R5, R6, R7, R8, R9, g, R11, R12, R14], (R13)
+	// The C arguments arrive in R0, R1, R2, and R3. We want to
+	// pass R0, R1, and R3 to Go, so we push those on the stack.
+	// Also, save C callee-save registers R4-R12.
+	MOVM.WP	[R0, R1, R3, R4, R5, R6, R7, R8, R9, g, R11, R12], (R13)
+	// Finally, save the link register R14. This also puts the
+	// arguments we pushed for cgocallback where they need to be,
+	// starting at 4(R13).
+	MOVW.W	R14, -4(R13)
 
 	// Skip floating point registers on GOARM < 6.
 	MOVB    runtime·goarm(SB), R11
 	CMP $6, R11
 	BLT skipfpsave
-	MOVD	F8, (14*4+8*1)(R13)
-	MOVD	F9, (14*4+8*2)(R13)
-	MOVD	F10, (14*4+8*3)(R13)
-	MOVD	F11, (14*4+8*4)(R13)
-	MOVD	F12, (14*4+8*5)(R13)
-	MOVD	F13, (14*4+8*6)(R13)
-	MOVD	F14, (14*4+8*7)(R13)
-	MOVD	F15, (14*4+8*8)(R13)
+	MOVD	F8, (13*4+8*1)(R13)
+	MOVD	F9, (13*4+8*2)(R13)
+	MOVD	F10, (13*4+8*3)(R13)
+	MOVD	F11, (13*4+8*4)(R13)
+	MOVD	F12, (13*4+8*5)(R13)
+	MOVD	F13, (13*4+8*6)(R13)
+	MOVD	F14, (13*4+8*7)(R13)
+	MOVD	F15, (13*4+8*8)(R13)
 
 skipfpsave:
 	BL	runtime·load_g(SB)
-	MOVW	R15, R14 // R15 is PC.
-	MOVW	0(R13), R15
+	// We set up the arguments to cgocallback when saving registers above.
+	BL	runtime·cgocallback(SB)
 
 	MOVB    runtime·goarm(SB), R11
 	CMP $6, R11
 	BLT skipfprest
-	MOVD	(14*4+8*1)(R13), F8
-	MOVD	(14*4+8*2)(R13), F9
-	MOVD	(14*4+8*3)(R13), F10
-	MOVD	(14*4+8*4)(R13), F11
-	MOVD	(14*4+8*5)(R13), F12
-	MOVD	(14*4+8*6)(R13), F13
-	MOVD	(14*4+8*7)(R13), F14
-	MOVD	(14*4+8*8)(R13), F15
+	MOVD	(13*4+8*1)(R13), F8
+	MOVD	(13*4+8*2)(R13), F9
+	MOVD	(13*4+8*3)(R13), F10
+	MOVD	(13*4+8*4)(R13), F11
+	MOVD	(13*4+8*5)(R13), F12
+	MOVD	(13*4+8*6)(R13), F13
+	MOVD	(13*4+8*7)(R13), F14
+	MOVD	(13*4+8*8)(R13), F15
 
 skipfprest:
-	MOVM.IAW	(R13), [R0, R1, R2, R3, R4, R5, R6, R7, R8, R9, g, R11, R12, R14]
+	MOVW.P	4(R13), R14
+	MOVM.IAW	(R13), [R0, R1, R3, R4, R5, R6, R7, R8, R9, g, R11, R12]
 	ADD	$(8*9), R13
 	MOVW	R14, R15
diff --git a/src/runtime/cgo/asm_arm64.s b/src/runtime/cgo/asm_arm64.s
index ce56f9b1c7..1cb25cf89e 100644
--- a/src/runtime/cgo/asm_arm64.s
+++ b/src/runtime/cgo/asm_arm64.s
@@ -5,19 +5,20 @@
 #include "textflag.h"
 
 // Called by C code generated by cmd/cgo.
-// func crosscall2(fn func(a unsafe.Pointer, n int32, ctxt uintptr), a unsafe.Pointer, n int32, ctxt uintptr)
-// Saves C callee-saved registers and calls fn with three arguments.
+// func crosscall2(fn, a unsafe.Pointer, n int32, ctxt uintptr)
+// Saves C callee-saved registers and calls cgocallback with three arguments.
+// fn is the PC of a func(a unsafe.Pointer) function.
 TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 	/*
 	 * We still need to save all callee save register as before, and then
-	 *  push 3 args for fn (R1, R2, R3).
+	 *  push 3 args for fn (R0, R1, R3), skipping R2.
 	 * Also note that at procedure entry in gc world, 8(RSP) will be the
 	 *  first arg.
 	 * TODO(minux): use LDP/STP here if it matters.
 	 */
 	SUB	$(8*24), RSP
-	MOVD	R1, (8*1)(RSP)
-	MOVD	R2, (8*2)(RSP)
+	MOVD	R0, (8*1)(RSP)
+	MOVD	R1, (8*2)(RSP)
 	MOVD	R3, (8*3)(RSP)
 	MOVD	R19, (8*4)(RSP)
 	MOVD	R20, (8*5)(RSP)
@@ -40,15 +41,11 @@ TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 	FMOVD	F14, (8*22)(RSP)
 	FMOVD	F15, (8*23)(RSP)
 
-	MOVD	R0, R19
-
 	// Initialize Go ABI environment
 	BL	runtime·load_g(SB)
-	BL	(R19)
 
-	MOVD	(8*1)(RSP), R1
-	MOVD	(8*2)(RSP), R2
-	MOVD	(8*3)(RSP), R3
+	BL	runtime·cgocallback(SB)
+
 	MOVD	(8*4)(RSP), R19
 	MOVD	(8*5)(RSP), R20
 	MOVD	(8*6)(RSP), R21
diff --git a/src/runtime/cgo/asm_mips64x.s b/src/runtime/cgo/asm_mips64x.s
index 1235852dbe..e51cdf3d12 100644
--- a/src/runtime/cgo/asm_mips64x.s
+++ b/src/runtime/cgo/asm_mips64x.s
@@ -6,14 +6,14 @@
 
 #include "textflag.h"
 
-/*
- * void crosscall2(void (*fn)(void*, int32, uintptr), void*, int32, uintptr)
- * Save registers and call fn with two arguments.
- */
+// Called by C code generated by cmd/cgo.
+// func crosscall2(fn, a unsafe.Pointer, n int32, ctxt uintptr)
+// Saves C callee-saved registers and calls cgocallback with three arguments.
+// fn is the PC of a func(a unsafe.Pointer) function.
 TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 	/*
 	 * We still need to save all callee save register as before, and then
-	 *  push 3 args for fn (R5, R6, R7).
+	 *  push 3 args for fn (R4, R5, R7), skipping R6.
 	 * Also note that at procedure entry in gc world, 8(R29) will be the
 	 *  first arg.
 	 */
@@ -22,9 +22,9 @@ TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 #else
 	ADDV	$(-8*15), R29
 #endif
-	MOVV	R5, (8*1)(R29) // void*
-	MOVW	R6, (8*2)(R29) // int32
-	MOVV	R7, (8*3)(R29) // uintptr
+	MOVV	R4, (8*1)(R29) // fn unsafe.Pointer
+	MOVV	R5, (8*2)(R29) // a unsafe.Pointer
+	MOVV	R7, (8*3)(R29) // ctxt uintptr
 	MOVV	R16, (8*4)(R29)
 	MOVV	R17, (8*5)(R29)
 	MOVV	R18, (8*6)(R29)
@@ -52,7 +52,8 @@ TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 	SRLV	$32, R31, RSB
 	SLLV	$32, RSB
 	JAL	runtime·load_g(SB)
-	JAL	(R4)
+
+	JAL	runtime·cgocallback(SB)
 
 	MOVV	(8*4)(R29), R16
 	MOVV	(8*5)(R29), R17
diff --git a/src/runtime/cgo/asm_mipsx.s b/src/runtime/cgo/asm_mipsx.s
index e3090da223..1127c8beb4 100644
--- a/src/runtime/cgo/asm_mipsx.s
+++ b/src/runtime/cgo/asm_mipsx.s
@@ -6,14 +6,14 @@
 
 #include "textflag.h"
 
-/*
- * void crosscall2(void (*fn)(void*, int32, uintptr), void*, int32, uintptr)
- * Save registers and call fn with two arguments.
- */
+// Called by C code generated by cmd/cgo.
+// func crosscall2(fn, a unsafe.Pointer, n int32, ctxt uintptr)
+// Saves C callee-saved registers and calls cgocallback with three arguments.
+// fn is the PC of a func(a unsafe.Pointer) function.
 TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 	/*
 	 * We still need to save all callee save register as before, and then
-	 *  push 3 args for fn (R5, R6, R7).
+	 *  push 3 args for fn (R4, R5, R7), skipping R6.
 	 * Also note that at procedure entry in gc world, 4(R29) will be the
 	 *  first arg.
 	 */
@@ -25,9 +25,9 @@ TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 #else
 	SUBU	$(4*14-16), R29	// For soft-float, no FPR.
 #endif
-	MOVW	R5, (4*1)(R29)
-	MOVW	R6, (4*2)(R29)
-	MOVW	R7, (4*3)(R29)
+	MOVW	R4, (4*1)(R29)	// fn unsafe.Pointer
+	MOVW	R5, (4*2)(R29)	// a unsafe.Pointer
+	MOVW	R7, (4*3)(R29)	// ctxt uintptr
 	MOVW	R16, (4*4)(R29)
 	MOVW	R17, (4*5)(R29)
 	MOVW	R18, (4*6)(R29)
@@ -47,7 +47,8 @@ TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 	MOVD	F30, (4*14+8*5)(R29)
 #endif
 	JAL	runtime·load_g(SB)
-	JAL	(R4)
+
+	JAL	runtime·cgocallback(SB)
 
 	MOVW	(4*4)(R29), R16
 	MOVW	(4*5)(R29), R17
diff --git a/src/runtime/cgo/asm_ppc64x.s b/src/runtime/cgo/asm_ppc64x.s
index 3876f9389c..f4efc1e67d 100644
--- a/src/runtime/cgo/asm_ppc64x.s
+++ b/src/runtime/cgo/asm_ppc64x.s
@@ -8,8 +8,9 @@
 #include "asm_ppc64x.h"
 
 // Called by C code generated by cmd/cgo.
-// func crosscall2(fn func(a unsafe.Pointer, n int32, ctxt uintptr), a unsafe.Pointer, n int32, ctxt uintptr)
-// Saves C callee-saved registers and calls fn with three arguments.
+// func crosscall2(fn, a unsafe.Pointer, n int32, ctxt uintptr)
+// Saves C callee-saved registers and calls cgocallback with three arguments.
+// fn is the PC of a func(a unsafe.Pointer) function.
 TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 	// Start with standard C stack frame layout and linkage
 	MOVD	LR, R0
@@ -26,19 +27,18 @@ TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 	BL	runtime·reginit(SB)
 	BL	runtime·load_g(SB)
 
-	MOVD	R3, R12
 #ifdef GOARCH_ppc64
 	// ppc64 use elf ABI v1. we must get the real entry address from
 	// first slot of the function descriptor before call.
 	// Same for AIX.
-	MOVD	8(R12), R2
-	MOVD	(R12), R12
+	MOVD	8(R3), R2
+	MOVD	(R3), R3
 #endif
-	MOVD	R12, CTR
-	MOVD	R4, FIXED_FRAME+0(R1)
-	MOVW	R5, FIXED_FRAME+8(R1)
-	MOVD	R6, FIXED_FRAME+16(R1)
-	BL	(CTR)
+	MOVD	R3, FIXED_FRAME+0(R1)	// fn unsafe.Pointer
+	MOVD	R4, FIXED_FRAME+8(R1)	// a unsafe.Pointer
+	// Skip R5 = n uint32
+	MOVD	R6, FIXED_FRAME+16(R1)	// ctxt uintptr
+	BL	runtime·cgocallback(SB)
 
 	ADD	$(288+3*8+FIXED_FRAME), R1
 
diff --git a/src/runtime/cgo/asm_s390x.s b/src/runtime/cgo/asm_s390x.s
index 7eab8f652a..8bf16e75e2 100644
--- a/src/runtime/cgo/asm_s390x.s
+++ b/src/runtime/cgo/asm_s390x.s
@@ -5,8 +5,9 @@
 #include "textflag.h"
 
 // Called by C code generated by cmd/cgo.
-// func crosscall2(fn func(a unsafe.Pointer, n int32, ctxt uintptr), a unsafe.Pointer, n int32, ctxt uintptr)
-// Saves C callee-saved registers and calls fn with three arguments.
+// func crosscall2(fn, a unsafe.Pointer, n int32, ctxt uintptr)
+// Saves C callee-saved registers and calls cgocallback with three arguments.
+// fn is the PC of a func(a unsafe.Pointer) function.
 TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 	// Start with standard C stack frame layout and linkage.
 
@@ -29,10 +30,11 @@ TEXT crosscall2(SB),NOSPLIT|NOFRAME,$0
 	// Initialize Go ABI environment.
 	BL	runtime·load_g(SB)
 
-	MOVD	R3, 8(R15)  // arg1
-	MOVW	R4, 16(R15) // arg2
-	MOVD	R5, 24(R15) // arg3
-	BL	(R2)        // fn(arg1, arg2, arg3)
+	MOVD	R2, 8(R15)	// fn unsafe.Pointer
+	MOVD	R3, 16(R15)	// a unsafe.Pointer
+	// Skip R4 = n uint32
+	MOVD	R5, 24(R15)	// ctxt uintptr
+	BL	runtime·cgocallback(SB)
 
 	FMOVD	32(R15), F8
 	FMOVD	40(R15), F9
diff --git a/src/runtime/cgo/callbacks.go b/src/runtime/cgo/callbacks.go
index 14a218ec92..cd8b795387 100644
--- a/src/runtime/cgo/callbacks.go
+++ b/src/runtime/cgo/callbacks.go
@@ -9,20 +9,18 @@ import "unsafe"
 // These utility functions are available to be called from code
 // compiled with gcc via crosscall2.
 
-// cgocallback is defined in runtime
-//go:linkname _runtime_cgocallback runtime.cgocallback
-func _runtime_cgocallback(unsafe.Pointer, unsafe.Pointer, uintptr, uintptr)
-
 // The declaration of crosscall2 is:
-//   void crosscall2(void (*fn)(void *, int), void *, int);
+//   void crosscall2(void (*fn)(void *), void *, int);
 //
 // We need to export the symbol crosscall2 in order to support
 // callbacks from shared libraries. This applies regardless of
 // linking mode.
 //
-// Compatibility note: crosscall2 actually takes four arguments, but
-// it works to call it with three arguments when calling _cgo_panic.
-// That is supported for backward compatibility.
+// Compatibility note: SWIG uses crosscall2 in exactly one situation:
+// to call _cgo_panic using the pattern shown below. We need to keep
+// that pattern working. In particular, crosscall2 actually takes four
+// arguments, but it works to call it with three arguments when
+// calling _cgo_panic.
 //go:cgo_export_static crosscall2
 //go:cgo_export_dynamic crosscall2
 
@@ -34,21 +32,18 @@ func _runtime_cgocallback(unsafe.Pointer, unsafe.Pointer, uintptr, uintptr)
 //   crosscall2(_cgo_panic, &a, sizeof a);
 //   /* The function call will not return.  */
 
+// TODO: We should export a regular C function to panic, change SWIG
+// to use that instead of the above pattern, and then we can drop
+// backwards-compatibility from crosscall2 and stop exporting it.
+
 //go:linkname _runtime_cgo_panic_internal runtime._cgo_panic_internal
 func _runtime_cgo_panic_internal(p *byte)
 
 //go:linkname _cgo_panic _cgo_panic
 //go:cgo_export_static _cgo_panic
 //go:cgo_export_dynamic _cgo_panic
-//go:nosplit
-//go:norace
-func _cgo_panic(a unsafe.Pointer, n int32) {
-	f := _runtime_cgo_panic_internal
-	type funcval struct {
-		pc unsafe.Pointer
-	}
-	fv := *(**funcval)(unsafe.Pointer(&f))
-	_runtime_cgocallback(fv.pc, a, uintptr(n), 0)
+func _cgo_panic(a *struct{ cstr *byte }) {
+	_runtime_cgo_panic_internal(a.cstr)
 }
 
 //go:cgo_import_static x_cgo_init
diff --git a/src/runtime/cgo/cgo.go b/src/runtime/cgo/cgo.go
index c02b837978..4d2caf6c4f 100644
--- a/src/runtime/cgo/cgo.go
+++ b/src/runtime/cgo/cgo.go
@@ -21,6 +21,7 @@ package cgo
 #cgo openbsd LDFLAGS: -lpthread
 #cgo aix LDFLAGS: -Wl,-berok
 #cgo solaris LDFLAGS: -lxnet
+#cgo illumos LDFLAGS: -lsocket
 
 // Issue 35247.
 #cgo darwin CFLAGS: -Wno-nullability-completeness
diff --git a/src/runtime/cgo/gcc_darwin_arm64.c b/src/runtime/cgo/gcc_darwin_arm64.c
index fd7d4084c9..dbe848b4ee 100644
--- a/src/runtime/cgo/gcc_darwin_arm64.c
+++ b/src/runtime/cgo/gcc_darwin_arm64.c
@@ -10,12 +10,16 @@
 #include <unistd.h>
 #include <stdlib.h>
 
-#include <CoreFoundation/CFBundle.h>
-#include <CoreFoundation/CFString.h>
-
 #include "libcgo.h"
 #include "libcgo_unix.h"
 
+#include <TargetConditionals.h>
+
+#if TARGET_OS_IPHONE
+#include <CoreFoundation/CFBundle.h>
+#include <CoreFoundation/CFString.h>
+#endif
+
 #define magic (0xc476c475c47957UL)
 
 // inittls allocates a thread-local storage slot for g.
@@ -87,14 +91,18 @@ threadentry(void *v)
 	ts = *(ThreadStart*)v;
 	free(v);
 
+#if TARGET_OS_IPHONE
 	darwin_arm_init_thread_exception_port();
+#endif
 
 	crosscall1(ts.fn, setg_gcc, (void*)ts.g);
 	return nil;
 }
 
+#if TARGET_OS_IPHONE
+
 // init_working_dir sets the current working directory to the app root.
-// By default darwin/arm64 processes start in "/".
+// By default ios/arm64 processes start in "/".
 static void
 init_working_dir()
 {
@@ -131,7 +139,7 @@ init_working_dir()
 		fprintf(stderr, "runtime/cgo: chdir(%s) failed\n", dir);
 	}
 
-	// The test harness in go_darwin_arm_exec passes the relative working directory
+	// The test harness in go_ios_exec passes the relative working directory
 	// in the GoExecWrapperWorkingDirectory property of the app bundle.
 	CFStringRef wd_ref = CFBundleGetValueForInfoDictionaryKey(bundle, CFSTR("GoExecWrapperWorkingDirectory"));
 	if (wd_ref != NULL) {
@@ -145,6 +153,8 @@ init_working_dir()
 	}
 }
 
+#endif // TARGET_OS_IPHONE
+
 void
 x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
 {
@@ -161,8 +171,9 @@ x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
 	// yes, tlsbase from mrs might not be correctly aligned.
 	inittls(tlsg, (void**)((uintptr)tlsbase & ~7));
 
+#if TARGET_OS_IPHONE
 	darwin_arm_init_mach_exception_handler();
 	darwin_arm_init_thread_exception_port();
-
 	init_working_dir();
+#endif
 }
diff --git a/src/runtime/cgo/gcc_libinit_windows.c b/src/runtime/cgo/gcc_libinit_windows.c
index 9fd7d36bfb..2732248bdc 100644
--- a/src/runtime/cgo/gcc_libinit_windows.c
+++ b/src/runtime/cgo/gcc_libinit_windows.c
@@ -3,6 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build cgo
+
 #define WIN64_LEAN_AND_MEAN
 #include <windows.h>
 #include <process.h>
diff --git a/src/runtime/cgo/gcc_signal2_darwin_arm64.c b/src/runtime/cgo/gcc_signal2_ios_arm64.c
index 5b8a18ffd6..5b8a18ffd6 100644
--- a/src/runtime/cgo/gcc_signal2_darwin_arm64.c
+++ b/src/runtime/cgo/gcc_signal2_ios_arm64.c
diff --git a/src/runtime/cgo/gcc_signal_darwin_arm64.c b/src/runtime/cgo/gcc_signal_ios_arm64.c
index 6519edd4cc..6519edd4cc 100644
--- a/src/runtime/cgo/gcc_signal_darwin_arm64.c
+++ b/src/runtime/cgo/gcc_signal_ios_arm64.c
diff --git a/src/runtime/cgo/gcc_signal_darwin_lldb.c b/src/runtime/cgo/gcc_signal_ios_nolldb.c
index 0ccdae324e..cfa4025414 100644
--- a/src/runtime/cgo/gcc_signal_darwin_lldb.c
+++ b/src/runtime/cgo/gcc_signal_ios_nolldb.c
@@ -3,7 +3,7 @@
 // license that can be found in the LICENSE file.
 
 // +build !lldb
-// +build darwin
+// +build ios
 // +build arm64
 
 #include <stdint.h>
diff --git a/src/runtime/cgo/linux.go b/src/runtime/cgo/linux.go
new file mode 100644
index 0000000000..76c0192c20
--- /dev/null
+++ b/src/runtime/cgo/linux.go
@@ -0,0 +1,74 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Linux system call wrappers that provide POSIX semantics through the
+// corresponding cgo->libc (nptl) wrappers for various system calls.
+
+// +build linux
+
+package cgo
+
+import "unsafe"
+
+// Each of the following entries is needed to ensure that the
+// syscall.syscall_linux code can conditionally call these
+// function pointers:
+//
+//  1. find the C-defined function start
+//  2. force the local byte alias to be mapped to that location
+//  3. map the Go pointer to the function to the syscall package
+
+//go:cgo_import_static _cgo_libc_setegid
+//go:linkname _cgo_libc_setegid _cgo_libc_setegid
+//go:linkname cgo_libc_setegid syscall.cgo_libc_setegid
+var _cgo_libc_setegid byte
+var cgo_libc_setegid = unsafe.Pointer(&_cgo_libc_setegid)
+
+//go:cgo_import_static _cgo_libc_seteuid
+//go:linkname _cgo_libc_seteuid _cgo_libc_seteuid
+//go:linkname cgo_libc_seteuid syscall.cgo_libc_seteuid
+var _cgo_libc_seteuid byte
+var cgo_libc_seteuid = unsafe.Pointer(&_cgo_libc_seteuid)
+
+//go:cgo_import_static _cgo_libc_setregid
+//go:linkname _cgo_libc_setregid _cgo_libc_setregid
+//go:linkname cgo_libc_setregid syscall.cgo_libc_setregid
+var _cgo_libc_setregid byte
+var cgo_libc_setregid = unsafe.Pointer(&_cgo_libc_setregid)
+
+//go:cgo_import_static _cgo_libc_setresgid
+//go:linkname _cgo_libc_setresgid _cgo_libc_setresgid
+//go:linkname cgo_libc_setresgid syscall.cgo_libc_setresgid
+var _cgo_libc_setresgid byte
+var cgo_libc_setresgid = unsafe.Pointer(&_cgo_libc_setresgid)
+
+//go:cgo_import_static _cgo_libc_setresuid
+//go:linkname _cgo_libc_setresuid _cgo_libc_setresuid
+//go:linkname cgo_libc_setresuid syscall.cgo_libc_setresuid
+var _cgo_libc_setresuid byte
+var cgo_libc_setresuid = unsafe.Pointer(&_cgo_libc_setresuid)
+
+//go:cgo_import_static _cgo_libc_setreuid
+//go:linkname _cgo_libc_setreuid _cgo_libc_setreuid
+//go:linkname cgo_libc_setreuid syscall.cgo_libc_setreuid
+var _cgo_libc_setreuid byte
+var cgo_libc_setreuid = unsafe.Pointer(&_cgo_libc_setreuid)
+
+//go:cgo_import_static _cgo_libc_setgroups
+//go:linkname _cgo_libc_setgroups _cgo_libc_setgroups
+//go:linkname cgo_libc_setgroups syscall.cgo_libc_setgroups
+var _cgo_libc_setgroups byte
+var cgo_libc_setgroups = unsafe.Pointer(&_cgo_libc_setgroups)
+
+//go:cgo_import_static _cgo_libc_setgid
+//go:linkname _cgo_libc_setgid _cgo_libc_setgid
+//go:linkname cgo_libc_setgid syscall.cgo_libc_setgid
+var _cgo_libc_setgid byte
+var cgo_libc_setgid = unsafe.Pointer(&_cgo_libc_setgid)
+
+//go:cgo_import_static _cgo_libc_setuid
+//go:linkname _cgo_libc_setuid _cgo_libc_setuid
+//go:linkname cgo_libc_setuid syscall.cgo_libc_setuid
+var _cgo_libc_setuid byte
+var cgo_libc_setuid = unsafe.Pointer(&_cgo_libc_setuid)
diff --git a/src/runtime/cgo/linux_syscall.c b/src/runtime/cgo/linux_syscall.c
new file mode 100644
index 0000000000..c8e91918a1
--- /dev/null
+++ b/src/runtime/cgo/linux_syscall.c
@@ -0,0 +1,85 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build linux
+
+#ifndef _GNU_SOURCE // setres[ug]id() API.
+#define _GNU_SOURCE
+#endif
+
+#include <grp.h>
+#include <sys/types.h>
+#include <sys/unistd.h>
+#include <errno.h>
+#include "libcgo.h"
+
+/*
+ * Assumed POSIX compliant libc system call wrappers. For linux, the
+ * glibc/nptl/setxid mechanism ensures that POSIX semantics are
+ * honored for all pthreads (by default), and this in turn with cgo
+ * ensures that all Go threads launched with cgo are kept in sync for
+ * these function calls.
+ */
+
+// argset_t matches runtime/cgocall.go:argset.
+typedef struct {
+	uintptr_t* args;
+	uintptr_t retval;
+} argset_t;
+
+// libc backed posix-compliant syscalls.
+
+#define SET_RETVAL(fn) \
+  uintptr_t ret = (uintptr_t) fn ; \
+  if (ret == -1) {                 \
+    x->retval = (uintptr_t) errno; \
+  } else                           \
+    x->retval = ret
+
+void
+_cgo_libc_setegid(argset_t* x) {
+	SET_RETVAL(setegid((gid_t) x->args[0]));
+}
+
+void
+_cgo_libc_seteuid(argset_t* x) {
+	SET_RETVAL(seteuid((uid_t) x->args[0]));
+}
+
+void
+_cgo_libc_setgid(argset_t* x) {
+	SET_RETVAL(setgid((gid_t) x->args[0]));
+}
+
+void
+_cgo_libc_setgroups(argset_t* x) {
+	SET_RETVAL(setgroups((size_t) x->args[0], (const gid_t *) x->args[1]));
+}
+
+void
+_cgo_libc_setregid(argset_t* x) {
+	SET_RETVAL(setregid((gid_t) x->args[0], (gid_t) x->args[1]));
+}
+
+void
+_cgo_libc_setresgid(argset_t* x) {
+	SET_RETVAL(setresgid((gid_t) x->args[0], (gid_t) x->args[1],
+			     (gid_t) x->args[2]));
+}
+
+void
+_cgo_libc_setresuid(argset_t* x) {
+	SET_RETVAL(setresuid((uid_t) x->args[0], (uid_t) x->args[1],
+			     (uid_t) x->args[2]));
+}
+
+void
+_cgo_libc_setreuid(argset_t* x) {
+	SET_RETVAL(setreuid((uid_t) x->args[0], (uid_t) x->args[1]));
+}
+
+void
+_cgo_libc_setuid(argset_t* x) {
+	SET_RETVAL(setuid((uid_t) x->args[0]));
+}
diff --git a/src/runtime/cgo/signal_darwin_arm64.go b/src/runtime/cgo/signal_ios_arm64.go
index 3425c448c4..3425c448c4 100644
--- a/src/runtime/cgo/signal_darwin_arm64.go
+++ b/src/runtime/cgo/signal_ios_arm64.go
diff --git a/src/runtime/cgo/signal_darwin_arm64.s b/src/runtime/cgo/signal_ios_arm64.s
index 1ae00d13f3..1ae00d13f3 100644
--- a/src/runtime/cgo/signal_darwin_arm64.s
+++ b/src/runtime/cgo/signal_ios_arm64.s