cmd/compile, runtime: add comparison tracing for libFuzzer

This CL extends cmd/compile's experimental libFuzzer support with
calls to __sanitizer_cov_trace_{,const_}cmp{1,2,4,8}. This allows much
more efficient fuzzing of comparisons.

Only supports amd64 and arm64 for now.

Updates #14565.

Change-Id: Ibf82a8d9658f2bc50d955bdb1ae26723a3f0584d
Reviewed-on: https://go-review.googlesource.com/c/go/+/203887
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/gc/builtin.go

@@ -183,6 +183,14 @@ var runtimeDecls = [...]struct {
 	{"msanwrite", funcTag, 119},
 	{"checkptrAlignment", funcTag, 120},
 	{"checkptrArithmetic", funcTag, 122},
+	{"libfuzzerTraceCmp1", funcTag, 124},
+	{"libfuzzerTraceCmp2", funcTag, 126},
+	{"libfuzzerTraceCmp4", funcTag, 127},
+	{"libfuzzerTraceCmp8", funcTag, 128},
+	{"libfuzzerTraceConstCmp1", funcTag, 124},
+	{"libfuzzerTraceConstCmp2", funcTag, 126},
+	{"libfuzzerTraceConstCmp4", funcTag, 127},
+	{"libfuzzerTraceConstCmp8", funcTag, 128},
 	{"x86HasPOPCNT", varTag, 15},
 	{"x86HasSSE41", varTag, 15},
 	{"x86HasFMA", varTag, 15},
@@ -191,7 +199,7 @@ var runtimeDecls = [...]struct {
 }
 
 func runtimeTypes() []*types.Type {
-	var typs [123]*types.Type
+	var typs [129]*types.Type
 	typs[0] = types.Bytetype
 	typs[1] = types.NewPtr(typs[0])
 	typs[2] = types.Types[TANY]
@@ -315,5 +323,11 @@ func runtimeTypes() []*types.Type {
 	typs[120] = functype(nil, []*Node{anonfield(typs[56]), anonfield(typs[1]), anonfield(typs[50])}, nil)
 	typs[121] = types.NewSlice(typs[56])
 	typs[122] = functype(nil, []*Node{anonfield(typs[56]), anonfield(typs[121])}, nil)
+	typs[123] = types.Types[TUINT8]
+	typs[124] = functype(nil, []*Node{anonfield(typs[123]), anonfield(typs[123])}, nil)
+	typs[125] = types.Types[TUINT16]
+	typs[126] = functype(nil, []*Node{anonfield(typs[125]), anonfield(typs[125])}, nil)
+	typs[127] = functype(nil, []*Node{anonfield(typs[64]), anonfield(typs[64])}, nil)
+	typs[128] = functype(nil, []*Node{anonfield(typs[21]), anonfield(typs[21])}, nil)
 	return typs[:]
 }

src/cmd/compile/internal/gc/builtin/runtime.go

@@ -238,6 +238,15 @@ func msanwrite(addr, size uintptr)
 func checkptrAlignment(unsafe.Pointer, *byte, uintptr)
 func checkptrArithmetic(unsafe.Pointer, []unsafe.Pointer)
 
+func libfuzzerTraceCmp1(uint8, uint8)
+func libfuzzerTraceCmp2(uint16, uint16)
+func libfuzzerTraceCmp4(uint32, uint32)
+func libfuzzerTraceCmp8(uint64, uint64)
+func libfuzzerTraceConstCmp1(uint8, uint8)
+func libfuzzerTraceConstCmp2(uint16, uint16)
+func libfuzzerTraceConstCmp4(uint32, uint32)
+func libfuzzerTraceConstCmp8(uint64, uint64)
+
 // architecture variants
 var x86HasPOPCNT bool
 var x86HasSSE41 bool

src/cmd/compile/internal/gc/walk.go

@@ -3139,6 +3139,52 @@ func walkcompare(n *Node, init *Nodes) *Node {
 
 	switch t.Etype {
 	default:
+		if Debug_libfuzzer != 0 && t.IsInteger() {
+			n.Left = cheapexpr(n.Left, init)
+			n.Right = cheapexpr(n.Right, init)
+
+			// If exactly one comparison operand is
+			// constant, invoke the constcmp functions
+			// instead, and arrange for the constant
+			// operand to be the first argument.
+			l, r := n.Left, n.Right
+			if r.Op == OLITERAL {
+				l, r = r, l
+			}
+			constcmp := l.Op == OLITERAL && r.Op != OLITERAL
+
+			var fn string
+			var paramType *types.Type
+			switch t.Size() {
+			case 1:
+				fn = "libfuzzerTraceCmp1"
+				if constcmp {
+					fn = "libfuzzerTraceConstCmp1"
+				}
+				paramType = types.Types[TUINT8]
+			case 2:
+				fn = "libfuzzerTraceCmp2"
+				if constcmp {
+					fn = "libfuzzerTraceConstCmp2"
+				}
+				paramType = types.Types[TUINT16]
+			case 4:
+				fn = "libfuzzerTraceCmp4"
+				if constcmp {
+					fn = "libfuzzerTraceConstCmp4"
+				}
+				paramType = types.Types[TUINT32]
+			case 8:
+				fn = "libfuzzerTraceCmp8"
+				if constcmp {
+					fn = "libfuzzerTraceConstCmp8"
+				}
+				paramType = types.Types[TUINT64]
+			default:
+				Fatalf("unexpected integer size %d for %v", t.Size(), t)
+			}
+			init.Append(mkcall(fn, nil, init, tracecmpArg(l, paramType, init), tracecmpArg(r, paramType, init)))
+		}
 		return n
 	case TARRAY:
 		// We can compare several elements at once with 2/4/8 byte integer compares
@@ -3276,6 +3322,15 @@ func walkcompare(n *Node, init *Nodes) *Node {
 	return n
 }
 
+func tracecmpArg(n *Node, t *types.Type, init *Nodes) *Node {
+	// Ugly hack to avoid "constant -1 overflows uintptr" errors, etc.
+	if n.Op == OLITERAL && n.Type.IsSigned() && n.Int64() < 0 {
+		n = copyexpr(n, n.Type, init)
+	}
+
+	return conv(n, t)
+}
+
 func walkcompareInterface(n *Node, init *Nodes) *Node {
 	// ifaceeq(i1 any-1, i2 any-2) (ret bool);
 	if !types.Identical(n.Left.Type, n.Right.Type) {

src/runtime/libfuzzer.go

+// 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 libfuzzer
+
+package runtime
+
+import _ "unsafe" // for go:linkname
+
+func libfuzzerCall(fn *byte, arg0, arg1 uintptr)
+
+func libfuzzerTraceCmp1(arg0, arg1 uint8) {
+	libfuzzerCall(&__sanitizer_cov_trace_cmp1, uintptr(arg0), uintptr(arg1))
+}
+
+func libfuzzerTraceCmp2(arg0, arg1 uint16) {
+	libfuzzerCall(&__sanitizer_cov_trace_cmp2, uintptr(arg0), uintptr(arg1))
+}
+
+func libfuzzerTraceCmp4(arg0, arg1 uint32) {
+	libfuzzerCall(&__sanitizer_cov_trace_cmp4, uintptr(arg0), uintptr(arg1))
+}
+
+func libfuzzerTraceCmp8(arg0, arg1 uint64) {
+	libfuzzerCall(&__sanitizer_cov_trace_cmp8, uintptr(arg0), uintptr(arg1))
+}
+
+func libfuzzerTraceConstCmp1(arg0, arg1 uint8) {
+	libfuzzerCall(&__sanitizer_cov_trace_const_cmp1, uintptr(arg0), uintptr(arg1))
+}
+
+func libfuzzerTraceConstCmp2(arg0, arg1 uint16) {
+	libfuzzerCall(&__sanitizer_cov_trace_const_cmp2, uintptr(arg0), uintptr(arg1))
+}
+
+func libfuzzerTraceConstCmp4(arg0, arg1 uint32) {
+	libfuzzerCall(&__sanitizer_cov_trace_const_cmp4, uintptr(arg0), uintptr(arg1))
+}
+
+func libfuzzerTraceConstCmp8(arg0, arg1 uint64) {
+	libfuzzerCall(&__sanitizer_cov_trace_const_cmp8, uintptr(arg0), uintptr(arg1))
+}
+
+//go:linkname __sanitizer_cov_trace_cmp1 __sanitizer_cov_trace_cmp1
+//go:cgo_import_static __sanitizer_cov_trace_cmp1
+var __sanitizer_cov_trace_cmp1 byte
+
+//go:linkname __sanitizer_cov_trace_cmp2 __sanitizer_cov_trace_cmp2
+//go:cgo_import_static __sanitizer_cov_trace_cmp2
+var __sanitizer_cov_trace_cmp2 byte
+
+//go:linkname __sanitizer_cov_trace_cmp4 __sanitizer_cov_trace_cmp4
+//go:cgo_import_static __sanitizer_cov_trace_cmp4
+var __sanitizer_cov_trace_cmp4 byte
+
+//go:linkname __sanitizer_cov_trace_cmp8 __sanitizer_cov_trace_cmp8
+//go:cgo_import_static __sanitizer_cov_trace_cmp8
+var __sanitizer_cov_trace_cmp8 byte
+
+//go:linkname __sanitizer_cov_trace_const_cmp1 __sanitizer_cov_trace_const_cmp1
+//go:cgo_import_static __sanitizer_cov_trace_const_cmp1
+var __sanitizer_cov_trace_const_cmp1 byte
+
+//go:linkname __sanitizer_cov_trace_const_cmp2 __sanitizer_cov_trace_const_cmp2
+//go:cgo_import_static __sanitizer_cov_trace_const_cmp2
+var __sanitizer_cov_trace_const_cmp2 byte
+
+//go:linkname __sanitizer_cov_trace_const_cmp4 __sanitizer_cov_trace_const_cmp4
+//go:cgo_import_static __sanitizer_cov_trace_const_cmp4
+var __sanitizer_cov_trace_const_cmp4 byte
+
+//go:linkname __sanitizer_cov_trace_const_cmp8 __sanitizer_cov_trace_const_cmp8
+//go:cgo_import_static __sanitizer_cov_trace_const_cmp8
+var __sanitizer_cov_trace_const_cmp8 byte

src/runtime/libfuzzer_amd64.s

+// 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 libfuzzer
+
+#include "go_asm.h"
+#include "go_tls.h"
+#include "textflag.h"
+
+// Based on race_amd64.s; see commentary there.
+
+#ifdef GOOS_windows
+#define RARG0 CX
+#define RARG1 DX
+#else
+#define RARG0 DI
+#define RARG1 SI
+#endif
+
+// void runtime·libfuzzerCall(fn, arg0, arg1 uintptr)
+// Calls C function fn from libFuzzer and passes 2 arguments to it.
+TEXT	runtime·libfuzzerCall(SB), NOSPLIT, $0-24
+	MOVQ	fn+0(FP), AX
+	MOVQ	arg0+8(FP), RARG0
+	MOVQ	arg1+16(FP), RARG1
+
+	get_tls(R12)
+	MOVQ	g(R12), R14
+	MOVQ	g_m(R14), R13
+
+	// Switch to g0 stack.
+	MOVQ	SP, R12		// callee-saved, preserved across the CALL
+	MOVQ	m_g0(R13), R10
+	CMPQ	R10, R14
+	JE	call	// already on g0
+	MOVQ	(g_sched+gobuf_sp)(R10), SP
+call:
+	ANDQ	$~15, SP	// alignment for gcc ABI
+	CALL	AX
+	MOVQ	R12, SP
+	RET

src/runtime/libfuzzer_arm64.s

+// 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 libfuzzer
+
+#include "go_asm.h"
+#include "textflag.h"
+
+// Based on race_arm64.s; see commentary there.
+
+// func runtime·libfuzzerCall(fn, arg0, arg1 uintptr)
+// Calls C function fn from libFuzzer and passes 2 arguments to it.
+TEXT	runtime·libfuzzerCall(SB), NOSPLIT, $0-24
+	MOVD	fn+0(FP), R9
+	MOVD	arg0+8(FP), R0
+	MOVD	arg1+16(FP), R1
+
+	MOVD	g_m(g), R10
+
+	// Switch to g0 stack.
+	MOVD	RSP, R19	// callee-saved, preserved across the CALL
+	MOVD	m_g0(R10), R11
+	CMP	R11, g
+	BEQ	call	// already on g0
+	MOVD	(g_sched+gobuf_sp)(R11), R12
+	MOVD	R12, RSP
+call:
+	BL	R9
+	MOVD	R19, RSP
+	RET