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>

3 files changed, 148 insertions, 0 deletions

diff --git a/src/runtime/libfuzzer.go b/src/runtime/libfuzzer.go
new file mode 100644
index 0000000000..0161955f09
--- /dev/null
+++ b/src/runtime/libfuzzer.go
@@ -0,0 +1,75 @@
+// 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
diff --git a/src/runtime/libfuzzer_amd64.s b/src/runtime/libfuzzer_amd64.s
new file mode 100644
index 0000000000..890fde341b
--- /dev/null
+++ b/src/runtime/libfuzzer_amd64.s
@@ -0,0 +1,42 @@
+// 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
diff --git a/src/runtime/libfuzzer_arm64.s b/src/runtime/libfuzzer_arm64.s
new file mode 100644
index 0000000000..121673e092
--- /dev/null
+++ b/src/runtime/libfuzzer_arm64.s
@@ -0,0 +1,31 @@
+// 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