runtime: use precise bounds of Go data/bss for race detector

We only want to call into the race detector for Go global variables.
By rounding up the region bounds, we can include some C globals.
Even worse, we can include only *part* of a C global, leading to
race{read,write}range calls which straddle the end of shadow memory.
That causes the race detector to barf.

Fix some off-by-one errors in the assembly comparisons. We want to
skip calling the race detector when addr == racedataend.

Fixes #73483

Change-Id: I436b0f588d6165b61f30cb7653016ba9b7cbf585
Reviewed-on: https://go-review.googlesource.com/c/go/+/667655
Reviewed-by: Keith Randall <[email protected]>
Auto-Submit: Keith Randall <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitry Vyukov <[email protected]>

Author: randall77

src/runtime/race.go

@@ -455,7 +455,6 @@ func raceinit() (gctx, pctx uintptr) {
 
 	racecall(&__tsan_init, uintptr(unsafe.Pointer(&gctx)), uintptr(unsafe.Pointer(&pctx)), abi.FuncPCABI0(racecallbackthunk), 0)
 
-	// Round data segment to page boundaries, because it's used in mmap().
 	start := ^uintptr(0)
 	end := uintptr(0)
 	if start > firstmoduledata.noptrdata {
@@ -482,10 +481,13 @@ func raceinit() (gctx, pctx uintptr) {
 	if end < firstmoduledata.ebss {
 		end = firstmoduledata.ebss
 	}
-	size := alignUp(end-start, _PageSize)
-	racecall(&__tsan_map_shadow, start, size, 0, 0)
+	// Use exact bounds for boundary check in racecalladdr. See issue 73483.
 	racedatastart = start
-	racedataend = start + size
+	racedataend = end
+	// Round data segment to page boundaries for race detector (TODO: still needed?)
+	start = alignDown(start, _PageSize)
+	end = alignUp(end, _PageSize)
+	racecall(&__tsan_map_shadow, start, end-start, 0, 0)
 
 	return
 }

src/runtime/race_arm64.s

@@ -163,7 +163,7 @@ data:
 	BLT	ret
 	MOVD	runtime·racedataend(SB), R10
 	CMP	R10, R1
-	BGT	ret
+	BGE	ret
 call:
 	JMP	racecall<>(SB)
 ret:

src/runtime/race_ppc64le.s

@@ -153,7 +153,7 @@ data:
 	BLT	ret
 	MOVD	runtime·racedataend(SB), R9
 	CMP	R4, R9
-	BGT	ret
+	BGE	ret
 call:
 	// Careful!! racecall will save LR on its
 	// stack, which is OK as long as racecalladdr

test/fixedbugs/issue73483.go

@@ -0,0 +1,20 @@
+// run -race
+
+//go:build race && cgo
+
+// Copyright 2025 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.
+
+package main
+
+/*
+   int v[8192];
+*/
+import "C"
+
+var x [8192]C.int
+
+func main() {
+	copy(C.v[:], x[:])
+}