internal/fakecgo: correct the explanation of using closure calls (#85)

PR #73 circumvent go 1.20 race mode on darwin. However, the explanation
for using the closure calls are partly wrong, and also not so much clear
about how the trick works.

This commit reworks the comments, and adding a more detail explanation.

Updates #71

commit: a7c4d8fb43b1fe6b3cbde6e9495935f06f538af2
author: Cuong Manh Le · 3y ago · 2023-01-07 01:10 UTC
committer: GitHub · 3y ago · 2023-01-07 01:10 UTC
parent: 9e27b96
signature: GPG Unverified4AEE18F83AFDEB23 The key is unknown

1 file · +10 -4

M internal/fakecgo/callbacks.go +10 -4


@@ -46,10 +46,16 @@ var (
46	46		// In Go 1.20 the race detector was rewritten to pure Go
47	47		// on darwin. This means that when CGO_ENABLED=0 is set
48	48		// fakecgo is built with race detector code. This is not
49		-	// good since this code is pretending to be C. The
50		-	// go:norace comments are not enough since the ABI wrappers
51		-	// still have race code. These variables will circumvent
52		-	// that issue by calling the function directly.
	49	+	// good since this code is pretending to be C. The go:norace
	50	+	// pragma is not enough, since it only applies to the native
	51	+	// ABIInternal function. The ABIO wrapper (which is necessary,
	52	+	// since all references to text symbols from assembly will use it)
	53	+	// does not inherit the go:norace pragma, so it will still be
	54	+	// instrumented by the race detector.
	55	+	//
	56	+	// To circumvent this issue, using closure calls in the
	57	+	// assembly, which forces the compiler to use the ABIInternal
	58	+	// native implementation (which has go:norace) instead.
53	59		threadentry_call = threadentry
54	60		x_cgo_init_call = x_cgo_init
55	61		x_cgo_setenv_call = x_cgo_setenv

 	// In Go 1.20 the race detector was rewritten to pure Go
 	// on darwin. This means that when CGO_ENABLED=0 is set
 	// fakecgo is built with race detector code. This is not
-	// good since this code is pretending to be C. The
+	// good since this code is pretending to be C. The go:norace
-	// go:norace comments are not enough since the ABI wrappers
+	// pragma is not enough, since it only applies to the native
-	// still have race code. These variables will circumvent
+	// ABIInternal function. The ABIO wrapper (which is necessary,
-	// that issue by calling the function directly.
+	// since all references to text symbols from assembly will use it)
+	// does not inherit the go:norace pragma, so it will still be
+	// instrumented by the race detector.
+	//
+	// To circumvent this issue, using closure calls in the
+	// assembly, which forces the compiler to use the ABIInternal
+	// native implementation (which has go:norace) instead.
 	threadentry_call        = threadentry
 	x_cgo_init_call         = x_cgo_init
 	x_cgo_setenv_call       = x_cgo_setenv