cmd/cgo: document generated cgo directives
This took me a while to figure out. Save the next person some trouble.
Change-Id: Ifab2d426f67c21b08ef225c79125805a9008e578
Reviewed-on: https://go-review.googlesource.com/c/go/+/309336
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/src/cmd/cgo/out.go b/src/cmd/cgo/out.go
index 2d8d692..8c31d5b 100644
--- a/src/cmd/cgo/out.go
+++ b/src/cmd/cgo/out.go
@@ -1021,11 +1021,25 @@
}
fmt.Fprintf(fgcc, "}\n")
+ // In internal linking mode, the Go linker sees both
+ // the C wrapper written above and the Go wrapper it
+ // references. Hence, export the C wrapper (e.g., for
+ // if we're building a shared object). The Go linker
+ // will resolve the C wrapper's reference to the Go
+ // wrapper without a separate export.
+ fmt.Fprintf(fgo2, "//go:cgo_export_dynamic %s\n", exp.ExpName)
+ // cgo_export_static refers to a symbol by its linker
+ // name, so set the linker name of the Go wrapper.
+ fmt.Fprintf(fgo2, "//go:linkname _cgoexp%s_%s _cgoexp%s_%s\n", cPrefix, exp.ExpName, cPrefix, exp.ExpName)
+ // In external linking mode, the Go linker sees the Go
+ // wrapper, but not the C wrapper. For this case,
+ // export the Go wrapper so the host linker can
+ // resolve the reference from the C wrapper to the Go
+ // wrapper.
+ fmt.Fprintf(fgo2, "//go:cgo_export_static _cgoexp%s_%s\n", cPrefix, exp.ExpName)
+
// Build the wrapper function compiled by cmd/compile.
// This unpacks the argument struct above and calls the Go function.
- fmt.Fprintf(fgo2, "//go:cgo_export_dynamic %s\n", exp.ExpName)
- fmt.Fprintf(fgo2, "//go:linkname _cgoexp%s_%s _cgoexp%s_%s\n", cPrefix, exp.ExpName, cPrefix, exp.ExpName)
- fmt.Fprintf(fgo2, "//go:cgo_export_static _cgoexp%s_%s\n", cPrefix, exp.ExpName)
fmt.Fprintf(fgo2, "func _cgoexp%s_%s(a *%s) {\n", cPrefix, exp.ExpName, gotype)
fmt.Fprintf(fm, "int _cgoexp%s_%s;\n", cPrefix, exp.ExpName)
