cmd/go, cmd/link: support failure to create _cgo_import.go

For a package that uses cgo, the file _cgo_import.go is created to
record information required for internal linking: the non-Go dynamic
symbols and libraries that the package depends on. Generating this
information sometimes fails, because it can require recreating all the
dependencies of all transitively imported packages. And the
information is rarely needed, since by default we use external linking
when there are packages outside of the standard library that use cgo.

With this CL, if generating _cgo_import.go fails, we don't report an
error. Instead, we mark the package as requiring external linking, by
adding an empty file named "dynimportfail" into the generated archive.
If the linker sees a file with that name, it rejects an attempt to use
internal linking.

Fixes #52863

Change-Id: Ie586e6753a5b67e49bb14533cd7603d9defcf0ea
Reviewed-on: https://go-review.googlesource.com/c/go/+/413460
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go
index 9a5d89a6f7..a3d8202e2c 100644
--- a/src/cmd/link/internal/ld/lib.go
+++ b/src/cmd/link/internal/ld/lib.go
@@ -344,6 +344,11 @@ var (
 	// to support internal linking mode.
 	externalobj = false
 
+	// dynimportfail is a list of packages for which generating
+	// the dynimport file, _cgo_import.go, failed. If there are
+	// any of these objects, we must link externally. Issue 52863.
+	dynimportfail []string
+
 	// unknownObjFormat is set to true if we see an object whose
 	// format we don't recognize.
 	unknownObjFormat = false
@@ -1030,6 +1035,10 @@ func loadobjfile(ctxt *Link, lib *sym.Library) {
 			continue
 		}
 
+		if arhdr.name == "dynimportfail" {
+			dynimportfail = append(dynimportfail, lib.Pkg)
+		}
+
 		// Skip other special (non-object-file) sections that
 		// build tools may have added. Such sections must have
 		// short names so that the suffix is not truncated.