checklinkname: rudimentary type-checking of linkname directives

This CL introduces a 'checklinkname' analyzer, which provides rudimentary
type-checking that verifies that function signatures on the local and remote
sides of //go:linkname directives match expected values.

If the Go standard library changes the definitions of any of these function,
checklinkname will flag the change as a finding, providing an error informing
the gVisor team to adapt to the upstream changes. This allows us to eliminate
the majority of gVisor's forward-looking negative build tags, as we can catch
mismatches in testing [1].

The remaining forward-looking negative build tags are covering shared struct
definitions, which I hope to add to checklinkname in a future CL.

[1] Of course, semantics/requirements can change without the signature
changing, so we still must be careful, but this covers the common case.

PiperOrigin-RevId: 387873847

1 files changed, 4 insertions, 3 deletions

diff --git a/pkg/tcpip/link/rawfile/blockingpoll_yield_unsafe.go b/pkg/tcpip/link/rawfile/blockingpoll_yield_unsafe.go
index da900c24b..0b7b9e3de 100644
--- a/pkg/tcpip/link/rawfile/blockingpoll_yield_unsafe.go
+++ b/pkg/tcpip/link/rawfile/blockingpoll_yield_unsafe.go
@@ -12,12 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build ((linux && amd64) || (linux && arm64)) && go1.12 && !go1.18
+//go:build ((linux && amd64) || (linux && arm64)) && go1.12
 // +build linux,amd64 linux,arm64
 // +build go1.12
-// +build !go1.18
 
-// Check go:linkname function signatures when updating Go version.
+// //go:linkname directives type-checked by checklinkname. Any other
+// non-linkname assumptions outside the Go 1 compatibility guarantee should
+// have an accompanied vet check or version guard build tag.
 
 package rawfile