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

3 files changed, 16 insertions, 10 deletions

diff --git a/pkg/sentry/platform/kvm/bluepill_unsafe.go b/pkg/sentry/platform/kvm/bluepill_unsafe.go
index f63ab6aba..0f0c1e73b 100644
--- a/pkg/sentry/platform/kvm/bluepill_unsafe.go
+++ b/pkg/sentry/platform/kvm/bluepill_unsafe.go
@@ -12,10 +12,12 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build go1.12 && !go1.18
-// +build go1.12,!go1.18
+//go:build go1.12
+// +build go1.12
 
-// 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 kvm
 
@@ -28,7 +30,7 @@ import (
 )
 
 //go:linkname throw runtime.throw
-func throw(string)
+func throw(s string)
 
 // vCPUPtr returns a CPU for the given address.
 //
diff --git a/pkg/sentry/platform/kvm/machine_unsafe.go b/pkg/sentry/platform/kvm/machine_unsafe.go
index 35660e827..cc3a1253b 100644
--- a/pkg/sentry/platform/kvm/machine_unsafe.go
+++ b/pkg/sentry/platform/kvm/machine_unsafe.go
@@ -12,10 +12,12 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build go1.12 && !go1.18
-// +build go1.12,!go1.18
+//go:build go1.12
+// +build go1.12
 
-// 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 kvm
 
diff --git a/pkg/sentry/platform/ptrace/subprocess_unsafe.go b/pkg/sentry/platform/ptrace/subprocess_unsafe.go
index ffd4665f4..304722200 100644
--- a/pkg/sentry/platform/ptrace/subprocess_unsafe.go
+++ b/pkg/sentry/platform/ptrace/subprocess_unsafe.go
@@ -12,10 +12,12 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-//go:build go1.12 && !go1.18
-// +build go1.12,!go1.18
+//go:build go1.12
+// +build go1.12
 
-// 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 ptrace