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, 9 insertions, 4 deletions

diff --git a/pkg/sync/runtime_unsafe.go b/pkg/sync/runtime_unsafe.go
index 1d9cf304e..49d4109a9 100644
--- a/pkg/sync/runtime_unsafe.go
+++ b/pkg/sync/runtime_unsafe.go
@@ -6,8 +6,13 @@
 //go:build go1.13 && !go1.18
 // +build go1.13,!go1.18
 
-// Check go:linkname function signatures, type definitions, and constants 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.
+
+// Check type definitions and constants when updating Go version.
+//
+// TODO(b/165820485): add these checks to checklinkname.
 
 package sync
 
@@ -109,10 +114,10 @@ type maptype struct {
 // These functions are only used within the sync package.
 
 //go:linkname semacquire sync.runtime_Semacquire
-func semacquire(s *uint32)
+func semacquire(addr *uint32)
 
 //go:linkname semrelease sync.runtime_Semrelease
-func semrelease(s *uint32, handoff bool, skipframes int)
+func semrelease(addr *uint32, handoff bool, skipframes int)
 
 //go:linkname canSpin sync.runtime_canSpin
 func canSpin(i int) bool