runtime: add hook to register coverage-instrumented packages

Add support to the runtime for registering coverage-instrumented
packages, using a new hook that can be called from the init function
of an instrumented package. The hook records the meta-data symbol for
the package (chaining it onto a list), and returns a package ID to be
used to identify functions in the package. This new hook is not yet
called; that will be added in a subsequent patch. The list of
registered meta-data objects will be used (again in a future patch) as
part of coverage data file writing.

Special handling is required for packages such as "runtime" or
"internal/cpu", where functions in the package execute before the
package "init" func runs. For these packages hard-code the package ID,
then record the position of the package in the overall list so that we
can fix things up later on.

Updates #51430.

Change-Id: I6ca3ddf535197442a2603c6d7a0a9798b8496f40
Reviewed-on: https://go-review.googlesource.com/c/go/+/401234
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Than McIntosh <thanm@google.com>

1 files changed, 82 insertions, 0 deletions

diff --git a/src/runtime/covermeta.go b/src/runtime/covermeta.go
new file mode 100644
index 0000000000..90bc20f45b
--- /dev/null
+++ b/src/runtime/covermeta.go
@@ -0,0 +1,82 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime
+
+import (
+	"internal/coverage/rtcov"
+	"unsafe"
+)
+
+// covMeta is the top-level container for bits of state related to
+// code coverage meta-data in the runtime.
+var covMeta struct {
+	// metaList contains the list of currently registered meta-data
+	// blobs for the running program.
+	metaList []rtcov.CovMetaBlob
+
+	// pkgMap records mappings from hard-coded package IDs to
+	// slots in the covMetaList above.
+	pkgMap map[int]int
+
+	// Set to true if we discover a package mapping glitch.
+	hardCodedListNeedsUpdating bool
+}
+
+func reportErrorInHardcodedList(slot int32, pkgId int32) {
+	println("internal error in coverage meta-data tracking:")
+	println("encountered bad pkg ID ", pkgId, " at slot ", slot)
+	println("list of hard-coded runtime package IDs needs revising.")
+	println("[see the comment on the 'rtPkgs' var in ")
+	println(" <goroot>/src/internal/coverage/pkid.go]")
+	println("registered list:")
+	for k, b := range covMeta.metaList {
+		print("slot: ", k, " path='", b.PkgPath, "' ")
+		if b.PkgID != -1 {
+			print(" hard-coded id: ", b.PkgID)
+		}
+		println("")
+	}
+	println("remap table:")
+	for from, to := range covMeta.pkgMap {
+		println("from ", from, " to ", to)
+	}
+}
+
+// addCovMeta is invoked during package "init" functions by the
+// compiler when compiling for coverage instrumentation; here 'p' is a
+// meta-data blob of length 'dlen' for the package in question, 'hash'
+// is a compiler-computed md5.sum for the blob, 'pkpath' is the
+// package path, 'pkid' is the hard-coded ID that the compiler is
+// using for the package (or -1 if the compiler doesn't think a
+// hard-coded ID is needed), and 'cmode'/'cgran' are the coverage
+// counter mode and granularity requested by the user. Return value is
+// the ID for the package for use by the package code itself.
+func addCovMeta(p unsafe.Pointer, dlen uint32, hash [16]byte, pkpath string, pkid int, cmode uint8, cgran uint8) uint32 {
+	slot := len(covMeta.metaList)
+	covMeta.metaList = append(covMeta.metaList,
+		rtcov.CovMetaBlob{
+			P:                  (*byte)(p),
+			Len:                dlen,
+			Hash:               hash,
+			PkgPath:            pkpath,
+			PkgID:              pkid,
+			CounterMode:        cmode,
+			CounterGranularity: cgran,
+		})
+	if pkid != -1 {
+		if covMeta.pkgMap == nil {
+			covMeta.pkgMap = make(map[int]int)
+		}
+		if _, ok := covMeta.pkgMap[pkid]; ok {
+			throw("runtime.addCovMeta: coverage package map collision")
+		}
+		// Record the real slot (position on meta-list) for this
+		// package; we'll use the map to fix things up later on.
+		covMeta.pkgMap[pkid] = slot
+	}
+
+	// ID zero is reserved as invalid.
+	return uint32(slot + 1)
+}