cmd/compile: add coverage fixup mode

Adds a -coveragecfg=<configfile> command line option to the compiler
to help support a cooperative "tool and compiler" mode for coverage
instrumentation. In this mode the cmd/cover tool generates most of the
counter instrumentation via source-to-source rewriting, but the
compiler fixes up the result if passed the "-coveragecfg" option. The
fixups include:

  - reclassifying counter variables (special storage class)
  - marking meta-data variables are read-only
  - adding in an init call to do registation

Updates #51430.

Change-Id: Iead72b85209725ee044542374465f118a3ee72e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/395895
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 66 insertions, 0 deletions

diff --git a/src/internal/coverage/cmddefs.go b/src/internal/coverage/cmddefs.go
new file mode 100644
index 0000000000..a146ca53e4
--- /dev/null
+++ b/src/internal/coverage/cmddefs.go
@@ -0,0 +1,66 @@
+// 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 coverage
+
+// CoverPkgConfig is a bundle of information passed from the Go
+// command to the cover command during "go build -cover" runs. The
+// Go command creates and fills in a struct as below, then passes
+// file containing the encoded JSON for the struct to the "cover"
+// tool when instrumenting the source files in a Go package.
+type CoverPkgConfig struct {
+	// File into which cmd/cover should emit summary info
+	// when instrumentation is complete.
+	OutConfig string
+
+	// Import path for the package being instrumented.
+	PkgPath string
+
+	// Package name.
+	PkgName string
+
+	// Instrumentation granularity: one of "perfunc" or "perblock" (default)
+	Granularity string
+
+	// Module path for this package (empty if no go.mod in use)
+	ModulePath string
+}
+
+// CoverFixupConfig contains annotations/notes generated by the
+// cmd/cover tool (during instrumentation) to be passed on to the
+// compiler when the instrumented code is compiled. The cmd/cover tool
+// creates a struct of this type, JSON-encodes it, and emits the
+// result to a file, which the Go command then passes to the compiler
+// when the instrumented package is built.
+type CoverFixupConfig struct {
+	// Name of the variable (created by cmd/cover) containing the
+	// encoded meta-data for the package.
+	MetaVar string
+
+	// Length of the meta-data.
+	MetaLen int
+
+	// Hash computed by cmd/cover of the meta-data.
+	MetaHash string
+
+	// Instrumentation strategy. For now this is always set to
+	// "normal", but in the future we may add new values (for example,
+	// if panic paths are instrumented, or if the instrumenter
+	// eliminates redundant counters).
+	Strategy string
+
+	// Prefix assigned to the names of counter variables generated
+	// during instrumentation by cmd/cover.
+	CounterPrefix string
+
+	// Name chosen for the package ID variable generated during
+	// instrumentation.
+	PkgIdVar string
+
+	// Counter mode (e.g. set/count/atomic)
+	CounterMode string
+
+	// Counter granularity (perblock or perfunc).
+	CounterGranularity string
+}