[dev.link] add compilation unit index to func

Not used yet, but add the compilation unit for a function to func.

Change-Id: I7c43fa9f1da044ca63bab030062519771b9f4418
Reviewed-on: https://go-review.googlesource.com/c/go/+/244547
Run-TryBot: Jeremy Faller <jeremy@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/src/cmd/link/internal/sym/compilation_unit.go b/src/cmd/link/internal/sym/compilation_unit.go
index d9bfc84936..dc37a36cba 100644
--- a/src/cmd/link/internal/sym/compilation_unit.go
+++ b/src/cmd/link/internal/sym/compilation_unit.go
@@ -10,12 +10,19 @@ import "cmd/internal/dwarf"
 // type from the sym package since loader imports sym.
 type LoaderSym int
 
-// CompilationUnit is an abstraction used by DWARF to represent a chunk of
-// debug-related data. We create a CompilationUnit per Object file in a
-// library (so, one for all the Go code, one for each assembly file, etc.).
+// A CompilationUnit represents a set of source files that are compiled
+// together. Since all Go sources in a Go package are compiled together,
+// there's one CompilationUnit per package that represents all Go sources in
+// that package, plus one for each assembly file.
+//
+// Equivalently, there's one CompilationUnit per object file in each Library
+// loaded by the linker.
+//
+// These are used for both DWARF and pclntab generation.
 type CompilationUnit struct {
 	Pkg            string        // The package name, eg ("fmt", or "runtime")
 	Lib            *Library      // Our library
+	PclnIndex      int           // Index of this CU in pclntab
 	PCs            []dwarf.Range // PC ranges, relative to Textp[0]
 	DWInfo         *dwarf.DWDie  // CU root DIE
 	DWARFFileTable []string      // The file table used to generate the .debug_lines