cmd/internal/objabi: extract shared functionality from obj

Now only cmd/asm and cmd/compile depend on cmd/internal/obj. Changing
the assembler backends no longer requires reinstalling cmd/link or
cmd/addr2line.

There's also now one canonical definition of the object file format in
cmd/internal/objabi/doc.go, with a warning to update all three
implementations.

objabi is still something of a grab bag of unrelated code (e.g., flag
and environment variable handling probably belong in a separate "tool"
package), but this is still progress.

Fixes #15165.
Fixes #20026.

Change-Id: Ic4b92fac7d0d35438e0d20c9579aad4085c5534c
Reviewed-on: https://go-review.googlesource.com/40972
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/src/cmd/internal/objabi/funcdata.go b/src/cmd/internal/objabi/funcdata.go
new file mode 100644
index 0000000000..80874edeb0
--- /dev/null
+++ b/src/cmd/internal/objabi/funcdata.go
@@ -0,0 +1,25 @@
+// Copyright 2013 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 objabi
+
+// This file defines the IDs for PCDATA and FUNCDATA instructions
+// in Go binaries.
+//
+// These must agree with ../../../runtime/funcdata.h and
+// ../../../runtime/symtab.go.
+
+const (
+	PCDATA_StackMapIndex       = 0
+	PCDATA_InlTreeIndex        = 1
+	FUNCDATA_ArgsPointerMaps   = 0
+	FUNCDATA_LocalsPointerMaps = 1
+	FUNCDATA_InlTree           = 2
+
+	// ArgsSizeUnknown is set in Func.argsize to mark all functions
+	// whose argument size is unknown (C vararg functions, and
+	// assembly code without an explicit specification).
+	// This value is generated by the compiler, assembler, or linker.
+	ArgsSizeUnknown = -0x80000000
+)