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, 20 insertions, 0 deletions

diff --git a/src/cmd/internal/objabi/stack.go b/src/cmd/internal/objabi/stack.go
new file mode 100644
index 0000000000..11433932e2
--- /dev/null
+++ b/src/cmd/internal/objabi/stack.go
@@ -0,0 +1,20 @@
+// Copyright 2011 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
+
+// For the linkers. Must match Go definitions.
+
+const (
+	STACKSYSTEM = 0
+	StackSystem = STACKSYSTEM
+	StackBig    = 4096
+	StackGuard  = 880*stackGuardMultiplier + StackSystem
+	StackSmall  = 128
+	StackLimit  = StackGuard - StackSystem - StackSmall
+)
+
+const (
+	StackPreempt = -1314 // 0xfff...fade
+)