cmd/go: remove cross-package assembly reference discovery

This removes the special case for finding assembly references to Go
symbols in runtime and runtime/internal/atomic. These are no longer
necessary because we've now marked all symbols in these packages that
must be accessible from assembly in other packages.

Fixes #31230.

Change-Id: I70c90b70e13b922a6669f3d46c53347f98d6fc3f
Reviewed-on: https://go-review.googlesource.com/c/go/+/179863
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/internal/work/exec.go

@@ -1682,25 +1682,6 @@ func (b *Builder) writeFile(file string, text []byte) error {
 	return ioutil.WriteFile(file, text, 0666)
 }
 
-// appendFile appends the text to file.
-func (b *Builder) appendFile(file string, text []byte) error {
-	if cfg.BuildN || cfg.BuildX {
-		b.Showcmd("", "cat >>%s << 'EOF' # internal\n%sEOF", file, text)
-	}
-	if cfg.BuildN {
-		return nil
-	}
-	f, err := os.OpenFile(file, os.O_WRONLY|os.O_CREATE|os.O_APPEND, 0666)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-	if _, err = f.Write(text); err != nil {
-		return err
-	}
-	return f.Close()
-}
-
 // Install the cgo export header file, if there is one.
 func (b *Builder) installHeader(a *Action) error {
 	src := a.Objdir + "_cgo_install.h"

src/cmd/go/internal/work/gc.go

@@ -309,55 +309,6 @@ func (gcToolchain) symabis(b *Builder, a *Action, sfiles []string) (string, erro
 		}
 	}
 
-	// Gather known cross-package references from assembly code.
-	var otherPkgs []string
-	if p.ImportPath == "runtime" {
-		// Assembly in the following packages references
-		// symbols in runtime.
-		otherPkgs = []string{"syscall", "internal/syscall/unix", "runtime/cgo"}
-	} else if p.ImportPath == "runtime/internal/atomic" {
-		// sync/atomic is an assembly wrapper around
-		// runtime/internal/atomic.
-		otherPkgs = []string{"sync/atomic"}
-	}
-	for _, p2name := range otherPkgs {
-		p2 := load.LoadImportWithFlags(p2name, p.Dir, p, &load.ImportStack{}, nil, 0)
-		if len(p2.SFiles) == 0 {
-			continue
-		}
-
-		symabis2 := a.Objdir + "symabis2"
-		if err := mkSymabis(p2, p2.SFiles, symabis2); err != nil {
-			return "", err
-		}
-
-		// Filter out just the symbol refs and append them to
-		// the symabis file.
-		if cfg.BuildN {
-			// -x will print the lines from symabis2 that are actually appended
-			// to symabis. With -n, we don't know what those lines will be.
-			b.Showcmd("", `grep '^ref' <%s | grep -v '^ref\s*""\.' >>%s`, symabis2, a.Objdir+"symabis")
-			continue
-		}
-		abis2, err := ioutil.ReadFile(symabis2)
-		if err != nil {
-			return "", err
-		}
-		var refs bytes.Buffer
-		for _, line := range strings.Split(string(abis2), "\n") {
-			fs := strings.Fields(line)
-			if len(fs) >= 2 && fs[0] == "ref" && !strings.HasPrefix(fs[1], `"".`) {
-				fmt.Fprintf(&refs, "%s\n", line)
-			}
-		}
-		if refs.Len() != 0 {
-			symabis = a.Objdir + "symabis"
-			if err := b.appendFile(symabis, refs.Bytes()); err != nil {
-				return "", err
-			}
-		}
-	}
-
 	return symabis, nil
 }