unix: add ptrace definitions for compatible GOARCH pairs

For pairs of GOARCH values that can execute each other's binaries on
the same system, such as 386 and amd64, add the definitions and
functions required to fetch and set registers when debugging either
variant.

Fixes golang/go#9739

Change-Id: I7896ddef7d341ffaee56614ebd080dc38c708ed4
Reviewed-on: https://go-review.googlesource.com/73555
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

unix/linux/mkall.go

@@ -15,12 +15,17 @@
 package main
 
 import (
+	"bufio"
+	"bytes"
 	"fmt"
+	"io"
+	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"runtime"
 	"strings"
+	"unicode"
 )
 
 // These will be paths to the appropriate source directories.
@@ -128,6 +133,15 @@ var targets = []target{
 	// },
 }
 
+// ptracePairs is a list of pairs of targets that can, in some cases,
+// run each other's binaries.
+var ptracePairs = []struct{ a1, a2 string }{
+	{"386", "amd64"},
+	{"arm", "arm64"},
+	{"mips", "mips64"},
+	{"mipsle", "mips64le"},
+}
+
 func main() {
 	if runtime.GOOS != GOOS || runtime.GOARCH != BuildArch {
 		fmt.Printf("Build system has GOOS_GOARCH = %s_%s, need %s_%s\n",
@@ -158,6 +172,17 @@ func main() {
 			fmt.Printf("----- SUCCESS:    %s -----\n\n", t.GoArch)
 		}
 	}
+
+	fmt.Printf("----- GENERATING ptrace pairs -----\n")
+	ok := true
+	for _, p := range ptracePairs {
+		if err := generatePtracePair(p.a1, p.a2); err != nil {
+			fmt.Printf("%v\n***** FAILURE: %s/%s *****\n\n", err, p.a1, p.a2)
+		}
+	}
+	if ok {
+		fmt.Printf("----- SUCCESS ptrace pairs    -----\n\n")
+	}
 }
 
 // Makes an exec.Cmd with Stderr attached to os.Stderr
@@ -377,3 +402,80 @@ func (t *target) mksyscallFlags() (flags []string) {
 	}
 	return
 }
+
+// generatePtracePair takes a pair of GOARCH values that can run each
+// other's binaries, such as 386 and amd64. It extracts the PtraceRegs
+// type for each one. It writes a new file defining the types
+// PtraceRegsArch1 and PtraceRegsArch2 and the corresponding functions
+// Ptrace{Get,Set}Regs{arch1,arch2}. This permits debugging the other
+// binary on a native system.
+func generatePtracePair(arch1, arch2 string) error {
+	def1, err := ptraceDef(arch1)
+	if err != nil {
+		return err
+	}
+	def2, err := ptraceDef(arch2)
+	if err != nil {
+		return err
+	}
+	f, err := os.Create(fmt.Sprintf("zptrace%s_linux.go", arch1))
+	if err != nil {
+		return err
+	}
+	buf := bufio.NewWriter(f)
+	fmt.Fprintf(buf, "// Code generated by linux/mkall.go generatePtracePair(%s, %s).  DO NOT EDIT.\n", arch1, arch2)
+	fmt.Fprintf(buf, "\n")
+	fmt.Fprintf(buf, "// +build linux\n")
+	fmt.Fprintf(buf, "// +build %s %s\n", arch1, arch2)
+	fmt.Fprintf(buf, "\n")
+	fmt.Fprintf(buf, "package unix\n")
+	fmt.Fprintf(buf, "\n")
+	fmt.Fprintf(buf, "%s\n", `import "unsafe"`)
+	fmt.Fprintf(buf, "\n")
+	writeOnePtrace(buf, arch1, def1)
+	fmt.Fprintf(buf, "\n")
+	writeOnePtrace(buf, arch2, def2)
+	if err := buf.Flush(); err != nil {
+		return err
+	}
+	if err := f.Close(); err != nil {
+		return err
+	}
+	return nil
+}
+
+// ptraceDef returns the definition of PtraceRegs for arch.
+func ptraceDef(arch string) (string, error) {
+	filename := fmt.Sprintf("ztypes_linux_%s.go", arch)
+	data, err := ioutil.ReadFile(filename)
+	if err != nil {
+		return "", fmt.Errorf("reading %s: %v", filename, err)
+	}
+	start := bytes.Index(data, []byte("type PtraceRegs struct"))
+	if start < 0 {
+		return "", fmt.Errorf("%s: no definition of PtraceRegs", filename)
+	}
+	data = data[start:]
+	end := bytes.Index(data, []byte("\n}\n"))
+	if end < 0 {
+		return "", fmt.Errorf("%s: can't find end of PtraceRegs definition", filename)
+	}
+	return string(data[:end+2]), nil
+}
+
+// writeOnePtrace writes out the ptrace definitions for arch.
+func writeOnePtrace(w io.Writer, arch, def string) {
+	uarch := string(unicode.ToUpper(rune(arch[0]))) + arch[1:]
+	fmt.Fprintf(w, "// PtraceRegs%s is the registers used by %s binaries.\n", uarch, arch)
+	fmt.Fprintf(w, "%s\n", strings.Replace(def, "PtraceRegs", "PtraceRegs"+uarch, 1))
+	fmt.Fprintf(w, "\n")
+	fmt.Fprintf(w, "// PtraceGetRegs%s fetches the registers used by %s binaries.\n", uarch, arch)
+	fmt.Fprintf(w, "func PtraceGetRegs%s(pid int, regsout *PtraceRegs%s) error {\n", uarch, uarch)
+	fmt.Fprintf(w, "\treturn ptrace(PTRACE_GETREGS, pid, 0, uintptr(unsafe.Pointer(regsout)))\n")
+	fmt.Fprintf(w, "}\n")
+	fmt.Fprintf(w, "\n")
+	fmt.Fprintf(w, "// PtraceSetRegs%s sets the registers used by %s binaries.\n", uarch, arch)
+	fmt.Fprintf(w, "func PtraceSetRegs%s(pid int, regs *PtraceRegs%s) error {\n", uarch, uarch)
+	fmt.Fprintf(w, "\treturn ptrace(PTRACE_SETREGS, pid, 0, uintptr(unsafe.Pointer(regs)))\n")
+	fmt.Fprintf(w, "}\n")
+}