Added support for parsing multiple filename tables

[Omie]

refs #143 #215 (may be #79 )

• added a type DebugLines that can hold number of DebugLineInfo
• added a supporting attribute to DebugLineInfo called 'Lookup' which is to be
  used to quickly lookup if file exists in FileNames slice
• added supporting methods to lookup and return corresponding DebugLineInfo
• changed the debug_line parsing behavior to read all the available tables and
  push them to DebugLines
• since Process.lineInfo is now a slice, it was breaking AllPCsBetween as well
• updated that function's definition to accept a new filename parameter to be
  able to extract related DebugLineInfo
• updated calls to AllPCsBetween
• fixed tests that were broken due to attribute type change in Process
• updated _fixtures/cgotest program to include stdio.h, so that it updates
  .debug_line header
• added a test to check 'next' in a cgo binary

[Omie]

Someone has to see whats going wrong with osx-go1.4.2, I don't have Macbook :-(

[derekparker]

Does this test fail without your patch? I think there is already a CGO next test (I know it was my suggestion to write this test), but I want to make sure we have a test that triggers the behavior.

[Omie]

Yes. This test fails without my patch with exact same error. (with updated cgotest fixture only).
Another cgo test passes (with/without extra C header).

[Omie]

wonder whats wrong with Linux+1.4.2 on Travis now. All tests pass fine for me on 1.4.2, 1.5.
Linux+1.4.2 passed on Travis for earlier build, cleanup commit shouldn't break anything as I only altered comments and a blank line there.

[derekparker]

Merged, thanks!

I squashed the commits and applied the following cleanup:

diff --git a/dwarf/line/line_parser.go b/dwarf/line/line_parser.go
index da07468..def5a11 100644
--- a/dwarf/line/line_parser.go
+++ b/dwarf/line/line_parser.go
@@ -37,28 +37,22 @@ type FileEntry struct {
 type DebugLines []*DebugLineInfo

 func (d *DebugLines) GetLineInfo(name string) *DebugLineInfo {
-   //Find in which table file exists.
-   //Return that table
+   // Find in which table file exists and return it.
    for _, l := range *d {
-       if fe := l.GetFileEntry(name); fe != nil {
+       if _, ok := l.Lookup[name]; ok {
            return l
        }
    }
-
    return nil
 }

-func (d *DebugLineInfo) GetFileEntry(name string) *FileEntry {
-   return d.Lookup[name]
-}
-
 func Parse(data []byte) DebugLines {
    var (
        lines = make(DebugLines, 0)
        buf   = bytes.NewBuffer(data)
    )

-   // we have to scan multiple file name tables here
+   // We have to parse multiple file name tables here.
    for buf.Len() > 0 {
        dbl := new(DebugLineInfo)
        dbl.Lookup = make(map[string]*FileEntry)
@@ -67,10 +61,10 @@ func Parse(data []byte) DebugLines {
        parseIncludeDirs(dbl, buf)
        parseFileEntries(dbl, buf)

-       //Instructions size calculation breakdown:
-       //- dbl.Prologue.UnitLength is the length of the entire unit, not including the 4 bytes to represent that length.
-       //- dbl.Prologue.Length is the length of the prologue not including unit length, version or the prologue length itself.
-       //- So you have UnitLength - PrologueLength - (version_length_bytes(2) + prologue_length_bytes(4)).
+       // Instructions size calculation breakdown:
+       //   - dbl.Prologue.UnitLength is the length of the entire unit, not including the 4 bytes to represent that length.
+       //   - dbl.Prologue.Length is the length of the prologue not including unit length, version or prologue length itself.
+       //   - So you have UnitLength - PrologueLength - (version_length_bytes(2) + prologue_length_bytes(4)).
        dbl.Instructions = buf.Next(int(dbl.Prologue.UnitLength - dbl.Prologue.Length - 6))

        lines = append(lines, dbl)
diff --git a/dwarf/line/state_machine.go b/dwarf/line/state_machine.go
index 6cc1c8b..b9255f8 100644
--- a/dwarf/line/state_machine.go
+++ b/dwarf/line/state_machine.go
@@ -75,13 +75,12 @@ func newStateMachine(dbl *DebugLineInfo) *StateMachine {
 // Returns all PCs for a given file/line. Useful for loops where the 'for' line
 // could be split amongst 2 PCs.
 func (dbl *DebugLines) AllPCsForFileLine(f string, l int) (pcs []uint64) {
-   lineInfo := dbl.GetLineInfo(f)
-
    var (
-       sm        = newStateMachine(lineInfo)
-       buf       = bytes.NewBuffer(lineInfo.Instructions)
        foundFile bool
        lastAddr  uint64
+       lineInfo  = dbl.GetLineInfo(f)
+       sm        = newStateMachine(lineInfo)
+       buf       = bytes.NewBuffer(lineInfo.Instructions)
    )

    for b, err := buf.ReadByte(); err == nil; b, err = buf.ReadByte() {
diff --git a/proc/proc_test.go b/proc/proc_test.go
index 5e91b31..c685fbe 100644
--- a/proc/proc_test.go
+++ b/proc/proc_test.go
@@ -496,8 +496,7 @@ func TestSwitchThread(t *testing.T) {
 }

 func TestCGONext(t *testing.T) {
-   //test if one can do 'next' in a cgo binary
-
+   // Test if one can do 'next' in a cgo binary
    // On OSX with Go < 1.5 CGO is not supported due to: https://github.com/golang/go/issues/8973
    if runtime.GOOS == "darwin" && strings.Contains(runtime.Version(), "1.4") {
        return