Change the linux verison of proc/native and proc/gdbserial (with
debugserver) so that they let the target process use the terminal when
delve is launched in headless mode.

Windows already worked, proc/gdbserial (with rr) already worked.
I couldn't find a way to make proc/gdbserial (with lldb-server) work.

No tests are added because I can't think of a way to test for
foregroundness of a process.

Fixes #65

Go seems to be generating multiple compilation units that have
the same file. I think this happens for functions that get inlined.
Without this patch, those inlined functions break the ability to set
a breakpoint at other lines in the file. I was able to load the same
binary in gdb and set a breakpoints throughout the file without issue.

```
➜ objdump --dwarf=decodedline automate-gateway | grep handler/users.go
.../handler/users.go:[++]
s/.../handler/users.go           20            0xb6dd88
.../handler/users.go:[++]
s/.../handler/users.go           20            0xb6e50f
.../handler/users.go:[++]
s/automate-gateway/handler/users.go           32            0xb66640
```

Inlined functions are still a little weird. setting a breakpoint on
a function that gets inlined picks the first occurence. That being
said, I think delve should still do something reasonable for the rest
of the lines in the file.

Fixes #1203

So we don't have to worry about having a nil conf field, even if there
is no configuration.

Previously to 4e177bb9 it was possible
to use --log without arguments to enable logging, this commit reenables
that use case.

The new functionality of the --log flag moved to a new flag name
--logx.

Fixes #1188

Fixes #951

Caching the frame in variablesByTag is problematic:

1. accounting for variables that are (partially) stored in registers is
complicated (see issue #1106)
2. for some types (strings, interfaces...) simply creating the Variable
object reads memory, which therefore happens before we can do any
caching.

Instead cache the entire frame when the EvalScope object is created.
The cached range is between the SP value of the current frame and the
CFA of the preceeding frame, if available, or the CFA of the current
frame otherwise.

Fixes #1106

Change memCache so that the preloaded memory is not read immediately
but only after the actual read to the preloaded range.

This allows us to request caching the entire stack frame every time we
create an eval scope and no unnecessary reads will be made even if the
user is just trying to evaluate a global variable.

Vet found the following errors:
	pkg/proc/moduledata.go:152: namedata[1] (8 bits) too small for shift of 8
	pkg/proc/moduledata.go:170: taglendata[0] (8 bits) too small for shift of 8

The fix is to convert before shifting.

Since we always forget to update the documentation lets check this
automatically.

Change evaluation of binary operators so that both && and || only
evaluate their second argument conditionally, like go does.

I've seen TestFrameEvaluation fail in CI in the past. It's been a while
since the last time and I couldn't reproduce it locally at all. I'd
like to have some instrumentation in case it happens again.

printcontext should use SelectedGoroutine instead of trusting that the
goroutine running on current thread matches the SelectedGoroutine.

When the user switches to a parked goroutine CurrentThread and
SelectedGoroutine will diverge.

Almost all calls to printcontext are safe, they happen after a continue
command returns when SelectedGoroutine and CurrentThread always agree,
but the calls in frameCommand and listCommand are wrong.

Additionally we should stop reporting an error when the debugger is
stopped on an unknown PC address.

The g command is bugged and causes that version of debugserver to
crash. See: https://bugs.llvm.org/show_bug.cgi?id=36968

Fixes #1165

When gdbserial can not find debugserver or lldb-server the error
message is always the same and it complains about lldb-server not being
found.

This is fine on linux (where the backend is unnecessary) but incomplete
on macOS (where the backend is actually used).

Make the error message clearer so that users who do not bother reading
install instructions are not confused.

I found this issue (https://github.com/derekparker/delve/issues/514) where user alexbrainman gave a very helpful answer. Adding this to the official install-guide might help a lot of users.

Go 1.10 added inlined calls to debug_info, this commit adds support
for DW_TAG_inlined_call to delve, both for stack traces (where
inlined calls will appear as normal stack frames) and to correct
the behavior of next, step and stepout.

The calls to Next and Frame of stackIterator continue to work
unchanged and only return real stack frames, after reading each line
appendInlinedCalls is called to unpacked all the inlined calls that
involve the current PC.

The fake stack frames produced by appendInlinedCalls are
distinguished from real stack frames by having the Inlined attribute
set to true. Also their Current and Call locations are treated
differently. The Call location will be changed to represent the
position inside the inlined call, while the Current location will
always reference the real stack frame. This is done because:

* next, step and stepout need to access the debug_info entry of
the real function they are stepping through
* we are already manipulating Call in different ways while Current
is just what we read from the call stack

The strategy remains mostly the same, we disassemble the function
and we set a breakpoint on each instruction corresponding to a
different file:line. The function in question will be the one
corresponding to the first real (i.e. non-inlined) stack frame.

* If the current function contains inlined calls, 'next' will not
set any breakpoints on instructions that belong to inlined calls. We
do not do this for 'step'.

* If we are inside an inlined call that makes other inlined
functions, 'next' will not set any breakpoints that belong to
inlined calls that are children of the current inlined call.

* If the current function is inlined the breakpoint on the return
address won't be set, because inlined frames don't have a return
address.

* The code we use for stepout doesn't work at all if we are inside
an inlined call, instead we call 'next' but instruct it to remove
all PCs belonging to the current inlined call.

* Extend the "frame" command to set the current frame.

Command

  frame 3

sets up so that subsequent "print", "set", "whatis" command
will operate on frame 3.

  frame 3 print foo

continues to work.

Added "up", "down". They move the current frame up or down.

Implementation note:

This changes removes "scopePrefix" mode from the terminal/command.go and instead
have the command examine the goroutine/frame value to see if it is invoked in a
scoped context.

* Rename Command.Frame -> Command.frame.

updates vendored version of x86asm, adds a symbol lookup function to
pass to the disassembler.

This will show global symbol names in the disassembly like go tool
objdump does.

Fixes #1151

Registers XMM1 and XMM2 get sometimes clobbered between the time we set
them and the panic. There is no guarantee that they won't in the go
spec so we shouldn't expect any register to keep its value. However
since this seems to only affect 1 and 2 let's try to use 9 and 10
instead.

Fixes #1145

Every time we read an empty string we accidentally issue a read for 0
bytes at address 0, this is fine for real memory but the core file
reader doesn't like it.

Fixes an issue reported on the mailing list.

The windows backend isn't using the halt field so it can be removed
there.
On linux it can be replaced with a parameter passed to trapWait.

Windows and macOS aren't using this field so move it to the os-specific
thread struct and remove it from everything except linux.

The proper way to stop a running process is to call RequestManualStop,
which most code already did with the exception of some old test code.

the proper way to kill the target process is to pass true to Detach.
Everything except old test code did that already.

If a breakpoint is hit close to process death on a thread that isn't
the group leader the process could die while we are trying to stop it.

This can be easily reproduced by having the goroutine that's executing
main.main (which will almost always run on the thread group leader)
wait for a second goroutine before exiting, then setting a breakpoint
on the second goroutine and stepping through it (see TestIssue1101 in
proc_test.go).

When stepping over the return instruction of main.f the deferred
wg.Done() call will be executed which will cause the main goroutine to
resume and proceed to exit. Both the temporary breakpoint on wg.Done
and the temporary breakpoint on the return address of main.f will be in
close proximity to main.main calling os.Exit() and causing the death of
the thread group leader.

Under these circumstances the call to native.(*Thread).waitFast in
native.(*Thread).halt can hang forever due to a bug similar to
https://sourceware.org/bugzilla/show_bug.cgi?id=12702 (see comment in
native.(*Thread).wait for an explanation).

Replacing waitFast with a normal wait work in most circumstances,
however, besides the performance hit, it looks like in this
circumstances trapWait sometimes receives a spurious SIGTRAP on the
dying group leader which would cause the subsequent call to wait in
halt to accidentally reap the process without noting that it did exit.

Instead this patch removes the call to wait from halt and instead calls
trapWait in a loop in setCurrentBreakpoints until all threads are set
to running=false. This is also a better fix than the workaround to
ESRCH error while setting current breakpoints implemented in 94b50d.

Fixes #1101

The formula is broken and produces an endless stream of duplicate bug
reports yet nobody steps up to fix it. Using the formula isn't
necessary and hasn't been in almost a year, the maintainers of delve
aren't using it and the original maintainer of the formula vacated.