Implement debugging function for 386 on linux with reference to AMD64.
There are a few remaining problems that need to be solved in another time.

1. The stacktrace of cgo are not exactly as expected.
2. Not implement `core` for now.
3. Not implement `call` for now. Can't not find `runtime·debugCallV1` or
   similar function in $GOROOT/src/runtime/asm_386.s.

Update #20

* proc/native/linux: only set breakpoints on threads that receive SIGTRAP

* proc/native/linux: do not call (*Thread).Stopped inside (*Process).stop

(*Thread).Stopped is slow because it needs to open, read and parse a
file in /proc, we don't actually need to do that, we can just rely on
the value of Thread.os.running.

Benchmark before:

BenchmarkConditionalBreakpoints-4              1        12476166303 ns/op

Benchmark after:

BenchmarkConditionalBreakpoints-4   	       1	10403533675 ns/op

Conditional breakpoint evaluation: 1.24ms -> 1ms

Updates #1549

* logflags: Add pid to server-listening-at message

* Address review comments: use logger
Co-authored-by: NPolina Sokolova <polinasok@users.noreply.github.com>

There are too many commands, for clarity they should be divided into
categories when printing and generating documentation.

* service/dap: Add support for debug and test modes

* Address code review comments

* Remove //dap comment

* OptFlags() => optfalgs()

* If mode => switch mode

Disables async preemption on macOS

Fixes #1905

Use strings.Builder and tabwriter to format the output of the examine
memory command instead of doing direct string manipulation and
allocating.

This also removes Go 1.11 from the test matrix.

Now that 1.14 has been released, as always it should be included in the
test matrix.

This change adds `ProcessVmRead` and `ProcessVmWrite` wrappers around
the syscalls `process_vm_readv` and `process_vm_writev`, available since
Linux 3.2. These follow the same permission model as `ptrace`, but they
don't actually require being attached, which means they can be called
directly from any thread in the debugger. They also use `iovec` to write
entire blocks at once, rather than having to peek/poke each `uintptr`.

These wrappers are used in `Thread.ReadMemory` and `WriteMemory`, still
falling back to `ptrace` if that fails for any reason.  Notably,
`process_vm_writev` respects memory protection, so it can't modify
read-only memory like `ptrace`. This frequently occurs when writing
breakpoints in read-only `.text`, so to avoid a lot of wasted `EFAULT`
calls, we only try `process_vm_writev` for larger writes.

1. Don't use intelligent '#' in fmt of go because it is not always satisfying
for diffrent version of golang. Always keep one leading zero for octal and
one leading '0x' for hex manually. Then keep alignment for every byte.

2. Always keep addr alignment when the lens of two adjacent address are
different.

Update #1814.

Using a stop channel to signal clean shutdown to the server's
goroutines. Also updates the tests to trigger disconnectChan.

This helps avoid spurious error logs when the client disconnects, when
Ctrl+C is pressed, etc.

Go 1.14 has more fake file names, apparently (also go fmt).

* Panic guard for DAP request handling

* Use GetSeq

* Re-vendor new version of go-dap

* Remove comment

* Update error message

* Reuse er.Message in Format

Fixes a bug introduced by the logical breakpoint change, where creating
the same breakpoint twice deletes the breakpoint.

Adds an optional scope prefix to the `regs` command which allows
printing registers for any stack frame (as long as they were somehow
saved). Issue #1838 is not yet to be closed since we are still not
recovering the registers of a segfaulting frame.

Updates #1838

As we rearrange the code and the Go compiler changes the error message
returned by the compiler on unsupported architectures will change too,
making it un-googlable. Since the error message tends to be rather
obscure too this regularly confuses newbies.

This is an effort to make the error message for unsupported GOOS/GOARCH
combinations the same across all unsupported combinations and to make
it more user friendly.

Directories containing Go source code are supposed to contain a single
package. This property happens to be checked by cmd/go itself so it
will happen even before the syntax is fully checked and therefore has a
high probability of being the first (and only) error message being
print.

Here we take advantage of this by adding to the pkg/proc/native
directory a file with a bad package line that only gets compiled in on
unsupported GOOS/GOARCH combinations.

At present the error message for compiling Delve on unsupported systems
will be:

service/debugger/debugger.go:21:2: found packages native (proc.go) and your_operating_system_and_architecture_combination_is_not_supported_by_delve (support_sentinel.go) in $PATH_TO_DELVE/pkg/proc/native

* Remove hardcoded tests

* Cleanup - consistent naming, simplify some code, remove unused func

* Address review comments

* Add Seq checks back

* Address more review comments

* Remove hardcoded tests

* Cleanup - consistent naming, simplify some code, remove unused func

* Address review comments

* Add Seq checks back

* Address more review comments

* Make more consistent

* More consistency

* Simplify Except* methods with a helper

Mark t.Helper() where appropriate

Avoid always showing `no G executing on thread 0` when ErrNoGoroutine on
g0 stack in GetG.

macOS hasn't /usr/include/sys/types.h header with Canalina or later.
switch types.h path to CommandLineTools if kernel minor version up to 15 or later.

- Move package doc comments so they are recognized as package doc.
- Use t.Helper when appropriate.

* Fixed DirIdx (index starts at one)

I am using the elf to load C++ based elf and there the index starts at one and not zero, hence the minor fix.

* Added test

* Added proper test for c-generated elf & replaced index offset by adding build dir

* Changed other IncludeDir test

* Format fix & replace print with actual test

* Format fixes @derekparker requested.

Go 1.8 has been out of date for a while and the code to support it is
potentially dangerous if a future version of Go removes the runtime
types from debug_info and also changes their representation.

Removes the restriction that the DWARF type for the receiver of a method
must be a TypeDef. This seems reasonable in practice, but it turns out
Go DWARF does not consider

```
type X int
```

to be a typedef. This patch also allows for calling a method where the
receiver is not used or passed in, such as:

```
func (_ X) Method() { println("why") }
```

Avoid panic if start addr is greater than end addr when disasm.

Signed-off-by: NSylvain Rabot <s.rabot@lectra.com>

* proc/native: optimize native.status through buffering (#1865)

Benchmark before:

BenchmarkConditionalBreakpoints-4              1        15649407130 ns/op

Benchmark after:

BenchmarkConditionalBreakpoints-4   	       1	14586710018 ns/op

Conditional breakpoint evaluation 1.56ms -> 1.45ms

Updates #1549

* proc/core: Review Comments Incorporated
Signed-off-by: Nossdev07 <ossdev@puresoftware.com>
Co-authored-by: NAlessandro Arzilli <alessandro.arzilli@gmail.com>

runtime.g is a large and growing struct, we only need a few fields.
Instead of using loadValue to load the full contents of g, cache its
memory and then only load the fields we care about.

Benchmark before:

BenchmarkConditionalBreakpoints-4              1        14586710018 ns/op

Benchmark after:

BenchmarkConditionalBreakpoints-4   	       1	12476166303 ns/op

Conditional breakpoint evaluation: 1.45ms -> 1.24ms

Updates #1549

Benchmark before:

BenchmarkConditionalBreakpoints-4              1        15649407130 ns/op

Benchmark after:

BenchmarkConditionalBreakpoints-4   	       1	14586710018 ns/op

Conditional breakpoint evaluation 1.56ms -> 1.45ms

Updates #1549

* Initial implementation for 'dlv dap'

* Fix Travis and AppVeyor failures

* Address review comments

* Address review comments

* Regenrate documentation

* Replace dap server printfs with log.Error

* Update 'dap log'

* Fix typos

* Revert logflags changes that got mixed in by accident

Logged errors should be visible even if the corresponding flag was not
selected.

Instead of reloading the registers for every thread every time the
process executes, reload the registers on demand for individual threads
and memoize the result.

According to #1800 #1584 #1038, `dlv` should enable the user to dive into
memory. User can print binary data in specific memory address range.
But not support for sepecific variable name or structures temporarily.(Because
I have no idea that modify `print` command.)

Close #1584.

The stacktrace code occasionally needs the value of g.m.g0.sched.sp to
switch stacks. Since this is only needed rarely and calling parseG is
relatively expensive we should delay doing it until we know it will be
needed.

Benchmark before:

BenchmarkConditionalBreakpoints-4              1        17326345671 ns/op

Benchmark after:

BenchmarkConditionalBreakpoints-4   	       1	15649407130 ns/op

Reduces conditional breakpoint latency from 1.7ms to 1.56ms.

Updates #1549

A significant amount of time is spent generating the string
representation for the proc.Registers object of each thread, since this
field is rarely used (only when the Registers API is called) it should
be generated on demand.

Also by changing the internal representation of proc.Register to be
closer to that of op.DwarfRegister it will help us implement #1838
(when Delve will need to be able to display the registers of an
internal frame, which we currently represent using op.DwarfRegister
objects).

Benchmark before:

BenchmarkConditionalBreakpoints-4   	       1	22292554301 ns/op

Benchmark after:

BenchmarkConditionalBreakpoints-4   	       1	17326345671 ns/op

Reduces conditional breakpoint latency from 2.2ms to 1.7ms.

Updates #1549, #1838