The comment on the advanceRegs() method was referencing several
nonexistent fields. This patch fixes that, and improves the comment to
reference the peculiar interaction between the method and it.regs.

Fixes #852
Co-authored-by: Na <a@kra>

evalFunctionCall needs to remove the breakpoint from the current thread
after starting the function call injection, otherwise Continue will
think that the thread is stopped at a breakpoint and return to the user
instead of continuing the call injection.

Adds a flag that distinguishes the return values of an injected
function call from the return values of a function call executed by the
target program.

Thank you to: @polinasok, @aurkenb, @pohzipohzi, @chainhelen,
@hitzhangjie, @eliben, @suzmue, @andreimatei, @aaronsky.

Fix some stale comments and add some comments that I would have found
useful.

This is needed to fix the problem we have with 1.15.4+ after the
backport is applied to it. The DWARF standard isn't clear on what
should happen with the end_of_sequence opcode but this is consistent
with debug/dwarf.LineReader as well as gdb.

* Use the active xcode-select path instead of a hardcoded Xcode path

* Refactored exec.Command to invoke Output instead of running with a custom buffer for stdout

Addresses review comment by @derekparker

Change FindLocation to apply substitute path rules to location
expressions. Changes terminal to always print paths after applying
substitutions.

Implements #2203

1. Forward stdin/stdout/stderr to the target process when in foreground
   mode instead of always forwarding the current tty (issue #1964)
2. When redirecting a file descriptor make sure to also specify
   something for all three otherwise debugserver will misbehave (either
   exit on launch or run but giving the target process a closed file
   descriptor).

Fixes #1964

This patch adds some comments around RequestManualStop().

* Support evaluate request

* Fix failing tests

* Call support

* Remove debugger.CurrentThread() that got accidentally reintroduced during merge

* Address review comments

* Function to stringify stop reason

* Add resetHandlesForStop

* Handle stop inside call

* More tests

* Address review comments

* Check all threads to determine if call completed

* Fix test

* Fix test

* Fix test

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

On linux we can not read memory if the thread we use to do it is
occupied doing certain system calls. The exact conditions when this
happens have never been clear.

This problem was worked around by using the Blocked method which
recognized the most common circumstances where this would happen.

However this is a hack: Blocked returning true doesn't mean that the
problem will manifest and Blocked returning false doesn't necessarily
mean the problem will not manifest. A side effect of this is issue
#2151 where sometimes we can't read the memory of a thread and find its
associated goroutine.

This commit fixes this problem by always reading memory using a thread
we know to be good for this, specifically the one returned by
ContinueOnce. In particular the changes are as follows:

1. Remove (ProcessInternal).CurrentThread and
(ProcessInternal).SetCurrentThread, the "current thread" becomes a
field of Target, CurrentThread becomes a (*Target) method and
(*Target).SwitchThread basically just sets a field Target.

2. The backends keep track of their own internal idea of what the
current thread is, to use it to read memory, this is the thread they
return from ContinueOnce as trapthread

3. The current thread in the backend and the current thread in Target
only ever get synchronized in two places: when the backend creates a
Target object the currentThread field of Target is initialized with the
backend's current thread and when (*Target).Restart gets called (when a
recording is rewound the currentThread used by Target might not exist
anymore).

4. We remove the MemoryReadWriter interface embedded in Thread and
instead add a Memory method to Process that returns a MemoryReadWriter.
The  backends will return something here that will read memory using
the current thread saved by the backend.

5. The Thread.Blocked method is removed

One possible problem with this change is processes that have threads
with different memory maps. As far as I can determine this could happen
on old versions of linux but this option was removed in linux 2.5.

Fixes #2151

TestStepConcurrentDirect will occasionally fail (7% of the time on my
setup) by either causing the target processs to execute an invalid
instruction or (more infrequently) by switching to the wrong thread.

Both of those are caused by receiving SIGTRAPs for threads hitting a
breakpoint after it has been removed (the thread hits the breakpoint,
we stop everything and remove the breakpoint and only after we receive
the signal).

Change native.(*nativeProcess).stop to handle SIGTRAPs that can't be
attributed to a breakpoint, a hardcoded breakpoint in the program's
text, or manual stops (and therefore are likely caused by phantom
breakpoint hits).
Co-authored-by: Na <a@kra>

Fixes #2219

* service/rpccommon: log error for conns rejected by --only-same-user

If no logger is enabled manually write to stderr instead.

Fixes #2209

* logflags: fix style complaints from DeepSource

Fixes #1847

It returns an unexported type and is only used in a single place.

Due to a missing check TestCgoStacktrace2 didn't actually check
anything. Enable it and then skip it on linux/386 and linux/arm64 where
it's broken.
Co-authored-by: Na <a@kra>

If the process receives a signal (or sends a singal to itself) and then
dies before we can route the signal back to it we still need to
retrieve its exit status.

Fixes a rare failure of TestIssue1101 in proc_test.go
Co-authored-by: Na <a@kra>

* proc/tests: keep track of tests skipped due to backend problems

Mark tests skipped due to backend problems and add a script to keep
track of them.

* Travis-CI: add ignorechecksum option to chocolatey command

Looks like a configuration problem on chocolatey's end.

* proc: use argument position for addr only when injecting function calls

We can not, in general, use the argument position to determine the
address of a formal parameter, it will not work in presence of
optimizations or inlining. In those cases formal arguments could be
stored in registers.

Fixes #2176

* Travis-CI: add ignorechecksum option to chocolatey command

Looks like a configuration problem on chocolatey's end.
Co-authored-by: Na <a@kra>

* dwarf/line: ignore end_of_sequence entry if AllPCsBetween

Go 1.15 (but possibly prior versions of Go too) has a tendency to use
an address in the middle of an instruction for this entry, but if it
was correct it would be after the last instruction of the function
anyway.

This problem manifests especially frequently as a target crash in
TestStepConcurrentPtr on linux/arm64 (~6% of the runs).

* Travis-CI: add ignorechecksum option to chocolatey command

Looks like a configuration problem on chocolatey's end.
Co-authored-by: Na <a@kra>

* Revert "proc: Find executable should follow symbol links."

This reverts commit 3e04ad0f.

* proc: resolve symlinks when searching for split debug_info if path is /proc/pid/exe

Fixes #2168

During the testing of the core dump generation feature two bugs were
discovered in gdbserial:

1. we don't check that both bytes of the checksum are read, if the
   buffer only has one byte we can end up reading only one byte instead
   of two and the second byte will mess up the parsing of the next
   packet
2. binary encoded packets can start with an 'E' and not be errors, when
   using binary responses add an extra check for the lenght of the
   response before deciding that the response is an error.
   Unfortunately this encoding is inherently ambiguous (we can't
   distinguish a 3 byte response starting with 'E' from an error) so
   binary requests that lead to short responses should be avoided.

Testing this is complicated, they will be tested implicitly by the
upcoming core dump test.
Co-authored-by: Na <a@kra>

Adds a -size argument to examinemem that specifies how to group bytes on output.

Since proc is supposed to work independently from the target
architecture it shouldn't use architecture-dependent types, like
uintptr. For example when reading a 64bit core file on a 32bit
architecture, uintptr will be 32bit but the addresses proc needs to
represent will be 64bit.

`sameFrameCond` should not be constructed as one `And Express` when
`sameGCond` which is the first child of `BinaryExpr` is nil.

Fixes: #2162

Adds features to support default file descriptor redirects for the
target process:

1. A new command line flag '--redirect' and '-r' are added to specify
   file redirects for the target process
2. New syntax is added to the 'restart' command to specify file
   redirects.
3. Interactive instances will check if stdin/stdout and stderr are
   terminals and print a helpful error message if they aren't.

An internal breakpoint condition shouldn't ever error:
* use a ThreadContext to evaluate conditions if a goroutine isn't
  available
* evaluate runtime.curg to a fake g variable containing only
  `goid == 0` when there is no current goroutine

Fixes #2113

Recent changes to the way registers are handled broke reporting of AVX
registers (i.e. YMMx). This change restores the functionality by:

- concatenating the higher half of the YMMx registers to their
  corresponding XMMx lower half (YMMx registers do not have an
  independent DWARF register number)
- modifying the formatSSEReg function to handle them when they are
  present.

Fixes #2033

Fixes #2138

(*gdbThread).StepInstruction is a single call to stepInstruction so
inline it.

If OnlyAddr is not set pretty printing an interface will fail with an
index out of bounds error.

* vendor: update starlark

* terminal: use new mechanism to cancel starlark threads

See: https://github.com/google/starlark-go/pull/298