Our current frame caching strategy doesn't handle extended locations
expressions correctly, disable it on variables that don't have a simple
address.

Fixes #1088

Fixes #1090

* core_test: fix TestCoreFpRegisters on go1.9

It was broken by 7bec20e5

* travis-ci: switch to VM builders for linux

Much like the bug in issue #1031 and commit
f6f6f0bf pointers can also escape to
the heap and then have a zero address (and no children) when we
autodereference.

1. Mark autodereferenced escaped variables with a 0 address as
   unreadable.
2. Add guards to the pretty printers for unsafe.Pointer and pointers.

Fixes #1075

Depending on how the runtime schedules our goroutines we can get
unlucky and have the first call to runtime.newstack we intercept be for
a different goroutine (usually the garbage collector).
Only check stacktraces that happen on the same goroutine that executed
main.main.

Help out those of us habituated to pdb. <:^)

https://docs.python.org/3/library/pdb.html

* command/terminal: allow restart to change process args

Add -args flag to "restart" command. For example, "restart -args a b c" will
pass args a b c to the new process.

Add "-c" flag to pass the checkpoint name. This is needed to disambiguate the
checkpoint name and arglist.

Reverted unnecessary changes.

* Applied reviewer comments.

Vendored argv.

Change the syntax of restart. When the target is is in recording mode, it always
interprets the args as a checkpoint. Otherwise, it interprets the args as
commandline args. The flag "-args" is still there, to handle the case in which
the user wants to pass an empty args on restart.

* Add restartargs.go.

Change "restart -args" to "restart -noargs" to clarify that this flag is used to
start a process with an empty arg.

The runtime calls into g0 in many places, not necessarily using
runtime.systemstack or runtime.asmcgocall.
One example of this is the call to runtime.newstack inside
runtime.morestack.

If we stop the process while one goroutine is executing
runtime.newstack we would be unable to fully scan its stack because we
don't know that we have to switch back to the goroutine stack after
runtime.newstack.

Instead of tracking down every possible way that the runtime switches
to g0 we switch to the goroutine stack immediately after the top of the
stack, unless cgo is being executed on the systemstack.

Fixes #1066

I saw a test failure related to this in Travis-CI, if it happens again
I would like to know what's causing it.

Fixes #1052

Adds a configuration option (show-location-expr) that when activated
will cause the whatis command to also print the DWARF location
expression for a variable.

The last entry of the debug_line table is supposed to be valid for
every PC address greater than its address.

So far we have evaluated the locspec "+0" the same way we evaluate all
"+n" locspecs, this means that we turn the current PC into a file:line
pair, then we turn back the file:line into a PC address.

Normally this is harmless, however all autogenerated code returns the
source position "<autogenerated>:1" which resolves back to the very
first autogenerated instruction in the code.

This messes up the behaviour of the "disassemble" command which uses
the locspec "+0" to figure out what code to disassemble if no arguments
are passed.

We should make +0 always resolve to the current PC (of the given scope)
so that clients can use +0 as a default locspec.

Fixes #186, #83

We need to reset the current file and line number.

Fixes #1008

On macOS, externally linked programs will have an abbrev for
DW_TAG_subprogram without the haschildren flag set. We should handle
this case instead of expecting all DW_TAG_subprogram entries to have
list of children.

Fixes #1034

Prints the frame and frame pointer offsets for each frame.

When creating a stack trace we should switch between the goroutine
stack and the system stack (where cgo code is executed) as appropriate
to reconstruct the logical stacktrace.

Goroutines that are currently executing on the system stack will have
the SystemStack flag set, frames of the goroutine stack will have a
negative FrameOffset (like always) and frames of the system stack will
have a positive FrameOffset (which is actually just the CFA value for
the frame).

Updates #935

Pass CGO_FLAGS='-O0 -g' to go build to disable optimizations when
calling the C compiler.

These are emitted by C compilers but also by the current development
version of the go compiler with the dwarflocationlists flag.

Either the CPU or the kernel may not support the calls we do when
retrieving floating point registers, this isn't an error we should
propagate.
Also improve the error reporint of pkg/proc/native.fpRegisters.

Fixes #1022

StepBreakpoints are set on CALL instructions, when they are hit we
disassemble the current instruction, figure out the destination address
and set a breakpoint after the prologue of the called function.

In order to disassemble the current instruction we disassemble the area
of memory starting from PC and going to PC+15 (because 15 bytes is the
maximum length of one instruction on AMD64). This means that we won't
just disassemble one instruction but also a few instructions following
it ending with one truncated instruction.

This usually works fine but sometimes the disassembler will panic with
an array out of bounds error when trying to disassemble a truncated
instruction. To avoid this problem this commit changes the funciton
disassemble to take one extra parameter, singleInstr, when singleInstr
is set disassemble will quit after disassembling a single instruction.

If 'iv' is an interface variable with a struct as a concrete value let
'iv.A' evaluate to the access to field 'A' of the concrete value of
'iv'.

Replace the unsafe.Pointer type of the buf field of channels with the
appropriate array type, allow expressions accessing member field of the
channel struct.

Fixes #962

Conditional breakpoints with unmet conditions would cause next and step
to skip the line.

This breakpoint changes the Kind field of proc.Breakpoint from a single
value to a bit field, each breakpoint object can represent
simultaneously a user breakpoint and one internal breakpoint (of which
we have several different kinds).

The breakpoint condition for internal breakpoints is stored in the new
internalCond field of proc.Breakpoint so that it will not conflict with
user specified conditions.

The breakpoint setting code is changed to allow overlapping one
internal breakpoint on a user breakpoint, or a user breakpoint on an
existing internal breakpoint. All other combinations are rejected. The
breakpoint clearing code is changed to clear the UserBreakpoint bit and
only remove the phisical breakpoint if no other bits are set in the
Kind field. ClearInternalBreakpoints does the same thing but clearing
all bits that aren't the UserBreakpoint bit.

Fixes #844

Move some duplicate code, related to breakpoints, that was in both
backends into a single place.
This is in preparation to solve issue #844 (conditional breakpoints
make step and next fail) which will make this common breakpoint code
more complicated.

Since it's just a scratchpad to calculate the new set of registers it
makes more sense to have it as a local variable in Next and
advanceRegs.

Instead of only tracking a few cherrypicked registers in stack.go track
all DWARF registers.

This is needed for cgo code and for the locationlists emitted by go in
1.10:
* The debug_frame sections emitted by C compilers can not be used
  without tracking all registers
* the loclists emitted by go1.10 need all registers of a frame to be
  interpreted.

A thread could terminate between the point when we stop for a
breakpoint and the point where we send a stop signal to all threads, if
this happens setCurrentBreakpoints will fail with an error.

We should tolerate this.

For some reason this happens very frequently when running delve on
processes with the race detector enabed.

Adds test command line flag to compile target fixtures using the -race flag.
Multiple tests will fail because of https://github.com/golang/go/issues/22600
but eventually this should work.

Some linkers will sometimes insert a zero length entry between the last
FDE of a CIE and the next CIE.