Enable stack traces with ghci -fexternal-interpreter -prof

Summary:
The main goal here is enable stack traces in GHCi.  After this change,
if you start GHCi like this:

  ghci -fexternal-interpreter -prof

(which requires packages to be built for profiling, but not GHC
itself) then the interpreter manages cost-centre stacks during
execution and can produce a stack trace on request.  Call locations
are available for all interpreted code, and any compiled code that was
built with the `-fprof-auto` familiy of flags.

There are a couple of ways to get a stack trace:

* `error`/`undefined` automatically get one attached
* `Debug.Trace.traceStack` can be used anywhere, and prints the current
  stack

Because the interpreter is running in a separate process, only the
interpreted code is running in profiled mode and the compiler itself
isn't slowed down by profiling.

The GHCi debugger still doesn't work with -fexternal-interpreter,
although this patch gets it a step closer.  Most of the functionality
of breakpoints is implemented, but the runtime value introspection is
still not supported.

Along the way I also did some refactoring and added type arguments to
the various remote pointer types in `GHCi.RemotePtr`, so there's
better type safety and documentation in the bridge code between GHC
and ghc-iserv.

Test Plan: validate

Reviewers: bgamari, ezyang, austin, hvr, goldfire, erikd

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1747

GHC Trac Issues: #11047, #11100

1 files changed, 10 insertions, 7 deletions

diff --git a/rts/Exception.cmm b/rts/Exception.cmm
index 8d19c143ee..a89bd19eb3 100644
--- a/rts/Exception.cmm
+++ b/rts/Exception.cmm
@@ -524,14 +524,17 @@ retry_pop_stack:
             // be per-thread.
             CInt[rts_stop_on_exception] = 0;
             ("ptr" ioAction) = ccall deRefStablePtr (W_[rts_breakpoint_io_action] "ptr");
-            Sp = Sp - WDS(6);
-            Sp(5) = exception;
-            Sp(4) = stg_raise_ret_info;
-            Sp(3) = exception;             // the AP_STACK
-            Sp(2) = ghczmprim_GHCziTypes_True_closure; // dummy breakpoint info
-            Sp(1) = ghczmprim_GHCziTypes_True_closure; // True <=> a breakpoint
+            Sp = Sp - WDS(9);
+            Sp(8) = exception;
+            Sp(7) = stg_raise_ret_info;
+            Sp(6) = exception;
+            Sp(5) = ghczmprim_GHCziTypes_True_closure; // True <=> a breakpoint
+            Sp(4) = stg_ap_ppv_info;
+            Sp(3) = 0;
+            Sp(2) = stg_ap_n_info;
+            Sp(1) = 0;
             R1 = ioAction;
-            jump RET_LBL(stg_ap_pppv) [R1];
+            jump RET_LBL(stg_ap_n) [R1];
         }
     }