add gbt macro to gdbinit, and fix a bug in program-arity

* gdbinit: Add gbt macro, to make a Guile backtrace whenever you want.
* module/system/vm/program.scm (program-arity): If ip is #f, just take
  the first arity.

1 files changed, 4 insertions, 0 deletions

diff --git a/gdbinit b/gdbinit
index 812f04b59..fdc9c759b 100644
--- a/gdbinit
+++ b/gdbinit
@@ -198,3 +198,7 @@ end
 define inst
   p scm_instruction_table[$arg0]
 end
+
+define gbt
+  call scm_display_backtrace (scm_make_stack(0x404,0x304), scm_current_error_port (), 0x704, 0x704, 0x704)
+end