Oh, I forgot to mention one important fact. I *do* get the expected result
if I eliminate the stuff with boxes. This works fine:

scheme@(guile-user)> (assemble-program '((begin-program foo)
 (assert-nargs-ge 0)
 (reserve-locals 4)
 (bind-rest 0)
 (cache-current-module! 2 foo)
 (cached-toplevel-ref 2 foo car)
 (tail-call 1 2)
 (end-program)))

Best,
Noah

On Thu, Apr 4, 2013 at 3:22 PM, Noah Lavine <noah.b.lavine@gmail.com> wrote:

> Hello,
>
> I'm actually testing on the wip-rtl-cps branch, but this error involves
> code that I believe is the same on that branch and on the wip-rtl branch.
> Try opening a new Guile and doing the following:
>
> scheme@(guile-user)> (use-modules (system vm rtl))
> scheme@(guile-user)> (assemble-program '((begin-program foo)
>  (assert-nargs-ge 0)
>  (reserve-locals 4)
>  (bind-rest 0)
>  (box 1 0)
>  (cache-current-module! 2 foo)
>  (cached-toplevel-ref 2 foo car)
>  (box-ref 3 1)
>  (mov 0 3)
>  (tail-call 1 2)
>  (end-program)))
> ... ... ... ... ... ... ... ... ... ... $1 = #<rtl-program dcec90 609bc0>
> scheme@(guile-user)> ($1 'hello)
>
> The expected result is
> $2 = hello
>
> What I actually get is,
>
> Program received signal SIGABRT, Aborted.
> 0x00007ffff7440425 in raise () from /lib/x86_64-linux-gnu/libc.so.6
>
> The full backtrace is below. The interesting part is that it seems to be
> tripping the check at libguile/vm-engine.c:1868, which checks whether an
> object is a variable before doing a box-ref on it. When I look at it in
> GDB, it seems that whatever is at register 1 does not satisfy
> scm_variable_p, although I'm not very experienced with debugging Guile.
> However, I am somewhat surprised at this, because I have used boxes and
> box-ref before in the past with no trouble.
>
> Another surprising thing is that if I open Guile, do some other things for
> a while, and then run this code, the problem sometimes doesn't appear. That
> is especially disturbing.
>
> Does anyone have any idea where the issue is or how I should find it?
>
> Thanks,
> Noah
>
> Here's the backtrace:
>
> (gdb) bt
> #0  0x00007ffff7440425 in raise ()
>    from /lib/x86_64-linux-gnu/libc.so.6
> #1  0x00007ffff7443b8b in abort ()
>    from /lib/x86_64-linux-gnu/libc.so.6
> #2  0x00007ffff7b30986 in rtl_vm_debug_engine (vm=0x6a6860,
>     program=0xdcec90, argv=0x6a9548, nargs_=1) at vm-engine.c:1868
> #3  0x00007ffff7b1aaf1 in vm_debug_engine (vm=0x6a6860,
>     program=0xdcec90, argv=0x7fffffffd028, nargs=1) at vm-engine.c:419
> #4  0x00007ffff7b38f6c in scm_c_vm_run (vm=0x6a6860,
>     program=0x75dbe0, argv=0x7fffffffd028, nargs=1) at vm.c:791
> #5  0x00007ffff7a5bff3 in scm_primitive_eval (exp=0x7fe7f0)
>     at eval.c:691
> #6  0x00007ffff7a5c0ad in scm_eval (exp=0x7fe7f0,
>     module_or_state=0x7e0090) at eval.c:725
> #7  0x00007ffff7acef2d in scm_shell (argc=1, argv=0x7fffffffe478)
>     at script.c:441
> #8  0x0000000000400bd0 in inner_main (closure=0x0, argc=1,
>     argv=0x7fffffffe478) at guile.c:62
> #9  0x00007ffff7a82663 in invoke_main_func (body_data=0x7fffffffe350)
>     at init.c:336
> #10 0x00007ffff7a563c9 in c_body (d=0x7fffffffe220)
>     at continuations.c:513
> #11 0x00007ffff7afc96c in apply_catch_closure (clo=0x81b360,
>     args=0x304) at throw.c:146
> #12 0x00007ffff7acf739 in apply_1 (smob=0x81b360, a=0x304)
>     at smob.c:141
> #13 0x00007ffff7b05cc8 in vm_regular_engine (vm=0x6a6860,
>     program=0x7443e0, argv=0x7fffffffe0c0, nargs=2)
>     at vm-i-system.c:873
> #14 0x00007ffff7b38f6c in scm_c_vm_run (vm=0x6a6860,
>     program=0x79d5d0, argv=0x7fffffffe0c0, nargs=4) at vm.c:791
> #15 0x00007ffff7a5b793 in scm_call_4 (proc=0x79d5d0, arg1=0x404,
>     arg2=0x81b360, arg3=0x81b340, arg4=0x81b320) at eval.c:513
> #16 0x00007ffff7afc767 in scm_catch_with_pre_unwind_handler (
>     key=0x404, thunk=0x81b360, handler=0x81b340,
>     pre_unwind_handler=0x81b320) at throw.c:86
> #17 0x00007ffff7afca44 in scm_c_catch (tag=0x404,
>     body=0x7ffff7a563a1 <c_body>, body_data=0x7fffffffe220,
>     handler=0x7ffff7a563d8 <c_handler>, handler_data=0x7fffffffe220,
>     pre_unwind_handler=0x7ffff7a5642c <pre_unwind_handler>,
>     pre_unwind_handler_data=0x751160) at throw.c:213
> #18 0x00007ffff7a5623d in scm_i_with_continuation_barrier (
>     body=0x7ffff7a563a1 <c_body>, body_data=0x7fffffffe220,
>     handler=0x7ffff7a563d8 <c_handler>, handler_data=0x7fffffffe220,
>     pre_unwind_handler=0x7ffff7a5642c <pre_unwind_handler>,
>     pre_unwind_handler_data=0x751160) at continuations.c:451
> #19 0x00007ffff7a564c3 in scm_c_with_continuation_barrier (
>     func=0x7ffff7a82613 <invoke_main_func>, data=0x7fffffffe350)
>     at continuations.c:547
> #20 0x00007ffff7af97ba in with_guile_and_parent (base=0x7fffffffe290,
>     base@entry=<error reading variable: value has been optimized out>,
> data=0x7fffffffe2d0,
>     data@entry=<error reading variable: value has been optimized out>)
>     at threads.c:907
> #21 0x00007ffff71b6f55 in GC_call_with_stack_base (
>     fn=<optimized out>, arg=<optimized out>) at misc.c:1553
> #22 0x00007ffff7af9894 in scm_i_with_guile_and_parent (
>     func=0x7ffff7a82613 <invoke_main_func>, data=0x7fffffffe350,
>     parent=0x0) at threads.c:950
> #23 0x00007ffff7af98c0 in scm_with_guile (
>     func=0x7ffff7a82613 <invoke_main_func>, data=0x7fffffffe350)
>     at threads.c:956
> #24 0x00007ffff7a825f4 in scm_boot_guile (argc=1,
>     argv=0x7fffffffe478, main_func=0x400bac <inner_main>, closure=0x0)
>     at init.c:319
> #25 0x0000000000400c35 in main (argc=1, argv=0x7fffffffe478)
>     at guile.c:81
>
>
>