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-rw-r--r--libguile/continuations.c521
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diff --git a/libguile/continuations.c b/libguile/continuations.c
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+/* Copyright 1995-1996,1998,2000-2001,2004,2006,2008-2014,2017-2018
+ Free Software Foundation, Inc.
+
+ This file is part of Guile.
+
+ Guile is free software: you can redistribute it and/or modify it
+ under the terms of the GNU Lesser General Public License as published
+ by the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
+
+ Guile is distributed in the hope that it will be useful, but WITHOUT
+ ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+ License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with Guile. If not, see
+ <https://www.gnu.org/licenses/>. */
+
+
+
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <assert.h>
+#include <string.h>
+#include <stdio.h>
+
+#if SCM_HAVE_AUXILIARY_STACK
+#include <ucontext.h>
+#endif
+
+#include "async.h"
+#include "backtrace.h"
+#include "boolean.h"
+#include "debug.h"
+#include "dynstack.h"
+#include "eval.h"
+#include "gsubr.h"
+#include "init.h"
+#include "instructions.h"
+#include "jit.h"
+#include "list.h"
+#include "numbers.h"
+#include "pairs.h"
+#include "ports.h"
+#include "smob.h"
+#include "stackchk.h"
+#include "stacks.h"
+#include "symbols.h"
+#include "vm.h"
+
+#include "continuations.h"
+
+
+
+
+static scm_t_bits tc16_continuation;
+#define SCM_CONTREGSP(x) SCM_TYP16_PREDICATE (tc16_continuation, x)
+
+#define SCM_CONTREGS(x) ((scm_t_contregs *) SCM_SMOB_DATA_1 (x))
+
+#define SCM_CONTINUATION_LENGTH(x) (SCM_CONTREGS (x)->num_stack_items)
+#define SCM_SET_CONTINUATION_LENGTH(x, n)\
+ (SCM_CONTREGS (x)->num_stack_items = (n))
+#define SCM_JMPBUF(x) ((SCM_CONTREGS (x))->jmpbuf)
+#define SCM_CONTINUATION_ROOT(x) ((SCM_CONTREGS (x))->root)
+#define SCM_DFRAME(x) ((SCM_CONTREGS (x))->dframe)
+
+
+
+/* scm_i_make_continuation will return a procedure whose code will
+ reinstate the continuation. Here, as in gsubr.c, we define the form
+ of that trampoline function.
+ */
+
+struct goto_continuation_code
+{
+ struct scm_jit_function_data data;
+ uint32_t code[3];
+};
+
+struct goto_continuation_code goto_continuation_code = {
+ {
+ /* mcode = */ 0,
+ /* counter = */ 0,
+ /* start = */ sizeof (struct scm_jit_function_data),
+ /* end = */ sizeof (struct scm_jit_function_data) + 12
+ },
+ {
+ SCM_PACK_OP_24 (instrument_entry, 0),
+ ((uint32_t) -(sizeof (struct scm_jit_function_data) / 4)),
+ SCM_PACK_OP_24 (continuation_call, 0),
+ }
+};
+
+static SCM
+make_continuation_trampoline (SCM contregs)
+{
+ SCM ret;
+ scm_t_bits nfree = 1;
+ scm_t_bits flags = SCM_F_PROGRAM_IS_CONTINUATION;
+
+ ret = scm_words (scm_tc7_program | (nfree << 16) | flags, nfree + 2);
+ SCM_SET_CELL_WORD_1 (ret, goto_continuation_code.code);
+ SCM_PROGRAM_FREE_VARIABLE_SET (ret, 0, contregs);
+
+ return ret;
+}
+
+
+/* {Continuations}
+ */
+
+
+static int
+continuation_print (SCM obj, SCM port, scm_print_state *state SCM_UNUSED)
+{
+ scm_t_contregs *continuation = SCM_CONTREGS (obj);
+
+ scm_puts ("#<continuation ", port);
+ scm_intprint (continuation->num_stack_items, 10, port);
+ scm_puts (" @ ", port);
+ scm_uintprint (SCM_SMOB_DATA_1 (obj), 16, port);
+ scm_putc ('>', port);
+ return 1;
+}
+
+/* James Clark came up with this neat one instruction fix for
+ * continuations on the SPARC. It flushes the register windows so
+ * that all the state of the process is contained in the stack.
+ */
+
+#if defined (sparc) || defined (__sparc__) || defined (__sparc)
+# define SCM_FLUSH_REGISTER_WINDOWS asm("ta 3")
+#else
+# define SCM_FLUSH_REGISTER_WINDOWS /* empty */
+#endif
+
+static void
+capture_auxiliary_stack (scm_thread *thread, scm_t_contregs *continuation)
+{
+#if SCM_HAVE_AUXILIARY_STACK
+# if !(defined __ia64 or defined __ia64__)
+# error missing auxiliary stack implementation for architecture
+# endif
+ char *top;
+ ucontext_t ctx;
+
+ if (getcontext (&ctx) != 0)
+ abort ();
+
+#if defined __hpux
+ __uc_get_ar_bsp (ctx, (uint64_t *) &top);
+#elif defined linux
+ top = (char *) ctx->uc_mcontext.sc_ar_bsp;
+#elif defined __FreeBSD__
+ top = (char *)(ctx->uc_mcontext.mc_special.bspstore
+ + ctx->uc_mcontext.mc_special.ndirty);
+#else
+#error missing auxiliary stack implementation for ia64 on this OS
+#endif
+
+ continuation->auxiliary_stack_size =
+ top - (char *) thread->auxiliary_stack_base;
+ continuation->auxiliary_stack =
+ scm_gc_malloc (continuation->auxiliary_stack_size,
+ "continuation auxiliary stack");
+ memcpy (continuation->auxiliary_stack, thread->auxiliary_stack_base,
+ continuation->auxiliary_stack_size);
+#endif /* SCM_HAVE_AUXILIARY_STACK */
+}
+
+static void
+restore_auxiliary_stack (scm_thread *thread, scm_t_contregs *continuation)
+{
+#if SCM_HAVE_AUXILIARY_STACK
+ memcpy (thread->auxiliary_stack_base, continuation->auxiliary_stack,
+ continuation->auxiliary_stack_size);
+#endif
+}
+
+SCM
+scm_i_make_continuation (scm_thread *thread, SCM vm_cont)
+{
+ SCM cont;
+ scm_t_contregs *continuation;
+ long stack_size;
+ SCM_STACKITEM * src;
+
+ SCM_FLUSH_REGISTER_WINDOWS;
+ stack_size = scm_stack_size (thread->continuation_base);
+ continuation = scm_gc_malloc (sizeof (scm_t_contregs)
+ + (stack_size - 1) * sizeof (SCM_STACKITEM),
+ "continuation");
+ continuation->num_stack_items = stack_size;
+ continuation->root = thread->continuation_root;
+ src = thread->continuation_base;
+#if ! SCM_STACK_GROWS_UP
+ src -= stack_size;
+#endif
+ continuation->offset = continuation->stack - src;
+ memcpy (continuation->stack, src, sizeof (SCM_STACKITEM) * stack_size);
+ memcpy (continuation->jmpbuf, thread->vm.registers, sizeof (jmp_buf));
+ continuation->vm_cont = vm_cont;
+ capture_auxiliary_stack (thread, continuation);
+
+ SCM_NEWSMOB (cont, tc16_continuation, continuation);
+
+ return make_continuation_trampoline (cont);
+}
+
+int
+scm_i_continuation_to_frame (SCM continuation, struct scm_frame *frame)
+{
+ SCM contregs;
+ scm_t_contregs *cont;
+
+ contregs = SCM_PROGRAM_FREE_VARIABLE_REF (continuation, 0);
+ cont = SCM_CONTREGS (contregs);
+
+ if (scm_is_true (cont->vm_cont))
+ {
+ struct scm_vm_cont *data = SCM_VM_CONT_DATA (cont->vm_cont);
+
+ frame->stack_holder = data;
+ frame->fp_offset = data->fp_offset;
+ frame->sp_offset = data->stack_size;
+ frame->ip = data->vra;
+
+ return 1;
+ }
+ else
+ return 0;
+}
+
+scm_t_contregs *
+scm_i_contregs (SCM contregs)
+{
+ if (!SCM_CONTREGSP (contregs))
+ abort ();
+
+ return SCM_CONTREGS (contregs);
+}
+
+
+/* {Apply}
+ */
+
+/* Invoking a continuation proceeds as follows:
+ *
+ * - the stack is made large enough for the called continuation
+ * - the old windchain is unwound down to the branching point
+ * - the continuation stack is copied into place
+ * - the windchain is rewound up to the continuation's context
+ * - the continuation is invoked via longjmp (or setcontext)
+ *
+ * This order is important so that unwind and rewind handlers are run
+ * with their correct stack.
+ */
+
+static void scm_dynthrow (SCM, uint8_t *);
+
+/* Grow the stack by a fixed amount to provide space to copy in the
+ * continuation. Possibly this function has to be called several times
+ * recursively before enough space is available. Make sure the compiler does
+ * not optimize the growth array away by storing it's address into a global
+ * variable.
+ */
+
+static scm_t_bits scm_i_dummy;
+
+static void
+grow_stack (SCM cont, uint8_t *mra)
+{
+ scm_t_bits growth[100];
+
+ scm_i_dummy = (scm_t_bits) growth;
+ scm_dynthrow (cont, mra);
+}
+
+
+/* Copy the continuation stack into the current stack. Calling functions from
+ * within this function is safe, since only stack frames below this function's
+ * own frame are overwritten. Thus, memcpy can be used for best performance.
+ */
+
+static void
+copy_stack_and_call (scm_t_contregs *continuation,
+ SCM_STACKITEM * dst, uint8_t *mra)
+{
+ scm_t_dynstack *dynstack;
+ scm_t_bits *joint;
+ scm_thread *thread = SCM_I_CURRENT_THREAD;
+
+ dynstack = SCM_VM_CONT_DATA (continuation->vm_cont)->dynstack;
+
+ joint = scm_dynstack_unwind_fork (&thread->dynstack, dynstack);
+
+ memcpy (dst, continuation->stack,
+ sizeof (SCM_STACKITEM) * continuation->num_stack_items);
+ restore_auxiliary_stack (thread, continuation);
+
+ scm_dynstack_wind (&thread->dynstack, joint);
+
+ thread->vm.mra_after_abort = mra;
+ longjmp (continuation->jmpbuf, 1);
+}
+
+/* Call grow_stack until the stack space is large enough, then, as the current
+ * stack frame might get overwritten, let copy_stack_and_call perform the
+ * actual copying and continuation calling.
+ */
+static void
+scm_dynthrow (SCM cont, uint8_t *mra)
+{
+ scm_thread *thread = SCM_I_CURRENT_THREAD;
+ scm_t_contregs *continuation = SCM_CONTREGS (cont);
+ SCM_STACKITEM *dst = thread->continuation_base;
+ SCM_STACKITEM stack_top_element;
+
+#if SCM_STACK_GROWS_UP
+ if (dst + continuation->num_stack_items >= &stack_top_element)
+ grow_stack (cont);
+#else
+ dst -= continuation->num_stack_items;
+ if (dst <= &stack_top_element)
+ grow_stack (cont, mra);
+#endif /* def SCM_STACK_GROWS_UP */
+
+ SCM_FLUSH_REGISTER_WINDOWS;
+ copy_stack_and_call (continuation, dst, mra);
+}
+
+void
+scm_i_reinstate_continuation (SCM cont, uint8_t *mra)
+{
+ scm_dynthrow (cont, mra);
+ abort (); /* Unreachable. */
+}
+
+SCM
+scm_i_with_continuation_barrier (scm_t_catch_body body,
+ void *body_data,
+ scm_t_catch_handler handler,
+ void *handler_data,
+ scm_t_catch_handler pre_unwind_handler,
+ void *pre_unwind_handler_data)
+{
+ SCM_STACKITEM stack_item;
+ scm_thread *thread = SCM_I_CURRENT_THREAD;
+ SCM old_controot;
+ SCM_STACKITEM *old_contbase;
+ SCM result;
+
+ /* Establish a fresh continuation root.
+ */
+ old_controot = thread->continuation_root;
+ old_contbase = thread->continuation_base;
+ thread->continuation_root = scm_cons (thread->handle, old_controot);
+ thread->continuation_base = &stack_item;
+
+ /* Call FUNC inside a catch all. This is now guaranteed to return
+ directly and exactly once.
+ */
+ result = scm_c_catch (SCM_BOOL_T,
+ body, body_data,
+ handler, handler_data,
+ pre_unwind_handler, pre_unwind_handler_data);
+
+ /* Return to old continuation root.
+ */
+ thread->continuation_base = old_contbase;
+ thread->continuation_root = old_controot;
+
+ return result;
+}
+
+
+
+static int
+should_print_backtrace (SCM tag, SCM stack)
+{
+ return SCM_BACKTRACE_P
+ && scm_is_true (stack)
+ && scm_initialized_p
+ /* It's generally not useful to print backtraces for errors reading
+ or expanding code in these fallback catch statements. */
+ && !scm_is_eq (tag, scm_from_latin1_symbol ("read-error"))
+ && !scm_is_eq (tag, scm_from_latin1_symbol ("syntax-error"));
+}
+
+static void
+print_exception_and_backtrace (SCM port, SCM tag, SCM args)
+{
+ SCM stack, frame;
+
+ /* We get here via a throw to a catch-all. In that case there is the
+ throw frame active, and this catch closure, so narrow by two
+ frames. */
+ stack = scm_make_stack (SCM_BOOL_T, scm_list_1 (scm_from_int (2)));
+ frame = scm_is_true (stack) ? scm_stack_ref (stack, SCM_INUM0) : SCM_BOOL_F;
+
+ if (should_print_backtrace (tag, stack))
+ {
+ scm_puts ("Backtrace:\n", port);
+ scm_display_backtrace_with_highlights (stack, port,
+ SCM_BOOL_F, SCM_BOOL_F,
+ SCM_EOL);
+ scm_newline (port);
+ }
+
+ scm_print_exception (port, frame, tag, args);
+}
+
+
+
+struct c_data {
+ void *(*func) (void *);
+ void *data;
+ void *result;
+};
+
+static SCM
+c_body (void *d)
+{
+ struct c_data *data = (struct c_data *)d;
+ data->result = data->func (data->data);
+ return SCM_UNSPECIFIED;
+}
+
+static SCM
+c_handler (void *d, SCM tag, SCM args)
+{
+ struct c_data *data;
+
+ /* If TAG is `quit', exit() the process. */
+ if (scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
+ exit (scm_exit_status (args));
+
+ data = (struct c_data *)d;
+ data->result = NULL;
+ return SCM_UNSPECIFIED;
+}
+
+static SCM
+pre_unwind_handler (void *error_port, SCM tag, SCM args)
+{
+ /* Print the exception unless TAG is `quit'. */
+ if (!scm_is_eq (tag, scm_from_latin1_symbol ("quit")))
+ print_exception_and_backtrace (SCM_PACK_POINTER (error_port), tag, args);
+
+ return SCM_UNSPECIFIED;
+}
+
+void *
+scm_c_with_continuation_barrier (void *(*func) (void *), void *data)
+{
+ struct c_data c_data;
+ c_data.func = func;
+ c_data.data = data;
+ scm_i_with_continuation_barrier (c_body, &c_data,
+ c_handler, &c_data,
+ pre_unwind_handler,
+ SCM_UNPACK_POINTER (scm_current_error_port ()));
+ return c_data.result;
+}
+
+struct scm_data {
+ SCM proc;
+};
+
+static SCM
+scm_body (void *d)
+{
+ struct scm_data *data = (struct scm_data *)d;
+ return scm_call_0 (data->proc);
+}
+
+static SCM
+scm_handler (void *d, SCM tag, SCM args)
+{
+ /* Print a message. Note that if TAG is `quit', this will exit() the
+ process. */
+ scm_handle_by_message_noexit (NULL, tag, args);
+
+ return SCM_BOOL_F;
+}
+
+SCM_DEFINE (scm_with_continuation_barrier, "with-continuation-barrier", 1,0,0,
+ (SCM proc),
+"Call @var{proc} and return its result. Do not allow the invocation of\n"
+"continuations that would leave or enter the dynamic extent of the call\n"
+"to @code{with-continuation-barrier}. Such an attempt causes an error\n"
+"to be signaled.\n"
+"\n"
+"Throws (such as errors) that are not caught from within @var{proc} are\n"
+"caught by @code{with-continuation-barrier}. In that case, a short\n"
+"message is printed to the current error port and @code{#f} is returned.\n"
+"\n"
+"Thus, @code{with-continuation-barrier} returns exactly once.\n")
+#define FUNC_NAME s_scm_with_continuation_barrier
+{
+ struct scm_data scm_data;
+ scm_data.proc = proc;
+ return scm_i_with_continuation_barrier (scm_body, &scm_data,
+ scm_handler, &scm_data,
+ pre_unwind_handler,
+ SCM_UNPACK_POINTER (scm_current_error_port ()));
+}
+#undef FUNC_NAME
+
+void
+scm_init_continuations ()
+{
+ tc16_continuation = scm_make_smob_type ("continuation", 0);
+ scm_set_smob_print (tc16_continuation, continuation_print);
+#include "continuations.x"
+}