\f
#if !defined(LISP_FEATURE_X86) && !defined(LISP_FEATURE_X86_64)
-/* scavenging interrupt contexts */
+/* Scavenging Interrupt Contexts */
static int boxed_registers[] = BOXED_REGISTERS;
+/* The GC has a notion of an "interior pointer" register, an unboxed
+ * register that typically contains a pointer to inside an object
+ * referenced by another pointer. The most obvious of these is the
+ * program counter, although many compiler backends define a "Lisp
+ * Interior Pointer" register known to the runtime as reg_LIP, and
+ * various CPU architectures have other registers that also partake of
+ * the interior-pointer nature. As the code for pairing an interior
+ * pointer value up with its "base" register, and fixing it up after
+ * scavenging is complete is horribly repetitive, a few macros paper
+ * over the monotony. --AB, 2010-Jul-14 */
+
+/* These macros are only ever used over a lexical environment which
+ * defines a pointer to an os_context_t called context, thus we don't
+ * bother to pass that context in as a parameter. */
+
+/* Define how to access a given interior pointer. */
+#define ACCESS_INTERIOR_POINTER_pc \
+ *os_context_pc_addr(context)
+#define ACCESS_INTERIOR_POINTER_lip \
+ *os_context_register_addr(context, reg_LIP)
+#define ACCESS_INTERIOR_POINTER_lr \
+ *os_context_lr_addr(context)
+#define ACCESS_INTERIOR_POINTER_npc \
+ *os_context_npc_addr(context)
+
+#define INTERIOR_POINTER_VARS(name) \
+ unsigned long name##_offset; \
+ int name##_register_pair
+
+#define PAIR_INTERIOR_POINTER(name) \
+ pair_interior_pointer(context, \
+ ACCESS_INTERIOR_POINTER_##name, \
+ &name##_offset, \
+ &name##_register_pair)
+
+/* One complexity here is that if a paired register is not found for
+ * an interior pointer, then that pointer does not get updated.
+ * Originally, there was some commentary about using an index of -1
+ * when calling os_context_register_addr() on SPARC referring to the
+ * program counter, but the real reason is to allow an interior
+ * pointer register to point to the runtime, read-only space, or
+ * static space without problems. */
+#define FIXUP_INTERIOR_POINTER(name) \
+ do { \
+ if (name##_register_pair >= 0) { \
+ ACCESS_INTERIOR_POINTER_##name = \
+ (*os_context_register_addr(context, \
+ name##_register_pair) \
+ & ~LOWTAG_MASK) \
+ + name##_offset; \
+ } \
+ } while (0)
+
+
static void
-scavenge_interrupt_context(os_context_t *context)
+pair_interior_pointer(os_context_t *context, unsigned long pointer,
+ unsigned long *saved_offset, int *register_pair)
{
int i;
-#ifdef reg_LIP
- unsigned long lip;
- unsigned long lip_offset;
- int lip_register_pair;
-#endif
- unsigned long pc_code_offset;
-
-#ifdef ARCH_HAS_LINK_REGISTER
- unsigned long lr_code_offset;
-#endif
-#ifdef ARCH_HAS_NPC_REGISTER
- unsigned long npc_code_offset;
-#endif
-#ifdef DEBUG_SCAVENGE_VERBOSE
- fprintf(stderr, "Scavenging interrupt context at 0x%x\n",context);
-#endif
-
-#ifdef reg_LIP
- /* Find the LIP's register pair and calculate its offset */
- /* before we scavenge the context. */
-
/*
* I (RLT) think this is trying to find the boxed register that is
* closest to the LIP address, without going past it. Usually, it's
* reg_CODE or reg_LRA. But sometimes, nothing can be found.
*/
- lip = *os_context_register_addr(context, reg_LIP);
/* 0x7FFFFFFF on 32-bit platforms;
0x7FFFFFFFFFFFFFFF on 64-bit platforms */
- lip_offset = (((unsigned long)1) << (N_WORD_BITS - 1)) - 1;
- lip_register_pair = -1;
- for (i = 0; i < (int)(sizeof(boxed_registers) / sizeof(int)); i++) {
+ *saved_offset = (((unsigned long)1) << (N_WORD_BITS - 1)) - 1;
+ *register_pair = -1;
+ for (i = 0; i < (sizeof(boxed_registers) / sizeof(int)); i++) {
unsigned long reg;
- unsigned long offset;
+ long offset;
int index;
index = boxed_registers[i];
reg = *os_context_register_addr(context, index);
- /* would be using PTR if not for integer length issues */
- if ((reg & ~((1L<<N_LOWTAG_BITS)-1)) <= lip) {
- offset = lip - reg;
- if (offset < lip_offset) {
- lip_offset = offset;
- lip_register_pair = index;
+
+ /* An interior pointer is never relative to a non-pointer
+ * register (an oversight in the original implementation).
+ * The simplest argument for why this is true is to consider
+ * the fixnum that happens by coincide to be the word-index in
+ * memory of the header for some object plus two. This is
+ * happenstance would cause the register containing the fixnum
+ * to be selected as the register_pair if the interior pointer
+ * is to anywhere after the first two words of the object.
+ * The fixnum won't be changed during GC, but the object might
+ * move, thus destroying the interior pointer. --AB,
+ * 2010-Jul-14 */
+
+ if (is_lisp_pointer(reg) &&
+ ((reg & ~LOWTAG_MASK) <= pointer)) {
+ offset = pointer - (reg & ~LOWTAG_MASK);
+ if (offset < *saved_offset) {
+ *saved_offset = offset;
+ *register_pair = index;
}
}
}
-#endif /* reg_LIP */
+}
+
+static void
+scavenge_interrupt_context(os_context_t * context)
+{
+ int i;
+
+ /* FIXME: The various #ifdef noise here is precisely that: noise.
+ * Is it possible to fold it into the macrology so that we have
+ * one set of #ifdefs and then INTERIOR_POINTER_VARS /et alia/
+ * compile out for the registers that don't exist on a given
+ * platform? */
- /* Compute the PC's offset from the start of the CODE */
- /* register. */
- pc_code_offset = *os_context_pc_addr(context)
- - *os_context_register_addr(context, reg_CODE);
+ INTERIOR_POINTER_VARS(pc);
+#ifdef reg_LIP
+ INTERIOR_POINTER_VARS(lip);
+#endif
+#ifdef ARCH_HAS_LINK_REGISTER
+ INTERIOR_POINTER_VARS(lr);
+#endif
#ifdef ARCH_HAS_NPC_REGISTER
- npc_code_offset = *os_context_npc_addr(context)
- - *os_context_register_addr(context, reg_CODE);
-#endif /* ARCH_HAS_NPC_REGISTER */
+ INTERIOR_POINTER_VARS(npc);
+#endif
+ PAIR_INTERIOR_POINTER(pc);
+#ifdef reg_LIP
+ PAIR_INTERIOR_POINTER(lip);
+#endif
#ifdef ARCH_HAS_LINK_REGISTER
- lr_code_offset =
- *os_context_lr_addr(context) -
- *os_context_register_addr(context, reg_CODE);
+ PAIR_INTERIOR_POINTER(lr);
+#endif
+#ifdef ARCH_HAS_NPC_REGISTER
+ PAIR_INTERIOR_POINTER(npc);
#endif
/* Scavenge all boxed registers in the context. */
- for (i = 0; i < (int)(sizeof(boxed_registers) / sizeof(int)); i++) {
+ for (i = 0; i < (sizeof(boxed_registers) / sizeof(int)); i++) {
int index;
lispobj foo;
index = boxed_registers[i];
- foo = *os_context_register_addr(context,index);
- scavenge((lispobj *) &foo, 1);
- *os_context_register_addr(context,index) = foo;
+ foo = *os_context_register_addr(context, index);
+ scavenge(&foo, 1);
+ *os_context_register_addr(context, index) = foo;
/* this is unlikely to work as intended on bigendian
* 64 bit platforms */
scavenge((lispobj *) os_context_register_addr(context, index), 1);
}
+ /* Now that the scavenging is done, repair the various interior
+ * pointers. */
+ FIXUP_INTERIOR_POINTER(pc);
#ifdef reg_LIP
- /* Fix the LIP */
-
- /*
- * But what happens if lip_register_pair is -1?
- * *os_context_register_addr on Solaris (see
- * solaris_register_address in solaris-os.c) will return
- * &context->uc_mcontext.gregs[2]. But gregs[2] is REG_nPC. Is
- * that what we really want? My guess is that that is not what we
- * want, so if lip_register_pair is -1, we don't touch reg_LIP at
- * all. But maybe it doesn't really matter if LIP is trashed?
- */
- if (lip_register_pair >= 0) {
- *os_context_register_addr(context, reg_LIP) =
- *os_context_register_addr(context, lip_register_pair)
- + lip_offset;
- }
-#endif /* reg_LIP */
-
- /* Fix the PC if it was in from space */
- if (from_space_p(*os_context_pc_addr(context)))
- *os_context_pc_addr(context) =
- *os_context_register_addr(context, reg_CODE) + pc_code_offset;
-
+ FIXUP_INTERIOR_POINTER(lip);
+#endif
#ifdef ARCH_HAS_LINK_REGISTER
- /* Fix the LR ditto; important if we're being called from
- * an assembly routine that expects to return using blr, otherwise
- * harmless */
- if (from_space_p(*os_context_lr_addr(context)))
- *os_context_lr_addr(context) =
- *os_context_register_addr(context, reg_CODE) + lr_code_offset;
+ FIXUP_INTERIOR_POINTER(lr);
#endif
-
#ifdef ARCH_HAS_NPC_REGISTER
- if (from_space_p(*os_context_npc_addr(context)))
- *os_context_npc_addr(context) =
- *os_context_register_addr(context, reg_CODE) + npc_code_offset;
-#endif /* ARCH_HAS_NPC_REGISTER */
+ FIXUP_INTERIOR_POINTER(npc);
+#endif
}
-void scavenge_interrupt_contexts(struct thread *th)
+void
+scavenge_interrupt_contexts(struct thread *th)
{
int i, index;
os_context_t *context;
index = fixnum_value(SymbolValue(FREE_INTERRUPT_CONTEXT_INDEX,th));
-#ifdef DEBUG_SCAVENGE_VERBOSE
- fprintf(stderr, "%d interrupt contexts to scan\n",index);
+#if defined(DEBUG_PRINT_CONTEXT_INDEX)
+ printf("Number of active contexts: %d\n", index);
#endif
for (i = 0; i < index; i++) {
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