unwind.c

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#include "unwind_decoder.c"


/* Unwind scripts. */

static inline unw_hash_index_t
hash (unsigned long ip)
{
#	define magic	0x9e3779b97f4a7c16	/* based on (sqrt(5)/2-1)*2^64 */

	return (ip >> 4)*magic >> (64 - UNW_LOG_HASH_SIZE);
}

static inline long
cache_match (struct unw_script *script, unsigned long ip, unsigned long pr)
{
	read_lock(&script->lock);
	if (ip == script->ip && ((pr ^ script->pr_val) & script->pr_mask) == 0)
		/* keep the read lock... */
		return 1;
	read_unlock(&script->lock);
	return 0;
}

static inline struct unw_script *
script_lookup (struct unw_frame_info *info)
{
	struct unw_script *script = unw.cache + info->hint;
	unsigned short index;
	unsigned long ip, pr;

	STAT(++unw.stat.cache.lookups);

	ip = info->ip;
	pr = info->pr;

	if (cache_match(script, ip, pr)) {
		STAT(++unw.stat.cache.hinted_hits);
		return script;
	}

	index = unw.hash[hash(ip)];
	if (index >= UNW_CACHE_SIZE)
		return 0;

	script = unw.cache + index;
	while (1) {
		if (cache_match(script, ip, pr)) {
			/* update hint; no locking required as single-word writes are atomic */
			STAT(++unw.stat.cache.normal_hits);
			unw.cache[info->prev_script].hint = script - unw.cache;
			return script;
		}
		if (script->coll_chain >= UNW_HASH_SIZE)
			return 0;
		script = unw.cache + script->coll_chain;
		STAT(++unw.stat.cache.collision_chain_traversals);
	}
}

/*
 * On returning, a write lock for the SCRIPT is still being held.
 */
static inline struct unw_script *
script_new (unsigned long ip)
{
	struct unw_script *script, *prev, *tmp;
	unw_hash_index_t index;
	unsigned long flags;
	unsigned short head;

	STAT(++unw.stat.script.news);

	/*
	 * Can't (easily) use cmpxchg() here because of ABA problem
	 * that is intrinsic in cmpxchg()...
	 */
	spin_lock_irqsave(&unw.lock, flags);
	{
		head = unw.lru_head;
		script = unw.cache + head;
		unw.lru_head = script->lru_chain;
	}
	spin_unlock(&unw.lock);

	/*
	 * XXX We'll deadlock here if we interrupt a thread that is
	 * holding a read lock on script->lock.  A try_write_lock()
	 * might be mighty handy here...  Alternatively, we could
	 * disable interrupts whenever we hold a read-lock, but that
	 * seems silly.
	 */
	write_lock(&script->lock);

	spin_lock(&unw.lock);
	{
		/* re-insert script at the tail of the LRU chain: */
		unw.cache[unw.lru_tail].lru_chain = head;
		unw.lru_tail = head;

		/* remove the old script from the hash table (if it's there): */
		if (script->ip) {
			index = hash(script->ip);
			tmp = unw.cache + unw.hash[index];
			prev = 0;
			while (1) {
				if (tmp == script) {
					if (prev)
						prev->coll_chain = tmp->coll_chain;
					else
						unw.hash[index] = tmp->coll_chain;
					break;
				} else
					prev = tmp;
				if (tmp->coll_chain >= UNW_CACHE_SIZE)
				/* old script wasn't in the hash-table */
					break;
				tmp = unw.cache + tmp->coll_chain;
			}
		}

		/* enter new script in the hash table */
		index = hash(ip);
		script->coll_chain = unw.hash[index];
		unw.hash[index] = script - unw.cache;

		script->ip = ip;	/* set new IP while we're holding the locks */

		STAT(if (script->coll_chain < UNW_CACHE_SIZE) ++unw.stat.script.collisions);
	}
	spin_unlock_irqrestore(&unw.lock, flags);

	script->flags = 0;
	script->hint = 0;
	script->count = 0;
	return script;
}

static void
script_finalize (struct unw_script *script, struct unw_state_record *sr)
{
	script->pr_mask = sr->pr_mask;
	script->pr_val = sr->pr_val;
	/*
	 * We could down-grade our write-lock on script->lock here but
	 * the rwlock API doesn't offer atomic lock downgrading, so
	 * we'll just keep the write-lock and release it later when
	 * we're done using the script.
	 */
}

static inline void
script_emit (struct unw_script *script, struct unw_insn insn)
{
	if (script->count >= UNW_MAX_SCRIPT_LEN) {
		dprintk("unwind: script exceeds maximum size of %u instructions!\n",
			UNW_MAX_SCRIPT_LEN);
		return;
	}
	script->insn[script->count++] = insn;
}

static inline void
emit_nat_info (struct unw_state_record *sr, int i, struct unw_script *script)
{
	struct unw_reg_info *r = sr->curr.reg + i;
	enum unw_insn_opcode opc;
	struct unw_insn insn;
	unsigned long val = 0;

	switch (r->where) {
	      case UNW_WHERE_GR:
		if (r->val >= 32) {
			/* register got spilled to a stacked register */
			opc = UNW_INSN_SETNAT_TYPE;
			val = UNW_NAT_REGSTK;
		} else
			/* register got spilled to a scratch register */
			opc = UNW_INSN_SETNAT_MEMSTK;
		break;

	      case UNW_WHERE_FR:
		opc = UNW_INSN_SETNAT_TYPE;
		val = UNW_NAT_VAL;
		break;

	      case UNW_WHERE_BR:
		opc = UNW_INSN_SETNAT_TYPE;
		val = UNW_NAT_NONE;
		break;

	      case UNW_WHERE_PSPREL:
	      case UNW_WHERE_SPREL:
		opc = UNW_INSN_SETNAT_MEMSTK;
		break;

	      default:
		dprintk("unwind: don't know how to emit nat info for where = %u\n", r->where);
		return;
	}
	insn.opc = opc;
	insn.dst = unw.preg_index[i];
	insn.val = val;
	script_emit(script, insn);
}

static void
compile_reg (struct unw_state_record *sr, int i, struct unw_script *script)
{
	struct unw_reg_info *r = sr->curr.reg + i;
	enum unw_insn_opcode opc;
	unsigned long val, rval;
	struct unw_insn insn;
	long need_nat_info;

	if (r->where == UNW_WHERE_NONE || r->when >= sr->when_target)
		return;

	opc = UNW_INSN_MOVE;
	val = rval = r->val;
	need_nat_info = (i >= UNW_REG_R4 && i <= UNW_REG_R7);

	switch (r->where) {
	      case UNW_WHERE_GR:
		if (rval >= 32) {
			opc = UNW_INSN_MOVE_STACKED;
			val = rval - 32;
		} else if (rval >= 4 && rval <= 7) {
			if (need_nat_info) {
				opc = UNW_INSN_MOVE2;
				need_nat_info = 0;
			}
			val = unw.preg_index[UNW_REG_R4 + (rval - 4)];
		} else {
			opc = UNW_INSN_ADD_SP;
			val = -sizeof(struct pt_regs) + pt_regs_off(rval);
		}
		break;

	      case UNW_WHERE_FR:
		if (rval <= 5)
			val = unw.preg_index[UNW_REG_F2  + (rval -  1)];
		else if (rval >= 16 && rval <= 31)
			val = unw.preg_index[UNW_REG_F16 + (rval - 16)];
		else {
			opc = UNW_INSN_ADD_SP;
			val = -sizeof(struct pt_regs);
			if (rval <= 9)
				val += struct_offset(struct pt_regs, f6) + 16*(rval - 6);
			else
				dprintk("unwind: kernel may not touch f%lu\n", rval);
		}
		break;

	      case UNW_WHERE_BR:
		if (rval >= 1 && rval <= 5)
			val = unw.preg_index[UNW_REG_B1 + (rval - 1)];
		else {
			opc = UNW_INSN_ADD_SP;
			val = -sizeof(struct pt_regs);
			if (rval == 0)
				val += struct_offset(struct pt_regs, b0);
			else if (rval == 6)
				val += struct_offset(struct pt_regs, b6);
			else
				val += struct_offset(struct pt_regs, b7);
		}
		break;

	      case UNW_WHERE_SPREL:
		opc = UNW_INSN_ADD_SP;
		break;

	      case UNW_WHERE_PSPREL:
		opc = UNW_INSN_ADD_PSP;
		break;

	      default:
		dprintk("unwind: register %u has unexpected `where' value of %u\n", i, r->where);
		break;
	}
	insn.opc = opc;
	insn.dst = unw.preg_index[i];
	insn.val = val;
	script_emit(script, insn);
	if (need_nat_info)
		emit_nat_info(sr, i, script);

	if (i == UNW_REG_PSP) {
		/*
		 * info->psp must contain the _value_ of the previous
		 * sp, not it's save location.  We get this by
		 * dereferencing the value we just stored in
		 * info->psp:
		 */
		insn.opc = UNW_INSN_LOAD;
		insn.dst = insn.val = unw.preg_index[UNW_REG_PSP];
		script_emit(script, insn);
	}
}

static inline struct unw_table_entry *
lookup (struct unw_table *table, unsigned long rel_ip)
{
	struct unw_table_entry *e = 0;
	unsigned long lo, hi, mid;

	/* do a binary search for right entry: */
	for (lo = 0, hi = table->length; lo < hi; ) {
		mid = (lo + hi) / 2;
		e = &table->array[mid];
		if (rel_ip < e->start_offset)
			hi = mid;
		else if (rel_ip >= e->end_offset)
			lo = mid + 1;
		else
			break;
	}
	return e;
}

/*
 * Build an unwind script that unwinds from state OLD_STATE to the
 * entrypoint of the function that called OLD_STATE.
 */
static inline struct unw_script *
build_script (struct unw_frame_info *info)
{
	struct unw_reg_state *rs, *next;
	struct unw_table_entry *e = 0;
	struct unw_script *script = 0;
	unsigned long ip = info->ip;
	struct unw_state_record sr;
	struct unw_table *table;
	struct unw_reg_info *r;
	struct unw_insn insn;
	u8 *dp, *desc_end;
	u64 hdr;
	int i;
	STAT(unsigned long start, parse_start;)

	STAT(++unw.stat.script.builds; start = ia64_get_itc());

	/* build state record */
	memset(&sr, 0, sizeof(sr));
	for (r = sr.curr.reg; r < sr.curr.reg + UNW_NUM_REGS; ++r)
		r->when = UNW_WHEN_NEVER;
	sr.pr_val = info->pr;

	script = script_new(ip);
	if (!script) {
		dprintk("unwind: failed to create unwind script\n");
		STAT(unw.stat.script.build_time += ia64_get_itc() - start);
		return 0;
	}
	unw.cache[info->prev_script].hint = script - unw.cache;

	/* search the kernels and the modules' unwind tables for IP: */

	STAT(parse_start = ia64_get_itc());

	for (table = unw.tables; table; table = table->next) {
		if (ip >= table->start && ip < table->end) {
			e = lookup(table, ip - table->segment_base);
			break;
		}
	}
	if (!e) {
		/* no info, return default unwinder (leaf proc, no mem stack, no saved regs)  */
		dprintk("unwind: no unwind info for ip=0x%lx (prev ip=0x%lx)\n", ip,
			unw.cache[info->prev_script].ip);
		sr.curr.reg[UNW_REG_RP].where = UNW_WHERE_BR;
		sr.curr.reg[UNW_REG_RP].when = -1;
		sr.curr.reg[UNW_REG_RP].val = 0;
		compile_reg(&sr, UNW_REG_RP, script);
		script_finalize(script, &sr);
		STAT(unw.stat.script.parse_time += ia64_get_itc() - parse_start);
		STAT(unw.stat.script.build_time += ia64_get_itc() - start);
		return script;
	}

	sr.when_target = (3*((ip & ~0xfUL) - (table->segment_base + e->start_offset))/16
			  + (ip & 0xfUL));
	hdr = *(u64 *) (table->segment_base + e->info_offset);
	dp =   (u8 *)  (table->segment_base + e->info_offset + 8);
	desc_end = dp + 8*UNW_LENGTH(hdr);

	while (!sr.done && dp < desc_end)
		dp = unw_decode(dp, sr.in_body, &sr);

	if (sr.when_target > sr.epilogue_start) {
		/*
		 * sp has been restored and all values on the memory stack below
		 * psp also have been restored.
		 */
		sr.curr.reg[UNW_REG_PSP].where = UNW_WHERE_NONE;
		sr.curr.reg[UNW_REG_PSP].val = 0;
		for (r = sr.curr.reg; r < sr.curr.reg + UNW_NUM_REGS; ++r)
			if ((r->where == UNW_WHERE_PSPREL && r->val <= 0x10)
			    || r->where == UNW_WHERE_SPREL)
				r->where = UNW_WHERE_NONE;
	}

	script->flags = sr.flags;

	/*
	 * If RP did't get saved, generate entry for the return link
	 * register.
	 */
	if (sr.curr.reg[UNW_REG_RP].when >= sr.when_target) {
		sr.curr.reg[UNW_REG_RP].where = UNW_WHERE_BR;
		sr.curr.reg[UNW_REG_RP].when = -1;
		sr.curr.reg[UNW_REG_RP].val = sr.return_link_reg;
	}

#if UNW_DEBUG
	printk("unwind: state record for func 0x%lx, t=%u:\n",
	       table->segment_base + e->start_offset, sr.when_target);
	for (r = sr.curr.reg; r < sr.curr.reg + UNW_NUM_REGS; ++r) {
		if (r->where != UNW_WHERE_NONE || r->when != UNW_WHEN_NEVER) {
			printk("  %s <- ", unw.preg_name[r - sr.curr.reg]);
			switch (r->where) {
			      case UNW_WHERE_GR:     printk("r%lu", r->val); break;
			      case UNW_WHERE_FR:     printk("f%lu", r->val); break;
			      case UNW_WHERE_BR:     printk("b%lu", r->val); break;
			      case UNW_WHERE_SPREL:  printk("[sp+0x%lx]", r->val); break;
			      case UNW_WHERE_PSPREL: printk("[psp+0x%lx]", r->val); break;
			      case UNW_WHERE_NONE:
				printk("%s+0x%lx", unw.preg_name[r - sr.curr.reg], r->val);
				break; 
			      default:		     printk("BADWHERE(%d)", r->where); break;
			}
			printk("\t\t%d\n", r->when);
		}
	}
#endif

	STAT(unw.stat.script.parse_time += ia64_get_itc() - parse_start);

	/* translate state record into unwinder instructions: */

	/*
	 * First, set psp if we're dealing with a fixed-size frame;
	 * subsequent instructions may depend on this value.
	 */
	if (sr.when_target > sr.curr.reg[UNW_REG_PSP].when
	    && (sr.curr.reg[UNW_REG_PSP].where == UNW_WHERE_NONE)
	    && sr.curr.reg[UNW_REG_PSP].val != 0) {
		/* new psp is sp plus frame size */
		insn.opc = UNW_INSN_ADD;
		insn.dst = struct_offset(struct unw_frame_info, psp)/8;
		insn.val = sr.curr.reg[UNW_REG_PSP].val;	/* frame size */
		script_emit(script, insn);
	}

	/* determine where the primary UNaT is: */
	if (sr.when_target < sr.curr.reg[UNW_REG_PRI_UNAT_GR].when)
		i = UNW_REG_PRI_UNAT_MEM;
	else if (sr.when_target < sr.curr.reg[UNW_REG_PRI_UNAT_MEM].when)
		i = UNW_REG_PRI_UNAT_GR;
	else if (sr.curr.reg[UNW_REG_PRI_UNAT_MEM].when > sr.curr.reg[UNW_REG_PRI_UNAT_GR].when)
		i = UNW_REG_PRI_UNAT_MEM;
	else
		i = UNW_REG_PRI_UNAT_GR;

	compile_reg(&sr, i, script);

	for (i = UNW_REG_BSP; i < UNW_NUM_REGS; ++i)
		compile_reg(&sr, i, script);

	/* free labelled register states & stack: */

	STAT(parse_start = ia64_get_itc());
	for (rs = sr.reg_state_list; rs; rs = next) {
		next = rs->next;
		free_reg_state(rs);
	}
	while (sr.stack)
		pop(&sr);
	STAT(unw.stat.script.parse_time += ia64_get_itc() - parse_start);

	script_finalize(script, &sr);
	STAT(unw.stat.script.build_time += ia64_get_itc() - start);
	return script;
}

/*
 * Apply the unwinding actions represented by OPS and update SR to
 * reflect the state that existed upon entry to the function that this
 * unwinder represents.
 */
static inline void
run_script (struct unw_script *script, struct unw_frame_info *state)
{
	struct unw_insn *ip, *limit, next_insn;
	unsigned long opc, dst, val, off;
	unsigned long *s = (unsigned long *) state;
	STAT(unsigned long start;)

	STAT(++unw.stat.script.runs; start = ia64_get_itc());
	state->flags = script->flags;
	ip = script->insn;
	limit = script->insn + script->count;
	next_insn = *ip;

	while (ip++ < limit) {
		opc = next_insn.opc;
		dst = next_insn.dst;
		val = next_insn.val;
		next_insn = *ip;

	  redo:
		switch (opc) {
		      case UNW_INSN_ADD:
			s[dst] += val;
			break;

		      case UNW_INSN_MOVE2:
			if (!s[val])
				goto lazy_init;
			s[dst+1] = s[val+1];
			s[dst] = s[val];
			break;

		      case UNW_INSN_MOVE: