1 files changed, 621 insertions, 0 deletions

diff --git a/arch/tile/kernel/backtrace.c b/arch/tile/kernel/backtrace.c
new file mode 100644
index 000000000000..77265f3b58d6
--- /dev/null
+++ b/arch/tile/kernel/backtrace.c
@@ -0,0 +1,621 @@
+/*
+ * Copyright 2010 Tilera Corporation. All Rights Reserved.
+ *
+ *   This program is free software; you can redistribute it and/or
+ *   modify it under the terms of the GNU General Public License
+ *   as published by the Free Software Foundation, version 2.
+ *
+ *   This program 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, GOOD TITLE or
+ *   NON INFRINGEMENT.  See the GNU General Public License for
+ *   more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/string.h>
+
+#include <asm/backtrace.h>
+
+#include <arch/chip.h>
+
+#if TILE_CHIP < 10
+
+
+#include <asm/opcode-tile.h>
+
+
+#define TREG_SP 54
+#define TREG_LR 55
+
+
+/** A decoded bundle used for backtracer analysis. */
+struct BacktraceBundle {
+        tile_bundle_bits bits;
+        int num_insns;
+        struct tile_decoded_instruction
+        insns[TILE_MAX_INSTRUCTIONS_PER_BUNDLE];
+};
+
+
+/* This implementation only makes sense for native tools. */
+/** Default function to read memory. */
+static bool bt_read_memory(void *result, VirtualAddress addr,
+                           size_t size, void *extra)
+{
+        /* FIXME: this should do some horrible signal stuff to catch
+         * SEGV cleanly and fail.
+         *
+         * Or else the caller should do the setjmp for efficiency.
+         */
+
+        memcpy(result, (const void *)addr, size);
+        return true;
+}
+
+
+/** Locates an instruction inside the given bundle that
+ * has the specified mnemonic, and whose first 'num_operands_to_match'
+ * operands exactly match those in 'operand_values'.
+ */
+static const struct tile_decoded_instruction *find_matching_insn(
+        const struct BacktraceBundle *bundle,
+        tile_mnemonic mnemonic,
+        const int *operand_values,
+        int num_operands_to_match)
+{
+        int i, j;
+        bool match;
+
+        for (i = 0; i < bundle->num_insns; i++) {
+                const struct tile_decoded_instruction *insn =
+                        &bundle->insns[i];
+
+                if (insn->opcode->mnemonic != mnemonic)
+                        continue;
+
+                match = true;
+                for (j = 0; j < num_operands_to_match; j++) {
+                        if (operand_values[j] != insn->operand_values[j]) {
+                                match = false;
+                                break;
+                        }
+                }
+
+                if (match)
+                        return insn;
+        }
+
+        return NULL;
+}
+
+/** Does this bundle contain an 'iret' instruction? */
+static inline bool bt_has_iret(const struct BacktraceBundle *bundle)
+{
+        return find_matching_insn(bundle, TILE_OPC_IRET, NULL, 0) != NULL;
+}
+
+/** Does this bundle contain an 'addi sp, sp, OFFSET' or
+ * 'addli sp, sp, OFFSET' instruction, and if so, what is OFFSET?
+ */
+static bool bt_has_addi_sp(const struct BacktraceBundle *bundle, int *adjust)
+{
+        static const int vals[2] = { TREG_SP, TREG_SP };
+
+        const struct tile_decoded_instruction *insn =
+                find_matching_insn(bundle, TILE_OPC_ADDI, vals, 2);
+        if (insn == NULL)
+                insn = find_matching_insn(bundle, TILE_OPC_ADDLI, vals, 2);
+        if (insn == NULL)
+                return false;
+
+        *adjust = insn->operand_values[2];
+        return true;
+}
+
+/** Does this bundle contain any 'info OP' or 'infol OP'
+ * instruction, and if so, what are their OP?  Note that OP is interpreted
+ * as an unsigned value by this code since that's what the caller wants.
+ * Returns the number of info ops found.
+ */
+static int bt_get_info_ops(const struct BacktraceBundle *bundle,
+                int operands[MAX_INFO_OPS_PER_BUNDLE])
+{
+        int num_ops = 0;
+        int i;
+
+        for (i = 0; i < bundle->num_insns; i++) {
+                const struct tile_decoded_instruction *insn =
+                        &bundle->insns[i];
+
+                if (insn->opcode->mnemonic == TILE_OPC_INFO ||
+                    insn->opcode->mnemonic == TILE_OPC_INFOL) {
+                        operands[num_ops++] = insn->operand_values[0];
+                }
+        }
+
+        return num_ops;
+}
+
+/** Does this bundle contain a jrp instruction, and if so, to which
+ * register is it jumping?
+ */
+static bool bt_has_jrp(const struct BacktraceBundle *bundle, int *target_reg)
+{
+        const struct tile_decoded_instruction *insn =
+                find_matching_insn(bundle, TILE_OPC_JRP, NULL, 0);
+        if (insn == NULL)
+                return false;
+
+        *target_reg = insn->operand_values[0];
+        return true;
+}
+
+/** Does this bundle modify the specified register in any way? */
+static bool bt_modifies_reg(const struct BacktraceBundle *bundle, int reg)
+{
+        int i, j;
+        for (i = 0; i < bundle->num_insns; i++) {
+                const struct tile_decoded_instruction *insn =
+                        &bundle->insns[i];
+
+                if (insn->opcode->implicitly_written_register == reg)
+                        return true;
+
+                for (j = 0; j < insn->opcode->num_operands; j++)
+                        if (insn->operands[j]->is_dest_reg &&
+                            insn->operand_values[j] == reg)
+                                return true;
+        }
+
+        return false;
+}
+
+/** Does this bundle modify sp? */
+static inline bool bt_modifies_sp(const struct BacktraceBundle *bundle)
+{
+        return bt_modifies_reg(bundle, TREG_SP);
+}
+
+/** Does this bundle modify lr? */
+static inline bool bt_modifies_lr(const struct BacktraceBundle *bundle)
+{
+        return bt_modifies_reg(bundle, TREG_LR);
+}
+
+/** Does this bundle contain the instruction 'move fp, sp'? */
+static inline bool bt_has_move_r52_sp(const struct BacktraceBundle *bundle)
+{
+        static const int vals[2] = { 52, TREG_SP };
+        return find_matching_insn(bundle, TILE_OPC_MOVE, vals, 2) != NULL;
+}
+
+/** Does this bundle contain the instruction 'sw sp, lr'? */
+static inline bool bt_has_sw_sp_lr(const struct BacktraceBundle *bundle)
+{
+        static const int vals[2] = { TREG_SP, TREG_LR };
+        return find_matching_insn(bundle, TILE_OPC_SW, vals, 2) != NULL;
+}
+
+/** Locates the caller's PC and SP for a program starting at the
+ * given address.
+ */
+static void find_caller_pc_and_caller_sp(CallerLocation *location,
+                                         const VirtualAddress start_pc,
+                                         BacktraceMemoryReader read_memory_func,
+                                         void *read_memory_func_extra)
+{
+        /* Have we explicitly decided what the sp is,
+         * rather than just the default?
+         */
+        bool sp_determined = false;
+
+        /* Has any bundle seen so far modified lr? */
+        bool lr_modified = false;
+
+        /* Have we seen a move from sp to fp? */
+        bool sp_moved_to_r52 = false;
+
+        /* Have we seen a terminating bundle? */
+        bool seen_terminating_bundle = false;
+
+        /* Cut down on round-trip reading overhead by reading several
+         * bundles at a time.
+         */
+        tile_bundle_bits prefetched_bundles[32];
+        int num_bundles_prefetched = 0;
+        int next_bundle = 0;
+        VirtualAddress pc;
+
+        /* Default to assuming that the caller's sp is the current sp.
+         * This is necessary to handle the case where we start backtracing
+         * right at the end of the epilog.
+         */
+        location->sp_location = SP_LOC_OFFSET;
+        location->sp_offset = 0;
+
+        /* Default to having no idea where the caller PC is. */
+        location->pc_location = PC_LOC_UNKNOWN;
+
+        /* Don't even try if the PC is not aligned. */
+        if (start_pc % TILE_BUNDLE_ALIGNMENT_IN_BYTES != 0)
+                return;
+
+        for (pc = start_pc;; pc += sizeof(tile_bundle_bits)) {
+
+                struct BacktraceBundle bundle;
+                int num_info_ops, info_operands[MAX_INFO_OPS_PER_BUNDLE];
+                int one_ago, jrp_reg;
+                bool has_jrp;
+
+                if (next_bundle >= num_bundles_prefetched) {
+                        /* Prefetch some bytes, but don't cross a page
+                         * boundary since that might cause a read failure we
+                         * don't care about if we only need the first few
+                         * bytes. Note: we don't care what the actual page
+                         * size is; using the minimum possible page size will
+                         * prevent any problems.
+                         */
+                        unsigned int bytes_to_prefetch = 4096 - (pc & 4095);
+                        if (bytes_to_prefetch > sizeof prefetched_bundles)
+                                bytes_to_prefetch = sizeof prefetched_bundles;
+
+                        if (!read_memory_func(prefetched_bundles, pc,
+                                              bytes_to_prefetch,
+                                              read_memory_func_extra)) {
+                                if (pc == start_pc) {
+                                        /* The program probably called a bad
+                                         * address, such as a NULL pointer.
+                                         * So treat this as if we are at the
+                                         * start of the function prolog so the
+                                         * backtrace will show how we got here.
+                                         */
+                                        location->pc_location = PC_LOC_IN_LR;
+                                        return;
+                                }
+
+                                /* Unreadable address. Give up. */
+                                break;
+                        }
+
+                        next_bundle = 0;
+                        num_bundles_prefetched =
+                                bytes_to_prefetch / sizeof(tile_bundle_bits);
+                }
+
+                /* Decode the next bundle. */
+                bundle.bits = prefetched_bundles[next_bundle++];
+                bundle.num_insns =
+                        parse_insn_tile(bundle.bits, pc, bundle.insns);
+                num_info_ops = bt_get_info_ops(&bundle, info_operands);
+
+                /* First look at any one_ago info ops if they are interesting,
+                 * since they should shadow any non-one-ago info ops.
+                 */
+                for (one_ago = (pc != start_pc) ? 1 : 0;
+                     one_ago >= 0; one_ago--) {
+                        int i;
+                        for (i = 0; i < num_info_ops; i++) {
+                                int info_operand = info_operands[i];
+                                if (info_operand < CALLER_UNKNOWN_BASE) {
+                                        /* Weird; reserved value, ignore it. */
+                                        continue;
+                                }
+
+                                /* Skip info ops which are not in the
+                                 * "one_ago" mode we want right now.
+                                 */
+                                if (((info_operand & ONE_BUNDLE_AGO_FLAG) != 0)
+                                    != (one_ago != 0))
+                                        continue;
+
+                                /* Clear the flag to make later checking
+                                 * easier. */
+                                info_operand &= ~ONE_BUNDLE_AGO_FLAG;
+
+                                /* Default to looking at PC_IN_LR_FLAG. */
+                                if (info_operand & PC_IN_LR_FLAG)
+                                        location->pc_location =
+                                                PC_LOC_IN_LR;
+                                else
+                                        location->pc_location =
+                                                PC_LOC_ON_STACK;
+
+                                switch (info_operand) {
+                                case CALLER_UNKNOWN_BASE:
+                                        location->pc_location = PC_LOC_UNKNOWN;
+                                        location->sp_location = SP_LOC_UNKNOWN;
+                                        return;
+
+                                case CALLER_SP_IN_R52_BASE:
+                                case CALLER_SP_IN_R52_BASE | PC_IN_LR_FLAG:
+                                        location->sp_location = SP_LOC_IN_R52;
+                                        return;
+
+                                default:
+                                {
+                                        const unsigned int val = info_operand
+                                                - CALLER_SP_OFFSET_BASE;
+                                        const unsigned int sp_offset =
+                                                (val >> NUM_INFO_OP_FLAGS) * 8;
+                                        if (sp_offset < 32768) {
+                                                /* This is a properly encoded
+                                                 * SP offset. */
+                                                location->sp_location =
+                                                        SP_LOC_OFFSET;
+                                                location->sp_offset =
+                                                        sp_offset;
+                                                return;
+                                        } else {
+                                                /* This looked like an SP
+                                                 * offset, but it's outside
+                                                 * the legal range, so this
+                                                 * must be an unrecognized
+                                                 * info operand.  Ignore it.
+                                                 */
+                                        }
+                                }
+                                break;
+                                }
+                        }
+                }
+
+                if (seen_terminating_bundle) {
+                        /* We saw a terminating bundle during the previous
+                         * iteration, so we were only looking for an info op.
+                         */
+                        break;
+                }
+
+                if (bundle.bits == 0) {
+                        /* Wacky terminating bundle. Stop looping, and hope
+                         * we've already seen enough to find the caller.
+                         */
+                        break;
+                }
+
+                /*
+                 * Try to determine caller's SP.
+                 */
+
+                if (!sp_determined) {
+                        int adjust;
+                        if (bt_has_addi_sp(&bundle, &adjust)) {
+                                location->sp_location = SP_LOC_OFFSET;
+
+                                if (adjust <= 0) {
+                                        /* We are in prolog about to adjust
+                                         * SP. */
+                                        location->sp_offset = 0;
+                                } else {
+                                        /* We are in epilog restoring SP. */
+                                        location->sp_offset = adjust;
+                                }
+
+                                sp_determined = true;
+                        } else {
+                                if (bt_has_move_r52_sp(&bundle)) {
+                                        /* Maybe in prolog, creating an
+                                         * alloca-style frame.  But maybe in
+                                         * the middle of a fixed-size frame
+                                         * clobbering r52 with SP.
+                                         */
+                                        sp_moved_to_r52 = true;
+                                }
+
+                                if (bt_modifies_sp(&bundle)) {
+                                        if (sp_moved_to_r52) {
+                                                /* We saw SP get saved into
+                                                 * r52 earlier (or now), which
+                                                 * must have been in the
+                                                 * prolog, so we now know that
+                                                 * SP is still holding the
+                                                 * caller's sp value.
+                                                 */
+                                                location->sp_location =
+                                                        SP_LOC_OFFSET;
+                                                location->sp_offset = 0;
+                                        } else {
+                                                /* Someone must have saved
+                                                 * aside the caller's SP value
+                                                 * into r52, so r52 holds the
+                                                 * current value.
+                                                 */
+                                                location->sp_location =
+                                                        SP_LOC_IN_R52;
+                                        }
+                                        sp_determined = true;
+                                }
+                        }
+                }
+
+                if (bt_has_iret(&bundle)) {
+                        /* This is a terminating bundle. */
+                        seen_terminating_bundle = true;
+                        continue;
+                }
+
+                /*
+                 * Try to determine caller's PC.
+                 */
+
+                jrp_reg = -1;
+                has_jrp = bt_has_jrp(&bundle, &jrp_reg);
+                if (has_jrp)
+                        seen_terminating_bundle = true;
+
+                if (location->pc_location == PC_LOC_UNKNOWN) {
+                        if (has_jrp) {
+                                if (jrp_reg == TREG_LR && !lr_modified) {
+                                        /* Looks like a leaf function, or else
+                                         * lr is already restored. */
+                                        location->pc_location =
+                                                PC_LOC_IN_LR;
+                                } else {
+                                        location->pc_location =
+                                                PC_LOC_ON_STACK;
+                                }
+                        } else if (bt_has_sw_sp_lr(&bundle)) {
+                                /* In prolog, spilling initial lr to stack. */
+                                location->pc_location = PC_LOC_IN_LR;
+                        } else if (bt_modifies_lr(&bundle)) {
+                                lr_modified = true;
+                        }
+                }
+        }
+}
+
+void backtrace_init(BacktraceIterator *state,
+                    BacktraceMemoryReader read_memory_func,
+                    void *read_memory_func_extra,
+                    VirtualAddress pc, VirtualAddress lr,
+                    VirtualAddress sp, VirtualAddress r52)
+{
+        CallerLocation location;
+        VirtualAddress fp, initial_frame_caller_pc;
+
+        if (read_memory_func == NULL) {
+                read_memory_func = bt_read_memory;
+        }
+
+        /* Find out where we are in the initial frame. */
+        find_caller_pc_and_caller_sp(&location, pc,
+                                     read_memory_func, read_memory_func_extra);
+
+        switch (location.sp_location) {
+        case SP_LOC_UNKNOWN:
+                /* Give up. */
+                fp = -1;
+                break;
+
+        case SP_LOC_IN_R52:
+                fp = r52;
+                break;
+
+        case SP_LOC_OFFSET:
+                fp = sp + location.sp_offset;
+                break;
+
+        default:
+                /* Give up. */
+                fp = -1;
+                break;
+        }
+
+        /* The frame pointer should theoretically be aligned mod 8. If
+         * it's not even aligned mod 4 then something terrible happened
+         * and we should mark it as invalid.
+         */
+        if (fp % 4 != 0)
+                fp = -1;
+
+        /* -1 means "don't know initial_frame_caller_pc". */
+        initial_frame_caller_pc = -1;
+
+        switch (location.pc_location) {
+        case PC_LOC_UNKNOWN:
+                /* Give up. */
+                fp = -1;
+                break;
+
+        case PC_LOC_IN_LR:
+                if (lr == 0 || lr % TILE_BUNDLE_ALIGNMENT_IN_BYTES != 0) {
+                        /* Give up. */
+                        fp = -1;
+                } else {
+                        initial_frame_caller_pc = lr;
+                }
+                break;
+
+        case PC_LOC_ON_STACK:
+                /* Leave initial_frame_caller_pc as -1,
+                 * meaning check the stack.
+                 */
+                break;
+
+        default:
+                /* Give up. */
+                fp = -1;
+                break;
+        }
+
+        state->pc = pc;
+        state->sp = sp;
+        state->fp = fp;
+        state->initial_frame_caller_pc = initial_frame_caller_pc;
+        state->read_memory_func = read_memory_func;
+        state->read_memory_func_extra = read_memory_func_extra;
+}
+
+bool backtrace_next(BacktraceIterator *state)
+{
+        VirtualAddress next_fp, next_pc, next_frame[2];
+
+        if (state->fp == -1) {
+                /* No parent frame. */
+                return false;
+        }
+
+        /* Try to read the frame linkage data chaining to the next function. */
+        if (!state->read_memory_func(&next_frame, state->fp, sizeof next_frame,
+                                     state->read_memory_func_extra)) {
+                return false;
+        }
+
+        next_fp = next_frame[1];
+        if (next_fp % 4 != 0) {
+                /* Caller's frame pointer is suspect, so give up.
+                 * Technically it should be aligned mod 8, but we will
+                 * be forgiving here.
+                 */
+                return false;
+        }
+
+        if (state->initial_frame_caller_pc != -1) {
+                /* We must be in the initial stack frame and already know the
+                 * caller PC.
+                 */
+                next_pc = state->initial_frame_caller_pc;
+
+                /* Force reading stack next time, in case we were in the
+                 * initial frame.  We don't do this above just to paranoidly
+                 * avoid changing the struct at all when we return false.
+                 */
+                state->initial_frame_caller_pc = -1;
+        } else {
+                /* Get the caller PC from the frame linkage area. */
+                next_pc = next_frame[0];
+                if (next_pc == 0 ||
+                    next_pc % TILE_BUNDLE_ALIGNMENT_IN_BYTES != 0) {
+                        /* The PC is suspect, so give up. */
+                        return false;
+                }
+        }
+
+        /* Update state to become the caller's stack frame. */
+        state->pc = next_pc;
+        state->sp = state->fp;
+        state->fp = next_fp;
+
+        return true;
+}
+
+#else /* TILE_CHIP < 10 */
+
+void backtrace_init(BacktraceIterator *state,
+                    BacktraceMemoryReader read_memory_func,
+                    void *read_memory_func_extra,
+                    VirtualAddress pc, VirtualAddress lr,
+                    VirtualAddress sp, VirtualAddress r52)
+{
+        state->pc = pc;
+        state->sp = sp;
+        state->fp = -1;
+        state->initial_frame_caller_pc = -1;
+        state->read_memory_func = read_memory_func;
+        state->read_memory_func_extra = read_memory_func_extra;
+}
+
+bool backtrace_next(BacktraceIterator *state) { return false; }
+
+#endif /* TILE_CHIP < 10 */