diff --git a/gdb/ChangeLog b/gdb/ChangeLog index 2a601a9626d8..7b5ff1af95d6 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,16 @@ +2016-10-28 Markus Metzger + + * btrace.c (bfun_s): New typedef. + (ftrace_update_caller): Print caller in debug dump. + (ftrace_get_caller, ftrace_match_backtrace, ftrace_fixup_level) + (ftrace_compute_global_level_offset, ftrace_connect_bfun) + (ftrace_connect_backtrace, ftrace_bridge_gap, btrace_bridge_gaps): New. + (btrace_compute_ftrace_bts): Pass vector of gaps. Collect gaps. + (btrace_compute_ftrace_pt): Likewise. + (btrace_compute_ftrace): Split into this, ... + (btrace_compute_ftrace_1): ... this, and ... + (btrace_finalize_ftrace): ... this. Call btrace_bridge_gaps. + 2016-10-28 Markus Metzger * btrace.c (ftrace_new_return): Start from the previous function's diff --git a/gdb/btrace.c b/gdb/btrace.c index 10b6db47ee66..39d537c368de 100644 --- a/gdb/btrace.c +++ b/gdb/btrace.c @@ -49,6 +49,10 @@ static struct cmd_list_element *maint_btrace_pt_show_cmdlist; /* Control whether to skip PAD packets when computing the packet history. */ static int maint_btrace_pt_skip_pad = 1; +/* A vector of function segments. */ +typedef struct btrace_function * bfun_s; +DEF_VEC_P (bfun_s); + static void btrace_add_pc (struct thread_info *tp); /* Print a record debug message. Use do ... while (0) to avoid ambiguities @@ -234,6 +238,7 @@ ftrace_update_caller (struct btrace_function *bfun, bfun->flags = flags; ftrace_debug (bfun, "set caller"); + ftrace_debug (caller, "..to"); } /* Fix up the caller for all segments of a function. */ @@ -296,6 +301,18 @@ ftrace_new_tailcall (struct btrace_function *caller, return bfun; } +/* Return the caller of BFUN or NULL if there is none. This function skips + tail calls in the call chain. */ +static struct btrace_function * +ftrace_get_caller (struct btrace_function *bfun) +{ + for (; bfun != NULL; bfun = bfun->up) + if ((bfun->flags & BFUN_UP_LINKS_TO_TAILCALL) == 0) + return bfun->up; + + return NULL; +} + /* Find the innermost caller in the back trace of BFUN with MFUN/FUN symbol information. */ @@ -599,23 +616,359 @@ ftrace_classify_insn (struct gdbarch *gdbarch, CORE_ADDR pc) return iclass; } +/* Try to match the back trace at LHS to the back trace at RHS. Returns the + number of matching function segments or zero if the back traces do not + match. */ + +static int +ftrace_match_backtrace (struct btrace_function *lhs, + struct btrace_function *rhs) +{ + int matches; + + for (matches = 0; lhs != NULL && rhs != NULL; ++matches) + { + if (ftrace_function_switched (lhs, rhs->msym, rhs->sym)) + return 0; + + lhs = ftrace_get_caller (lhs); + rhs = ftrace_get_caller (rhs); + } + + return matches; +} + +/* Add ADJUSTMENT to the level of BFUN and succeeding function segments. */ + +static void +ftrace_fixup_level (struct btrace_function *bfun, int adjustment) +{ + if (adjustment == 0) + return; + + DEBUG_FTRACE ("fixup level (%+d)", adjustment); + ftrace_debug (bfun, "..bfun"); + + for (; bfun != NULL; bfun = bfun->flow.next) + bfun->level += adjustment; +} + +/* Recompute the global level offset. Traverse the function trace and compute + the global level offset as the negative of the minimal function level. */ + +static void +ftrace_compute_global_level_offset (struct btrace_thread_info *btinfo) +{ + struct btrace_function *bfun, *end; + int level; + + if (btinfo == NULL) + return; + + bfun = btinfo->begin; + if (bfun == NULL) + return; + + /* The last function segment contains the current instruction, which is not + really part of the trace. If it contains just this one instruction, we + stop when we reach it; otherwise, we let the below loop run to the end. */ + end = btinfo->end; + if (VEC_length (btrace_insn_s, end->insn) > 1) + end = NULL; + + level = INT_MAX; + for (; bfun != end; bfun = bfun->flow.next) + level = std::min (level, bfun->level); + + DEBUG_FTRACE ("setting global level offset: %d", -level); + btinfo->level = -level; +} + +/* Connect the function segments PREV and NEXT in a bottom-to-top walk as in + ftrace_connect_backtrace. */ + +static void +ftrace_connect_bfun (struct btrace_function *prev, + struct btrace_function *next) +{ + DEBUG_FTRACE ("connecting..."); + ftrace_debug (prev, "..prev"); + ftrace_debug (next, "..next"); + + /* The function segments are not yet connected. */ + gdb_assert (prev->segment.next == NULL); + gdb_assert (next->segment.prev == NULL); + + prev->segment.next = next; + next->segment.prev = prev; + + /* We may have moved NEXT to a different function level. */ + ftrace_fixup_level (next, prev->level - next->level); + + /* If we run out of back trace for one, let's use the other's. */ + if (prev->up == NULL) + { + if (next->up != NULL) + { + DEBUG_FTRACE ("using next's callers"); + ftrace_fixup_caller (prev, next->up, next->flags); + } + } + else if (next->up == NULL) + { + if (prev->up != NULL) + { + DEBUG_FTRACE ("using prev's callers"); + ftrace_fixup_caller (next, prev->up, prev->flags); + } + } + else + { + /* PREV may have a tailcall caller, NEXT can't. If it does, fixup the up + link to add the tail callers to NEXT's back trace. + + This removes NEXT->UP from NEXT's back trace. It will be added back + when connecting NEXT and PREV's callers - provided they exist. + + If PREV's back trace consists of a series of tail calls without an + actual call, there will be no further connection and NEXT's caller will + be removed for good. To catch this case, we handle it here and connect + the top of PREV's back trace to NEXT's caller. */ + if ((prev->flags & BFUN_UP_LINKS_TO_TAILCALL) != 0) + { + struct btrace_function *caller; + btrace_function_flags flags; + + /* We checked NEXT->UP above so CALLER can't be NULL. */ + caller = next->up; + flags = next->flags; + + DEBUG_FTRACE ("adding prev's tail calls to next"); + + ftrace_fixup_caller (next, prev->up, prev->flags); + + for (prev = prev->up; prev != NULL; prev = prev->up) + { + /* At the end of PREV's back trace, continue with CALLER. */ + if (prev->up == NULL) + { + DEBUG_FTRACE ("fixing up link for tailcall chain"); + ftrace_debug (prev, "..top"); + ftrace_debug (caller, "..up"); + + ftrace_fixup_caller (prev, caller, flags); + + /* If we skipped any tail calls, this may move CALLER to a + different function level. + + Note that changing CALLER's level is only OK because we + know that this is the last iteration of the bottom-to-top + walk in ftrace_connect_backtrace. + + Otherwise we will fix up CALLER's level when we connect it + to PREV's caller in the next iteration. */ + ftrace_fixup_level (caller, prev->level - caller->level - 1); + break; + } + + /* There's nothing to do if we find a real call. */ + if ((prev->flags & BFUN_UP_LINKS_TO_TAILCALL) == 0) + { + DEBUG_FTRACE ("will fix up link in next iteration"); + break; + } + } + } + } +} + +/* Connect function segments on the same level in the back trace at LHS and RHS. + The back traces at LHS and RHS are expected to match according to + ftrace_match_backtrace. */ + +static void +ftrace_connect_backtrace (struct btrace_function *lhs, + struct btrace_function *rhs) +{ + while (lhs != NULL && rhs != NULL) + { + struct btrace_function *prev, *next; + + gdb_assert (!ftrace_function_switched (lhs, rhs->msym, rhs->sym)); + + /* Connecting LHS and RHS may change the up link. */ + prev = lhs; + next = rhs; + + lhs = ftrace_get_caller (lhs); + rhs = ftrace_get_caller (rhs); + + ftrace_connect_bfun (prev, next); + } +} + +/* Bridge the gap between two function segments left and right of a gap if their + respective back traces match in at least MIN_MATCHES functions. + + Returns non-zero if the gap could be bridged, zero otherwise. */ + +static int +ftrace_bridge_gap (struct btrace_function *lhs, struct btrace_function *rhs, + int min_matches) +{ + struct btrace_function *best_l, *best_r, *cand_l, *cand_r; + int best_matches; + + DEBUG_FTRACE ("checking gap at insn %u (req matches: %d)", + rhs->insn_offset - 1, min_matches); + + best_matches = 0; + best_l = NULL; + best_r = NULL; + + /* We search the back traces of LHS and RHS for valid connections and connect + the two functon segments that give the longest combined back trace. */ + + for (cand_l = lhs; cand_l != NULL; cand_l = ftrace_get_caller (cand_l)) + for (cand_r = rhs; cand_r != NULL; cand_r = ftrace_get_caller (cand_r)) + { + int matches; + + matches = ftrace_match_backtrace (cand_l, cand_r); + if (best_matches < matches) + { + best_matches = matches; + best_l = cand_l; + best_r = cand_r; + } + } + + /* We need at least MIN_MATCHES matches. */ + gdb_assert (min_matches > 0); + if (best_matches < min_matches) + return 0; + + DEBUG_FTRACE ("..matches: %d", best_matches); + + /* We will fix up the level of BEST_R and succeeding function segments such + that BEST_R's level matches BEST_L's when we connect BEST_L to BEST_R. + + This will ignore the level of RHS and following if BEST_R != RHS. I.e. if + BEST_R is a successor of RHS in the back trace of RHS (phases 1 and 3). + + To catch this, we already fix up the level here where we can start at RHS + instead of at BEST_R. We will ignore the level fixup when connecting + BEST_L to BEST_R as they will already be on the same level. */ + ftrace_fixup_level (rhs, best_l->level - best_r->level); + + ftrace_connect_backtrace (best_l, best_r); + + return best_matches; +} + +/* Try to bridge gaps due to overflow or decode errors by connecting the + function segments that are separated by the gap. */ + +static void +btrace_bridge_gaps (struct thread_info *tp, VEC (bfun_s) **gaps) +{ + VEC (bfun_s) *remaining; + struct cleanup *old_chain; + int min_matches; + + DEBUG ("bridge gaps"); + + remaining = NULL; + old_chain = make_cleanup (VEC_cleanup (bfun_s), &remaining); + + /* We require a minimum amount of matches for bridging a gap. The number of + required matches will be lowered with each iteration. + + The more matches the higher our confidence that the bridging is correct. + For big gaps or small traces, however, it may not be feasible to require a + high number of matches. */ + for (min_matches = 5; min_matches > 0; --min_matches) + { + /* Let's try to bridge as many gaps as we can. In some cases, we need to + skip a gap and revisit it again after we closed later gaps. */ + while (!VEC_empty (bfun_s, *gaps)) + { + struct btrace_function *gap; + unsigned int idx; + + for (idx = 0; VEC_iterate (bfun_s, *gaps, idx, gap); ++idx) + { + struct btrace_function *lhs, *rhs; + int bridged; + + /* We may have a sequence of gaps if we run from one error into + the next as we try to re-sync onto the trace stream. Ignore + all but the leftmost gap in such a sequence. + + Also ignore gaps at the beginning of the trace. */ + lhs = gap->flow.prev; + if (lhs == NULL || lhs->errcode != 0) + continue; + + /* Skip gaps to the right. */ + for (rhs = gap->flow.next; rhs != NULL; rhs = rhs->flow.next) + if (rhs->errcode == 0) + break; + + /* Ignore gaps at the end of the trace. */ + if (rhs == NULL) + continue; + + bridged = ftrace_bridge_gap (lhs, rhs, min_matches); + + /* Keep track of gaps we were not able to bridge and try again. + If we just pushed them to the end of GAPS we would risk an + infinite loop in case we simply cannot bridge a gap. */ + if (bridged == 0) + VEC_safe_push (bfun_s, remaining, gap); + } + + /* Let's see if we made any progress. */ + if (VEC_length (bfun_s, remaining) == VEC_length (bfun_s, *gaps)) + break; + + VEC_free (bfun_s, *gaps); + + *gaps = remaining; + remaining = NULL; + } + + /* We get here if either GAPS is empty or if GAPS equals REMAINING. */ + if (VEC_empty (bfun_s, *gaps)) + break; + + VEC_free (bfun_s, remaining); + } + + do_cleanups (old_chain); + + /* We may omit this in some cases. Not sure it is worth the extra + complication, though. */ + ftrace_compute_global_level_offset (&tp->btrace); +} + /* Compute the function branch trace from BTS trace. */ static void btrace_compute_ftrace_bts (struct thread_info *tp, - const struct btrace_data_bts *btrace) + const struct btrace_data_bts *btrace, + VEC (bfun_s) **gaps) { struct btrace_thread_info *btinfo; struct btrace_function *begin, *end; struct gdbarch *gdbarch; - unsigned int blk, ngaps; + unsigned int blk; int level; gdbarch = target_gdbarch (); btinfo = &tp->btrace; begin = btinfo->begin; end = btinfo->end; - ngaps = btinfo->ngaps; level = begin != NULL ? -btinfo->level : INT_MAX; blk = VEC_length (btrace_block_s, btrace->blocks); @@ -642,7 +995,7 @@ btrace_compute_ftrace_bts (struct thread_info *tp, if (begin == NULL) begin = end; - ngaps += 1; + VEC_safe_push (bfun_s, *gaps, end); warning (_("Recorded trace may be corrupted at instruction " "%u (pc = %s)."), end->insn_offset - 1, @@ -687,7 +1040,8 @@ btrace_compute_ftrace_bts (struct thread_info *tp, /* Indicate the gap in the trace. We just added INSN so we're not at the beginning. */ end = ftrace_new_gap (end, BDE_BTS_INSN_SIZE); - ngaps += 1; + + VEC_safe_push (bfun_s, *gaps, end); warning (_("Recorded trace may be incomplete at instruction %u " "(pc = %s)."), end->insn_offset - 1, @@ -711,7 +1065,6 @@ btrace_compute_ftrace_bts (struct thread_info *tp, btinfo->begin = begin; btinfo->end = end; - btinfo->ngaps = ngaps; /* LEVEL is the minimal function level of all btrace function segments. Define the global level offset to -LEVEL so all function levels are @@ -759,7 +1112,7 @@ static void ftrace_add_pt (struct pt_insn_decoder *decoder, struct btrace_function **pbegin, struct btrace_function **pend, int *plevel, - unsigned int *ngaps) + VEC (bfun_s) **gaps) { struct btrace_function *begin, *end, *upd; uint64_t offset; @@ -799,7 +1152,8 @@ ftrace_add_pt (struct pt_insn_decoder *decoder, if (insn.enabled) { *pend = end = ftrace_new_gap (end, BDE_PT_DISABLED); - *ngaps += 1; + + VEC_safe_push (bfun_s, *gaps, end); pt_insn_get_offset (decoder, &offset); @@ -816,7 +1170,7 @@ ftrace_add_pt (struct pt_insn_decoder *decoder, if (begin == NULL) *pbegin = begin = end; - *ngaps += 1; + VEC_safe_push (bfun_s, *gaps, end); pt_insn_get_offset (decoder, &offset); @@ -852,7 +1206,8 @@ ftrace_add_pt (struct pt_insn_decoder *decoder, *pend = end = ftrace_new_gap (end, errcode); if (begin == NULL) *pbegin = begin = end; - *ngaps += 1; + + VEC_safe_push (bfun_s, *gaps, end); pt_insn_get_offset (decoder, &offset); @@ -927,7 +1282,8 @@ static void btrace_finalize_ftrace_pt (struct pt_insn_decoder *decoder, static void btrace_compute_ftrace_pt (struct thread_info *tp, - const struct btrace_data_pt *btrace) + const struct btrace_data_pt *btrace, + VEC (bfun_s) **gaps) { struct btrace_thread_info *btinfo; struct pt_insn_decoder *decoder; @@ -971,8 +1327,7 @@ btrace_compute_ftrace_pt (struct thread_info *tp, error (_("Failed to configure the Intel Processor Trace decoder: " "%s."), pt_errstr (pt_errcode (errcode))); - ftrace_add_pt (decoder, &btinfo->begin, &btinfo->end, &level, - &btinfo->ngaps); + ftrace_add_pt (decoder, &btinfo->begin, &btinfo->end, &level, gaps); } CATCH (error, RETURN_MASK_ALL) { @@ -980,7 +1335,8 @@ btrace_compute_ftrace_pt (struct thread_info *tp, if (error.reason == RETURN_QUIT && btinfo->end != NULL) { btinfo->end = ftrace_new_gap (btinfo->end, BDE_PT_USER_QUIT); - btinfo->ngaps++; + + VEC_safe_push (bfun_s, *gaps, btinfo->end); } btrace_finalize_ftrace_pt (decoder, tp, level); @@ -996,7 +1352,8 @@ btrace_compute_ftrace_pt (struct thread_info *tp, static void btrace_compute_ftrace_pt (struct thread_info *tp, - const struct btrace_data_pt *btrace) + const struct btrace_data_pt *btrace, + VEC (bfun_s) **gaps) { internal_error (__FILE__, __LINE__, _("Unexpected branch trace format.")); } @@ -1007,7 +1364,8 @@ btrace_compute_ftrace_pt (struct thread_info *tp, a thread given by BTINFO. */ static void -btrace_compute_ftrace (struct thread_info *tp, struct btrace_data *btrace) +btrace_compute_ftrace_1 (struct thread_info *tp, struct btrace_data *btrace, + VEC (bfun_s) **gaps) { DEBUG ("compute ftrace"); @@ -1017,17 +1375,53 @@ btrace_compute_ftrace (struct thread_info *tp, struct btrace_data *btrace) return; case BTRACE_FORMAT_BTS: - btrace_compute_ftrace_bts (tp, &btrace->variant.bts); + btrace_compute_ftrace_bts (tp, &btrace->variant.bts, gaps); return; case BTRACE_FORMAT_PT: - btrace_compute_ftrace_pt (tp, &btrace->variant.pt); + btrace_compute_ftrace_pt (tp, &btrace->variant.pt, gaps); return; } internal_error (__FILE__, __LINE__, _("Unkown branch trace format.")); } +static void +btrace_finalize_ftrace (struct thread_info *tp, VEC (bfun_s) **gaps) +{ + if (!VEC_empty (bfun_s, *gaps)) + { + tp->btrace.ngaps += VEC_length (bfun_s, *gaps); + btrace_bridge_gaps (tp, gaps); + } +} + +static void +btrace_compute_ftrace (struct thread_info *tp, struct btrace_data *btrace) +{ + VEC (bfun_s) *gaps; + struct cleanup *old_chain; + + gaps = NULL; + old_chain = make_cleanup (VEC_cleanup (bfun_s), &gaps); + + TRY + { + btrace_compute_ftrace_1 (tp, btrace, &gaps); + } + CATCH (error, RETURN_MASK_ALL) + { + btrace_finalize_ftrace (tp, &gaps); + + throw_exception (error); + } + END_CATCH + + btrace_finalize_ftrace (tp, &gaps); + + do_cleanups (old_chain); +} + /* Add an entry for the current PC. */ static void