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1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * Use DWARF Debug information to skip unnecessary callchain entries.4 *5 * Copyright (C) 2014 Sukadev Bhattiprolu, IBM Corporation.6 * Copyright (C) 2014 Ulrich Weigand, IBM Corporation.7 */8#include <inttypes.h>9#include <dwarf.h>10#include <elfutils/libdwfl.h>11 12#include "util/thread.h"13#include "util/callchain.h"14#include "util/debug.h"15#include "util/dso.h"16#include "util/event.h" // struct ip_callchain17#include "util/map.h"18#include "util/symbol.h"19 20/*21 * When saving the callchain on Power, the kernel conservatively saves22 * excess entries in the callchain. A few of these entries are needed23 * in some cases but not others. If the unnecessary entries are not24 * ignored, we end up with duplicate arcs in the call-graphs. Use25 * DWARF debug information to skip over any unnecessary callchain26 * entries.27 *28 * See function header for arch_adjust_callchain() below for more details.29 *30 * The libdwfl code in this file is based on code from elfutils31 * (libdwfl/argp-std.c, libdwfl/tests/addrcfi.c, etc).32 */33static char *debuginfo_path;34 35static const Dwfl_Callbacks offline_callbacks = {36 .debuginfo_path = &debuginfo_path,37 .find_debuginfo = dwfl_standard_find_debuginfo,38 .section_address = dwfl_offline_section_address,39};40 41 42/*43 * Use the DWARF expression for the Call-frame-address and determine44 * if return address is in LR and if a new frame was allocated.45 */46static int check_return_reg(int ra_regno, Dwarf_Frame *frame)47{48 Dwarf_Op ops_mem[3];49 Dwarf_Op dummy;50 Dwarf_Op *ops = &dummy;51 size_t nops;52 int result;53 54 result = dwarf_frame_register(frame, ra_regno, ops_mem, &ops, &nops);55 if (result < 0) {56 pr_debug("dwarf_frame_register() %s\n", dwarf_errmsg(-1));57 return -1;58 }59 60 /*61 * Check if return address is on the stack. If return address62 * is in a register (typically R0), it is yet to be saved on63 * the stack.64 */65 if ((nops != 0 || ops != NULL) &&66 !(nops == 1 && ops[0].atom == DW_OP_regx &&67 ops[0].number2 == 0 && ops[0].offset == 0))68 return 0;69 70 /*71 * Return address is in LR. Check if a frame was allocated72 * but not-yet used.73 */74 result = dwarf_frame_cfa(frame, &ops, &nops);75 if (result < 0) {76 pr_debug("dwarf_frame_cfa() returns %d, %s\n", result,77 dwarf_errmsg(-1));78 return -1;79 }80 81 /*82 * If call frame address is in r1, no new frame was allocated.83 */84 if (nops == 1 && ops[0].atom == DW_OP_bregx && ops[0].number == 1 &&85 ops[0].number2 == 0)86 return 1;87 88 /*89 * A new frame was allocated but has not yet been used.90 */91 return 2;92}93 94/*95 * Get the DWARF frame from the .eh_frame section.96 */97static Dwarf_Frame *get_eh_frame(Dwfl_Module *mod, Dwarf_Addr pc)98{99 int result;100 Dwarf_Addr bias;101 Dwarf_CFI *cfi;102 Dwarf_Frame *frame;103 104 cfi = dwfl_module_eh_cfi(mod, &bias);105 if (!cfi) {106 pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));107 return NULL;108 }109 110 result = dwarf_cfi_addrframe(cfi, pc-bias, &frame);111 if (result) {112 pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));113 return NULL;114 }115 116 return frame;117}118 119/*120 * Get the DWARF frame from the .debug_frame section.121 */122static Dwarf_Frame *get_dwarf_frame(Dwfl_Module *mod, Dwarf_Addr pc)123{124 Dwarf_CFI *cfi;125 Dwarf_Addr bias;126 Dwarf_Frame *frame;127 int result;128 129 cfi = dwfl_module_dwarf_cfi(mod, &bias);130 if (!cfi) {131 pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));132 return NULL;133 }134 135 result = dwarf_cfi_addrframe(cfi, pc-bias, &frame);136 if (result) {137 pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));138 return NULL;139 }140 141 return frame;142}143 144/*145 * Return:146 * 0 if return address for the program counter @pc is on stack147 * 1 if return address is in LR and no new stack frame was allocated148 * 2 if return address is in LR and a new frame was allocated (but not149 * yet used)150 * -1 in case of errors151 */152static int check_return_addr(struct dso *dso, u64 map_start, Dwarf_Addr pc)153{154 int rc = -1;155 Dwfl *dwfl;156 Dwfl_Module *mod;157 Dwarf_Frame *frame;158 int ra_regno;159 Dwarf_Addr start = pc;160 Dwarf_Addr end = pc;161 bool signalp;162 const char *exec_file = dso__long_name(dso);163 164 dwfl = RC_CHK_ACCESS(dso)->dwfl;165 166 if (!dwfl) {167 dwfl = dwfl_begin(&offline_callbacks);168 if (!dwfl) {169 pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));170 return -1;171 }172 173 mod = dwfl_report_elf(dwfl, exec_file, exec_file, -1,174 map_start, false);175 if (!mod) {176 pr_debug("dwfl_report_elf() failed %s\n",177 dwarf_errmsg(-1));178 /*179 * We normally cache the DWARF debug info and never180 * call dwfl_end(). But to prevent fd leak, free in181 * case of error.182 */183 dwfl_end(dwfl);184 goto out;185 }186 RC_CHK_ACCESS(dso)->dwfl = dwfl;187 }188 189 mod = dwfl_addrmodule(dwfl, pc);190 if (!mod) {191 pr_debug("dwfl_addrmodule() failed, %s\n", dwarf_errmsg(-1));192 goto out;193 }194 195 /*196 * To work with split debug info files (eg: glibc), check both197 * .eh_frame and .debug_frame sections of the ELF header.198 */199 frame = get_eh_frame(mod, pc);200 if (!frame) {201 frame = get_dwarf_frame(mod, pc);202 if (!frame)203 goto out;204 }205 206 ra_regno = dwarf_frame_info(frame, &start, &end, &signalp);207 if (ra_regno < 0) {208 pr_debug("Return address register unavailable: %s\n",209 dwarf_errmsg(-1));210 goto out;211 }212 213 rc = check_return_reg(ra_regno, frame);214 215out:216 return rc;217}218 219/*220 * The callchain saved by the kernel always includes the link register (LR).221 *222 * 0: PERF_CONTEXT_USER223 * 1: Program counter (Next instruction pointer)224 * 2: LR value225 * 3: Caller's caller226 * 4: ...227 *228 * The value in LR is only needed when it holds a return address. If the229 * return address is on the stack, we should ignore the LR value.230 *231 * Further, when the return address is in the LR, if a new frame was just232 * allocated but the LR was not saved into it, then the LR contains the233 * caller, slot 4: contains the caller's caller and the contents of slot 3:234 * (chain->ips[3]) is undefined and must be ignored.235 *236 * Use DWARF debug information to determine if any entries need to be skipped.237 *238 * Return:239 * index: of callchain entry that needs to be ignored (if any)240 * -1 if no entry needs to be ignored or in case of errors241 */242int arch_skip_callchain_idx(struct thread *thread, struct ip_callchain *chain)243{244 struct addr_location al;245 struct dso *dso = NULL;246 int rc;247 u64 ip;248 u64 skip_slot = -1;249 250 if (!chain || chain->nr < 3)251 return skip_slot;252 253 addr_location__init(&al);254 ip = chain->ips[1];255 256 thread__find_symbol(thread, PERF_RECORD_MISC_USER, ip, &al);257 258 if (al.map)259 dso = map__dso(al.map);260 261 if (!dso) {262 pr_debug("%" PRIx64 " dso is NULL\n", ip);263 addr_location__exit(&al);264 return skip_slot;265 }266 267 rc = check_return_addr(dso, map__start(al.map), ip);268 269 pr_debug("[DSO %s, sym %s, ip 0x%" PRIx64 "] rc %d\n",270 dso__long_name(dso), al.sym->name, ip, rc);271 272 if (rc == 0) {273 /*274 * Return address on stack. Ignore LR value in callchain275 */276 skip_slot = 2;277 } else if (rc == 2) {278 /*279 * New frame allocated but return address still in LR.280 * Ignore the caller's caller entry in callchain.281 */282 skip_slot = 3;283 }284 285 addr_location__exit(&al);286 return skip_slot;287}288