tools/perf/arch/powerpc/util/skip-callchain-idx.c

   1 /*
   2  * Use DWARF Debug information to skip unnecessary callchain entries.
   3  *
   4  * Copyright (C) 2014 Sukadev Bhattiprolu, IBM Corporation.
   5  * Copyright (C) 2014 Ulrich Weigand, IBM Corporation.
   6  *
   7  * This program is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU General Public License
   9  * as published by the Free Software Foundation; either version
  10  * 2 of the License, or (at your option) any later version.
  11  */
  12 #include <inttypes.h>
  13 #include <dwarf.h>
  14 #include <elfutils/libdwfl.h>
  15
  16 #include "util/thread.h"
  17 #include "util/callchain.h"
  18 #include "util/debug.h"
  19
  20 /*
  21  * When saving the callchain on Power, the kernel conservatively saves
  22  * excess entries in the callchain. A few of these entries are needed
  23  * in some cases but not others. If the unnecessary entries are not
  24  * ignored, we end up with duplicate arcs in the call-graphs. Use
  25  * DWARF debug information to skip over any unnecessary callchain
  26  * 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 elfutils
  31  * (libdwfl/argp-std.c, libdwfl/tests/addrcfi.c, etc).
  32  */
  33 static char *debuginfo_path;
  34
  35 static 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 determine
  44  * if return address is in LR and if a new frame was allocated.
  45  */
  46 static int check_return_reg(int ra_regno, Dwarf_Frame *frame)
  47 {
  48         Dwarf_Op ops_mem[2];
  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.
  62          */
  63         if (nops != 0 || ops != NULL)
  64                 return 0;
  65
  66         /*
  67          * Return address is in LR. Check if a frame was allocated
  68          * but not-yet used.
  69          */
  70         result = dwarf_frame_cfa(frame, &ops, &nops);
  71         if (result < 0) {
  72                 pr_debug("dwarf_frame_cfa() returns %d, %s\n", result,
  73                                         dwarf_errmsg(-1));
  74                 return -1;
  75         }
  76
  77         /*
  78          * If call frame address is in r1, no new frame was allocated.
  79          */
  80         if (nops == 1 && ops[0].atom == DW_OP_bregx && ops[0].number == 1 &&
  81                                 ops[0].number2 == 0)
  82                 return 1;
  83
  84         /*
  85          * A new frame was allocated but has not yet been used.
  86          */
  87         return 2;
  88 }
  89
  90 /*
  91  * Get the DWARF frame from the .eh_frame section.
  92  */
  93 static Dwarf_Frame *get_eh_frame(Dwfl_Module *mod, Dwarf_Addr pc)
  94 {
  95         int             result;
  96         Dwarf_Addr      bias;
  97         Dwarf_CFI       *cfi;
  98         Dwarf_Frame     *frame;
  99
 100         cfi = dwfl_module_eh_cfi(mod, &bias);
 101         if (!cfi) {
 102                 pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));
 103                 return NULL;
 104         }
 105
 106         result = dwarf_cfi_addrframe(cfi, pc-bias, &frame);
 107         if (result) {
 108                 pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));
 109                 return NULL;
 110         }
 111
 112         return frame;
 113 }
 114
 115 /*
 116  * Get the DWARF frame from the .debug_frame section.
 117  */
 118 static Dwarf_Frame *get_dwarf_frame(Dwfl_Module *mod, Dwarf_Addr pc)
 119 {
 120         Dwarf_CFI       *cfi;
 121         Dwarf_Addr      bias;
 122         Dwarf_Frame     *frame;
 123         int             result;
 124
 125         cfi = dwfl_module_dwarf_cfi(mod, &bias);
 126         if (!cfi) {
 127                 pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));
 128                 return NULL;
 129         }
 130
 131         result = dwarf_cfi_addrframe(cfi, pc-bias, &frame);
 132         if (result) {
 133                 pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));
 134                 return NULL;
 135         }
 136
 137         return frame;
 138 }
 139
 140 /*
 141  * Return:
 142  *      0 if return address for the program counter @pc is on stack
 143  *      1 if return address is in LR and no new stack frame was allocated
 144  *      2 if return address is in LR and a new frame was allocated (but not
 145  *              yet used)
 146  *      -1 in case of errors
 147  */
 148 static int check_return_addr(struct dso *dso, u64 map_start, Dwarf_Addr pc)
 149 {
 150         int             rc = -1;
 151         Dwfl            *dwfl;
 152         Dwfl_Module     *mod;
 153         Dwarf_Frame     *frame;
 154         int             ra_regno;
 155         Dwarf_Addr      start = pc;
 156         Dwarf_Addr      end = pc;
 157         bool            signalp;
 158         const char      *exec_file = dso->long_name;
 159
 160         dwfl = dso->dwfl;
 161
 162         if (!dwfl) {
 163                 dwfl = dwfl_begin(&offline_callbacks);
 164                 if (!dwfl) {
 165                         pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));
 166                         return -1;
 167                 }
 168
 169                 mod = dwfl_report_elf(dwfl, exec_file, exec_file, -1,
 170                                                 map_start, false);
 171                 if (!mod) {
 172                         pr_debug("dwfl_report_elf() failed %s\n",
 173                                                 dwarf_errmsg(-1));
 174                         /*
 175                          * We normally cache the DWARF debug info and never
 176                          * call dwfl_end(). But to prevent fd leak, free in
 177                          * case of error.
 178                          */
 179                         dwfl_end(dwfl);
 180                         goto out;
 181                 }
 182                 dso->dwfl = dwfl;
 183         }
 184
 185         mod = dwfl_addrmodule(dwfl, pc);
 186         if (!mod) {
 187                 pr_debug("dwfl_addrmodule() failed, %s\n", dwarf_errmsg(-1));
 188                 goto out;
 189         }
 190
 191         /*
 192          * To work with split debug info files (eg: glibc), check both
 193          * .eh_frame and .debug_frame sections of the ELF header.
 194          */
 195         frame = get_eh_frame(mod, pc);
 196         if (!frame) {
 197                 frame = get_dwarf_frame(mod, pc);
 198                 if (!frame)
 199                         goto out;
 200         }
 201
 202         ra_regno = dwarf_frame_info(frame, &start, &end, &signalp);
 203         if (ra_regno < 0) {
 204                 pr_debug("Return address register unavailable: %s\n",
 205                                 dwarf_errmsg(-1));
 206                 goto out;
 207         }
 208
 209         rc = check_return_reg(ra_regno, frame);
 210
 211 out:
 212         return rc;
 213 }
 214
 215 /*
 216  * The callchain saved by the kernel always includes the link register (LR).
 217  *
 218  *      0:      PERF_CONTEXT_USER
 219  *      1:      Program counter (Next instruction pointer)
 220  *      2:      LR value
 221  *      3:      Caller's caller
 222  *      4:      ...
 223  *
 224  * The value in LR is only needed when it holds a return address. If the
 225  * return address is on the stack, we should ignore the LR value.
 226  *
 227  * Further, when the return address is in the LR, if a new frame was just
 228  * allocated but the LR was not saved into it, then the LR contains the
 229  * caller, slot 4: contains the caller's caller and the contents of slot 3:
 230  * (chain->ips[3]) is undefined and must be ignored.
 231  *
 232  * Use DWARF debug information to determine if any entries need to be skipped.
 233  *
 234  * Return:
 235  *      index:  of callchain entry that needs to be ignored (if any)
 236  *      -1      if no entry needs to be ignored or in case of errors
 237  */
 238 int arch_skip_callchain_idx(struct thread *thread, struct ip_callchain *chain)
 239 {
 240         struct addr_location al;
 241         struct dso *dso = NULL;
 242         int rc;
 243         u64 ip;
 244         u64 skip_slot = -1;
 245
 246         if (chain->nr < 3)
 247                 return skip_slot;
 248
 249         ip = chain->ips[2];
 250
 251         thread__find_addr_location(thread, PERF_RECORD_MISC_USER,
 252                         MAP__FUNCTION, ip, &al);
 253
 254         if (al.map)
 255                 dso = al.map->dso;
 256
 257         if (!dso) {
 258                 pr_debug("%" PRIx64 " dso is NULL\n", ip);
 259                 return skip_slot;
 260         }
 261
 262         rc = check_return_addr(dso, al.map->start, ip);
 263
 264         pr_debug("[DSO %s, sym %s, ip 0x%" PRIx64 "] rc %d\n",
 265                                 dso->long_name, al.sym->name, ip, rc);
 266
 267         if (rc == 0) {
 268                 /*
 269                  * Return address on stack. Ignore LR value in callchain
 270                  */
 271                 skip_slot = 2;
 272         } else if (rc == 2) {
 273                 /*
 274                  * New frame allocated but return address still in LR.
 275                  * Ignore the caller's caller entry in callchain.
 276                  */
 277                 skip_slot = 3;
 278         }
 279         return skip_slot;
 280 }