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

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   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_callchain
  17 #include "util/map.h"
  18 #include "util/symbol.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. If return address
  62          * is in a register (typically R0), it is yet to be saved on
  63          * 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 allocated
  72          * 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  */
  97 static 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  */
 122 static 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 stack
 147  *      1 if return address is in LR and no new stack frame was allocated
 148  *      2 if return address is in LR and a new frame was allocated (but not
 149  *              yet used)
 150  *      -1 in case of errors
 151  */
 152 static 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;
 163
 164         dwfl = 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 never
 180                          * call dwfl_end(). But to prevent fd leak, free in
 181                          * case of error.
 182                          */
 183                         dwfl_end(dwfl);
 184                         goto out;
 185                 }
 186                 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 both
 197          * .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
 215 out:
 216         return rc;
 217 }
 218
 219 /*
 220  * The callchain saved by the kernel always includes the link register (LR).
 221  *
 222  *      0:      PERF_CONTEXT_USER
 223  *      1:      Program counter (Next instruction pointer)
 224  *      2:      LR value
 225  *      3:      Caller's caller
 226  *      4:      ...
 227  *
 228  * The value in LR is only needed when it holds a return address. If the
 229  * 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 just
 232  * allocated but the LR was not saved into it, then the LR contains the
 233  * 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 errors
 241  */
 242 int 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         ip = chain->ips[1];
 254
 255         thread__find_symbol(thread, PERF_RECORD_MISC_USER, ip, &al);
 256
 257         if (al.map)
 258                 dso = al.map->dso;
 259
 260         if (!dso) {
 261                 pr_debug("%" PRIx64 " dso is NULL\n", ip);
 262                 return skip_slot;
 263         }
 264
 265         rc = check_return_addr(dso, al.map->start, ip);
 266
 267         pr_debug("[DSO %s, sym %s, ip 0x%" PRIx64 "] rc %d\n",
 268                                 dso->long_name, al.sym->name, ip, rc);
 269
 270         if (rc == 0) {
 271                 /*
 272                  * Return address on stack. Ignore LR value in callchain
 273                  */
 274                 skip_slot = 2;
 275         } else if (rc == 2) {
 276                 /*
 277                  * New frame allocated but return address still in LR.
 278                  * Ignore the caller's caller entry in callchain.
 279                  */
 280                 skip_slot = 3;
 281         }
 282         return skip_slot;
 283 }