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/map.h"
  17 #include "util/symbol.h"
  18
  19 /*
  20  * When saving the callchain on Power, the kernel conservatively saves
  21  * excess entries in the callchain. A few of these entries are needed
  22  * in some cases but not others. If the unnecessary entries are not
  23  * ignored, we end up with duplicate arcs in the call-graphs. Use
  24  * DWARF debug information to skip over any unnecessary callchain
  25  * entries.
  26  *
  27  * See function header for arch_adjust_callchain() below for more details.
  28  *
  29  * The libdwfl code in this file is based on code from elfutils
  30  * (libdwfl/argp-std.c, libdwfl/tests/addrcfi.c, etc).
  31  */
  32 static char *debuginfo_path;
  33
  34 static const Dwfl_Callbacks offline_callbacks = {
  35         .debuginfo_path = &debuginfo_path,
  36         .find_debuginfo = dwfl_standard_find_debuginfo,
  37         .section_address = dwfl_offline_section_address,
  38 };
  39
  40
  41 /*
  42  * Use the DWARF expression for the Call-frame-address and determine
  43  * if return address is in LR and if a new frame was allocated.
  44  */
  45 static int check_return_reg(int ra_regno, Dwarf_Frame *frame)
  46 {
  47         Dwarf_Op ops_mem[2];
  48         Dwarf_Op dummy;
  49         Dwarf_Op *ops = &dummy;
  50         size_t nops;
  51         int result;
  52
  53         result = dwarf_frame_register(frame, ra_regno, ops_mem, &ops, &nops);
  54         if (result < 0) {
  55                 pr_debug("dwarf_frame_register() %s\n", dwarf_errmsg(-1));
  56                 return -1;
  57         }
  58
  59         /*
  60          * Check if return address is on the stack. If return address
  61          * is in a register (typically R0), it is yet to be saved on
  62          * the stack.
  63          */
  64         if ((nops != 0 || ops != NULL) &&
  65                 !(nops == 1 && ops[0].atom == DW_OP_regx &&
  66                         ops[0].number2 == 0 && ops[0].offset == 0))
  67                 return 0;
  68
  69         /*
  70          * Return address is in LR. Check if a frame was allocated
  71          * but not-yet used.
  72          */
  73         result = dwarf_frame_cfa(frame, &ops, &nops);
  74         if (result < 0) {
  75                 pr_debug("dwarf_frame_cfa() returns %d, %s\n", result,
  76                                         dwarf_errmsg(-1));
  77                 return -1;
  78         }
  79
  80         /*
  81          * If call frame address is in r1, no new frame was allocated.
  82          */
  83         if (nops == 1 && ops[0].atom == DW_OP_bregx && ops[0].number == 1 &&
  84                                 ops[0].number2 == 0)
  85                 return 1;
  86
  87         /*
  88          * A new frame was allocated but has not yet been used.
  89          */
  90         return 2;
  91 }
  92
  93 /*
  94  * Get the DWARF frame from the .eh_frame section.
  95  */
  96 static Dwarf_Frame *get_eh_frame(Dwfl_Module *mod, Dwarf_Addr pc)
  97 {
  98         int             result;
  99         Dwarf_Addr      bias;
 100         Dwarf_CFI       *cfi;
 101         Dwarf_Frame     *frame;
 102
 103         cfi = dwfl_module_eh_cfi(mod, &bias);
 104         if (!cfi) {
 105                 pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));
 106                 return NULL;
 107         }
 108
 109         result = dwarf_cfi_addrframe(cfi, pc-bias, &frame);
 110         if (result) {
 111                 pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));
 112                 return NULL;
 113         }
 114
 115         return frame;
 116 }
 117
 118 /*
 119  * Get the DWARF frame from the .debug_frame section.
 120  */
 121 static Dwarf_Frame *get_dwarf_frame(Dwfl_Module *mod, Dwarf_Addr pc)
 122 {
 123         Dwarf_CFI       *cfi;
 124         Dwarf_Addr      bias;
 125         Dwarf_Frame     *frame;
 126         int             result;
 127
 128         cfi = dwfl_module_dwarf_cfi(mod, &bias);
 129         if (!cfi) {
 130                 pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));
 131                 return NULL;
 132         }
 133
 134         result = dwarf_cfi_addrframe(cfi, pc-bias, &frame);
 135         if (result) {
 136                 pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));
 137                 return NULL;
 138         }
 139
 140         return frame;
 141 }
 142
 143 /*
 144  * Return:
 145  *      0 if return address for the program counter @pc is on stack
 146  *      1 if return address is in LR and no new stack frame was allocated
 147  *      2 if return address is in LR and a new frame was allocated (but not
 148  *              yet used)
 149  *      -1 in case of errors
 150  */
 151 static int check_return_addr(struct dso *dso, u64 map_start, Dwarf_Addr pc)
 152 {
 153         int             rc = -1;
 154         Dwfl            *dwfl;
 155         Dwfl_Module     *mod;
 156         Dwarf_Frame     *frame;
 157         int             ra_regno;
 158         Dwarf_Addr      start = pc;
 159         Dwarf_Addr      end = pc;
 160         bool            signalp;
 161         const char      *exec_file = dso->long_name;
 162
 163         dwfl = dso->dwfl;
 164
 165         if (!dwfl) {
 166                 dwfl = dwfl_begin(&offline_callbacks);
 167                 if (!dwfl) {
 168                         pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));
 169                         return -1;
 170                 }
 171
 172                 mod = dwfl_report_elf(dwfl, exec_file, exec_file, -1,
 173                                                 map_start, false);
 174                 if (!mod) {
 175                         pr_debug("dwfl_report_elf() failed %s\n",
 176                                                 dwarf_errmsg(-1));
 177                         /*
 178                          * We normally cache the DWARF debug info and never
 179                          * call dwfl_end(). But to prevent fd leak, free in
 180                          * case of error.
 181                          */
 182                         dwfl_end(dwfl);
 183                         goto out;
 184                 }
 185                 dso->dwfl = dwfl;
 186         }
 187
 188         mod = dwfl_addrmodule(dwfl, pc);
 189         if (!mod) {
 190                 pr_debug("dwfl_addrmodule() failed, %s\n", dwarf_errmsg(-1));
 191                 goto out;
 192         }
 193
 194         /*
 195          * To work with split debug info files (eg: glibc), check both
 196          * .eh_frame and .debug_frame sections of the ELF header.
 197          */
 198         frame = get_eh_frame(mod, pc);
 199         if (!frame) {
 200                 frame = get_dwarf_frame(mod, pc);
 201                 if (!frame)
 202                         goto out;
 203         }
 204
 205         ra_regno = dwarf_frame_info(frame, &start, &end, &signalp);
 206         if (ra_regno < 0) {
 207                 pr_debug("Return address register unavailable: %s\n",
 208                                 dwarf_errmsg(-1));
 209                 goto out;
 210         }
 211
 212         rc = check_return_reg(ra_regno, frame);
 213
 214 out:
 215         return rc;
 216 }
 217
 218 /*
 219  * The callchain saved by the kernel always includes the link register (LR).
 220  *
 221  *      0:      PERF_CONTEXT_USER
 222  *      1:      Program counter (Next instruction pointer)
 223  *      2:      LR value
 224  *      3:      Caller's caller
 225  *      4:      ...
 226  *
 227  * The value in LR is only needed when it holds a return address. If the
 228  * return address is on the stack, we should ignore the LR value.
 229  *
 230  * Further, when the return address is in the LR, if a new frame was just
 231  * allocated but the LR was not saved into it, then the LR contains the
 232  * caller, slot 4: contains the caller's caller and the contents of slot 3:
 233  * (chain->ips[3]) is undefined and must be ignored.
 234  *
 235  * Use DWARF debug information to determine if any entries need to be skipped.
 236  *
 237  * Return:
 238  *      index:  of callchain entry that needs to be ignored (if any)
 239  *      -1      if no entry needs to be ignored or in case of errors
 240  */
 241 int arch_skip_callchain_idx(struct thread *thread, struct ip_callchain *chain)
 242 {
 243         struct addr_location al;
 244         struct dso *dso = NULL;
 245         int rc;
 246         u64 ip;
 247         u64 skip_slot = -1;
 248
 249         if (!chain || chain->nr < 3)
 250                 return skip_slot;
 251
 252         ip = chain->ips[1];
 253
 254         thread__find_symbol(thread, PERF_RECORD_MISC_USER, ip, &al);
 255
 256         if (al.map)
 257                 dso = al.map->dso;
 258
 259         if (!dso) {
 260                 pr_debug("%" PRIx64 " dso is NULL\n", ip);
 261                 return skip_slot;
 262         }
 263
 264         rc = check_return_addr(dso, al.map->start, ip);
 265
 266         pr_debug("[DSO %s, sym %s, ip 0x%" PRIx64 "] rc %d\n",
 267                                 dso->long_name, al.sym->name, ip, rc);
 268
 269         if (rc == 0) {
 270                 /*
 271                  * Return address on stack. Ignore LR value in callchain
 272                  */
 273                 skip_slot = 2;
 274         } else if (rc == 2) {
 275                 /*
 276                  * New frame allocated but return address still in LR.
 277                  * Ignore the caller's caller entry in callchain.
 278                  */
 279                 skip_slot = 3;
 280         }
 281         return skip_slot;
 282 }