Author | Tokens | Token Proportion | Commits | Commit Proportion |
---|---|---|---|---|
Sukadev Bhattiprolu | 848 | 90.12% | 4 | 23.53% |
Sandipan Das | 30 | 3.19% | 3 | 17.65% |
Arnaldo Carvalho de Melo | 24 | 2.55% | 4 | 23.53% |
Athira Rajeev | 18 | 1.91% | 1 | 5.88% |
Ian Rogers | 18 | 1.91% | 3 | 17.65% |
Thomas Gleixner | 2 | 0.21% | 1 | 5.88% |
Jiri Olsa | 1 | 0.11% | 1 | 5.88% |
Total | 941 | 17 |
// SPDX-License-Identifier: GPL-2.0-or-later /* * Use DWARF Debug information to skip unnecessary callchain entries. * * Copyright (C) 2014 Sukadev Bhattiprolu, IBM Corporation. * Copyright (C) 2014 Ulrich Weigand, IBM Corporation. */ #include <inttypes.h> #include <dwarf.h> #include <elfutils/libdwfl.h> #include "util/thread.h" #include "util/callchain.h" #include "util/debug.h" #include "util/dso.h" #include "util/event.h" // struct ip_callchain #include "util/map.h" #include "util/symbol.h" /* * When saving the callchain on Power, the kernel conservatively saves * excess entries in the callchain. A few of these entries are needed * in some cases but not others. If the unnecessary entries are not * ignored, we end up with duplicate arcs in the call-graphs. Use * DWARF debug information to skip over any unnecessary callchain * entries. * * See function header for arch_adjust_callchain() below for more details. * * The libdwfl code in this file is based on code from elfutils * (libdwfl/argp-std.c, libdwfl/tests/addrcfi.c, etc). */ static char *debuginfo_path; static const Dwfl_Callbacks offline_callbacks = { .debuginfo_path = &debuginfo_path, .find_debuginfo = dwfl_standard_find_debuginfo, .section_address = dwfl_offline_section_address, }; /* * Use the DWARF expression for the Call-frame-address and determine * if return address is in LR and if a new frame was allocated. */ static int check_return_reg(int ra_regno, Dwarf_Frame *frame) { Dwarf_Op ops_mem[3]; Dwarf_Op dummy; Dwarf_Op *ops = &dummy; size_t nops; int result; result = dwarf_frame_register(frame, ra_regno, ops_mem, &ops, &nops); if (result < 0) { pr_debug("dwarf_frame_register() %s\n", dwarf_errmsg(-1)); return -1; } /* * Check if return address is on the stack. If return address * is in a register (typically R0), it is yet to be saved on * the stack. */ if ((nops != 0 || ops != NULL) && !(nops == 1 && ops[0].atom == DW_OP_regx && ops[0].number2 == 0 && ops[0].offset == 0)) return 0; /* * Return address is in LR. Check if a frame was allocated * but not-yet used. */ result = dwarf_frame_cfa(frame, &ops, &nops); if (result < 0) { pr_debug("dwarf_frame_cfa() returns %d, %s\n", result, dwarf_errmsg(-1)); return -1; } /* * If call frame address is in r1, no new frame was allocated. */ if (nops == 1 && ops[0].atom == DW_OP_bregx && ops[0].number == 1 && ops[0].number2 == 0) return 1; /* * A new frame was allocated but has not yet been used. */ return 2; } /* * Get the DWARF frame from the .eh_frame section. */ static Dwarf_Frame *get_eh_frame(Dwfl_Module *mod, Dwarf_Addr pc) { int result; Dwarf_Addr bias; Dwarf_CFI *cfi; Dwarf_Frame *frame; cfi = dwfl_module_eh_cfi(mod, &bias); if (!cfi) { pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1)); return NULL; } result = dwarf_cfi_addrframe(cfi, pc-bias, &frame); if (result) { pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1)); return NULL; } return frame; } /* * Get the DWARF frame from the .debug_frame section. */ static Dwarf_Frame *get_dwarf_frame(Dwfl_Module *mod, Dwarf_Addr pc) { Dwarf_CFI *cfi; Dwarf_Addr bias; Dwarf_Frame *frame; int result; cfi = dwfl_module_dwarf_cfi(mod, &bias); if (!cfi) { pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1)); return NULL; } result = dwarf_cfi_addrframe(cfi, pc-bias, &frame); if (result) { pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1)); return NULL; } return frame; } /* * Return: * 0 if return address for the program counter @pc is on stack * 1 if return address is in LR and no new stack frame was allocated * 2 if return address is in LR and a new frame was allocated (but not * yet used) * -1 in case of errors */ static int check_return_addr(struct dso *dso, u64 map_start, Dwarf_Addr pc) { int rc = -1; Dwfl *dwfl; Dwfl_Module *mod; Dwarf_Frame *frame; int ra_regno; Dwarf_Addr start = pc; Dwarf_Addr end = pc; bool signalp; const char *exec_file = dso__long_name(dso); dwfl = RC_CHK_ACCESS(dso)->dwfl; if (!dwfl) { dwfl = dwfl_begin(&offline_callbacks); if (!dwfl) { pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1)); return -1; } mod = dwfl_report_elf(dwfl, exec_file, exec_file, -1, map_start, false); if (!mod) { pr_debug("dwfl_report_elf() failed %s\n", dwarf_errmsg(-1)); /* * We normally cache the DWARF debug info and never * call dwfl_end(). But to prevent fd leak, free in * case of error. */ dwfl_end(dwfl); goto out; } RC_CHK_ACCESS(dso)->dwfl = dwfl; } mod = dwfl_addrmodule(dwfl, pc); if (!mod) { pr_debug("dwfl_addrmodule() failed, %s\n", dwarf_errmsg(-1)); goto out; } /* * To work with split debug info files (eg: glibc), check both * .eh_frame and .debug_frame sections of the ELF header. */ frame = get_eh_frame(mod, pc); if (!frame) { frame = get_dwarf_frame(mod, pc); if (!frame) goto out; } ra_regno = dwarf_frame_info(frame, &start, &end, &signalp); if (ra_regno < 0) { pr_debug("Return address register unavailable: %s\n", dwarf_errmsg(-1)); goto out; } rc = check_return_reg(ra_regno, frame); out: return rc; } /* * The callchain saved by the kernel always includes the link register (LR). * * 0: PERF_CONTEXT_USER * 1: Program counter (Next instruction pointer) * 2: LR value * 3: Caller's caller * 4: ... * * The value in LR is only needed when it holds a return address. If the * return address is on the stack, we should ignore the LR value. * * Further, when the return address is in the LR, if a new frame was just * allocated but the LR was not saved into it, then the LR contains the * caller, slot 4: contains the caller's caller and the contents of slot 3: * (chain->ips[3]) is undefined and must be ignored. * * Use DWARF debug information to determine if any entries need to be skipped. * * Return: * index: of callchain entry that needs to be ignored (if any) * -1 if no entry needs to be ignored or in case of errors */ int arch_skip_callchain_idx(struct thread *thread, struct ip_callchain *chain) { struct addr_location al; struct dso *dso = NULL; int rc; u64 ip; u64 skip_slot = -1; if (!chain || chain->nr < 3) return skip_slot; addr_location__init(&al); ip = chain->ips[1]; thread__find_symbol(thread, PERF_RECORD_MISC_USER, ip, &al); if (al.map) dso = map__dso(al.map); if (!dso) { pr_debug("%" PRIx64 " dso is NULL\n", ip); addr_location__exit(&al); return skip_slot; } rc = check_return_addr(dso, map__start(al.map), ip); pr_debug("[DSO %s, sym %s, ip 0x%" PRIx64 "] rc %d\n", dso__long_name(dso), al.sym->name, ip, rc); if (rc == 0) { /* * Return address on stack. Ignore LR value in callchain */ skip_slot = 2; } else if (rc == 2) { /* * New frame allocated but return address still in LR. * Ignore the caller's caller entry in callchain. */ skip_slot = 3; } addr_location__exit(&al); return skip_slot; }
Information contained on this website is for historical information purposes only and does not indicate or represent copyright ownership.
Created with Cregit http://github.com/cregit/cregit
Version 2.0-RC1