| /* |
| * Use DWARF Debug information to skip unnecessary callchain entries. |
| * |
| * Copyright (C) 2014 Sukadev Bhattiprolu, IBM Corporation. |
| * Copyright (C) 2014 Ulrich Weigand, IBM Corporation. |
| * |
| * This program is free software; you can redistribute it and/or |
| * modify it under the terms of the GNU General Public License |
| * as published by the Free Software Foundation; either version |
| * 2 of the License, or (at your option) any later version. |
| */ |
| #include <inttypes.h> |
| #include <dwarf.h> |
| #include <elfutils/libdwfl.h> |
| |
| #include "util/thread.h" |
| #include "util/callchain.h" |
| #include "util/debug.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[2]; |
| 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 (nops != 0 || ops != NULL) |
| 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, &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, &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, 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; |
| |
| dwfl = dso->dwfl; |
| |
| if (!dwfl) { |
| dwfl = dwfl_begin(&offline_callbacks); |
| if (!dwfl) { |
| pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1)); |
| return -1; |
| } |
| |
| if (dwfl_report_offline(dwfl, "", dso->long_name, -1) == NULL) { |
| pr_debug("dwfl_report_offline() 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; |
| } |
| 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 machine *machine, 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->nr < 3) |
| return skip_slot; |
| |
| ip = chain->ips[2]; |
| |
| thread__find_addr_location(thread, machine, PERF_RECORD_MISC_USER, |
| MAP__FUNCTION, ip, &al); |
| |
| if (al.map) |
| dso = al.map->dso; |
| |
| if (!dso) { |
| pr_debug("%" PRIx64 " dso is NULL\n", ip); |
| return skip_slot; |
| } |
| |
| rc = check_return_addr(dso, ip); |
| |
| pr_debug("DSO %s, nr %" PRIx64 ", ip 0x%" PRIx64 "rc %d\n", |
| dso->long_name, chain->nr, 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; |
| } |
| return skip_slot; |
| } |