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