c++ - 故障排除段错误

Question

我在某些 C 代码中遇到了段错误，我无法弄清楚如何读取它以便找出问题所在。

有没有人有什么技巧可以帮助我？有什么让你突然想到的吗？

这是 gdb 输出:

GNU gdb 6.8 for GNAT Pro 6.2.1 (20090115) [rev:143235]Copyright (C) 2008 Free Software Foundation, Inc.License GPLv3+: GNU GPL version 3 or later This is free software: you are free to change and redistribute it.See your support agreement for details of warranty and support.If you do not have a current support agreement, then there is absolutelyno warranty for this version of GDB.  Type "show copying"and "show warranty" for details.This GDB was configured as "sparc-sun-solaris2.8"...Reading symbols from /usr/lib/libsocket.so.1...done.Loaded symbols for /usr/lib/libsocket.so.1Reading symbols from /usr/lib/libnsl.so.1...done.Loaded symbols for /usr/lib/libnsl.so.1Reading symbols from /usr/lib/libgen.so.1...done.Loaded symbols for /usr/lib/libgen.so.1Reading symbols from /usr/lib/libintl.so.1...warning: Lowest section in /usr/lib/libintl.so.1 is .dynamic at 00000074done.Loaded symbols for /usr/lib/libintl.so.1Reading symbols from /usr/lib/libw.so.1...warning: Lowest section in /usr/lib/libw.so.1 is .dynamic at 00000074done.Loaded symbols for /usr/lib/libw.so.1Reading symbols from /usr/lib/libm.so.1...done.Loaded symbols for /usr/lib/libm.so.1Reading symbols from /opt/services/AZJCommonZJX/solaris/lib/libazjcommonjcxC.so...done.Loaded symbols for /opt/services/AZJCommonZJX/solaris/lib/libazjcommonjcxC.soReading symbols from /usr/openwin/lib/libXext.so.0...done.Loaded symbols for /usr/openwin/lib/libXext.so.0Reading symbols from /usr/openwin/lib/libX11.so.4...done.Loaded symbols for /usr/openwin/lib/libX11.so.4Reading symbols from /usr/openwin/lib/libXmu.so.4...done.Loaded symbols for /usr/openwin/lib/libXmu.so.4Reading symbols from /usr/openwin/lib/libXt.so.4...done.Loaded symbols for /usr/openwin/lib/libXt.so.4Reading symbols from /usr/dt/lib/libXm.so.3...done.Loaded symbols for /usr/dt/lib/libXm.so.3Reading symbols from /usr/lib/libc.so.1...done.Loaded symbols for /usr/lib/libc.so.1Reading symbols from /opt/services/AZJCommonWork/solaris/lib/libazjcommonwork.so...done.Loaded symbols for /opt/services/AZJCommonWork/solaris/lib/libazjcommonwork.soReading symbols from /opt/services/AZJCommonWork/solaris/lib/libazjcommonworkC.so...done.Loaded symbols for /opt/services/AZJCommonWork/solaris/lib/libazjcommonworkC.soReading symbols from /app/gnatpro6.2.1/lib/gcc/sparc-sun-solaris2.8/4.3.3/rts-native/adalib/libgnarl-6.2.so...done.Loaded symbols for /opt/tools/SunOS/gnatpro6.2.1/lib/gcc/sparc-sun-solaris2.8/4.3.3/adalib/libgnarl-6.2.soReading symbols from /app/gnatpro6.2.1/lib/gcc/sparc-sun-solaris2.8/4.3.3/rts-native/adalib/libgnat-6.2.so...done.Loaded symbols for /opt/tools/SunOS/gnatpro6.2.1/lib/gcc/sparc-sun-solaris2.8/4.3.3/adalib/libgnat-6.2.soReading symbols from /usr/lib/libpthread.so.1...warning: Lowest section in /usr/lib/libpthread.so.1 is .dynamic at 00000074done.Loaded symbols for /usr/lib/libpthread.so.1Reading symbols from /usr/lib/librt.so.1...done.Loaded symbols for /usr/lib/librt.so.1Reading symbols from /app/gnatpro6.2.1/lib/libstdc++.so.6...done.Loaded symbols for /opt/tools/SunOS/gnatpro6.2.1/lib/libstdc++.so.6Reading symbols from /app/gnatpro6.2.1/lib/libgcc_s.so.1...done.Loaded symbols for /opt/tools/SunOS/gnatpro6.2.1/lib/libgcc_s.so.1Reading symbols from /usr/lib/libthread.so.1...warning: Lowest section in /usr/lib/libthread.so.1 is .dynamic at 00000074done.Loaded symbols for /usr/lib/libthread.so.1Reading symbols from /usr/lib/libaio.so.1...done.Loaded symbols for /usr/lib/libaio.so.1Reading symbols from /usr/lib/libmd.so.1...done.Loaded symbols for /usr/lib/libmd.so.1Reading symbols from /usr/lib/libm.so.2...done.Loaded symbols for /usr/lib/libm.so.2Reading symbols from /platform/sun4v/lib/libc_psr.so.1...done.Loaded symbols for /platform/SUNW,Sun-Fire-T200/lib/libc_psr.so.1Reading symbols from /lib/ld.so.1...done.Loaded symbols for /lib/ld.so.1Core was generated by `./solaris/apsui -aps_instance 1006 -aps_ato 0 -reject_menu_tearoff -aps_ipc_'.Program terminated with signal 11, Segmentation fault.[New process 75224    ]#0  0x7f1e4d00 in _XmGetFocusData () from /usr/dt/lib/libXm.so.3

Here is what gdb backtrace full shows:

(gdb) bt full#0  0x7f1e4d00 in _XmGetFocusData () from /usr/dt/lib/libXm.so.3No symbol table info available.#1  0x7f1e2768 in _XmNavigInitialize () from /usr/dt/lib/libXm.so.3No symbol table info available.#2  0x7f1e8adc in Initialize () from /usr/dt/lib/libXm.so.3No symbol table info available.#3  0x7f357760 in CallInitialize () from /usr/openwin/lib/libXt.so.4No symbol table info available.#4  0x7f3576b4 in CallInitialize () from /usr/openwin/lib/libXt.so.4No symbol table info available.#5  0x7f3576b4 in CallInitialize () from /usr/openwin/lib/libXt.so.4No symbol table info available.#6  0x7f353804 in xtCreate () from /usr/openwin/lib/libXt.so.4No symbol table info available.#7  0x7f35bf0c in _XtCreateWidget () from /usr/openwin/lib/libXt.so.4No symbol table info available.#8  0x7f35bc8c in XtCreateWidget () from /usr/openwin/lib/libXt.so.4No symbol table info available.#9  0x7f6026f8 in create_my_window (win=0xd3bc0)    at /opt/services/AZJCommonZJX/src/uim/create/create_my_window.c:180    n_args = 0    args = {{name = 0x0, value = 0} }    err_msg = '\0' , "ÿ¿Ïä", '\0' , "main_window_menu\000T_CMD MARITIME_TGT_CMD TEST \000K1\177}al\000\000\000\004\000\000\000\001\000\000\000\000"...    shell = (Widget) 0xd50b8    object_width = 0    object_height = 1660944384    window_name = "TBM_PrimaryWin\000ä\000\000\000\000\177ÿÿø\177ÿü\000\177\023\222¤\000\000 \000\000\f\215ð\000\f\217 \177\023\222¬\177ÿü\000\000\000\000\000ÿ¿Î\200\177\005f,\000\000\000\000\177\023Vx\000\fO \000\aÀ\020\000\fO \1772*\000ui_ipc_xref."    icon_pixmap = 8332422    obj = (gen_obj_list_t *) 0x6b0    vis = (vis_list_t *) 0x7f832bb8    toolbar = (toolbar_t *) 0x0#10 0x7f5f524c in create_my_window (in_buff=0x19750 "main_window_menu")    at /opt/services/AZJCommonZJX/src/uim/create/create_my_window.c:431    func_name = "create_my_window"    str = "\000\000\000\000\000\000\000\000¿¿Ä6'yC \000\000\000\000\000\000\000\000\177\235p0\000\000\000\000\000\003eÈ\000\003e¸\000\000\000\004ÿÿ\000\000\000\000\000\000ÿÿÿß\000\000\000\017\000\000\000\017\000\003^\200ÿ¿Ô\000\000\000\000\000\000\000\000\001\000\000\000\004\000\000\000\017ÿ¿Ó \177\2133, "\001\000\000\000\234\000\000\000\000\000\000\000\036\000\000\000\000\000\rP\000ÿ¿Ô \177\213\022\020\000"...    ptr = 0x19760 ""    keyword = 0x8a130 ""    window_name = 0x8a130 ""---Type  to continue, or q  to quit---    title_name = "\000¿ÒØ\177\211îÄ\000\000\000\000\000\000\000\004", '\0' , "\003e¸\000\000\000\004ÿÿ\000\000\000\000\000\000ÿÿÿß\000\000\000\017\000\000\000 \000\001\023T\177¿sÈ\177·\fà\005øص\000\000\000@\177·\020Xÿ¿Ó8"    full_title_name = 0x2b870 "TAP"    object_width = 2141025804    object_height = 1    window_width = 0    window_height = 0    first_object = 1    other_obj = 0    centered_max_width = 18866798

Here is dbx output:

For information about new features see `help changes'
To remove this message, put `dbxenv suppress_startup_message 7.7' in your .dbxrc
Reading apsui
core file header read successfully
Reading ld.so.1
Reading libsocket.so.1
Reading libnsl.so.1
Reading libgen.so.1
Reading libintl.so.1
Reading libw.so.1
Reading libm.so.1
Reading librt.so.1
Reading libazjcommonjcxC.so
Reading libXext.so.0
Reading libX11.so.4
Reading libXmu.so.4
Reading libXt.so.4
Reading libXm.so.3
Reading libazjcommonwork.so
Reading libazjcommonworkC.so
Reading libgnarl-6.2.so
Reading libgnat-6.2.so
Reading libpthread.so.1
Reading libc.so.1
Reading libaio.so.1
Reading libmd.so.1
Reading libstdc++.so.6.0.10
Reading libgcc_s.so.1
Reading libthread.so.1
Reading libm.so.2
Reading libc_psr.so.1
t@1 (l@1) program terminated by signal SEGV (no mapping at the fault address)
0x7f264d00: _XmGetFocusData+0x0098: ld       [%o0], %o1
Current function is create_my_window
  180     win->main_window = MyWindow(shell, win->name, args, n_args);
>check -all
access checking - ON
memuse checking - ON
Running: apsui 
(process id 18052)
Reading rtcapihook.so
Reading libdl.so.1
Reading rtcaudit.so
Reading libmapmalloc.so.1
Reading rtcboot.so
Reading librtc.so
RTC: Enabling Error Checking...
RTC: Using UltraSparc trap mechanism
RTC: See `help rtc showmap' and `help rtc limitations' for details.
RTC: Running program...
azjcommonworkdummy.adb elaborated
 User Interface version TOOLKIT : 22 MAR 2010 UIMPID=18052
Read from unallocated (rua) on thread 1:
Attempting to read 4 bytes through NULL pointer
t@1 (l@1) stopped in _XmGetFocusData at 0x5d164d00
0x5d164d00: _XmGetFocusData+0x0098: ld       [%o0], %o1
Current function is create_my_window
  180     win->main_window = MyWindow(shell, win->name, args, n_args);

这是堆栈跟踪中我可以修改的最后一个函数调用(不在外部库中 - 在 create_my_window 中)。可以在此处查看此类的完整代码:http://utilitybase.com/paste/26607

void create_my_window( window_t *win)
{
  Cardinal n_args;
  Arg      args[MAX_ARGS];

  Widget   shell = NULL;

//MORE STUFF HERE

  memset(&(args), 0, sizeof(Arg)*MAX_ARGS); n_args = 0;
  if (win->attributes != PRIMARY_WINDOW) {
    XtSetArg(args[n_args], XmNtopAttachment, XmATTACH_FORM); n_args++;
    XtSetArg(args[n_args], XmNbottomAttachment, XmATTACH_FORM); n_args++;
    XtSetArg(args[n_args], XmNleftAttachment, XmATTACH_FORM); n_args++;
    XtSetArg(args[n_args], XmNrightAttachment, XmATTACH_FORM); n_args++;
    XtSetArg(args[n_args], XmNtopOffset, 0); n_args++;
    XtSetArg(args[n_args], XmNbottomOffset, 0); n_args++;
    XtSetArg(args[n_args], XmNleftOffset, 0); n_args++;
    XtSetArg(args[n_args], XmNrightOffset, 0); n_args++;
  }
  win->main_window = XmCreateMainWindow(shell, win->name, args, n_args);

编辑

我在函数调用之前在 gdb 中添加了一个断点，并打印了一些值(不确定这是否有帮助 - 我是 n00b):

Breakpoint 1, create_my_window (win=0x9b378)
    at /opt/services/AZJCommonZJX/src/jzs/create/create_my_window.c:179
179   printf("%d",n_args);
(gdb) p *win
$1 = {struct_type = 1045, next = 0x0, hash_name = 971, 
  name = 0x994e8 "error_log", widget = 0x0, main_window = 0x0, workarea = 0x0, 
  menu_bar = 0x0, message_window = 0x0, window_RC = 0x0, working_box = 0, 
  working_identifier = 0x0, has_message_area = 0, pos = {x = 0, y = 0}, 
  illegal_char_set = 0x0, height = 0, width = 0, configured = 0, 
  actions = 0x0, title = 0x99d18, help_text = 0x0, groups = 0x0, 
  scroll_bars = 0x0, write_protect = 0, attributes = 0, initial_focus = {
    obj_type = 0, obj_name = 0x0, area = 0x0}, text_edit = {
    text_selected_widget = 0x0, text_focus_widget = 0x0, updated_widget = 0x0, 
    start = 0, end = 0, updated_text = 0x0, last_operation = 0}, 
  close_rqt = 0x0, kill_application_action_list_name = 0x0, parent = 0x0, 
  gen_objs = 0x99da0, panes = 0x0, table_list = 0x0, selected_table = 0x0, 
  dialogs = 0x0, has_been_loaded = 0 '\0', source_file_name = 0x0}
(gdb) p *shell
$2 = {core = {self = 0x9db50, widget_class = 0xfec7897c, parent = 0x0, 
    xrm_name = 466, being_destroyed = 0 '\0', destroy_callbacks = 0x9ae58, 
    constraints = 0x0, x = 0, y = 0, width = 0, height = 0, border_width = 1, 
    managed = 0 '\0', sensitive = 1 '\001', ancestor_sensitive = 1 '\001', 
    event_table = 0x9ad98, tm = {translations = 0x0, proc_table = 0x0, 
      current_state = 0x0, lastEventTime = 0}, accelerators = 0x0, 
    border_pixel = 0, border_pixmap = 2, popup_list = 0x0, num_popups = 0, 
    name = 0x7776e "TBM_Dialog_Fixed", screen = 0x7a7e0, colormap = 32, 
    window = 0, depth = 24, background_pixel = 12825262, 
    background_pixmap = 2, visible = 1 '\001', mapped_when_managed = 1 '\001'}}
(gdb) p *args
$3 = {name = 0x0, value = 0}
(gdb) p *n_args
Cannot access memory at address 0x0
(gdb) p n_args
$4 = 0
(gdb) p args
$5 = {{name = 0x0, value = 0} <repeats 20 times>}

Answer 1

鉴于 dbx 表示“试图通过 NULL 指针读取 4 个字节”，并且错误是在函数调用行而不是在 XmCreateMainWindow 中报告的功能，我假设问题与语句 win->name 有关.这是这行 C 语言中唯一可以在实际调用函数之前读取指针的地方(它将读取存储在 win->name 中的数据拷贝并将拷贝传递给函数)。

尝试在调用 XmCreateMainWindow 的正上方的行中插入以下内容

assert(win != NULL);

您需要 #include <assert.h>如果还没有。这应该验证 win调用函数时不是 NULL 指针。为了彻底，您可能想为 shell 添加类似的行