Question

当我从计算机以root身份运行时，我的c ++程序给了我一个seg错误，但是当我启动远程会话时却没有。我的程序仅作为用户从我的计算机运行。可能是什么问题？我为嵌入式设备编写了程序，我正在使用它来编译：

gcc -Werror notify.cc -o notify `pkg-config --libs --cflags gtk+-2.0 hildon-notifymm hildonmm hildon-fmmm'

我没有收到任何错误。这可能是旗帜问题吗？我可以发布我的代码。

编辑：当我用gdb启动我的程序时，我得到了这个：

Program received signal SIGSEGV, Segmentation fault.
0x40eed060 in strcmp () from /lib/libc.so.6
0x40eed060 <strcmp+0>:  ldrb    r2, [r0], #1

Backtrace给出了这个：

(gdb) backtrace
 #0  0x40eed060 in strcmp () from /lib/libc.so.6
 #1  0x40b7f190 in dbus_set_g_error ()
 from /usr/lib/libdbus-glib-1.so.2
 #2  0x40b7d060 in dbus_g_bus_get () from /usr/lib/libdbus-glib-1.so.2
 #3  0x400558ec in notify_init () from /usr/lib/libnotify.so.1
 #4  0x4004a240 in Notify::init(Glib::ustring const&) ()
 from /usr/lib/libnotifymm-1.0.so.7
 #5  0x40033794 in Hildon::notify_init(Glib::ustring const&) ()
 from /usr/lib/libhildon-notifymm-1.0.so.1

这是我的代码：

#include <hildonmm.h>
#include <hildon-notifymm.h>
#include <hildon/hildon-notification.h>
#include <libnotifymm/init.h>
#include <gtkmm/stock.h>
#include <dbus/dbus.h>
#include <dbus/dbus-glib.h>
#include <dbus/dbus-glib-lowlevel.h>
#include <iostream>

int main(int argc, char *argv[])
{
// Initialize gtkmm and maemomm:

Hildon::init();
Hildon::notify_init("Notification Example");

// Initialize D-Bus (needed by hildon-notify):
DBusConnection* conn = dbus_bus_get(DBUS_BUS_SESSION, NULL);
dbus_connection_setup_with_g_main(conn, NULL);

// Create a new notification:
Glib::RefPtr<Hildon::Notification> notification =   Hildon::Notification::create("Something Happened", "A thing has just happened.", Gtk::Stock::OPEN);

// Show the notification:
std::auto_ptr<Glib::Error> ex;
notification->show(ex);
if(ex.get())
{ 
std::cerr << "Notification::show() failed: " << ex->what() << std::endl;
}
return 0;
}

编辑：问题解决了。程序需要在终端的env中使用DBUS_SESSION_ADDRESS。

Answer 1

问题是你在某处调用了未定义的行为。未定义的行为在不同的机器上可以表现不同，在同一台机器上运行不同，无论如何。你必须找到你让狂野指针发生的地方并处理它。

当您作为受限用户运行时，您很可能只是“幸运”，并且您的进程的页面权限被设置为允许您获得的任何无效内存访问，或者您有一些特定于root的特定代码仅在用户模式下运行时才会到达。

Answer 2

您可能希望在valgrind下运行您的程序。我写了一个小程序，写在一个已分配的数组之外：

$ valgrind ./segfault
==11830== Memcheck, a memory error detector
==11830== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==11830== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==11830== Command: ./segfault
==11830== 
==11830== Invalid write of size 1
==11830==    at 0x4004BF: main (in /tmp/segfault)
==11830==  Address 0x7feff65bf is not stack'd, malloc'd or (recently) free'd
==11830== 
==11830== 
==11830== Process terminating with default action of signal 11 (SIGSEGV)
==11830==  Access not within mapped region at address 0x7FEFF65BF
==11830==    at 0x4004BF: main (in /tmp/segfault)
==11830==  If you believe this happened as a result of a stack
==11830==  overflow in your program's main thread (unlikely but
==11830==  possible), you can try to increase the size of the
==11830==  main thread stack using the --main-stacksize= flag.
==11830==  The main thread stack size used in this run was 8388608.
==11830== 
==11830== HEAP SUMMARY:
==11830==     in use at exit: 0 bytes in 0 blocks
==11830==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==11830== 
==11830== All heap blocks were freed -- no leaks are possible
==11830== 
==11830== For counts of detected and suppressed errors, rerun with: -v
==11830== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)
Segmentation fault

此输出中最重要的部分是：

==11830== Invalid write of size 1
==11830==    at 0x4004BF: main (in /tmp/segfault)

write of size 1可能会帮助您确定涉及哪条线：

int main(int argc, char *argv[]) {
    char f[1];
    f[-40000]='c';
    return 0;
}

另一个非常有用的工具是gdb。如果您将rlimits设置为允许转储核心（有关限制的详细信息，请参阅setrlimit(2)，有关bash(1)内置的详细信息，请参阅您的shell手册（可能是ulimit）命令）然后你可以获得一个用于gdb的核心文件：

$ ulimit -c 1000
$ ./segfault 
Segmentation fault (core dumped)
$ gdb --core=core ./segfault
GNU gdb (GDB) 7.2-ubuntu
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /tmp/segfault...(no debugging symbols found)...done.
[New Thread 11951]

warning: Can't read pathname for load map: Input/output error.
Reading symbols from /lib/libc.so.6...Reading symbols from /usr/lib/debug/lib/libc-2.12.1.so...done.
done.
Loaded symbols for /lib/libc.so.6
Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug/lib/ld-2.12.1.so...done.
done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Core was generated by `./segfault'.
Program terminated with signal 11, Segmentation fault.
#0  0x00000000004004bf in main ()
(gdb) bt
#0  0x00000000004004bf in main ()
(gdb) quit

根据程序的大小，您可能需要让允许的核心文件超过1000块。如果这个程序远程复杂，了解调用链以获得段错误可能是至关重要的信息。

Answer 3

如果没有看到任何代码，很难说出具体的内容，所以我会给你一些通用的建议：学会使用你的调试器（可能是gdb），并尝试重现失败在调试器下。如果你很幸运，在调试器下仍会发生段错误，你将得到一个堆栈跟踪显示它失败的地方，这将为你提供一个起点，让你回到问题的真正来源。

如果你运气不好，如果使用调试支持进行编译，问题可能会消失，或者在gdb下运行它。在这种情况下，你将不得不求助于代码检查，并擦洗你的任何未定义行为的代码（例如，wild或uninitialized指针，如 Billy ONeal建议）。

Answer 4

设置ulimit -c unlimited。

运行程序并让它崩溃。它现在应该是核心转储。

运行gdb <program-name> core

如果您使用bt（回溯）命令，它应该可以让您知道崩溃发生的位置。这应该可以帮助您解决它。

以root身份运行时出现分段错误？

4 个答案: