c - 使用 GDB 进行 MPI 调试 - 当前上下文中没有符号 "i"

Question

我需要调试我用 C 编写的 MPI 应用程序。我想使用带有手动附加到进程的 GDB 的系统，这是推荐的 here (第 6 段)。

问题是，当我尝试打印变量“i”的值时，我得到了这个错误:

No symbol "i" in current context.

set var i=5 也有同样的问题。当我尝试运行 info local 时，它只是显示“无语言环境”。

• 系统 Ubuntu 14.04
• MPICC cc (Ubuntu 4.8.2-19ubuntu1) 4.8.2
• GDB GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1.

我用命令编译我的代码

mpicc -o hello hello.c

并用

执行

mpiexec -n 2 ./hello

我试图寻找这个问题，但解决方案通常是不在 GCC 中使用任何优化 (-O) 选项，但这对我没有用，因为我在这里不使用它们中的任何一个而且我正在使用 MPICC 进行编译。我已经尝试将“i”变量声明为 volatile，并使用 -g 和 -O0 启动 mpicc >，但没有任何帮助。

---

DBG消息

GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1

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Attaching to process 3778
Reading symbols from /home/martin/Dokumenty/Programovani/mpi_trenink/hello...done.
Reading symbols from /usr/lib/x86_64-linux-gnu/libmpich.so.10...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/x86_64-linux-gnu/libmpich.so.10
Reading symbols from /lib/x86_64-linux-gnu/libc.so.6...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libc-2.19.so...done.
done.
Loaded symbols for /lib/x86_64-linux-gnu/libc.so.6
Reading symbols from /usr/lib/x86_64-linux-gnu/libmpl.so.1...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/x86_64-linux-gnu/libmpl.so.1
Reading symbols from /lib/x86_64-linux-gnu/librt.so.1...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/librt-2.19.so...done.
done.
Loaded symbols for /lib/x86_64-linux-gnu/librt.so.1
Reading symbols from /usr/lib/libcr.so.0...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/libcr.so.0
Reading symbols from /lib/x86_64-linux-gnu/libpthread.so.0...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libpthread-2.19.so...done.
done.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Loaded symbols for /lib/x86_64-linux-gnu/libpthread.so.0
Reading symbols from /lib/x86_64-linux-gnu/libgcc_s.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib/x86_64-linux-gnu/libgcc_s.so.1
Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/ld-2.19.so...done.
done.
Loaded symbols for /lib64/ld-linux-x86-64.so.2
Reading symbols from /lib/x86_64-linux-gnu/libdl.so.2...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libdl-2.19.so...done.
done.
Loaded symbols for /lib/x86_64-linux-gnu/libdl.so.2
Reading symbols from /lib/x86_64-linux-gnu/libnss_files.so.2...Reading symbols from /usr/lib/debug//lib/x86_64-linux-gnu/libnss_files-2.19.so...done.
done.
Loaded symbols for /lib/x86_64-linux-gnu/libnss_files.so.2
0x00007f493e53c9a0 in __nanosleep_nocancel ()
    at ../sysdeps/unix/syscall-template.S:81
81  ../sysdeps/unix/syscall-template.S: No such file or directory.

---

我的代码

#include <stdio.h>
#include <mpi.h>

#include <unistd.h> // sleep()

int main(){
    MPI_Init(NULL, NULL);
    
    /* DEBUGGING STOP */

    int i = 0;
    while(i == 0){
        sleep(30);
    }

    int world_size;
    MPI_Comm_size( MPI_COMM_WORLD, &world_size );

    int process_id; // casto znaceno jako 'world_rank'
    MPI_Comm_rank( MPI_COMM_WORLD, &process_id );

    char processor_name[ MPI_MAX_PROCESSOR_NAME ];
    int name_len;
    MPI_Get_processor_name( processor_name, &name_len );

    printf("Hello! - sent from process %d running on processor %s.\n\
        Number of processors is %d.\n\
        Length of proc name is %d.\n\
        ***********************\n",
        process_id, processor_name, world_size, name_len);

    MPI_Finalize();
    return 0;
}

Answer 1

GDB 很可能会在深入执行 sleep(3) 函数时中断进程。您可以通过首先发出 bt(回溯)命令来检查:

(gdb) bt
#0  0x00000030e0caca3d in nanosleep () from /lib64/libc.so.6
#1  0x00000030e0cac8b0 in sleep () from /lib64/libc.so.6
#2  0x0000000000400795 in main (argc=1, argv=0x7fff64ae4688) at sleeper.c:9

i 不在 nanosleep 的帧中:

(gdb) info locals
No symbol table info available.

通过发出 frame x 命令选择 main 函数的堆栈帧(其中 x 是帧编号，2 在所示示例中)。

(gdb) f 2
#2  0x0000000000400795 in main (argc=1, argv=0x7fff64ae4688) at sleeper.c:9
9          while(i == 0) { sleep(30); }

i 现在应该在那里:

(gdb) info locals
i = 0

---

如果 GDB 碰巧附加到错误的线程，您可能还需要更改事件线程。许多 MPI 库产生额外的线程，例如使用英特尔 MPI:

(gdb) info threads
  3 Thread 0x7f8b9fada700 (LWP 39085)  0x00000030e0cdf1b3 in poll () from /lib64/libc.so.6
  2 Thread 0x7f8b9f0d9700 (LWP 39087)  0x00000030e0cdf1b3 in poll () from /lib64/libc.so.6
* 1 Thread 0x7f8ba1b51700 (LWP 39066)  0x00000030e0caca3d in nanosleep () from /lib64/libc.so.6

标有* 的线程是被检查的线程。如果其他线程处于事件状态，则使用 thread 1 命令切换到主线程。