我需要调试用C编写的MPI应用程序。我想使用手动附加GDB的系统进行处理，因为它推荐here（第6段）。
问题是，当我尝试打印变量＆＃34; i＆＃34;的值时，我收到此错误：
No symbol "i" in current context.
同样的问题是set var i=5。当我尝试运行info local时，它只是声明＆＃34;没有区域设置＆＃34;。
我使用命令
编译我的代码mpicc -o hello hello.c
并使用
执行它mpiexec -n 2 ./hello
我试图寻找这个问题，但解决方案通常不是在GCC中使用任何优化（-O）选项，但它对我没用，因为我没有＆＃39;在这里使用它们中的任何一个，我用MPICC编译。我已经尝试过宣布＆＃34;我＆＃34;变量为 volatile ，并使用mpicc和-g启动-O0，但没有任何帮助。
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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.
#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;
}
答案 0 :(得分：4)
GDB很有可能在深入实现sleep(3)函数的过程中打破这个过程。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
nanosleep通过发出(gdb) info locals
No symbol table info available.
命令选择main函数的堆栈帧（其中frame x是帧号，在显示的示例中为x）。
2 (gdb) f 2
#2 0x0000000000400795 in main (argc=1, argv=0x7fff64ae4688) at sleeper.c:9
9 while(i == 0) { sleep(30); }
现在应该在那里：
i如果GDB碰巧连接到错误的线程，您可能还需要更改活动线程。许多MPI库产生额外的线程，例如使用英特尔MPI：
(gdb) info locals
i = 0
标有(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
的主题是正在审核的主题。如果某个其他线程处于活动状态，请使用*命令切换到主线程。
答案 1 :(得分：3)
我终于解决了这个问题。关键是我必须先用向上命令检查某个帧的内容，然后再尝试打印变量“i”或更改其值。
使用mpicc -o hello hello.c -g -O0编译此代码。
使用mpiexec -n 2 ./hello启动该计划。
找出进程ID（PID）。
ps -e | grep hello。pstree。下一步是打开一个新终端并使用gdb --pid debugged_process_id命令启动GDB。
现在，在调试器类型bt中。
输出将与此类似：
#0 0x00007f63667e09a0 in __nanosleep_nocancel ()
at ../sysdeps/unix/syscall-template.S:81
#1 0x00007f63667e0854 in __sleep (seconds=0)
at ../sysdeps/unix/sysv/linux/sleep.c:137
#2 0x00000000004009ec in main () at hello.c:20
正如我们所看到的，第2段指向代码hello.c，因此我们可以更详细地查看它。输入up 2。
输出将与此类似：
#2 0x00000000004009ec in main () at hello.c:20
warning: Source file is more recent than executable.
20 sleep(30);
最后，现在我们可以打印出这个块中的所有局部变量了。输入info local。
输出：
i = 0
world_size = 0
process_id = 0
processor_name = "\000\000\000\000\000\000\000\000 5\026gc\177\000\000\200\306Η\377\177\000\000p\306Η\377\177\000\000.N=\366\000\000\000\000\272\005@\000\000\000\000\000\377\377\377\377\000\000\000\000%0`\236\060\000\000\000\250\361rfc\177\000\000x\n\026gc\177\000\000\320\067`\236\060\000\000\000\377\377\377\177\376\377\377\377\001\000\000\000\000\000\000\000\335\n@\000\000\000\000\000\377\377\377\377\377\377\377\377\000\000\000\000\000\000\000"
name_len = 1718986550
现在我们可以通过set var i=1释放限制器循环并继续调试。