GDB 可以使用静态链接库重新加载可执行文件吗？

Question

Normally when using gdb I can stop execution and rebuild the executable and restart without loosing my breakpoints. When I try this with an executable that has a statically linked library I get an error stating that I cannot open the executable file during the build.

A concrete example:

The library files:

libtest.h:

int square(int a);

libtest.c:

int square(int a) {
  return a * a;
}

The library is compiled with:

gcc -g -c libfile.c
ar rcs libtest.a libfile.o

Main file ac contains:

#include <stdio.h>
#include <stdlib.h>
#include "libfile.h"

int main() {
  printf( "2 squared is %d\n", square(2) );
  return 0;
}

The project is compiled and linked like this:

gcc -g -c a.c
gcc a.o -g --static -L. -ltest -o gdb_test

If I load the resulting file gdb_test into gdb it doesn't matter if it is running it not. As long is gdb is open a subsequent build will fail during the link step:

/usr/bin/ld: cannot open output file gdb_test: Permission denied

Is there a way around this? I would like to be able to work with gdb without having to restart it and loose my breakpoints.

Answer 1

It is probably a matter of versions of GDB or GCC; it works for me:

   % gcc -g -c libtest.c
  gcc -g -c libtest.c
   % ar rcs libtest.a libtest.o
  ar rcs libtest.a libtest.o
   % gcc -g -c -Wall a.c
  gcc -g -c -Wall a.c
   % gcc -Wall -g a.o -L. -ltest -o gdb_test
  gcc -Wall -g a.o -L. -ltest -o gdb_test
   % ./gdb_test
  2 squared is 4
   % gdb ./gdb_test
  GNU gdb (GDB) 7.3.50.20111117-cvs-debian
  Copyright (C) 2011 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 /home/basile/tmp/gdb_test...done.
  (gdb) r
  r
  Starting program: /home/basile/tmp/gdb_test 
  2 squared is 4
  [Inferior 1 (process 12271) exited normally]
  (gdb) quit
  quit
   % gcc -v
  gcc -v
  Using built-in specs.
  COLLECT_GCC=/usr/bin/gcc-4.6.real
  COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.6/lto-wrapper
  Target: x86_64-linux-gnu
  Configured with: ../src/configure -v --with-pkgversion='Debian 4.6.2-9' 
  --with-bugurl=file:///usr/share/doc/gcc-4.6/README.Bugs 
  --enable-languages=c,c++,fortran,objc,obj-c++,go --prefix=/usr 
  --program-suffix=-4.6 --enable-shared --enable-linker-build-id 
  --with-system-zlib --libexecdir=/usr/lib --without-included-gettext 
  --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.6 
  --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug 
  --enable-libstdcxx-time=yes --enable-plugin --enable-objc-gc 
  --with-arch-32=i586
  --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu 
  --host=x86_64-linux-gnu --target=x86_64-linux-gnu
  Thread model: posix
  gcc version 4.6.2 (Debian 4.6.2-9) 

My system is Debian/Sid/amd64. GCC is (Debian 4.6.2-9); ld = binutils = ar is GNU gold (GNU Binutils for Debian 2.22); GDB is GNU gdb (GDB) 7.3.50.20111117-cvs-debian; Gnu Libc is (Debian EGLIBC 2.13-24). Kernel is Linux version 3.1.0-1-amd64 (Debian 3.1.5-1)

And I am able to recompile the program from inside gdb and to run it:

  % gdb ./gdb_test 
 gdb ./gdb_test 
 GNU gdb (GDB) 7.3.50.20111117-cvs-debian
 Copyright (C) 2011 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 /home/basile/tmp/gdb_test...done.
 (gdb) shell  gcc -g -c -Wall a.c
 shell  gcc -g -c -Wall a.c
 (gdb) r
 r
 Starting program: /home/basile/tmp/gdb_test 
 2 squared is 4
 [Inferior 1 (process 12335) exited normally]
 (gdb) shell gcc -Wall -g a.o -L. -ltest -o gdb_test

 shell gcc -Wall -g a.o -L. -ltest -o gdb_test
 (gdb) 
 (gdb) r
 r
 `/home/basile/tmp/gdb_test' has changed; re-reading symbols.
 Starting program: /home/basile/tmp/gdb_test 
 2 squared is 4
 [Inferior 1 (process 12346) exited normally]
 (gdb) quit
 quit
  % 

Answer 2

/usr/bin/ld: cannot open output file gdb_test: Permission denied

This is unlikely to be related to either GDB or ld (or their versions), and is most certainly not related to your use of archive library.

Much more likely this is happening because you are using some "strange" filesystem. Perhaps you are using NTFS or CIFS mount? What does df . say?