Setting breakpoints on dlopen

[Jesse Marlin]

Adam Bottchen writes:
 >      I am running into a problem when attempting to set a breakpoint on
 > dlopen within gdb under Red Hat 7.1.  This problem doesn't happen at any 
 > other
 > level of the Red Hat distribution, only the 7.1 version.  
 >      The initial problem was found when running gdb on a perl script that
 > used C extensions.  The code was:
 > 
 > -----
 > #!/usr/bin/perl
 > #  Name: testperl
 > # Description:  Short Perl program using only a Perl to C extension that  is
 > #   shipped with Perl.
 > use Socket;
 > my $iaddr = gethostbyname("localhost");
 > my $host = gethostbyaddr($iaddr, AF_INET);
 > print "host is: $host \n";
 > print "Hello, testing Perl\n";
 > exit 0;                                                                      
 >  > -----
 > 
 > I then run gdb on that script:
 > 
 > -----
 > address@hidden /root]# gdb /usr/bin/perl
 > GNU gdb 5.0rh-5 Red Hat Linux 7.1
 > Copyright 2001 Free Software Foundation, Inc.
 > GDB is free software, covered by the GNU General Public License, and you are
 > welcome to change it and/or distribute copies of it under certain 
 > conditions.Type "show copying" to see the conditions.
 > There is absolutely no warranty for GDB.  Type "show warranty" for details.
 > This GDB was configured as "i386-redhat-linux"...
 > (no debugging symbols found)...
 > (gdb) break dlopen
 > Breakpoint 1 at 0x8059878
 > (gdb) run testperl
 > Starting program: /usr/bin/perl testperl
 > Error in re-setting breakpoint 1:
 > Cannot access memory at address 0x123
 > Error in re-setting breakpoint 1:
 > Cannot access memory at address 0x123
 > Error in re-setting breakpoint 1:
 > Cannot access memory at address 0x123
 > Error in re-setting breakpoint 1:
 > Cannot access memory at address 0x123
 > Error in re-setting breakpoint 1:
 > Cannot access memory at address 0x123
 > Error in re-setting breakpoint 1:
 > Cannot access memory at address 0x123
 > Error in re-setting breakpoint 1:
 > Cannot access memory at address 0x123
 > host is: aixlab
 > Hello, testing Perl
 >  
 > Program exited normally.
 > (gdb)  
 > -----

In gdb try loading the symbols manually:

(gdb) info shared

0x3000104a080       0x30002820c00       No          /usr/lib/mylib.so

(gdb) add-symbol-file /usr/lib/mylib.so 0x3000104a080
add symbol table from file "/usr/lib/mylib.so" at
        .text_addr = 0x3000104a080
(y or n) y
Reading symbols from /usr/lib/mylib.so...done.

Hope this helps.

 > 
 > The breakpoint is skipped and memory access errors are displayed.  This 
 > doesn't
 > happen under Red Hat 7.0 or 6.2.  This same problem will occur even when perl
 > is removed from the picture, using the c code below:
 > 
 > -----
 > #include <dlfcn.h>
 >  
 > main()
 > {
 > dlopen("libpthread",0);
 > } 
 > -----
 > 
 > Compiling with "gcc -o test test.c -ldl", the gdb output is the same when the
 > breakpoint is set on dlopen.  What is causing this?
 > Under Red Hat 7.1, gcc is at level 2.96-81 and gdb is 5.0rh-5.
 > 
 > 
 > 
 > _______________________________________________
 > Bug-gdb mailing list
 > address@hidden
 > http://mail.gnu.org/mailman/listinfo/bug-gdb



--
Jesse Marlin
Intec Telecom Systems
Software Engineer
Main 404-705-2800
Ph 404-705-2912
Fax 404-705-2805
Email address@hidden