[RFC] Prevent GDB from loading native libraries when debugging a cross-target corefile

[Edjunior Barbosa Machado <emachado@linux.vnet.ibm.com>]

Hi,

The GDB documentation recommends the following in the 'set solib-search-path'
description:

"If you want to use `solib-search-path' instead of `sysroot', be sure to set
`sysroot' to a nonexistent directory to prevent gdb from finding your host's
libraries." (http://sourceware.org/gdb/onlinedocs/gdb/Files.html)

However, when trying to debug cross-target corefiles using recent versions of
gdb, we noticed it's trying to load host libraries instead of libraries from a
cross-architecture jail (pointed by solib-search-path). Here's the example
showing the problem:

Using a faulty application foo that uses a shared library libfoo.so, generate a
corefile in the target system (a powerpc machine in my example here):

$ ls /usr/local/lib/libfoo.so
/usr/local/lib/libfoo.so
$ ./foo
Segmentation fault (core dumped)

Then copy the binary and the corefile for a cross-target debugging in the host
(an x86 machine here) that has his own libfoo.so at the same /usr/local/lib
and a cross environment at /opt/at6.0/ppc. Note that 'info sharedlibrary'
shows that GDB was trying to load the native library libfoo.so:

$ powerpc64-linux-gdb ./foo -q
Reading symbols from /home/emachado/bugs/ppc32-bin/foo...done.
(gdb) set sysroot /dev/null
(gdb) set solib-search-path /opt/at6.0/ppc/lib:/opt/at6.0/ppc/usr/lib
(gdb) core core.19304 
[New LWP 19304]
warning: `/usr/local/lib/libfoo.so': Shared library architecture unknown is not compatible with target architecture powerpc:common.
warning: .dynamic section for "/opt/at6.0/ppc/lib/libc.so.6" is not at the expected address (wrong library or version mismatch?)
warning: .dynamic section for "/opt/at6.0/ppc/lib/ld.so.1" is not at the expected address (wrong library or version mismatch?)
warning: Could not load shared library symbols for linux-vdso32.so.1.
Do you need "set solib-search-path" or "set sysroot"?
Core was generated by `./foo'.
Program terminated with signal 11, Segmentation fault.
#0  0x10000704 in main () at foo.c:7
7   printf("null dereference: %c\n", *p); 
(gdb) info sharedlibrary 
From        To          Syms Read   Shared Object Library
                        No          linux-vdso32.so.1
0x0ffdec50  0x0ffded58  Yes (*)     /usr/local/lib/libfoo.so
0x0fe49a5c  0x0ff6aacc  Yes         /opt/at6.0/ppc/lib/libc.so.6
0xf7eb2fb0  0xf7ece9d0  Yes         /opt/at6.0/ppc/lib/ld.so.1
(*): Shared library is missing debugging information.

It might be worth mentioning that this behavior was modified by this patch from
April 2010:
http://sourceware.org/ml/gdb-patches/2010-04/msg00758.html

Please consider the following patch as a fix for this issue.

Thanks,
--
Edjunior

gdb/
2012-09-28  Nathan Miller  <nathanm2@us.ibm.com>
	    Edjunior Machado  <emachado@linux.vnet.ibm.com>

	* solib.c (solib_find): Prevent GDB from loading native libraries when
	debugging a cross-target corefile.


---
 gdb/solib.c |    5 -----
 1 file changed, 5 deletions(-)

diff --git a/gdb/solib.c b/gdb/solib.c
index 01573f8..d795678 100644
--- a/gdb/solib.c
+++ b/gdb/solib.c
@@ -300,11 +300,6 @@ solib_find (char *in_pathname, int *fd)
   if (found_file < 0)
     temp_pathname = NULL;
 
-  /* If not found, search the solib_search_path (if any).  */
-  if (found_file < 0 && solib_search_path != NULL)
-    found_file = openp (solib_search_path, OPF_TRY_CWD_FIRST,
-			in_pathname, O_RDONLY | O_BINARY, &temp_pathname);
-
   /* If the search in gdb_sysroot failed, and the path name is
      absolute at this point, make it relative.  (openp will try and open the
      file according to its absolute path otherwise, which is not what we want.)
-- 
1.7.9.5