Please add code to pick up SOLIB_SEARCH_PATH env var.

[Yoshinori Toshima <yoshinori.toshima@oracle.com>]

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 Hello,

I have a small enhancement request for GDB to make it easier to
use when debugging core file from other systems which have
different libraries.

Description:
When debugging a core file from released product, it is convenient
to have gdb use shared libraries in a directory which contains the
libraries and executable taken from the system which caused the
crash. It is possible to perform this by gdb command "set
solib-search-path <path>". This means some commands are required
after starting gdb. If we can set solib-search-path at gdb startup,
it is easier to use. This is useful when we use GDB programmatically.

HP-UX port of GDB has this feature via env var GDB_SHLIB_PATH.
GDB does not have the feature yet, though it mentions SOLIB_SEARCH_PATH
in solib.c.

I changed solib.c to pick up SOLIB_SEARCH_PATH at startup and set
it to solib_search_path in solib.c initialization. It worked as
expected.

Attached solib-patch.diff is based on solib.c in gdb 7.2.

ChangeLog entry:
2010-12-16 Yoshinori Toshima <yoshinori.toshima@oracle.com>

* solib.c: Pick up SOLIB_SEARCH_PATH env var to set solib-search-path at
startup.

Regards,
Yoshinori Toshima

[-- Attachment #2: solib-patch.diff --]
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*** gdb.org/solib.c	2010-12-16 17:51:11.000000000 +0900
--- gdb/solib.c	2010-12-16 17:55:29.000000000 +0900
*************** solib_global_lookup (const struct objfil
*** 1448,1453 ****
--- 1448,1469 ----
    return NULL;
  }
  
+ void 
+ check_solib_search_path_env () 
+ {
+   char *envvar = getenv("SOLIB_SEARCH_PATH");
+   if (envvar != NULL) {
+     if (access(envvar, R_OK) == 0) {
+       solib_search_path = envvar;
+       fprintf_filtered (gdb_stdout, _("Picked up SOLIB_SEARCH_PATH %s.\n"),
+                     envvar);
+     } else {
+       warning (_("SOLIB_SEARCH_PATH %s is not accessible. "
+                "Ignored."), envvar);
+     }
+   }
+ }
+ 
  
  extern initialize_file_ftype _initialize_solib; /* -Wmissing-prototypes */
  
*************** For other (relative) files, you can add 
*** 1491,1496 ****
--- 1507,1514 ----
    add_alias_cmd ("solib-absolute-prefix", "sysroot", class_support, 0,
  		 &showlist);
  
+   check_solib_search_path_env();
+ 
    add_setshow_optional_filename_cmd ("solib-search-path", class_support,
  				     &solib_search_path, _("\
  Set the search path for loading non-absolute shared library symbol files."), _("\