[PATCH/RFA] Don't gdbarch_init for core files

[Jason R Thorpe <thorpej@wasabisystems.com>]

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As discussed on gdb@, there is a problem involving gdbarch and core
files.

At least GNU/Linux and NetBSD identify executables using note sections.
Many targets use this to select the OS/ABI variant for the target.

The problem is that if you are debugging a core file, the core file is
loaded after the executable, and the current code re-initializes the
current gdbarch based on the core file.

Since the core file lacks the same markings as the executable, the
gdbarch that results is unable to debug the executable+core.

There are other problems, as well.  The core file often doesn't have
the same flags as an executable -- consider the flags the MIPS target
uses to decide between o32, o64, n32, etc.  These flags may not be
present in the core file (indeed -- the core file is just a memory image,
and doens't really have an "ABI", per se).  The ABI, again, really comes
from the executable.

At the very least, it has befuddled Daniel and me :-)

The following patch fixes this problem (which can be easily demonstrated
by simply doing "gdb a.out a.out.core" on any target that supports OS/ABI
variants).

	* corelow.c (core_open): Don't reinitialize the current
	gdbarch.

-- 
        -- Jason R. Thorpe <thorpej@wasabisystems.com>

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Index: corelow.c
===================================================================
RCS file: /cvs/src/src/gdb/corelow.c,v
retrieving revision 1.21
diff -u -r1.21 corelow.c
--- corelow.c	5 May 2002 01:15:13 -0000	1.21
+++ corelow.c	10 May 2002 01:40:13 -0000
@@ -321,8 +321,6 @@
     error ("\"%s\": Can't find sections: %s",
 	   bfd_get_filename (core_bfd), bfd_errmsg (bfd_get_error ()));
 
-  set_gdbarch_from_file (core_bfd);
-
   ontop = !push_target (&core_ops);
   discard_cleanups (old_chain);