Re: [rfc] bi-arch for x86-64 corefile.

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> Date: Tue, 30 Oct 2012 12:57:41 +0000
> From: Pedro Alves <palves@redhat.com>
> 
> On 10/30/2012 12:37 PM, Yao Qi wrote:
> 
> > This requires something different in configure options.  In my previous patch, when configure i686-pc-linux-gnu-gdb to handle bi-arch, we run configure with '--enable-64-bit-bfd'.  In current trunk (w/ your patch), we have to run configure with '--enable-targets=x86_64-pc-linux-gnu'.
> > 
> > Copy gdb@ here to make sure GDB people are aware of this change, otherwise, configuring gdb with '--enable-64-bit-bfd' only still doesn't work for handling x86-64 corefile on x86 gdb.
> 
> That sounds like an unnecessary restriction.  A 32-bit GDB can debug a 64-bit
> inferior with gdbserver just fine (it can also debug a 64-bit core), provided GDB
> is built with --enable-64-bit-bfd.  Yes, debugging a native 64-bit inferior won't
> work due to ptrace limitations, but GDB's gcore command can generate cores
> even when remote debugging w/ gdbserver.
> 
> We have things like this, gdb/configure.tgt:
> 
> i[34567]86-*-linux*)
> 	# Target: Intel 386 running GNU/Linux
> 	gdb_target_obs="i386-tdep.o i386-linux-tdep.o glibc-tdep.o i387-tdep.o \
> 			solib-svr4.o symfile-mem.o \
> 			linux-tdep.o linux-record.o"
> 	if test "x$enable_64_bit_bfd" = "xyes"; then
> 	    # Target: GNU/Linux x86-64
> 	    gdb_target_obs="amd64-tdep.o amd64-linux-tdep.o ${gdb_target_obs}"
> 	fi
> 	build_gdbserver=yes
> 	;;
> 
> So it's be nice if bfd did the same in this case.  Thus, I'd very much
> prefer if --enable-64-bit-bfd was enough for making bi-arch corefiles
> work.

The problem is that the Linux core file support in bfd is still relies
on native headers.  Trying to "fix them up" for bi-arch like what's
been done for the last couple of years on Linux is never going to give
you true cross-debugging support.