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Re: Reporting unsupported things.

> Date: Mon, 24 Apr 2006 17:00:44 -0700
> On Mon, 2006-04-24 at 16:55 -0400, Daniel Jacobowitz wrote:
> > We want to say that reverse execution is not supported.
> I have been given a similar request.  My users want to see a message
> like "a 32-bit ppc GDB can't debug a 64-bit ppc target program".

They probably would see that message if the 64-bit powerpc support was
seperated out from the 32-bit code, and GDB was configured for
powerpc-ibm-linux-gnu instead of powerpc64-ibm-linux-gnu.  The former
would probably be a good thing to do (I've done it for sparc/sparc64),
the latter is a bit harder to accomplish since config.guess will
probably report powerpc64-ibm-linux-gnu even if only only the kernel
is 64-bit and all of userland is 32-bit.  It would really help if the
Linux distributions got their act together and reported the canonical
system name of the development environment instead of the kernel.

> In general, it would be nice if GDB could detect that it was being asked
> to do something it can't do as soon as it was asked.
> This kind of intersects with the multi-arch idea.  With that, GDB
> conceptually has a binary matrix where each column would represent a
> different target and each row a different host and the cell value would
> be true if the GDB configured for the given host could debug the given
> target.

Do you mean target in the sense if "ISA target" or "debugging interface"?

The long-term goal defenitely is for GDB to be able to debug all ISA
targets on all hosts.  But the native debugging interface may only
support a subset of the host's "personalities".  Where by personality
here may mean 64-bit or 32-bit personalities for the native operating
system, but also operating systems that can be emulated by the host.
On some of the BSD's for example, it is possible to debug Linux binaries.

> If the target is remote, it could tell GDB which column of the matrix is
> appropriate.
> For a native configuration, perhaps the appropriate row of the matrix
> could be built by some config script and the appropriate column could be
> chosen based on the type of the executable and/or corefile.  And
> 'attach' muddies up the water a bit.
> I guess what I am suggesting is that GDB have a concrete matrix like
> this and consult it as soon as it's known what the user is trying to do.
> Of course the 'matrix' would probably really be a hash.
> What do you think?

Unfortunately, I think the matrix idea doesn't really work.  There are
subtle differences between native targets (even Linux native targets)
that make 32-bitX64-bit debugging unfasable.

> PS:  In theory, a 32-bit GDB running on a 64-bit ppc host could debug a
> 64-bit target: "ptrace" allegedly supports this.  The current ppc port,
> however, does not.
> PPS: Do you know of any other "biarch" configurations of GDB?


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