Re: Help with cross-compiling GDB

[Pedro Alves <palves at redhat dot com>]

On 10/08/2012 09:01 PM, Paul Smith wrote:
> Hi all.  I'm trying to create a complete toolchain including GCC,
> binutils, plus tools like make, fakeroot, bison, flex, m4, and of course
> GDB.
> 
> What I need to do is have the tools compiled to be able to run on much
> older GNU/Linux distributions, even though my build system is very
> recent.  So I have a cross-compiler built that uses a sysroot from an
> older distribution and I'm using that to compile GDB.  I need to be able
> to compile and debug both 32bit and 64bit programs.  Originally I wanted
> to have a 32bit version of GDB which could debug both, but that doesn't
> appear to be possible.  That's OK, I'm willing to have GDB be a 64bit
> application, or else I'll build GDB twice.  For now I'm just trying to
> get the 64bit GDB working.
> 
> So, I configure GDB with something like this:
> 
>   ./configure --disable-nls --disable-werror --prefix=/tmp/invalid/generic \
>     --host=x86_64-olddist-linux-gnu --target=x86_64-generic-linux-gnu \

with --host != --target, you're configuring a cross debugger.  IOW, the
native debug support isn't included (gdb_native in configure.ac).

> (gdb) run
> Starting program: foo 
> Don't know how to run.  Try "help target".

And this means exactly that -- gdb doesn't know how to "run" with the
current target (none or just the executable), and there's no native target
support to default to.  The suggestion kind of hints at connecting with
"target remote" first, for example.

> This is a 32bit app but I get identical errors (although different show
> arch of course) when I try to debug a 64bit app.  I can set breakpoints,
> etc. but any attempt to run gives the "don't know how to run" error.
> 
> I'm not sure exactly what that means in this context.  It appears to
> have the right architecture and that architecture appears to be
> supported.  So what does GDB need from me?

IIUC, you want to use --build to point at x86_64-olddist-linux-gnu,
not --host.

-- 
Pedro Alves