Re: GDB 16.3: is it possible to cross-debug an x64 core from ARM?

[Simon Marchi via Gdb <gdb@sourceware.org>]

On 2025-12-01 10:36, Paul Smith via Gdb wrote:
> If I build an x86_64 GDB binary that has support for debugging ARM core
> files, it works fine.  The build is invoked (on x86_64) like:
> 
>   $ ../gdb-6.3/configure ... --enable-targets=aarch64-linux-gnu
>     ...
>   $ make -j$(nproc)
> 
> There's no problem and the resulting GDB works both for native x86_64
> cores and ARM cores.
> 
> But, if I try to build an aarch64 GDB (on an ARM system) that has
> support for debugging x86_64 core files, the build fails like this:
> 
>   $ ../gdb-6.3/configure ... --enable-targets=x86_64-linux-gnu
>     ...
>   $ make -j$(nprocs)
>     ...
>   make[2]: *** No rule to make target '../sim/aarch64/libsim.a', needed by 'gdb'.  Stop.
> 
> If I use the same configure arguments but omitting --enable-targets
> then I get a correctly built GDB that will work on ARM.
> 
> Comparing sim/config.log from the ARM build without --enable-targets
> (which works) versus the failing one, shows nothing too interesting; I
> get the same messages etc.  The only consequential difference is that
> in the working version (no extra enabled targets) I see:
> 
>   SIM_ENABLE_ARCH_aarch64_FALSE='#'
>   SIM_ENABLE_ARCH_aarch64_TRUE=''
> 
> while in the failing version (with x86_64 enabled target) I see:
> 
>   SIM_ENABLE_ARCH_aarch64_FALSE=''
>   SIM_ENABLE_ARCH_aarch64_TRUE='#'
> 
> Which could have been guessed from the error message I suppose :).
> 
> 
> Anyone have any further advice?  I guess the next step would be to run
> configure with sh -x and see if I can deduce where it gets confused
> (assuming this is a supported configuration).

I don't know why using `--enable-targets=...` makes the sim configure
script decide not to build the simulator for aarch64.
`--enable-targets` enables a target on top of the default one (in this
case aarch64).  So if the simulator is built and linked when not using
`--enable-targets=...`, then I think it would make sense to do the same
when using `--enable-targets...`.

If your goal is to get something working right now, you can try
--disable-sim, or use --target=x86_64-linux-gnu, which will produce a
GDB that runs on aarch64 but only knows about debugging x86_64 targets
and cores.

Simon