"make gdbserver" doesn't work properly for qemu_x86_long

[andrewboie]

When I run "make debugserver", I expect to be able to attach GDB in another terminal to interactively debug the kernel in the emulator. I do this all the time with qemu_x86.

However, with a build for qemu_x86_long, I am getting:

$ /opt/zephyr-sdk/x86_64-zephyr-elf/bin/x86_64-zephyr-elf-gdb zephyr/zephyr.elf -ex "target remote :1234"
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Reading symbols from zephyr/zephyr.elf...(no debugging symbols found)...done.
Remote debugging using :1234

Remote 'g' packet reply is too long (expected 308 bytes, got 608 bytes): 0000000000000000000000000000000000000000000000006306000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000f0ff0000000000000200000000f00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000010000060000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000007f0300000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000801f0000

This works as expected for qemu_x86.

Key error message is here:

warning: Selected architecture i386 is not compatible with reported target architecture i386:x86-64
warning: Architecture rejected target-supplied description

Not sure how "i386" is getting selected.

Impact:
Prevents interactive debugging for qemu_x86_long.

[andrewboie]

@gnuless have you run into this?

[ghost]

@gnuless have you run into this?

I didn't even know make gdbserver was a thing. Will take a look. Probably a simple fix.

[andrewboie]

I found a workaround:

set arch i386:x86-64
target remote :1234

If I make that set arch call before I connect to the target, it seems to work fine.

[andrewboie]

This might be something beyond our control: https://wiki.osdev.org/QEMU_and_GDB_in_long_mode

(osdev is such a godsend)

[ghost]

If I make that set arch call before I connect to the target, it seems to work fine.

We munge the ELF64 into an ELF32 before launching QEMU (it won't launch a 64-bit ELF directly), so that's probably why it's confused.

[andrewboie]

perhaps have the munge not be in-place, but to a separate artifact that gets passed to the emulator