Paul Brook <p...@codesourcery.com> writes: >> > starting your own toy kernel is a fun thing to do and there are many >> > tutorials out there on how to do it. Unfortunately when one wants to >> > write a kernel in 64bit it becomes much harder because one can't >> > compile 64bit code as elf32 image and converting a elf64 image to >> > elf32 format is a major hassle and looses debug information and symbols. > > So just have two versions of your image: > - The elf64 image that has debug info, symbols, etc. Point gdb at this. > - An elf32 image that you give to the bootloader (in this case kvm) > > Generating the latter from the former is a trivial objcopy invocation.
Is it? I tried for a while and couldn't figure it out. I checked how linux does it and it does quite a dance to achieve it. > The bootloader variant only needs enough information to get the loadable > sections into memory. We don't care about non-resident clutter like debug > info or symbols. Anything that cares about those will be using the full > elf64 > image. > > This is all standard practice. I don't think I've never actually used a > system where the image loaded by the target is the same file as the one that > comes out of the linker and is used by the debugger. > >> Yes, this is why I asked about support in other software. If each >> bootloader implements a different custom method then it will be a pain >> to run your binary on real hardware in the future. It's worth at >> least checking their source first - maybe there is already a similar >> code path that we can be compatible with, hence making life easier for >> developers who want to play with 64-bit payloads in multiboot >> executables. > > The whole idea of entering a 64-bit image in 32-bit mode seems distinctly > sketchy. Surely it'd make more sense to define a 64-bit multiboot variant > and > do the job properly. > > Paul That will happen in multiboot2 format and is a much larger patch, including a complete new boot rom actualy. I do have patches for that too but there aren't complete yet. I only support the bare minimum of the multiboot2 specs so far. MfG Goswin