From: Paul Brook <paul@codesourcery.com>
To: qemu-devel@nongnu.org
Cc: Stefan Hajnoczi <stefanha@gmail.com>,
Goswin von Brederlow <goswin-v-b@web.de>
Subject: Re: [Qemu-devel] Support for multiboot images in elf64 (EM_X86_64) format
Date: Thu, 9 Feb 2012 00:35:11 +0000 [thread overview]
Message-ID: <201202090035.12216.paul@codesourcery.com> (raw)
In-Reply-To: <CAJSP0QVr-5AER7fhbS_jO2FTzy0scnUYiy8eAc4cByuK_i5r1g@mail.gmail.com>
> > 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.
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
next prev parent reply other threads:[~2012-02-09 0:35 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-04 17:38 [Qemu-devel] Support for multiboot images in elf64 (EM_X86_64) format Goswin von Brederlow
2012-02-06 12:38 ` Stefan Hajnoczi
2012-02-08 9:53 ` Goswin von Brederlow
2012-02-08 11:30 ` Kevin Wolf
2012-02-08 12:06 ` Stefan Hajnoczi
2012-02-09 0:35 ` Paul Brook [this message]
2012-02-09 13:07 ` Goswin von Brederlow
2012-02-09 13:36 ` Paul Brook
2012-02-09 15:38 ` Goswin von Brederlow
2012-02-09 16:01 ` Paul Brook
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