On Wed, Jun 13, 2018 at 9:35 PM, Gedare Bloom <ged...@rtems.org> wrote: > On Wed, Jun 13, 2018 at 11:33 AM, Amaan Cheval <amaan.che...@gmail.com> wrote: >> Hi! >> >> As we discussed in the last thread on the topic[1], I'm trying to use >> FreeBSD's loader.efi directly with RTEMS' generated static binaries >> (since FreeBSD's loader.efi has an ELF loader). >> >> In brief, I did this by: >> - Installing FreeBSD in QEMU with UEFI firmware >> - Confirming that FreeBSD's loader.efi is in fact used >> - Replacing FreeBSD's ELF kernel with a "custom" kernel[2] with an RTEMS ELF >> - Verifying that the code running after FreeBSD's loader.efi is in >> fact the "RTEMS ELF" by attaching gdb to QEMU (the rtems ELF is simply >> a while(1) loop compiled with RTEMS' tools - see later on why I can't >> do something more elaborate) >> >> Some more details of the process I followed for testing this: >> https://gist.github.com/AmaanC/42faa131ee97a1d6c4c7c25c29f0fde9z >> >> I think this method is superior to the PIC RTEMS method because: >> - FreeBSD uses it >> - RTEMS retains static ELF binaries, which can likely easily be >> combined with a Multiboot header + protect mode starter code >> - FreeBSD has methods to provide ACPI related hints to their ELF >> kernel - this might make our implementation with regards to ACPI >> simpler too >> >> Regarding some concerns Chris had with linker options and whatnot, >> here's what FreeBSD uses: >> https://www.freebsd.org/doc/en/books/arch-handbook/boot-kernel.html >> >> Here's what I used (with the code being a simple while(1) loop): >> x86_64-rtems5-gcc ktest.c -c -nostdlib >> x86_64-rtems5-ld ktest.o -e main -o kernel >> >> ------------------------------------------------------------------------------------- >> >> What I need input on: >> - Right now, we use the following RTEMS code for testing: >> >> int main() { >> while(1) {} >> } >> > > It's not really an RTEMS code, it is a C program (ktest.c) compiled > with the RTEMS-flavored toolchain, right?
Yeah, for now that's right. I'm going to conduct the same gdb based debug-stepping style test for RTEMS setting boot_card as the entry point soon - for now, it crashes QEMU with: qemu: fatal: Trying to execute code outside RAM or ROM at 0x00000000000b0000 RAX=00000000006004c0 RBX=00000000006003d8 RCX=0000000037f36000 RDX=0000000000400000 RSI=0000000004000000 RDI=0000000000000180 RBP=00000000006003d8 RSP=000000003c589fb8 ... I see that it reaches that stage even from some code it ought not to be executing, so I'll look into what that may be about. > > It would be nice to get an RTEMS x86-64 BSP to start, at least to > confirm that you reach _start, and then even you can try to make it to > the "boot_card" startup sequence. Right, I'll aim to have that working soon (using boot_card as the entry, since "_start" usually does the bootloader stuff that we're now offloading to FreeBSD, and then calls boot_card anyway). > >> That's literally it, because we have no access to standard libraries, >> and loader.efi calls ExitBootServices, after which we can't just >> easily directly access video memory (at 0xb8000 for eg.) to print to >> the screen. The way FreeBSD handles this is by initializing the >> console and printing to that - I haven't been able to easily port that >> yet. >> >> The question is - should I start with that effort (i.e. bringing >> printk console functionality to RTEMS) the way FreeBSD does? This way, >> we skip the bootloader for now by simply using the one built on the >> real FreeBSD - if the console prints and more elaborate linking tests >> work fine, we can be certain that this works. If _not_, I believe the >> console initialization code will likely still remain the same since >> we'll want to do it similar to how FreeBSD does it. >> > > I think this approach to getting a console to work may be reasonable, > assuming the FreeBSD console is not much more complicated than what > RTEMS needs. ... I can't say about this yet, but I'll look into it (and perhaps simplifying it as we port it if it _is_ too complicated). > >> What do you think? >> >> Cheers, >> Amaan >> >> [1] https://lists.rtems.org/pipermail/devel/2018-June/022052.html >> [2] https://www.freebsd.org/doc/handbook/kernelconfig-building.html _______________________________________________ devel mailing list devel@rtems.org http://lists.rtems.org/mailman/listinfo/devel
