Currently, our s390-ccw.img sits at the fix address 126 MiB in memory. This has two big disadvantages: 1) We can not start guests with less than 128 MiB RAM and 2) if the guest uses a really huge ramdisk > 126 MiB, the s390-ccw BIOS gets overwritten and the boot silently crashes.
These two patches now fix these problems by relocating the s390-ccw BIOS to the end of the RAM. The basic idea here is to compile the BIOS with the "-fpie" compiler option to create position independent code. Sounds easy at a first glance - however, with -fpie, we only get position independent _code_ - and a so called GOT (global offset table) which contains absolute references to global variables again (this is normally needed for supporting dynamic libraries - in our s390-ccw BIOS, it's just bad luck that we get a GOT). So to be able to really move around our s390-ccw.img in RAM, we've got to relocate the entries in the GOT, too. This is what the first patch is good for. I've changed the ELF loader there to parse the reloc section of the ELF file. I only included the bare minimum of relocation types (R_390_RELATIVE) in the patch so far, but this can easily be extended in case we need more (with different compiler version etc.). The second patch then adds the required changes to the s390-ccw BIOS Makefile and our s390 ipl code in QEMU. Now I'd like to get some feedback on this approach: Is it ok to extend the ELF loader this way? Does anybody have better/nicer ideas to solve the problem of a relocatable BIOS? Thanks for any insights! Thomas Huth (2): elf-loader: Provide the possibility to relocate s390 ELF files s390/bios: Make the s390-ccw.img relocatable hw/core/loader.c | 2 + hw/s390x/ipl.c | 23 +++++++++++++++- include/elf.h | 2 + include/hw/elf_ops.h | 60 +++++++++++++++++++++++++++++++++++++++++++++ pc-bios/s390-ccw/Makefile | 11 ++++--- 5 files changed, 91 insertions(+), 7 deletions(-)
