This allows us to boot FreeBSD RISCV on QEMU using the -kernel command line
options. When using that option, QEMU maps the kernel ELF file to the
addresses specified in the LMAs in the program headers.
Since version 4.2 QEMU ships with OpenSBI fw_jump by default so this allows
booting FreeBSD using the following command line:
qemu-system-riscv64 -bios default -kernel /.../boot/kernel/kernel -nographic -M virt
Without this change the -kernel option cannot be used since the LMAs start
at address zero and QEMU already maps a ROM to these low physical addresses.
For targets that require a different kernel LMA the make variable
KERNEL_LMA can be overwritten in the config file. For example, adding
makeoptions KERNEL_LMA=0xc0200000 will create an ELF file that will be
loaded at 0xc0200000.
Before:
There are 4 program headers, starting at offset 64
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align LOAD 0x001000 0xffffffc000000000 0x0000000000000000 0x75e598 0x8be318 RWE 0x1000 DYNAMIC 0x71fb20 0xffffffc00071eb20 0x000000000071eb20 0x000100 0x000100 RW 0x8 GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW 0x0 NOTE 0x693400 0xffffffc000692400 0x0000000000692400 0x000024 0x000024 R 0x4
After:
There are 4 program headers, starting at offset 64
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align LOAD 0x001000 0xffffffc000000000 0x0000000080200000 0x734198 0x893e18 RWE 0x1000 DYNAMIC 0x6f7810 0xffffffc0006f6810 0x00000000808f6810 0x000100 0x000100 RW 0x8 GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW 0x0 NOTE 0x66ca70 0xffffffc00066ba70 0x000000008086ba70 0x000024 0x000024 R 0x4