Merge patch series "riscv: kexec: cleanup and fixups"

Merge patch series "riscv: kexec: cleanup and fixups"

Song Shuai <songshuaishuai@tinylab.org> says:

This series contains a cleanup for riscv_kexec_relocate() and two fixups
for KEXEC_FILE and had passed the basic kexec test in my 64bit Qemu-virt.

You can use this kexec-tools[3] to test the kexec-file-syscall and these patches.

riscv: kexec: Cleanup riscv_kexec_relocate (patch1)
==================================================

For readability and simplicity, cleanup the riscv_kexec_relocate code:

 - Re-sort the first 4 `mv` instructions against `riscv_kexec_method()`
 - Eliminate registers for debugging (s9,s10,s11) and storing const-value (s5,s6)
 - Replace `jalr` with `jr` for no-link jump

riscv: kexec: Align the kexeced kernel entry (patch2)
==================================================

The current riscv boot protocol requires 2MB alignment for RV64
and 4MB alignment for RV32.

In KEXEC_FILE path, the elf_find_pbase() function should align
the kexeced kernel entry according to the requirement, otherwise
the kexeced kernel would silently BUG at the setup_vm().

riscv: kexec: Remove -fPIE for PURGATORY_CFLAGS (patch3)
==================================================

With CONFIG_RELOCATABLE enabled, KBUILD_CFLAGS had a -fPIE option
and then the purgatory/string.o was built to reference _ctype symbol
via R_RISCV_GOT_HI20 relocations which can't be handled by purgatory.

As a consequence, the kernel failed kexec_load_file() with:

[  880.386562] kexec_image: The entry point of kernel at 0x80200000
[  880.388650] kexec_image: Unknown rela relocation: 20
[  880.389173] kexec_image: Error loading purgatory ret=-8

So remove the -fPIE option for PURGATORY_CFLAGS to generate
R_RISCV_PCREL_HI20 relocations type making puragtory work as it was.

 arch/riscv/kernel/elf_kexec.c      |  8 ++++-
 arch/riscv/kernel/kexec_relocate.S | 52 +++++++++++++-----------------
 arch/riscv/purgatory/Makefile      |  4 +++
 3 files changed, 34 insertions(+), 30 deletions(-)

* b4-shazam-merge:
  riscv: kexec: Remove -fPIE for PURGATORY_CFLAGS
  riscv: kexec: Align the kexeced kernel entry
  riscv: kexec: Cleanup riscv_kexec_relocate

Link: https://lore.kernel.org/r/20230907103304.590739-1-songshuaishuai@tinylab.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>