riscv: Move alternative length validation into subsection

riscv: Move alternative length validation into subsection

After commit ffd5e501a635 ("riscv: prevent compressed instructions in
alternatives"), builds with LLVM's integrated assembler fail:

  In file included from arch/riscv/mm/init.c:10:
  In file included from ./include/linux/mm.h:29:
  In file included from ./include/linux/pgtable.h:6:
  In file included from ./arch/riscv/include/asm/pgtable.h:108:
  ./arch/riscv/include/asm/tlbflush.h:23:2: error: expected assembly-time absolute expression
          ALT_FLUSH_TLB_PAGE(__asm__ __volatile__ ("sfence.vma %0" : : "r" (addr) : "memory"));
          ^
  ./arch/riscv/include/asm/errata_list.h:33:5: note: expanded from macro 'ALT_FLUSH_TLB_PAGE'
  asm(ALTERNATIVE("sfence.vma %0", "sfence.vma", SIFIVE_VENDOR_ID,        \
      ^
  ./arch/riscv/include/asm/alternative-macros.h:187:2: note: expanded from macro 'ALTERNATIVE'
          _ALTERNATIVE_CFG(old_content, new_content, vendor_id, errata_id, CONFIG_k)
          ^
  ./arch/riscv/include/asm/alternative-macros.h:113:2: note: expanded from macro '_ALTERNATIVE_CFG'
          __ALTERNATIVE_CFG(old_c, new_c, vendor_id, errata_id, IS_ENABLED(CONFIG_k))
          ^
  ./arch/riscv/include/asm/alternative-macros.h:110:2: note: expanded from macro '__ALTERNATIVE_CFG'
          ALT_NEW_CONTENT(vendor_id, errata_id, enable, new_c)
          ^
  ./arch/riscv/include/asm/alternative-macros.h:99:3: note: expanded from macro 'ALT_NEW_CONTENT'
          ".org   . - (889b - 888b) + (887b - 886b)\n"                    \
           ^
  <inline asm>:26:6: note: instantiated into assembly here
  .org    . - (889b - 888b) + (887b - 886b)
          ^

This error happens because LLVM's integrated assembler has a one-pass
design, which means it cannot figure out the instruction lengths when
the .org directive is outside of the subsection that contains the
instructions, which was changed by the .option directives added by the
above change.

Move the .org directives before the .previous directive so that these
directives are always within the same subsection, which resolves the
failures and does not introduce any new issues with GNU as. This was
done for arm64 in commit 4bf14e31bafd ("arm64/alternatives: move length
validation inside the subsection") and commit 95d14243743d ("arm64:
alternatives: Move length validation in alternative_{insn, endif}").

While there is no error from the assembly versions of the macro, they
appear to have the same problem so just make the same change there as
well so that there are no problems in the future.

Link: https://github.com/ClangBuiltLinux/linux/issues/1640
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20220516214520.3252074-1-nathan@kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>