riscv/mmio_test.c:40:9: error: impossible constraint in 'asm'

[kernel test robot <lkp@intel.com>]

:::::: 
:::::: Manual check reason: "low confidence bisect report"
:::::: 

BCC: lkp@intel.com
CC: oe-kbuild-all@lists.linux.dev
TO: Charlie Jenkins <thecharlesjenkins@gmail.com>
CC: 0day robot <lkp@intel.com>

tree:   https://github.com/intel-lab-lkp/linux/commits/Charlie-Jenkins-via-B4-Relay/riscv-Introduce-instruction-table-generation/20260622-233907
head:   0a20b3c57eced1789d7fe0d60aef35fb55dec1f0
commit: 323ee78f0df1f082442e03ba2bb04d7adb59eb3e KVM: riscv: selftests: Add mmio test
date:   19 hours ago
:::::: branch date: 19 hours ago
:::::: commit date: 19 hours ago
config: riscv-allnoconfig-bpf (https://download.01.org/0day-ci/archive/20260623/202606231259.RnRXckPo-lkp@intel.com/config)
compiler: riscv64-linux-gnu-gcc (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260623/202606231259.RnRXckPo-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/r/202606231259.RnRXckPo-lkp@intel.com/

All errors (new ones prefixed by >>):

   riscv/mmio_test.c: In function 'test_c_ldsp':
>> riscv/mmio_test.c:40:9: error: impossible constraint in 'asm'
      40 |         asm volatile (                                                                          \
         |         ^~~
   riscv/mmio_test.c:70:1: note: in expansion of macro 'test_sp_read'
      70 | test_sp_read(8, c.ldsp, c_ldsp)
         | ^~~~~~~~~~~~
   At top level:
   cc1: note: unrecognized command-line option '-Wno-gnu-variable-sized-type-not-at-end' may have been intended to silence earlier diagnostics

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