Hi! On Tue, Feb 03, 2026 at 08:30:41AM +0100, Christophe Leroy (CS GROUP) wrote: > Test robot reports the following error with clang-16.0.6: > > In file included from kernel/rseq.c:75: > include/linux/rseq_entry.h:141:3: error: invalid operand for instruction > unsafe_get_user(offset, &ucs->post_commit_offset, efault); > ^ > include/linux/uaccess.h:608:2: note: expanded from macro 'unsafe_get_user' > arch_unsafe_get_user(x, ptr, local_label); \ > ^ > arch/powerpc/include/asm/uaccess.h:518:2: note: expanded from macro > 'arch_unsafe_get_user' > __get_user_size_goto(__gu_val, __gu_addr, sizeof(*(p)), e); \ > ^ > arch/powerpc/include/asm/uaccess.h:284:2: note: expanded from macro > '__get_user_size_goto' > __get_user_size_allowed(x, ptr, size, __gus_retval); \ > ^ > arch/powerpc/include/asm/uaccess.h:275:10: note: expanded from macro > '__get_user_size_allowed' > case 8: __get_user_asm2(x, (u64 __user *)ptr, retval); break; \ > ^ > arch/powerpc/include/asm/uaccess.h:258:4: note: expanded from macro > '__get_user_asm2' > " li %1+1,0\n" \ > ^ > <inline asm>:7:5: note: instantiated into assembly here > li 31+1,0 > ^ > 1 error generated. > > On PPC32, for 64 bits vars a pair of registers is used. Usually the > lower register in the pair is the high part and the higher register is > the low part. GCC uses r3/r4 ... r11/r12 ... r14/r15 ... r30/r31 > > In older kernel code inline assembly was using %1 and %1+1 to represent > 64 bits values. However here it looks like clang uses r31 as high part, > allthough r32 doesn't exist hence the error. > > Allthoug %1+1 should work, most places now use %L1 instead of %1+1, so > let's do the same here. > > With that change, the build doesn't fail anymore and a disassembly shows > clang uses r17/r18 and r31/r14 pair when GCC would have used r16/r17 and > r30/r31:
This does not fix the problem that somehow LLVM thinks that GPR31/FPR0 is a valid pair for two-register integer things (well, 31+1 in assembler is not actually valid at all). Quite worrying. Maybe you can fix this in a more fundamental way? In LLVM itself? (The kernel patch of course is a nice workaround, if it in fact works reliably, but a big fat comment here would be useful. Pointing to the LLVM problem report where this is tracked, etc.) Segher
