linux-kernel - [PATCH] powerpc/uaccess: Fix inline assembly for clang build on PPC32

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Message-ID: <8ca3a657a650e497a96bfe7acde2f637dadab344.1770103646.git.chleroy@kernel.org>
Date: Tue,  3 Feb 2026 08:30:41 +0100
From: "Christophe Leroy (CS GROUP)" <chleroy@...nel.org>
To: Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Segher Boessenkool <segher@...nel.crashing.org>
Cc: "Christophe Leroy (CS GROUP)" <chleroy@...nel.org>,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	llvm@...ts.linux.dev,
	kernel test robot <lkp@...el.com>
Subject: [PATCH] powerpc/uaccess: Fix inline assembly for clang build on PPC32

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:

	Disassembly of section .fixup:

	00000000 <.fixup>:
	   0:	38 a0 ff f2 	li      r5,-14
	   4:	3a 20 00 00 	li      r17,0
	   8:	3a 40 00 00 	li      r18,0
	   c:	48 00 00 00 	b       c <.fixup+0xc>
				c: R_PPC_REL24	.text+0xbc
	  10:	38 a0 ff f2 	li      r5,-14
	  14:	3b e0 00 00 	li      r31,0
	  18:	39 c0 00 00 	li      r14,0
	  1c:	48 00 00 00 	b       1c <.fixup+0x1c>
				1c: R_PPC_REL24	.text+0x144

Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202602021825.otcItxGi-lkp@intel.com/
Fixes: c20beffeec3c ("powerpc/uaccess: Use flexible addressing with __put_user()/__get_user()")
Signed-off-by: Christophe Leroy (CS GROUP) <chleroy@...nel.org>
---
I set Fixes: tag to the commit that recently replaced %1+1 by %L1 in the main part of the macro as the fix would be uncomplete otherwise but the problem has been there since commit 2df5e8bcca53 ("powerpc: merge uaccess.h")
---
 arch/powerpc/include/asm/uaccess.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index ba1d878c3f404..570b3d91e2e40 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -255,7 +255,7 @@ __gus_failed:								\
 		".section .fixup,\"ax\"\n"		\
 		"4:	li %0,%3\n"			\
 		"	li %1,0\n"			\
-		"	li %1+1,0\n"			\
+		"	li %L1,0\n"			\
 		"	b 3b\n"				\
 		".previous\n"				\
 		EX_TABLE(1b, 4b)			\
-- 
2.49.0