linux-kernel - [PATCH 3/3] powerpc: lib: sstep: fix build errors

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Date:   Wed, 23 Feb 2022 14:58:20 +0100
From:   Anders Roxell <anders.roxell@...aro.org>
To:     mpe@...erman.id.au
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Anders Roxell <anders.roxell@...aro.org>,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: [PATCH 3/3] powerpc: lib: sstep: fix build errors

Building tinyconfig with gcc (Debian 11.2.0-16) and assembler (Debian
2.37.90.20220207) the following build error shows up:

{standard input}: Assembler messages:
{standard input}:10576: Error: unrecognized opcode: `stbcx.'
{standard input}:10680: Error: unrecognized opcode: `lharx'
{standard input}:10694: Error: unrecognized opcode: `lbarx'

Rework to add assembler directives [1] around the instruction.  The
problem with this might be that we can trick a power6 into
single-stepping through an stbcx. for instance, and it will execute that
in kernel mode.

[1] https://sourceware.org/binutils/docs/as/PowerPC_002dPseudo.html#PowerPC_002dPseudo

Cc: <stable@...r.kernel.org>
Co-developed-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Anders Roxell <anders.roxell@...aro.org>
---
 arch/powerpc/lib/sstep.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index d2d29243fa6d..b9f43bbdd55a 100644
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -1097,7 +1097,10 @@ NOKPROBE_SYMBOL(emulate_dcbz);
 
 #define __put_user_asmx(x, addr, err, op, cr)		\
 	__asm__ __volatile__(				\
+		".machine \"push\"\n"			\
+		".machine \"power8\"\n"			\
 		"1:	" op " %2,0,%3\n"		\
+		".machine \"pop\"\n"			\
 		"	mfcr	%1\n"			\
 		"2:\n"					\
 		".section .fixup,\"ax\"\n"		\
@@ -1110,7 +1113,10 @@ NOKPROBE_SYMBOL(emulate_dcbz);
 
 #define __get_user_asmx(x, addr, err, op)		\
 	__asm__ __volatile__(				\
+		".machine \"push\"\n"			\
+		".machine \"power8\"\n"			\
 		"1:	"op" %1,0,%2\n"			\
+		".machine \"pop\"\n"			\
 		"2:\n"					\
 		".section .fixup,\"ax\"\n"		\
 		"3:	li	%0,%3\n"		\
-- 
2.34.1