linux-kernel - [PATCH 5.16 0868/1017] powerpc/lib/sstep: Fix build errors with newer binutils

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Message-Id: <20220405070420.001577709@linuxfoundation.org>
Date:   Tue,  5 Apr 2022 09:29:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Anders Roxell <anders.roxell@...aro.org>,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: [PATCH 5.16 0868/1017] powerpc/lib/sstep: Fix build errors with newer binutils

From: Anders Roxell <anders.roxell@...aro.org>

commit 8219d31effa7be5dbc7ff915d7970672e028c701 upstream.

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

Fixes: 350779a29f11 ("powerpc: Handle most loads and stores in instruction emulation code")
Cc: stable@...r.kernel.org # v4.14+
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>
Reviewed-by: Segher Boessenkool <segher@...nel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/20220224162215.3406642-3-anders.roxell@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/powerpc/lib/sstep.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- 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"		\