powerpc/lib/sstep: Fix build errors with newer binutils

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@vger.kernel.org # v4.14+
Co-developed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Reviewed-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220224162215.3406642-3-anders.roxell@linaro.org

diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
index 31de2c5..ef6ea8e 100644 (file)
--- a/arch/powerpc/lib/sstep.c
+++ b/arch/powerpc/lib/sstep.c
@@ -1089,7 +1089,10 @@ 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"              \
@@ -1102,7 +1105,10 @@ 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"                \