[PATCH 5.4 029/100] powerpc/dcr: Use cmplwi instead of 3-argument cmpli

Greg Kroah-Hartman
2021-11-24T13:21:03Z

From: Michael Ellerman <mpe@ellerman.id.au>

[ Upstream commit fef071be57dc43679a32d5b0e6ee176d6f12e9f2 ]

In dcr-low.S we use cmpli with three arguments, instead of four
arguments as defined in the ISA:

cmpli cr0,r3,1024

This appears to be a PPC440-ism, looking at the "PPC440x5 CPU Core
User’s Manual" it shows cmpli having no L field, but implied to be 0 due
to the core being 32-bit. It mentions that the ISA defines four
arguments and recommends using cmplwi.

It also corresponds to the old POWER instruction set, which had no L
field there, a reserved bit instead.

dcr-low.S is only built 32-bit, because it is only built when
DCR_NATIVE=y, which is only selected by 40x and 44x. Looking at the
generated code (with gcc/gas) we see cmplwi as expected.

Although gas is happy with the 3-argument version when building for
32-bit, the LLVM assembler is not and errors out with:

arch/powerpc/sysdev/dcr-low.S:27:10: error: invalid operand for instruction
cmpli 0,%r3,1024; ...
^

Switch to the cmplwi extended opcode, which avoids any confusion when
reading the ISA, fixes the issue with the LLVM assembler, and also means
the code could be built 64-bit in future (though that's very unlikely).

Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
BugLink: https://github.com/ClangBuiltLinux/linux/issues/1419
Link: https://lore.kernel.org/r/20211014024424.528848-1-mpe@ellerman.id.au
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/sysdev/dcr-low.S | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/sysdev/dcr-low.S b/arch/powerpc/sysdev/dcr-low.S
index efeeb1b885a17..329b9c4ae5429 100644
--- a/arch/powerpc/sysdev/dcr-low.S
+++ b/arch/powerpc/sysdev/dcr-low.S
@@ -11,7 +11,7 @@
#include <asm/export.h>

#define DCR_ACCESS_PROLOG(table) \
- cmpli cr0,r3,1024; \
+ cmplwi cr0,r3,1024; \
rlwinm r3,r3,4,18,27; \
lis r5,table@h; \
ori r5,r5,table@l; \
--
2.33.0