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From: Michael Ellerman <mpe@ellerman.id.au>
To: <linuxppc-dev@lists.ozlabs.org>
Cc: ndesaulniers@google.com
Subject: [PATCH] powerpc/dcr: Use cmplwi instead of 3-argument cmpli
Date: Thu, 14 Oct 2021 13:44:24 +1100	[thread overview]
Message-ID: <20211014024424.528848-1-mpe@ellerman.id.au> (raw)

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.

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; ...
           ^

Switching to the four argument version 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>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 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 efeeb1b885a1..329b9c4ae542 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;   \
-- 
2.25.1


             reply	other threads:[~2021-10-14  2:45 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-14  2:44 Michael Ellerman [this message]
2021-10-14 10:56 ` [PATCH] powerpc/dcr: Use cmplwi instead of 3-argument cmpli Segher Boessenkool
2021-10-14 18:15 ` Nick Desaulniers
2021-10-14 18:15   ` Nick Desaulniers
2021-11-02 10:12 ` Michael Ellerman

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