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 d3098ef1404a2..3943d19d5f63b 100644 --- a/arch/powerpc/sysdev/dcr-low.S +++ b/arch/powerpc/sysdev/dcr-low.S @@ -14,7 +14,7 @@ #include <asm/bug.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; \