| Message ID | 20160430082927.2111f5ae@kryten (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
On Fri, 2016-29-04 at 22:29:27 UTC, Unknown sender due to SPF wrote: > In create_zero_mask() we have: > > addi %1,%2,-1 > andc %1,%1,%2 > popcntd %0,%1 > > using the "r" constraint for %2. r0 is a valid register in the "r" set, > but addi X,r0,X turns it into an li: > > li r7,-1 > andc r7,r7,r0 > popcntd r4,r7 > > Fix this by using the "b" constraint, for which r0 is not a valid > register. > > This was found with a kernel build using gcc trunk, narrowed down to > when -frename-registers was enabled at -O2. It is just luck however > that we aren't seeing this on older toolchains. > > Thanks to Segher for working with me to find this issue. > > Signed-off-by: Anton Blanchard <anton@samba.org> > Cc: <stable@vger.kernel.org> > Fixes: d0cebfa650a0 ("powerpc: word-at-a-time optimization for 64-bit Little Endian") Applied to powerpc fixes, thanks. https://git.kernel.org/powerpc/c/b4c112114aab9aff5ed4568ca5 cheers
diff --git a/arch/powerpc/include/asm/word-at-a-time.h b/arch/powerpc/include/asm/word-at-a-time.h index e4396a7..4afe66a 100644 --- a/arch/powerpc/include/asm/word-at-a-time.h +++ b/arch/powerpc/include/asm/word-at-a-time.h @@ -82,7 +82,7 @@ static inline unsigned long create_zero_mask(unsigned long bits) "andc %1,%1,%2\n\t" "popcntd %0,%1" : "=r" (leading_zero_bits), "=&r" (trailing_zero_bit_mask) - : "r" (bits)); + : "b" (bits)); return leading_zero_bits; }
In create_zero_mask() we have: addi %1,%2,-1 andc %1,%1,%2 popcntd %0,%1 using the "r" constraint for %2. r0 is a valid register in the "r" set, but addi X,r0,X turns it into an li: li r7,-1 andc r7,r7,r0 popcntd r4,r7 Fix this by using the "b" constraint, for which r0 is not a valid register. This was found with a kernel build using gcc trunk, narrowed down to when -frename-registers was enabled at -O2. It is just luck however that we aren't seeing this on older toolchains. Thanks to Segher for working with me to find this issue. Signed-off-by: Anton Blanchard <anton@samba.org> Cc: <stable@vger.kernel.org> Fixes: d0cebfa650a0 ("powerpc: word-at-a-time optimization for 64-bit Little Endian") ---