Message ID | b3d449de856982ed060a71e6ace8eeca4654e685.1580399657.git.christophe.leroy@c-s.fr (mailing list archive) |
---|---|
State | Superseded |
Headers | show |
Series | powerpc: switch VDSO to C implementation. | expand |
Context | Check | Description |
---|---|---|
snowpatch_ozlabs/apply_patch | success | Successfully applied on branch powerpc/merge (492a2f9203423062e77c862dd2256dc0e186690a) |
snowpatch_ozlabs/checkpatch | warning | total: 0 errors, 1 warnings, 0 checks, 21 lines checked |
snowpatch_ozlabs/needsstable | success | Patch has no Fixes tags |
diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c index 0b4b71880f22..a5ee53d1ecee 100644 --- a/lib/vdso/gettimeofday.c +++ b/lib/vdso/gettimeofday.c @@ -38,6 +38,13 @@ u64 vdso_calc_delta(u64 cycles, u64 last, u64 mask, u32 mult) } #endif +#ifndef vdso_shift_ns +static __always_inline u64 vdso_shift_ns(u64 ns, unsigned long shift) +{ + return ns >> shift; +} +#endif + #ifdef CONFIG_TIME_NS static int do_hres_timens(const struct vdso_data *vdns, clockid_t clk, struct __kernel_timespec *ts) @@ -134,7 +141,7 @@ static __always_inline int do_hres(const struct vdso_data *vd, clockid_t clk, #endif ns += vdso_calc_delta(cycles, last, vd->mask, vd->mult); - ns >>= vd->shift; + ns = vdso_shift_ns(ns, vd->shift); sec = vdso_ts->sec; } while (unlikely(vdso_read_retry(vd, seq)));
On powerpc/32, GCC (8.1) generates pretty bad code for the ns >>= vd->shift operation taking into account that the shift is always <= 32 and the upper part of the result is likely to be nul. GCC makes reversed assumptions considering the shift to be likely >= 32 and the upper part to be like not nul. unsigned long long shift(unsigned long long x, unsigned char s) { return x >> s; } results in: 00000018 <shift>: 18: 35 25 ff e0 addic. r9,r5,-32 1c: 41 80 00 10 blt 2c <shift+0x14> 20: 7c 64 4c 30 srw r4,r3,r9 24: 38 60 00 00 li r3,0 28: 4e 80 00 20 blr 2c: 54 69 08 3c rlwinm r9,r3,1,0,30 30: 21 45 00 1f subfic r10,r5,31 34: 7c 84 2c 30 srw r4,r4,r5 38: 7d 29 50 30 slw r9,r9,r10 3c: 7c 63 2c 30 srw r3,r3,r5 40: 7d 24 23 78 or r4,r9,r4 44: 4e 80 00 20 blr Even when forcing the shift with an &= 31, it still considers the shift as likely >= 32. Define a vdso_shift_ns() macro that can be overriden by architectures. Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> --- lib/vdso/gettimeofday.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)