From: Koakuma <koachan@xxxxxxxxxxxxxx>
Add helper function for 64-bit right shift on 32-bit target so that
clang does not emit a runtime library call.
Signed-off-by: Koakuma <koachan@xxxxxxxxxxxxxx>
---
Hi~
This adds a small function to do 64-bit right shifts for use in vDSO
code, needed so that clang does not emit a call to runtime library.
---
arch/sparc/vdso/vclock_gettime.c | 8 ++++----
include/vdso/math64.h | 28 ++++++++++++++++++++++++++++
2 files changed, 32 insertions(+), 4 deletions(-)
diff --git a/arch/sparc/vdso/vclock_gettime.c b/arch/sparc/vdso/vclock_gettime.c
index e794edde6755..c0251a632bdb 100644
--- a/arch/sparc/vdso/vclock_gettime.c
+++ b/arch/sparc/vdso/vclock_gettime.c
@@ -154,7 +154,7 @@ notrace static __always_inline int do_realtime(struct vvar_data *vvar,
ts->tv_sec = vvar->wall_time_sec;
ns = vvar->wall_time_snsec;
ns += vgetsns(vvar);
- ns >>= vvar->clock.shift;
+ ns = __shr64(ns, vvar->clock.shift);
} while (unlikely(vvar_read_retry(vvar, seq)));
ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
@@ -174,7 +174,7 @@ notrace static __always_inline int do_realtime_stick(struct vvar_data *vvar,
ts->tv_sec = vvar->wall_time_sec;
ns = vvar->wall_time_snsec;
ns += vgetsns_stick(vvar);
- ns >>= vvar->clock.shift;
+ ns = __shr64(ns, vvar->clock.shift);
} while (unlikely(vvar_read_retry(vvar, seq)));
ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
@@ -194,7 +194,7 @@ notrace static __always_inline int do_monotonic(struct vvar_data *vvar,
ts->tv_sec = vvar->monotonic_time_sec;
ns = vvar->monotonic_time_snsec;
ns += vgetsns(vvar);
- ns >>= vvar->clock.shift;
+ ns = __shr64(ns, vvar->clock.shift);
} while (unlikely(vvar_read_retry(vvar, seq)));
ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
@@ -214,7 +214,7 @@ notrace static __always_inline int do_monotonic_stick(struct vvar_data *vvar,
ts->tv_sec = vvar->monotonic_time_sec;
ns = vvar->monotonic_time_snsec;
ns += vgetsns_stick(vvar);
- ns >>= vvar->clock.shift;
+ ns = __shr64(ns, vvar->clock.shift);
} while (unlikely(vvar_read_retry(vvar, seq)));
ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns);
diff --git a/include/vdso/math64.h b/include/vdso/math64.h
index 22ae212f8b28..771d84faa8d7 100644
--- a/include/vdso/math64.h
+++ b/include/vdso/math64.h
@@ -21,6 +21,34 @@ __iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder)
return ret;
}
+#if BITS_PER_LONG == 32
+/* This is to prevent the compiler from emitting a call to __lshrdi3. */
+static __always_inline u64
+__shr64(u64 val, int amt)
+{
+ u32 mask = (1U << amt) - 1;
+ u32 lo = val;
+ u32 hi = val >> 32;
+ u32 mi;
+
+ if (amt >= 32)
+ return hi >> (amt - 32);
+
+
+ mi = (hi & mask) << (32 - amt);
+ hi >>= amt;
+ lo = (lo >> amt) | mi;
+
+ return ((u64) hi) << 32 | lo;
+}
+#else
+static __always_inline u64
+__shr64(u64 val, int amt)
+{
+ return val >> amt;
+}
+#endif /* BITS_PER_LONG == 32 */
+
#if defined(CONFIG_ARCH_SUPPORTS_INT128) && defined(__SIZEOF_INT128__)
#ifndef mul_u64_u32_add_u64_shr
---
base-commit: defaf1a2113a22b00dfa1abc0fd2014820eaf065
change-id: 20240717-sparc-shr64-2f00a7884770
Best regards,
--
Koakuma <koachan@xxxxxxxxxxxxxx>
