[PATCH AUTOSEL for 4.4 088/162] MIPS: VDSO: Add implementation of clock_gettime() fallback

[Sasha Levin]

From: Goran Ferenc 

[ Upstream commit 180902e08f051f72c89ffa366f4e4f7a8e9c753e ]

This patch adds clock_gettime_fallback() function that wraps assembly
invocation of clock_gettime() syscall using __NR_clock_gettime.

This function is used if pure VDSO implementation of clock_gettime()
does not succeed for any reason. For example, it is called if the
clkid parameter of clock_gettime() is not one of the clkids listed
in the switch-case block of the function __vdso_clock_gettime()
(one such case for clkid is CLOCK_BOOTIME).

If syscall invocation via __NR_clock_gettime fails, register a3 will
be set. So, after the syscall, register a3 is tested and the return
value is negated if it's set.

Signed-off-by: Goran Ferenc 
Signed-off-by: Miodrag Dinic 
Signed-off-by: Aleksandar Markovic 
Cc: Douglas Leung 
Cc: James Hogan 
Cc: Paul Burton 
Cc: Petar Jovanovic 
Cc: Raghu Gandham 
Cc: linux-m...@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16639/
Signed-off-by: Ralf Baechle 
Signed-off-by: Sasha Levin 
---
 arch/mips/vdso/gettimeofday.c | 25 ++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/mips/vdso/gettimeofday.c b/arch/mips/vdso/gettimeofday.c
index fd7d433970bf..5f6337545ee2 100644
--- a/arch/mips/vdso/gettimeofday.c
+++ b/arch/mips/vdso/gettimeofday.c
@@ -20,6 +20,24 @@
 #include 
 #include 
 
+static __always_inline long clock_gettime_fallback(clockid_t _clkid,
+  struct timespec *_ts)
+{
+   register struct timespec *ts asm("a1") = _ts;
+   register clockid_t clkid asm("a0") = _clkid;
+   register long ret asm("v0");
+   register long nr asm("v0") = __NR_clock_gettime;
+   register long error asm("a3");
+
+   asm volatile(
+   "   syscall\n"
+   : "=r" (ret), "=r" (error)
+   : "r" (clkid), "r" (ts), "r" (nr)
+   : "memory");
+
+   return error ? -ret : ret;
+}
+
 static __always_inline int do_realtime_coarse(struct timespec *ts,
  const union mips_vdso_data *data)
 {
@@ -207,7 +225,7 @@ int __vdso_gettimeofday(struct timeval *tv, struct timezone 
*tz)
 int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts)
 {
const union mips_vdso_data *data = get_vdso_data();
-   int ret;
+   int ret = -1;
 
switch (clkid) {
case CLOCK_REALTIME_COARSE:
@@ -223,10 +241,11 @@ int __vdso_clock_gettime(clockid_t clkid, struct timespec 
*ts)
ret = do_monotonic(ts, data);
break;
default:
-   ret = -ENOSYS;
break;
}
 
-   /* If we return -ENOSYS libc should fall back to a syscall. */
+   if (ret)
+   ret = clock_gettime_fallback(clkid, ts);
+
return ret;
 }
-- 
2.15.1

[PATCH AUTOSEL for 4.4 088/162] MIPS: VDSO: Add implementation of clock_gettime() fallback

[Sasha Levin]

From: Goran Ferenc 

[ Upstream commit 180902e08f051f72c89ffa366f4e4f7a8e9c753e ]

This patch adds clock_gettime_fallback() function that wraps assembly
invocation of clock_gettime() syscall using __NR_clock_gettime.

This function is used if pure VDSO implementation of clock_gettime()
does not succeed for any reason. For example, it is called if the
clkid parameter of clock_gettime() is not one of the clkids listed
in the switch-case block of the function __vdso_clock_gettime()
(one such case for clkid is CLOCK_BOOTIME).

If syscall invocation via __NR_clock_gettime fails, register a3 will
be set. So, after the syscall, register a3 is tested and the return
value is negated if it's set.

Signed-off-by: Goran Ferenc 
Signed-off-by: Miodrag Dinic 
Signed-off-by: Aleksandar Markovic 
Cc: Douglas Leung 
Cc: James Hogan 
Cc: Paul Burton 
Cc: Petar Jovanovic 
Cc: Raghu Gandham 
Cc: linux-m...@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16639/
Signed-off-by: Ralf Baechle 
Signed-off-by: Sasha Levin 
---
 arch/mips/vdso/gettimeofday.c | 25 ++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/mips/vdso/gettimeofday.c b/arch/mips/vdso/gettimeofday.c
index fd7d433970bf..5f6337545ee2 100644
--- a/arch/mips/vdso/gettimeofday.c
+++ b/arch/mips/vdso/gettimeofday.c
@@ -20,6 +20,24 @@
 #include 
 #include 
 
+static __always_inline long clock_gettime_fallback(clockid_t _clkid,
+  struct timespec *_ts)
+{
+   register struct timespec *ts asm("a1") = _ts;
+   register clockid_t clkid asm("a0") = _clkid;
+   register long ret asm("v0");
+   register long nr asm("v0") = __NR_clock_gettime;
+   register long error asm("a3");
+
+   asm volatile(
+   "   syscall\n"
+   : "=r" (ret), "=r" (error)
+   : "r" (clkid), "r" (ts), "r" (nr)
+   : "memory");
+
+   return error ? -ret : ret;
+}
+
 static __always_inline int do_realtime_coarse(struct timespec *ts,
  const union mips_vdso_data *data)
 {
@@ -207,7 +225,7 @@ int __vdso_gettimeofday(struct timeval *tv, struct timezone 
*tz)
 int __vdso_clock_gettime(clockid_t clkid, struct timespec *ts)
 {
const union mips_vdso_data *data = get_vdso_data();
-   int ret;
+   int ret = -1;
 
switch (clkid) {
case CLOCK_REALTIME_COARSE:
@@ -223,10 +241,11 @@ int __vdso_clock_gettime(clockid_t clkid, struct timespec 
*ts)
ret = do_monotonic(ts, data);
break;
default:
-   ret = -ENOSYS;
break;
}
 
-   /* If we return -ENOSYS libc should fall back to a syscall. */
+   if (ret)
+   ret = clock_gettime_fallback(clkid, ts);
+
return ret;
 }
-- 
2.15.1