linux-kernel - [PATCH AUTOSEL for 4.4 089/162] MIPS: VDSO: Add implementation of gettimeofday() fallback

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Message-ID: <20180409002738.163941-89-alexander.levin@microsoft.com>
Date:   Mon, 9 Apr 2018 00:28:49 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Goran Ferenc <goran.ferenc@...tec.com>,
        Miodrag Dinic <miodrag.dinic@...tec.com>,
        Aleksandar Markovic <aleksandar.markovic@...tec.com>,
        Douglas Leung <douglas.leung@...tec.com>,
        James Hogan <james.hogan@...tec.com>,
        Paul Burton <paul.burton@...tec.com>,
        Petar Jovanovic <petar.jovanovic@...tec.com>,
        Raghu Gandham <raghu.gandham@...tec.com>,
        "linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.4 089/162] MIPS: VDSO: Add implementation of
 gettimeofday() fallback

From: Goran Ferenc <goran.ferenc@...tec.com>

[ Upstream commit 0b523a85e134d41f57ddd8c5193bd9f0a5e20b0d ]

This patch adds gettimeofday_fallback() function that wraps assembly
invocation of gettimeofday() syscall using __NR_gettimeofday.

This function is used if pure VDSO implementation gettimeofday()
does not succeed for any reason. Its imeplementation is enclosed in
"#ifdef CONFIG_MIPS_CLOCK_VSYSCALL" to be in sync with the similar
arrangement for __vdso_gettimeofday().

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

Signed-off-by: Goran Ferenc <goran.ferenc@...tec.com>
Signed-off-by: Miodrag Dinic <miodrag.dinic@...tec.com>
Signed-off-by: Aleksandar Markovic <aleksandar.markovic@...tec.com>
Cc: Douglas Leung <douglas.leung@...tec.com>
Cc: James Hogan <james.hogan@...tec.com>
Cc: Paul Burton <paul.burton@...tec.com>
Cc: Petar Jovanovic <petar.jovanovic@...tec.com>
Cc: Raghu Gandham <raghu.gandham@...tec.com>
Cc: linux-mips@...ux-mips.org
Cc: linux-kernel@...r.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/16640/
Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 arch/mips/vdso/gettimeofday.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/mips/vdso/gettimeofday.c b/arch/mips/vdso/gettimeofday.c
index 5f6337545ee2..23305bf6c7a2 100644
--- a/arch/mips/vdso/gettimeofday.c
+++ b/arch/mips/vdso/gettimeofday.c
@@ -20,6 +20,28 @@
 #include <asm/unistd.h>
 #include <asm/vdso.h>
 
+#ifdef CONFIG_MIPS_CLOCK_VSYSCALL
+
+static __always_inline long gettimeofday_fallback(struct timeval *_tv,
+					  struct timezone *_tz)
+{
+	register struct timezone *tz asm("a1") = _tz;
+	register struct timeval *tv asm("a0") = _tv;
+	register long ret asm("v0");
+	register long nr asm("v0") = __NR_gettimeofday;
+	register long error asm("a3");
+
+	asm volatile(
+	"       syscall\n"
+	: "=r" (ret), "=r" (error)
+	: "r" (tv), "r" (tz), "r" (nr)
+	: "memory");
+
+	return error ? -ret : ret;
+}
+
+#endif
+
 static __always_inline long clock_gettime_fallback(clockid_t _clkid,
 					   struct timespec *_ts)
 {
@@ -205,7 +227,7 @@ int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
 
 	ret = do_realtime(&ts, data);
 	if (ret)
-		return ret;
+		return gettimeofday_fallback(tv, tz);
 
 	if (tv) {
 		tv->tv_sec = ts.tv_sec;
-- 
2.15.1