[Crash-utility] [PATCH] s390x: Fix s390dbf time stamps for kernels 4.11 and 4.14

[Michael Holzheu]

Hi Dave,

With kernel commit ea417aa8a38bc7db ("s390/debug: make debug event time
stamps relative to the boot TOD clock") for s390dbf time is stored
relative to the kernel boot time.

In order to still show absolute time since 1970 we have to detect
those kernels and re-add the boot time before printing the records.

We can use the tod_to_timeval() symbol to check for those kernels
because the patch has removed the symbol.

With commit 6e2ef5e4f6cc5734 ("s390/time: add support for the TOD clock
epoch extension") the symbol for storing the boot time has changed from
"sched_clock_base_cc" to "tod_clock_base".
This commit is currently on the s390 features branch and will be integrated
in linux 4.14:

https://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git/commit/?h=features&id=6e2ef5e4f6cc57344762932d70d38ba4ec65fa8b

Cc: Martin Schwidefsky <schwidefsky at de.ibm.com>
Signed-off-by: Michael Holzheu <holzheu at linux.vnet.ibm.com>
Reviewed-by: Mikhail Zaslonko <zaslonko at linux.vnet.ibm.com>
---
 s390dbf.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 46 insertions(+), 5 deletions(-)

diff --git a/s390dbf.c b/s390dbf.c
index d3581c2..f21cd3a 100644
--- a/s390dbf.c
+++ b/s390dbf.c
@@ -57,6 +57,9 @@
 #define KL_PTRSZ 4
 #endif
 
+/* Start TOD time of kernel in usecs for relative time stamps */
+static uint64_t tod_clock_base_us;
+
 typedef unsigned long uaddr_t;
 typedef unsigned long kaddr_t;
 
@@ -162,13 +165,23 @@ static inline int set_cmd_flags(command_t *cmd, int flags, char *extraops)
 	return 0;
 }
 
+/* Time of day clock value for 1970/01/01 */
+#define TOD_UNIX_EPOCH (0x8126d60e46000000LL - (0x3c26700LL * 1000000 * 4096))
+/* Time of day clock value for 1970/01/01 in usecs */
+#define TOD_UNIX_EPOCH_US (TOD_UNIX_EPOCH >> 12)
+
 static inline void kl_s390tod_to_timeval(uint64_t todval, struct timeval *xtime)
 {
-	todval -= 0x8126d60e46000000LL - (0x3c26700LL * 1000000 * 4096);
-
-	todval >>= 12;
-	xtime->tv_sec  = todval / 1000000;
-	xtime->tv_usec = todval % 1000000;
+	uint64_t todval_us;
+
+	/* Convert TOD to usec (51th bit of TOD is us) */
+	todval_us = todval >> 12;
+	/* Add base if we have relative time stamps */
+	todval_us += tod_clock_base_us;
+	/* Subtract EPOCH that we get time in usec since 1970 */
+	todval_us -= TOD_UNIX_EPOCH_US;
+	xtime->tv_sec  = todval_us / 1000000;
+	xtime->tv_usec = todval_us % 1000000;
 }
 
 static inline int kl_struct_len(char* struct_name)
@@ -846,10 +859,38 @@ find_debug_area(const char *area_name)
 	return NULL;
 }
 
+static void tod_clock_base_init(void)
+{
+	if (kernel_symbol_exists("tod_clock_base")) {
+		/*
+		 * Kernels >= 4.14 that contain 6e2ef5e4f6cc5734 ("s390/time:
+		 * add support for the TOD clock epoch extension")
+		 */
+		get_symbol_data("tod_clock_base", sizeof(tod_clock_base_us),
+				&tod_clock_base_us);
+		/* Bit for usecs is at position 59 - therefore shift 4 */
+		tod_clock_base_us >>= 4;
+	} else if (kernel_symbol_exists("sched_clock_base_cc") &&
+		   !kernel_symbol_exists("tod_to_timeval")) {
+		/*
+		 * Kernels >= 4.11 that contain ea417aa8a38bc7db ("s390/debug:
+		 * make debug event time stamps relative to the boot TOD clock")
+		 */
+		get_symbol_data("sched_clock_base_cc",
+				sizeof(tod_clock_base_us), &tod_clock_base_us);
+		/* Bit for usecs is at position 51 - therefore shift 12 */
+		tod_clock_base_us >>= 12;
+	} else {
+		/* All older kernels use absolute time stamps */
+		tod_clock_base_us = 0;
+	}
+}
+
 static void
 dbf_init(void)
 {
 	if (!initialized) {
+		tod_clock_base_init();
 		if(dbf_version >= DBF_VERSION_V2)
 			add_lcrash_debug_view(&pages_view);
 		add_lcrash_debug_view(&ascii_view);
-- 
2.11.2

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