[Crash-utility] [PATCH] fix error crash: cannot resolve "schedulers"

[Nikola Pajkovsky]

Since Xen commit 666aca08175b ("sched: use the auto-generated list of
schedulers") crash cannot open Xen vmcores, because symbol 'schedulers'
does not exits. Xen 4.7 implemented schedulers as its own section.

xen/arch/x86/xen.lds.S
       __start_schedulers_array = .;
       *(.data.schedulers)
       __end_schedulers_array = .;

Crash must not look up for "schedulers" symbol and fails, if symbol is
not found. It must check if __start_schedulers_array exits, and if it
does, use it and get size of the section. Otherwise, crash fallback to
looking up "schedulers" symbol. That way, crash can open vmcore before
and after Xen 4.7.

Signed-off-by: Nikola Pajkovsky <npajkovsky at suse.cz>
---
 xen_hyper.c | 40 +++++++++++++++++++++++++++++++++-------
 1 file changed, 33 insertions(+), 7 deletions(-)

diff --git a/xen_hyper.c b/xen_hyper.c
index 27e44c6e733d..e8268cf40c78 100644
--- a/xen_hyper.c
+++ b/xen_hyper.c
@@ -438,6 +438,19 @@ xen_hyper_misc_init(void)
 #define XEN_HYPER_SCHEDULERS_ARRAY_CNT 10
 #define XEN_HYPER_SCHEDULER_NAME 1024
 
+/*
+ * does similar function exits in crash??
+ */
+static int section_size(char *start_section, char *end_section)
+{
+	ulong sp_start, sp_end;
+
+	sp_start = symbol_value(start_section);
+	sp_end = symbol_value(end_section);
+
+	return (sp_end - sp_start) / sizeof(size_t);
+}
+
 static void
 xen_hyper_schedule_init(void)
 {
@@ -448,6 +461,8 @@ xen_hyper_schedule_init(void)
 	char *buf;
 	char opt_name_buf[XEN_HYPER_OPT_SCHED_SIZE];
 	int i, cpuid, flag;
+	char *sp_name;
+	int xen_hyper_nr_schedulers;
 
 	/* get scheduler information */
 	if((xhscht->scheduler_struct =
@@ -469,21 +484,32 @@ xen_hyper_schedule_init(void)
 	XEN_HYPER_OPT_SCHED_SIZE, "opt_sched,", RETURN_ON_ERROR)) {
 		error(FATAL, "cannot read opt_sched,.\n");
 	}
-	schedulers = symbol_value("schedulers");
+
+	if (symbol_exists("__start_schedulers_array")) {
+		sp_name = "__start_schedulers_array";
+		xen_hyper_nr_schedulers = section_size("__start_schedulers_array",
+						       "__end_schedulers_array");
+	} else {
+		sp_name = "schedulers";
+		xen_hyper_nr_schedulers = XEN_HYPER_SCHEDULERS_ARRAY_CNT;
+	}
+
+	schedulers = symbol_value(sp_name);
+
 	addr = schedulers;
 	while (xhscht->name == NULL) {
 		if (!readmem(addr, KVADDR, schedulers_buf,
-		sizeof(long) * XEN_HYPER_SCHEDULERS_ARRAY_CNT,
-		"schedulers", RETURN_ON_ERROR)) {
+			     sizeof(long) * xen_hyper_nr_schedulers,
+			     sp_name, RETURN_ON_ERROR)) {
 			error(FATAL, "cannot read schedulers.\n");
 		}
-		for (i = 0; i < XEN_HYPER_SCHEDULERS_ARRAY_CNT; i++) {
+		for (i = 0; i < xen_hyper_nr_schedulers; i++) {
 			if (schedulers_buf[i] == 0) {
 				error(FATAL, "schedule data not found.\n");
 			}
 			if (!readmem(schedulers_buf[i], KVADDR,
-			xhscht->scheduler_struct, XEN_HYPER_SIZE(scheduler),
-			"scheduler", RETURN_ON_ERROR)) {
+				     xhscht->scheduler_struct, XEN_HYPER_SIZE(scheduler),
+				     "scheduler", RETURN_ON_ERROR)) {
 				error(FATAL, "cannot read scheduler.\n");
 			}
 			opt_name = ULONG(xhscht->scheduler_struct +
@@ -514,7 +540,7 @@ xen_hyper_schedule_init(void)
 			strncpy(xhscht->name, buf, strlen(buf));
 			break;
 		}
-		addr += sizeof(long) * XEN_HYPER_SCHEDULERS_ARRAY_CNT;
+		addr += sizeof(long) * xen_hyper_nr_schedulers;
 	}
 	FREEBUF(buf);
 
-- 
2.13.6