[Crash-utility] [PATCH] Fix pvops Xen detection for arm machine

[Qi Zheng]

Since the xen_start_info on the arm/arm64 platform is static defined:

./arm/xen/enlighten.c:40:static struct start_info _xen_start_info;
./arm/xen/enlighten.c:41:struct start_info *xen_start_info = &_xen_start_info;
./arm/xen/enlighten.c:42:EXPORT_SYMBOL(xen_start_info);

The is_pvops_xen() in commit 4badc6229c69f5cd9da7eb7bdf400a53ec6db01a
("Fix pvops Xen detection for kernels >= v4.20") always return TRUE.
Then the following error will be reported because p2m_mid_missing
and xen_p2m_addr are not defined:

	crash: cannot resolve "p2m_top"

Fix it by using xen_vcpu_id instead of xen_start_info to detect Xen dumps.

Signed-off-by: Qi Zheng <zhengqi.arch at bytedance.com>
---
 kernel.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/kernel.c b/kernel.c
index f4598ea..24bf479 100644
--- a/kernel.c
+++ b/kernel.c
@@ -10745,6 +10745,9 @@ is_pvops_xen(void)
 {
 	ulong addr;
 	char *sym;
+	struct syment * sp;
+	ulong ptr;
+	int i;
 
 	if (!PVOPS())
 		return FALSE;
@@ -10757,11 +10760,19 @@ is_pvops_xen(void)
 	     STREQ(sym, "paravirt_patch_default")))
 		return TRUE;
 
-	if (symbol_exists("xen_start_info") &&
-	    readmem(symbol_value("xen_start_info"), KVADDR, &addr,
-	    sizeof(void *), "xen_start_info", RETURN_ON_ERROR) &&
-	    addr != 0)
-		return TRUE;
+	sp = per_cpu_symbol_search("xen_vcpu_id");
+	if (sp) {
+		for (i = 0; i < NR_CPUS; i++) {
+			if (!kt->__per_cpu_offset[i])
+				continue;
+
+			ptr = sp->value + kt->__per_cpu_offset[0];
+			if (ptr && readmem(ptr, KVADDR, &ptr, sizeof(uint32_t),
+			    "xen_vcpu_id", FAULT_ON_ERROR))
+				return TRUE;
+			return FALSE;
+		}
+	}
 
 	return FALSE;
 }
-- 
2.11.0