[PATCH v4 1/2] dt-ops: Add helper API to dump fdt blob

Bhupesh Sharma bhsharma at redhat.com
Thu Jun 21 03:24:37 PDT 2018


At several occasions it would be useful to dump the fdt
blob being passed to the second (kexec/kdump) kernel
when '-d' flag is specified while invoking kexec/kdump.

This allows one to look at the device-tree fields that
is being passed to the secondary kernel and accordingly
debug issues.

This can be specially useful for the arm64 case, where
kexec_load() or kdump passes important information like
'linux,usable-memory' ranges to the second kernel, and
the correctness of the ranges can be verified by
looking at the device-tree dump with '-d' flag specified.

Signed-off-by: Bhupesh Sharma <bhsharma at redhat.com>
---
 kexec/dt-ops.c | 141 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 kexec/dt-ops.h |   1 +
 2 files changed, 142 insertions(+)

diff --git a/kexec/dt-ops.c b/kexec/dt-ops.c
index 915dbf55afd2..80ebfd31b4b6 100644
--- a/kexec/dt-ops.c
+++ b/kexec/dt-ops.c
@@ -8,6 +8,10 @@
 #include "kexec.h"
 #include "dt-ops.h"
 
+#define ALIGN(x, a)	(((x) + ((a) - 1)) & ~((a) - 1))
+#define PALIGN(p, a)	((void *)(ALIGN((unsigned long)(p), (a))))
+#define GET_CELL(p)	(p += 4, *((const uint32_t *)(p - 4)))
+
 static const char n_chosen[] = "/chosen";
 
 static const char p_bootargs[] = "bootargs";
@@ -143,3 +147,140 @@ int dtb_delete_property(char *dtb, const char *node, const char *prop)
 
 	return result;
 }
+
+static uint64_t is_printable_string(const void* data, uint64_t len)
+{
+	const char *s = data;
+	const char *ss;
+
+	/* Check for zero length strings */
+	if (len == 0)
+		return 0;
+
+	/* String must be terminated with a '\0' */
+	if (s[len - 1] != '\0')
+		return 0;
+
+	ss = s;
+	while (*s)
+		s++;
+
+	/* Traverse till we hit a '\0' or reach 'len' */
+	if (*s != '\0')
+		return 0;
+
+	if ((s + 1 - ss) < len) {
+		/* Handle special cases such as 'bootargs' properties
+		 * in dtb which are actually strings, but they may have
+		 * a format where (s + 1 - ss) < len remains true.
+		 *
+		 * We can catch such cases by checking if (s + 1 - ss)
+		 * is greater than 1
+		 */
+		if ((s + 1 - ss) > 1)
+			return 1;
+
+		return 0;
+	}
+
+	return 1;
+}
+
+static void print_data(const char* data, uint64_t len)
+{
+	uint64_t i;
+	const char *p_data = data;
+
+	/* Check for non-zero length */
+	if (len == 0)
+		return;
+
+	if (is_printable_string(data, len)) {
+		dbgprintf(" = \"%s\"", (const char *)data);
+	} else if ((len % 4) == 0) {
+		dbgprintf(" = <");
+		for (i = 0; i < len; i += 4) {
+			dbgprintf("0x%08x%s",
+					fdt32_to_cpu(GET_CELL(p_data)),
+					i < (len - 4) ? " " : "");
+		}
+		dbgprintf(">");
+	} else {
+		dbgprintf(" = [");
+		for (i = 0; i < len; i++)
+			dbgprintf("%02x%s", *p_data++,
+					i < len - 1 ? " " : "");
+		dbgprintf("]");
+	}
+}
+
+void dump_fdt(void* fdt)
+{
+	struct fdt_header *bph;
+	const char* p_struct;
+	const char* p_strings;
+	const char* p_data;
+	const char* s_data;
+	uint32_t off_dt;
+	uint32_t off_str;
+	uint32_t tag;
+	uint64_t sz;
+	uint64_t depth;
+	uint64_t shift;
+	uint32_t version;
+
+	depth = 0;
+	shift = 4;
+
+	bph = fdt;
+	off_dt = fdt32_to_cpu(bph->off_dt_struct);
+	off_str = fdt32_to_cpu(bph->off_dt_strings);
+	p_struct = (const char*)fdt + off_dt;
+	p_strings = (const char*)fdt + off_str;
+	version = fdt32_to_cpu(bph->version);
+
+	p_data = p_struct;
+	while ((tag = fdt32_to_cpu(GET_CELL(p_data))) != FDT_END) {
+		if (tag == FDT_BEGIN_NODE) {
+			s_data = p_data;
+			p_data = PALIGN(p_data + strlen(s_data) + 1, 4);
+
+			if (*s_data == '\0')
+				s_data = "/";
+
+			dbgprintf("%*s%s {\n", (int)(depth * shift), " ", s_data);
+
+			depth++;
+			continue;
+		}
+
+		if (tag == FDT_END_NODE) {
+			depth--;
+
+			dbgprintf("%*s};\n", (int)(depth * shift), " ");
+			continue;
+		}
+
+		if (tag == FDT_NOP) {
+			dbgprintf("%*s// [NOP]\n", (int)(depth * shift), " ");
+			continue;
+		}
+
+		if (tag != FDT_PROP) {
+			dbgprintf("%*s ** Unknown tag 0x%08x\n",
+					(int)(depth * shift), " ", tag);
+			break;
+		}
+
+		sz = fdt32_to_cpu(GET_CELL(p_data));
+		s_data = p_strings + fdt32_to_cpu(GET_CELL(p_data));
+		if (version < 16 && sz >= 8)
+			p_data = PALIGN(p_data, 8);
+
+		dbgprintf("%*s%s", (int)(depth * shift), " ", s_data);
+		print_data(p_data, sz);
+		dbgprintf(";\n");
+
+		p_data = PALIGN(p_data + sz, 4);
+	}
+}
diff --git a/kexec/dt-ops.h b/kexec/dt-ops.h
index e70d15d8ffbf..25b9b569f2b7 100644
--- a/kexec/dt-ops.h
+++ b/kexec/dt-ops.h
@@ -9,5 +9,6 @@ int dtb_set_property(char **dtb, off_t *dtb_size, const char *node,
 	const char *prop, const void *value, int value_len);
 
 int dtb_delete_property(char *dtb, const char *node, const char *prop);
+void dump_fdt(void *fdt) ;
 
 #endif
-- 
2.7.4




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