From 2ed07609b2a8ed19ce3dda7a50b18373a6a8bd5c Mon Sep 17 00:00:00 2001

From: Dave Anderson <anderson@redhat.com>

Date: Mon, 25 Mar 2019 11:48:39 -0400

Subject: [PATCH 1/3] Fixes for the "trace.so" extension module: (1) The

 reader_page can be empty if it was never read, do not record     it if it is

 empty. Better yet, do not record any page that is     empty.  The struct

 buffer_page "real_end" is not available in     older kernels, so it needs to

 be tested if it exists before we     can use it. (2) In newer kernels, the

 sp->type of kernel module symbols does not     contain the symbol type

 character unless the module's debuginfo     data has been loaded into the

 crash session.  Writing a garbage     type to the kallsyms file for trace-cmd

 to read causes it to     crash, so just always write an 'm'. (3) Add the

 "trace dump -t <trace.dat>" option to the SYNOPSIS line     of the help page.

 (rostedt@goodmis.org)

---

 trace.c | 32 +++++++++++++++++++++++++++++---

 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/trace.c b/trace.c

index ad71951e8740..c26b6c7ec475 100644

--- a/trace.c

+++ b/trace.c

@@ -43,6 +43,11 @@ static int max_buffer_available;

  */

 static int multiple_instances_available;

+/*

+ * buffer_page has "real_end"

+ */

+static int buffer_page_real_end_available;

+

 #define koffset(struct, member) struct##_##member##_offset

 static int koffset(trace_array, current_trace);

@@ -70,6 +75,7 @@ static int koffset(ring_buffer_per_cpu, entries);

 static int koffset(buffer_page, read);

 static int koffset(buffer_page, list);

 static int koffset(buffer_page, page);

+static int koffset(buffer_page, real_end);

 static int koffset(list_head, next);

@@ -229,6 +235,7 @@ static int init_offsets(void)

 	init_offset(buffer_page, read);

 	init_offset(buffer_page, list);

 	init_offset(buffer_page, page);

+	init_offset(buffer_page, real_end);

 	init_offset(list_head, next);

@@ -281,6 +288,7 @@ static void print_offsets(void)

 	print_offset(buffer_page, read);

 	print_offset(buffer_page, list);

 	print_offset(buffer_page, page);

+	print_offset(buffer_page, real_end);

 	print_offset(list_head, next);

@@ -295,6 +303,20 @@ static void print_offsets(void)

 #undef print_offset

 }

+static int buffer_page_has_data(ulong page)

+{

+	uint end;

+

+	if (!buffer_page_real_end_available)

+		return 1;

+

+	/* Only write pages with data in it */

+	read_value(end, page, buffer_page, real_end);

+	return end;

+out_fail:

+	return 0;

+}

+

 static int ftrace_init_pages(struct ring_buffer_per_cpu *cpu_buffer,

 		unsigned nr_pages)

 {

@@ -361,7 +383,8 @@ static int ftrace_init_pages(struct ring_buffer_per_cpu *cpu_buffer,

 	/* Setup linear pages */

-	cpu_buffer->linear_pages[count++] = cpu_buffer->reader_page;

+	if (buffer_page_has_data(cpu_buffer->reader_page))

+		cpu_buffer->linear_pages[count++] = cpu_buffer->reader_page;

 	if (cpu_buffer->reader_page == cpu_buffer->commit_page)

 		goto done;

@@ -647,6 +670,8 @@ static int ftrace_init(void)

 		ftrace_trace_arrays = sym_ftrace_trace_arrays->value;

 	}

+	if (MEMBER_EXISTS("buffer_page", "real_end"))

+		buffer_page_real_end_available = 1;

 	if (MEMBER_EXISTS("trace_array", "current_trace")) {

 		encapsulated_current_trace = 1;

@@ -1809,7 +1834,7 @@ static void cmd_ftrace(void)

 static char *help_ftrace[] = {

 "trace",

 "show or dump the tracing info",

-"[ <show [-c <cpulist>] [-f [no]<flagname>]> | <dump [-sm] <dest-dir>> ]",

+"[ <show [-c <cpulist>] [-f [no]<flagname>]> | <dump [-sm] <dest-dir>> ] | <dump -t <trace.dat> ]",

 "trace",

 "    shows the current tracer and other informations.",

 "",

@@ -2184,7 +2209,8 @@ static int save_proc_kallsyms(int fd)

 			if (!strncmp(sp->name, "_MODULE_", strlen("_MODULE_")))

 				continue;

-			tmp_fprintf("%lx %c %s\t[%s]\n", sp->value, sp->type,

+			/* Currently sp->type for modules is not trusted */

+			tmp_fprintf("%lx %c %s\t[%s]\n", sp->value, 'm',

 					sp->name, lm->mod_name);

 		}

 	}

-- 

2.17.1