ftrace: Do not process kernel/trace/ftrace.o with C recordmcount program

The file kernel/trace/ftrace.c references the mcount() call to convert the mcount() callers to nops. But because it references mcount(), the mcount() address is placed in the relocation table. The C version of recordmcount reads the relocation table of all object files, and it will add all references to mcount to the __mcount_loc table that is used to find the places that call mcount() and change the call to a nop. When recordmcount finds the mcount reference in kernel/trace/ftrace.o, it saves that location even though the code is not a call, but references mcount as data. On boot up, when all calls are converted to nops, the code has a safety check to determine what op code it is actually replacing before it replaces it. If that op code at the address does not match, then a warning is printed and the function tracer is disabled. The reference to mcount in ftrace.c, causes this warning to trigger, since the reference is not a call to mcount(). The ftrace.c file is not compiled with the -pg flag, so no calls to mcount() should be expected. This patch simply makes recordmcount.c skip the kernel/trace/ftrace.c file. This was the same solution used by the perl version of recordmcount. Reported-by: Ingo Molnar <mingo@elte.hu> Cc: John Reiser <jreiser@bitwagon.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

ftrace: Do not process kernel/trace/ftrace.o with C recordmcount program
The file kernel/trace/ftrace.c references the mcount() call to convert the mcount() callers to nops. But because it references mcount(), the mcount() address is placed in the relocation table. The C version of recordmcount reads the relocation table of all object files, and it will add all references to mcount to the __mcount_loc table that is used to find the places that call mcount() and change the call to a nop. When recordmcount finds the mcount reference in kernel/trace/ftrace.o, it saves that location even though the code is not a call, but references mcount as data. On boot up, when all calls are converted to nops, the code has a safety check to determine what op code it is actually replacing before it replaces it. If that op code at the address does not match, then a warning is printed and the function tracer is disabled. The reference to mcount in ftrace.c, causes this warning to trigger, since the reference is not a call to mcount(). The ftrace.c file is not compiled with the -pg flag, so no calls to mcount() should be expected. This patch simply makes recordmcount.c skip the kernel/trace/ftrace.c file. This was the same solution used by the perl version of recordmcount. Reported-by: Ingo Molnar <mingo@elte.hu> Cc: John Reiser <jreiser@bitwagon.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Steven Rostedt · Steven Rostedt
1 parent cf4db2597a
Showing 1 changed file with 20 additions and 2 deletions Side-by-side Diff
scripts/recordmcount.c
@@ -313,12 +313,30 @@
 int
 main(int argc, char const *argv[])
 {
+	const char ftrace[] = "kernel/trace/ftrace.o";
+	int ftrace_size = sizeof(ftrace) - 1;
 	int n_error = 0;  /* gcc-4.3.0 false positive complaint */
-	if (argc <= 1)
+
+	if (argc <= 1) {
 		fprintf(stderr, "usage: recordmcount file.o...\n");
-	else  /* Process each file in turn, allowing deep failure. */
+		return 0;
+	}
+
+	/* Process each file in turn, allowing deep failure. */
 	for (--argc, ++argv; 0 < argc; --argc, ++argv) {
 		int const sjval = setjmp(jmpenv);
+		int len;
+
+		/*
+		 * The file kernel/trace/ftrace.o references the mcount
+		 * function but does not call it. Since ftrace.o should
+		 * not be traced anyway, we just skip it.
+		 */
+		len = strlen(argv[0]);
+		if (len >= ftrace_size &&
+		    strcmp(argv[0] + (len - ftrace_size), ftrace) == 0)
+			continue;
+
 		switch (sjval) {
 		default: {
 			fprintf(stderr, "internal error: %s\n", argv[0]);
...	...	@@ -313,12 +313,30 @@
313	313	int
314	314	main(int argc, char const *argv[])
315	315	{
	316	+ const char ftrace[] = "kernel/trace/ftrace.o";
	317	+ int ftrace_size = sizeof(ftrace) - 1;
316	318	int n_error = 0; /* gcc-4.3.0 false positive complaint */
317		- if (argc <= 1)
	319	+
	320	+ if (argc <= 1) {
318	321	fprintf(stderr, "usage: recordmcount file.o...\n");
319		- else /* Process each file in turn, allowing deep failure. */
	322	+ return 0;
	323	+ }
	324	+
	325	+ /* Process each file in turn, allowing deep failure. */
320	326	for (--argc, ++argv; 0 < argc; --argc, ++argv) {
321	327	int const sjval = setjmp(jmpenv);
	328	+ int len;
	329	+
	330	+ /*
	331	+ * The file kernel/trace/ftrace.o references the mcount
	332	+ * function but does not call it. Since ftrace.o should
	333	+ * not be traced anyway, we just skip it.
	334	+ */
	335	+ len = strlen(argv[0]);
	336	+ if (len >= ftrace_size &&
	337	+ strcmp(argv[0] + (len - ftrace_size), ftrace) == 0)
	338	+ continue;
	339	+
322	340	switch (sjval) {
323	341	default: {
324	342	fprintf(stderr, "internal error: %s\n", argv[0]);