Commit 44475863 authored Oct 15, 2010 by Steven Rostedt Committed by Steven Rostedt Oct 15, 2010

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>

parent cf4db259

scripts/recordmcount.c

+20 −2

Original line number	Diff line number	Diff line
		@@ -313,12 +313,30 @@ do_file(char const *const fname)
		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]);

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