[PATCH 0/2] [GIT PULL] ftrace: recordmcount fixes

[PATCH 0/2] [GIT PULL] ftrace: recordmcount fixes

[Steven Rostedt]

Ingo,

Please pull the latest tip/perf/recordmcount tree, which can be found at:

  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
tip/perf/recordmcount


Steven Rostedt (2):
      ftrace: Do not process kernel/trace/ftrace.o with C recordmcount program
      ftrace: Use objtree for C version of recordmcount

----
 scripts/Makefile.build |    2 +-
 scripts/recordmcount.c |   22 ++++++++++++++++++++--
 2 files changed, 21 insertions(+), 3 deletions(-)

[PATCH 1/2] ftrace: Do not process kernel/trace/ftrace.o with C recordmcount program

[Steven Rostedt]

[-- Attachment #1: 0001-ftrace-Do-not-process-kernel-trace-ftrace.o-with-C-r.patch --]
[-- Type: text/plain, Size: 2631 bytes --]

From: Steven Rostedt <srostedt@redhat.com>

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>
---
 scripts/recordmcount.c |   22 ++++++++++++++++++++--
 1 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index 7f7f718..26e1271 100644
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -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]);
-- 
1.7.1

[PATCH 2/2] ftrace: Use objtree for C version of recordmcount

[Steven Rostedt]

[-- Attachment #1: 0002-ftrace-Use-objtree-for-C-version-of-recordmcount.patch --]
[-- Type: text/plain, Size: 957 bytes --]

From: Steven Rostedt <srostedt@redhat.com>

The C version of recordmcount is compiled to a binary, which will
end up located in the objtree. If the kernel is built with O=path,
the srctree will not include the binary recordmcount caller.

Cc: Michal Marek <mmarek@suse.cz>
Cc: linux-kbuild@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 scripts/Makefile.build |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 4d03a7e..4db60b2 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -210,7 +210,7 @@ endif
 
 ifdef CONFIG_FTRACE_MCOUNT_RECORD
 ifdef BUILD_C_RECORDMCOUNT
-cmd_record_mcount = $(srctree)/scripts/recordmcount "$(@)";
+cmd_record_mcount = $(objtree)/scripts/recordmcount "$(@)";
 else
 cmd_record_mcount = set -e ; perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
 	"$(if $(CONFIG_CPU_BIG_ENDIAN),big,little)" \
-- 
1.7.1

Re: [PATCH 0/2] [GIT PULL] ftrace: recordmcount fixes

[Ingo Molnar]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> Ingo,
> 
> Please pull the latest tip/perf/recordmcount tree, which can be found at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git
> tip/perf/recordmcount
> 
> 
> Steven Rostedt (2):
>       ftrace: Do not process kernel/trace/ftrace.o with C recordmcount program
>       ftrace: Use objtree for C version of recordmcount
> 
> ----
>  scripts/Makefile.build |    2 +-
>  scripts/recordmcount.c |   22 ++++++++++++++++++++--
>  2 files changed, 21 insertions(+), 3 deletions(-)

Pulled, thanks Steve!

	Ingo