ftrace for MIPS

Under the help of the -mlong-calls option of gcc, This revision comes with the module tracing support. and there are also lots of cleanups and fixes. therefore, it is ready to upstream.

Currently, function graph tracer support have some overhead for searching the stack address of the return address(ra). we hope the PROFILE_BEFORE_PROLOGUE macro will be enabled by default in the next version of gcc, and then the overhead can be removed via hijacking the ra register directly for both non-leaf and leaf function.

Thanks very much to the people in the CC list for their feedbacks, all the lastest changes goes to this git repo:

git://dev.lemote.com/rt4ls.git linux-mips/dev/ftrace-upstream

Welcome to play with it and give more feedbacks.

Thanks & Regards,
Wu Zhangjin

Wu Zhangjin (11):
tracing: convert trace_clock_local() as weak function
MIPS: add mips_timecounter_read() to get high precision timestamp
tracing: add MIPS specific trace_clock_local()
tracing: add static function tracer support for MIPS
tracing: enable HAVE_FUNCTION_TRACE_MCOUNT_TEST for MIPS
tracing: add an endian argument to scripts/recordmcount.pl
tracing: add dynamic function tracer support for MIPS
tracing: not trace mips_timecounter_init() in MIPS
tracing: add IRQENTRY_EXIT for MIPS
tracing: add function graph tracer support for MIPS
tracing: add dynamic function graph tracer for MIPS

 arch/mips/Kconfig              |    5 +
 arch/mips/Makefile             |    4 +
 arch/mips/include/asm/ftrace.h |   37 ++++++++-
 arch/mips/include/asm/time.h   |   19 ++++
 arch/mips/kernel/Makefile      |    9 ++
 arch/mips/kernel/csrc-r4k.c    |   41 +++++++++
 arch/mips/kernel/ftrace.c      |  190 ++++++++++++++++++++++++++++++++++++++++
 arch/mips/kernel/mcount.S      |  177 +++++++++++++++++++++++++++++++++++++
 arch/mips/kernel/mips_ksyms.c  |    5 +
 arch/mips/kernel/time.c        |    2 +
 arch/mips/kernel/trace_clock.c |   33 +++++++
 arch/mips/kernel/vmlinux.lds.S |    1 +
 include/linux/clocksource.h    |    2 +-
 kernel/time/clocksource.c      |    4 +-
 kernel/trace/trace_clock.c     |    2 +-
 scripts/Makefile.build         |    1 +
 scripts/recordmcount.pl        |   44 +++++++++-
 17 files changed, 568 insertions(+), 8 deletions(-)
 create mode 100644 arch/mips/kernel/ftrace.c
 create mode 100644 arch/mips/kernel/mcount.S
 create mode 100644 arch/mips/kernel/trace_clock.c

trace_clock_local() is based on the arch-specific sched_clock(), in X86, it is tsc(64bit) based, which can give very high precision(about 1ns with 1GHz). but in MIPS, the sched_clock() is jiffies based, which can give only 10ms precison with 1000 HZ. which is not enough for tracing, especially for Real Time system.

so, we need to implement a MIPS specific sched_clock() to get higher precision. There is a tsc like clock counter register in MIPS, whose frequency is half of the processor, so, if the cpu frequency is 800MHz, the time precision reaches 2.5ns, which is very good for tracing, even for Real Time system.

but 'Cause it is only 32bit long, which will rollover quickly, so, such a sched_clock() will bring with extra load, which is not good for the whole system. so, we only need to implement a arch-specific trace_clock_local() for tracing. as a preparation, we convert it as a weak function.

The MIPS specific trace_clock_local() is coming in the next two patches.

---
 kernel/trace/trace_clock.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index 20c5f92..06b8cd2 100644
@@ -26,7 +26,7 @@
  * Useful for tracing that does not cross to other CPUs nor
  * does it go through idle events.
  */
-u64 notrace trace_clock_local(void)
+u64 __weak notrace trace_clock_local(void)
 {
 	unsigned long flags;
 	u64 clock;

1.6.2.1

This patch implement a mips_timecounter_read(), which can be used to get high precision timestamp without extra lock.

It is based on the clock counter register and the timecounter/cyclecounter abstraction layer of kernel.

---
 arch/mips/include/asm/time.h |   19 +++++++++++++++++++
 arch/mips/kernel/csrc-r4k.c  |   41 +++++++++++++++++++++++++++++++++++++++++
 arch/mips/kernel/time.c      |    2 ++
 3 files changed, 62 insertions(+), 0 deletions(-)

index df6a430..b8af7fa 100644
@@ -73,8 +73,18 @@ static inline int mips_clockevent_init(void)
  */
 #ifdef CONFIG_CSRC_R4K_LIB
 extern int init_r4k_clocksource(void);
+extern int init_r4k_timecounter(void);
+extern u64 r4k_timecounter_read(void);
 #endif
 
+static inline u64 mips_timecounter_read(void)
+{
+#ifdef CONFIG_CSRC_R4K
+	return r4k_timecounter_read();
+#else
+	return sched_clock();
+#endif
+}
 static inline int init_mips_clocksource(void)
 {
 #ifdef CONFIG_CSRC_R4K

@@ -84,6 +94,15 @@ static inline int init_mips_clocksource(void)
 #endif
 }
 
+static inline int init_mips_timecounter(void)
+{
+#ifdef CONFIG_CSRC_R4K
+	return init_r4k_timecounter();
+#else
+	return 0;
+#endif
+}
+
 extern void clocksource_set_clock(struct clocksource *cs, unsigned int clock);
 extern void clockevent_set_clock(struct clock_event_device *cd,
 		unsigned int clock);

index 1f467d5..e38cca1 100644
@@ -156,4 +156,6 @@ void __init time_init(void)
 
 	if (!mips_clockevent_init() || !cpu_has_mfc0_count_bug())
 		init_mips_clocksource();
+	if (!cpu_has_mfc0_count_bug())
+		init_mips_timecounter();
 }

1.6.2.1

This patch add the mips_timecounter_read() based high precision version of trace_clock_local().

---
 arch/mips/kernel/Makefile      |    6 ++++++
 arch/mips/kernel/trace_clock.c |   33 +++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 0 deletions(-)
 create mode 100644 arch/mips/kernel/trace_clock.c

index 8e26e9c..f228868 100644
@@ -8,6 +8,10 @@ obj-y		+= cpu-probe.o branch.o entry.o genex.o irq.o process.o \
 		   ptrace.o reset.o setup.o signal.o syscall.o \
 		   time.o topology.o traps.o unaligned.o watch.o
 
+ifdef CONFIG_FUNCTION_TRACER
+CFLAGS_REMOVE_trace_clock.o = -pg
+endif
+
 obj-$(CONFIG_CEVT_BCM1480)	+= cevt-bcm1480.o
 obj-$(CONFIG_CEVT_R4K_LIB)	+= cevt-r4k.o
 obj-$(CONFIG_MIPS_MT_SMTC)	+= cevt-smtc.o

@@ -24,6 +28,8 @@ obj-$(CONFIG_SYNC_R4K)		+= sync-r4k.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 obj-$(CONFIG_MODULES)		+= mips_ksyms.o module.o
 
+obj-$(CONFIG_FTRACE)		+= trace_clock.o
+
 obj-$(CONFIG_CPU_LOONGSON2)	+= r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_MIPS32)	+= r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_MIPS64)	+= r4k_fpu.o r4k_switch.o

new file mode 100644
index 0000000..0fe85ea
@@ -0,0 +1,33 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive for
+ * more details.
+ *
+ * Copyright (C) 2009 Lemote Inc. & DSLab, Lanzhou University, China
+ * Author: Wu Zhangjin <[email protected]>
+ */
+
+#include <linux/clocksource.h>
+#include <linux/sched.h>
+
+#include <asm/time.h>
+
+/*
+ * trace_clock_local(): the simplest and least coherent tracing clock.
+ *
+ * Useful for tracing that does not cross to other CPUs nor
+ * does it go through idle events.
+ */
+u64 trace_clock_local(void)
+{
+	unsigned long flags;
+	u64 clock;
+
+	raw_local_irq_save(flags);
+
+	clock = mips_timecounter_read();
+
+	raw_local_irq_restore(flags);
+
+	return clock;
+}

1.6.2.1

If -pg of gcc is enabled with CONFIG_FUNCTION_TRACER=y. a calling to _mcount will be inserted into each kernel function. so, there is a possibility to trace the kernel functions in _mcount.

This patch add the MIPS specific _mcount support for static function tracing. by deafult, ftrace_trace_function is initialized as ftrace_stub(an empty function), so, the default _mcount will introduce very little overhead. after enabling ftrace in user-space, it will jump to a real tracing function and do static function tracing for us.

And to support module tracing, we need to enable -mlong-calls for the long call from modules space to kernel space. -mlong-calls load the address of _mcount to a register and then jump to it, so, the address is allowed to be 32bit long, but without -mlong-calls, for the instruction "jal _mcount" only left 26bit for the address of _mcount, which is not enough for jumping from the module space to kernel space.

---
 arch/mips/Kconfig              |    1 +
 arch/mips/Makefile             |    4 ++
 arch/mips/include/asm/ftrace.h |   25 +++++++++++-
 arch/mips/kernel/Makefile      |    2 +
 arch/mips/kernel/mcount.S      |   89 ++++++++++++++++++++++++++++++++++++++++
 arch/mips/kernel/mips_ksyms.c  |    5 ++
 6 files changed, 125 insertions(+), 1 deletions(-)
 create mode 100644 arch/mips/kernel/mcount.S

index 03bd56a..6b33e88 100644
@@ -4,6 +4,7 @@ config MIPS
 	select HAVE_IDE
 	select HAVE_OPROFILE
 	select HAVE_ARCH_KGDB
+	select HAVE_FUNCTION_TRACER
 	# Horrible source of confusion.  Die, die, die ...
 	select EMBEDDED
 	select RTC_LIB if !LEMOTE_FULOONG2E

index 77f5021..041deca 100644
@@ -48,7 +48,11 @@ ifneq ($(SUBARCH),$(ARCH))
   endif
 endif
 
+ifndef CONFIG_FUNCTION_TRACER
 cflags-y := -ffunction-sections
+else
+cflags-y := -mlong-calls
+endif
 cflags-y += $(call cc-option, -mno-check-zero-division)
 
 ifdef CONFIG_32BIT

index 40a8c17..5f8ebcf 100644
@@ -1 +1,24 @@
-/* empty */
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive for
+ * more details.
+ *
+ * Copyright (C) 2009 DSLab, Lanzhou University, China
+ * Author: Wu Zhangjin <[email protected]>
+ */
+
+#ifndef _ASM_MIPS_FTRACE_H
+#define _ASM_MIPS_FTRACE_H
+
+#ifdef CONFIG_FUNCTION_TRACER
+
+#define MCOUNT_ADDR ((unsigned long)(_mcount))
+#define MCOUNT_INSN_SIZE 4		/* sizeof mcount call */
+
+#ifndef __ASSEMBLY__
+extern void _mcount(void);
+#define mcount _mcount
+
+#endif /* __ASSEMBLY__ */
+#endif /* CONFIG_FUNCTION_TRACER */
+#endif /* _ASM_MIPS_FTRACE_H */

index f228868..38e704a 100644
@@ -10,6 +10,7 @@ obj-y		+= cpu-probe.o branch.o entry.o genex.o irq.o process.o \
 
 ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_trace_clock.o = -pg
+CFLAGS_REMOVE_early_printk.o = -pg
 endif
 
 obj-$(CONFIG_CEVT_BCM1480)	+= cevt-bcm1480.o

@@ -29,6 +30,7 @@ obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 obj-$(CONFIG_MODULES)		+= mips_ksyms.o module.o
 
 obj-$(CONFIG_FTRACE)		+= trace_clock.o
+obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o
 
 obj-$(CONFIG_CPU_LOONGSON2)	+= r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_MIPS32)	+= r4k_fpu.o r4k_switch.o

index 225755d..1d04807 100644
@@ -13,6 +13,7 @@
 #include <asm/checksum.h>
 #include <asm/pgtable.h>
 #include <asm/uaccess.h>
+#include <asm/ftrace.h>
 
 extern void *__bzero(void *__s, size_t __count);
 extern long __strncpy_from_user_nocheck_asm(char *__to,

@@ -51,3 +52,7 @@ EXPORT_SYMBOL(csum_partial_copy_nocheck);
 EXPORT_SYMBOL(__csum_partial_copy_user);
 
 EXPORT_SYMBOL(invalid_pte_table);
+#ifdef CONFIG_FUNCTION_TRACER
+/* _mcount is defined in arch/mips/kernel/mcount.S */
+EXPORT_SYMBOL(_mcount);
+#endif

1.6.2.1

There is an exisiting common ftrace_test_stop_func() in kernel/trace/ftrace.c, which is used to check the global variable ftrace_trace_stop to determine whether stop the function tracing.

This patch implepment the MIPS specific one to speedup the procedure.

Thanks goes to Zhang Le for Cleaning it up.

---
 arch/mips/Kconfig         |    1 +
 arch/mips/kernel/mcount.S |    4 ++++
 2 files changed, 5 insertions(+), 0 deletions(-)

index 6b33e88..a9bd992 100644
@@ -5,6 +5,7 @@ config MIPS
 	select HAVE_OPROFILE
 	select HAVE_ARCH_KGDB
 	select HAVE_FUNCTION_TRACER
+	select HAVE_FUNCTION_TRACE_MCOUNT_TEST
 	# Horrible source of confusion.  Die, die, die ...
 	select EMBEDDED
 	select RTC_LIB if !LEMOTE_FULOONG2E

index 0c39bc8..5dfaca8 100644
@@ -64,6 +64,10 @@
 	.endm
 
 NESTED(_mcount, PT_SIZE, ra)
+	lw	t0, function_trace_stop
+	bnez	t0, ftrace_stub
+	nop
+
 	PTR_LA	t0, ftrace_stub
 	PTR_L	t1, ftrace_trace_function /* Prepare t1 for (1) */
 	bne	t0, t1, static_trace

1.6.2.1

MIPS and some other architectures need this argument to handle big/little endian respectively.

---
 scripts/Makefile.build  |    1 +
 scripts/recordmcount.pl |    6 +++---
 2 files changed, 4 insertions(+), 3 deletions(-)

index 341b589..0b94d2f 100644
@@ -207,6 +207,7 @@ endif
 
 ifdef CONFIG_FTRACE_MCOUNT_RECORD
 cmd_record_mcount = set -e ; perl $(srctree)/scripts/recordmcount.pl "$(ARCH)" \
+	"$(if $(CONFIG_CPU_BIG_ENDIAN),big,little)" \
 	"$(if $(CONFIG_64BIT),64,32)" \
 	"$(OBJDUMP)" "$(OBJCOPY)" "$(CC)" "$(LD)" "$(NM)" "$(RM)" "$(MV)" \
 	"$(if $(part-of-module),1,0)" "$(@)";

index 090d300..daee038 100755
@@ -99,13 +99,13 @@ $P =~ s@.*/@@g;
 
 my $V = '0.1';
 
-if ($#ARGV < 7) {
-	print "usage: $P arch bits objdump objcopy cc ld nm rm mv is_module inputfile\n";
+if ($#ARGV < 8) {
+	print "usage: $P arch endian bits objdump objcopy cc ld nm rm mv is_module inputfile\n";
 	print "version: $V\n";
 	exit(1);
 }
 
-my ($arch, $bits, $objdump, $objcopy, $cc,
+my ($arch, $endian, $bits, $objdump, $objcopy, $cc,
     $ld, $nm, $rm, $mv, $is_module, $inputfile) = @ARGV;
 
 # This file refers to mcount and shouldn't be ftraced, so lets' ignore it

1.6.2.1

With dynamic function tracer, by default, _mcount is defined as an "empty" function, it just return without any more action, just like the static function tracer does. When enabling it in user-space, it will jump to a real tracing function(ftrace_caller), and do some real job for us.

Differ from the static function tracer, dynamic function tracer provides two functions ftrace_make_call()/ftrace_make_nop() to enable/disable the tracing of some indicated kernel functions(set_ftrace_filter).

In the -v4 version, the implementation of this support is basically the same as X86 version does: _mcount is implemented as an empty function and ftrace_caller is implemented as a real tracing function respectively.

But in this version, to support module tracing with the help of -mlong-calls. the stuff becomes a little more complex, let's have a look at the new calling to _mcount with -mlong-calls(result of "objdump -hdr vmlinux").

	c:	3c030000 	lui	v1,0x0
			c: R_MIPS_HI16	_mcount
			c: R_MIPS_NONE	*ABS*
			c: R_MIPS_NONE	*ABS*
	10:	64630000 	daddiu	v1,v1,0
			10: R_MIPS_LO16	_mcount
			10: R_MIPS_NONE	*ABS*
			10: R_MIPS_NONE	*ABS*
	14:	03e0082d 	move	at,ra
	18:	0060f809 	jalr	v1

and the old version without -mlong-calls looks like this:

	108:   03e0082d        move    at,ra
	10c:   0c000000        jal     0 <fpcsr_pending>

10c: R_MIPS_26 _mcount
10c: R_MIPS_NONE *ABS*
10c: R_MIPS_NONE *ABS*
110: 00020021 nop

In the old version, there is only one "_mcount" string for every kernel function, so, we just need to match this one in mcount_regex of scripts/recordmcount.pl, but in the new version, we need to choose one of the two to match. Herein, I choose the first one with "R_MIPS_HI16 _mcount".

and In the old verion, without module tracing support, we just need to replace "jal _mcount" by "jal ftrace_caller" to do real tracing, and filter the tracing of some kernel functions via replacing it by a nop instruction.

but as we have described before, the instruction "jal ftrace_caller" only left 32bit length for the address of ftrace_caller, it will fail when calling from the module space. so, herein, we must replace something else.

the basic idea is loading the address of ftrace_caller to v1 via changing these two instructions:

	lui	v1,0x0
	addiu	v1,v1,0

If we want to enable the tracing, we need to replace the above instructions to:

	lui	v1, HI_16BIT_ftrace_caller
	addiu	v1, v1, LOW_16BIT_ftrace_caller

If we want to stop the tracing of the indicated kernel functions, we just need to replace the "jalr v1" to a nop instruction. but we need to replace two instructions and encode the above two instructions oursevles.

Is there a simpler solution, Yes! Here it is, in this version, we put _mcount and ftrace_caller together, which means the address of _mcount and ftrace_caller is the same:

_mcount:
ftrace_caller:

	j	ftrace_stub
	nop

	...(do real tracing here)...

ftrace_stub:
jr ra
move ra, at

By default, the kernel functions call _mcount, and then jump to ftrace_stub and return. and when we want to do real tracing, we just need to remove that "j ftrace_stub", and it will run through the two "nop" instructions and then do the real tracing job.

what about filtering job? we just need to switching the "jalr v1" and "nop" instruction.

In linux-mips64, there will be some local symbols, whose name are prefixed by $L, which need to be filtered. thanks goes to Steven for writing the mips64-specific function_regex.

In a conclusion, with RISC, things becomes easier with such a "stupid" trick, RISC is something like K.I.S.S, and also, there are lots of "simple" tricks in the whole ftrace support, thanks goes to Steven and the other folks for providing such a wonderful tracing framework!

---
 arch/mips/Kconfig              |    2 +
 arch/mips/include/asm/ftrace.h |   12 ++++++
 arch/mips/kernel/Makefile      |    3 +-
 arch/mips/kernel/ftrace.c      |   76 ++++++++++++++++++++++++++++++++++++++++
 arch/mips/kernel/mcount.S      |   29 +++++++++++++++
 scripts/recordmcount.pl        |   38 ++++++++++++++++++++
 6 files changed, 159 insertions(+), 1 deletions(-)
 create mode 100644 arch/mips/kernel/ftrace.c

index a9bd992..147fbbc 100644
@@ -6,6 +6,8 @@ config MIPS
 	select HAVE_ARCH_KGDB
 	select HAVE_FUNCTION_TRACER
 	select HAVE_FUNCTION_TRACE_MCOUNT_TEST
+	select HAVE_DYNAMIC_FTRACE
+	select HAVE_FTRACE_MCOUNT_RECORD
 	# Horrible source of confusion.  Die, die, die ...
 	select EMBEDDED
 	select RTC_LIB if !LEMOTE_FULOONG2E

index 5f8ebcf..d5771e8 100644
@@ -19,6 +19,18 @@
 extern void _mcount(void);
 #define mcount _mcount
 
+#ifdef CONFIG_DYNAMIC_FTRACE
+static inline unsigned long ftrace_call_adjust(unsigned long addr)
+{
+	/* 12 is the offset of "jalr v1" from the first loading instruction
+	 * "lui v1, HI_16BIT", please get more information from
+	 * scripts/recordmcount.pl */
+	return addr + 12;
+}
+
+struct dyn_arch_ftrace {
+};
+#endif /*  CONFIG_DYNAMIC_FTRACE */
 #endif /* __ASSEMBLY__ */
 #endif /* CONFIG_FUNCTION_TRACER */
 #endif /* _ASM_MIPS_FTRACE_H */

index 38e704a..3cda3ab 100644
@@ -10,6 +10,7 @@ obj-y		+= cpu-probe.o branch.o entry.o genex.o irq.o process.o \
 
 ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_trace_clock.o = -pg
+CFLAGS_REMOVE_ftrace.o = -pg
 CFLAGS_REMOVE_early_printk.o = -pg
 endif
 

@@ -30,7 +31,7 @@ obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 obj-$(CONFIG_MODULES)		+= mips_ksyms.o module.o
 
 obj-$(CONFIG_FTRACE)		+= trace_clock.o
-obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o
+obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o ftrace.o
 
 obj-$(CONFIG_CPU_LOONGSON2)	+= r4k_fpu.o r4k_switch.o
 obj-$(CONFIG_CPU_MIPS32)	+= r4k_fpu.o r4k_switch.o

index 5dfaca8..389be7b 100644
@@ -63,6 +63,33 @@
 	move ra, AT
 	.endm
 
+#ifdef CONFIG_DYNAMIC_FTRACE
+
+NESTED(ftrace_caller, PT_SIZE, ra)
+	.globl _mcount
+_mcount:
+	j	ftrace_stub
+	nop
+	lw	t0, function_trace_stop
+	bnez	t0, ftrace_stub
+	nop
+
+	MCOUNT_SAVE_REGS
+
+	MCOUNT_SET_ARGS
+	.globl ftrace_call
+ftrace_call:
+	nop	/* a placeholder for the call to a real tracing function */
+	nop	/* Do not touch me, I'm in the dealy slot of "jal func" */
+
+	MCOUNT_RESTORE_REGS
+	.globl ftrace_stub
+ftrace_stub:
+	RETURN_BACK
+	END(ftrace_caller)
+
+#else	/* ! CONFIG_DYNAMIC_FTRACE */
+
 NESTED(_mcount, PT_SIZE, ra)
 	lw	t0, function_trace_stop
 	bnez	t0, ftrace_stub

@@ -89,5 +116,7 @@ ftrace_stub:
 	RETURN_BACK
 	END(_mcount)
 
+#endif	/* ! CONFIG_DYNAMIC_FTRACE */
+
 	.set at
 	.set reorder

index daee038..aefe777 100755
@@ -245,6 +245,44 @@ if ($arch eq "x86_64") {
     $ld .= " -m elf64_sparc";
     $cc .= " -m64";
     $objcopy .= " -O elf64-sparc";
+
+} elsif ($arch eq "mips") {
+    # To enable module support, we need to enable the -mlong-calls option
+    # of gcc for MIPS, after using this option, we can not get the real
+    # offset of the calling to _mcount, but the offset of the first loading
+    # instruction or the second one, here we get the first one, and then,
+    # we plus it with 12 in arch/mips/kernel/asm/ftrace.h.
+    #
+    #       c:	3c030000 	lui	v1,0x0
+    #			c: R_MIPS_HI16	_mcount
+    #			c: R_MIPS_NONE	*ABS*
+    #			c: R_MIPS_NONE	*ABS*
+    #      10:	64630000 	daddiu	v1,v1,0
+    #			10: R_MIPS_LO16	_mcount
+    #			10: R_MIPS_NONE	*ABS*
+    #			10: R_MIPS_NONE	*ABS*
+    #      14:	03e0082d 	move	at,ra
+    #      18:	0060f809 	jalr	v1
+    $mcount_regex = "^\\s*([0-9a-fA-F]+): R_MIPS_HI16\\s+_mcount\$";
+    $objdump .= " -Melf-trad".$endian."mips ";
+
+    if ($endian eq "big") {
+	    $endian = " -EB ";
+	    $ld .= " -melf".$bits."btsmip";
+    } else {
+	    $endian = " -EL ";
+	    $ld .= " -melf".$bits."ltsmip";
+    }
+
+    $cc .= " -mno-abicalls -fno-pic -mabi=" . $bits . $endian;
+    $ld .= $endian;
+
+    if ($bits == 64) {
+	    $function_regex =
+		"^([0-9a-fA-F]+)\\s+<(.|[^\$]L.*?|\$[^L].*?|[^\$][^L].*?)>:";
+	    $type = ".dword";
+    }
+
 } else {
     die "Arch $arch is not supported with CONFIG_FTRACE_MCOUNT_RECORD";
 }

1.6.2.1

We use mips_timecounter_init() to get the timestamp in MIPS, so, it's better to not trace it, otherwise, it will goto recursion(hang) when using function graph tracer.

but this patch have touched the common part in kernel/time/clocksource.c and include/linux/clocksource.h, so it is not good, perhaps the better solution is moving the whole mips_timecounter_init() implementation into arch/mips, but that will introduce source code duplication. any other solution?

---
 arch/mips/include/asm/time.h |    2 +-
 arch/mips/kernel/csrc-r4k.c  |    4 ++--
 include/linux/clocksource.h  |    2 +-
 kernel/time/clocksource.c    |    4 ++--
 4 files changed, 6 insertions(+), 6 deletions(-)

index b8af7fa..e1c660f 100644
@@ -77,7 +77,7 @@ extern int init_r4k_timecounter(void);
 extern u64 r4k_timecounter_read(void);
 #endif
 
-static inline u64 mips_timecounter_read(void)
+static inline u64 notrace mips_timecounter_read(void)
 {
 #ifdef CONFIG_CSRC_R4K
 	return r4k_timecounter_read();

index 4e7705f..0690bea 100644
@@ -42,7 +42,7 @@ static struct timecounter r4k_tc = {
 	.cc = NULL,
 };
 
-static cycle_t r4k_cc_read(const struct cyclecounter *cc)
+static cycle_t notrace r4k_cc_read(const struct cyclecounter *cc)
 {
 	return read_c0_count();
 }

@@ -66,7 +66,7 @@ int __init init_r4k_timecounter(void)
 	return 0;
 }
 
-u64 r4k_timecounter_read(void)
+u64 notrace r4k_timecounter_read(void)
 {
 	u64 clock;
 

index 83d2fbd..2a02992 100644
@@ -73,7 +73,7 @@ struct timecounter {
  * XXX - This could use some mult_lxl_ll() asm optimization. Same code
  * as in cyc2ns, but with unsigned result.
  */
-static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
+static inline u64 notrace cyclecounter_cyc2ns(const struct cyclecounter *cc,
 				      cycle_t cycles)
 {
 	u64 ret = (u64)cycles;

index 5e18c6a..9ce9d02 100644
@@ -52,7 +52,7 @@ EXPORT_SYMBOL(timecounter_init);
  * The first call to this function for a new time counter initializes
  * the time tracking and returns an undefined result.
  */
-static u64 timecounter_read_delta(struct timecounter *tc)
+static u64 notrace timecounter_read_delta(struct timecounter *tc)
 {
 	cycle_t cycle_now, cycle_delta;
 	u64 ns_offset;

@@ -72,7 +72,7 @@ static u64 timecounter_read_delta(struct timecounter *tc)
 	return ns_offset;
 }
 
-u64 timecounter_read(struct timecounter *tc)
+u64 notrace timecounter_read(struct timecounter *tc)
 {
 	u64 nsec;
 

1.6.2.1

This patch fix the following error with FUNCTION_GRAPH_TRACER=y:

kernel/built-in.o: In function `print_graph_irq':
trace_functions_graph.c:(.text+0x6dba0): undefined reference to __irqentry_text_start' trace_functions_graph.c:(.text+0x6dba8): undefined reference to __irqentry_text_start' trace_functions_graph.c:(.text+0x6dbd0): undefined reference to __irqentry_text_end' trace_functions_graph.c:(.text+0x6dbd4): undefined reference to __irqentry_text_end'

(This patch is need to support function graph tracer of MIPS)

---
 arch/mips/kernel/vmlinux.lds.S |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

index 162b299..f25df73 100644
@@ -46,6 +46,7 @@ SECTIONS
 		SCHED_TEXT
 		LOCK_TEXT
 		KPROBES_TEXT
+		IRQENTRY_TEXT
 		*(.text.*)
 		*(.fixup)
 		*(.gnu.warning)

1.6.2.1

The implementation of function graph tracer for MIPS is a little different from X86.

in MIPS, gcc(with -pg) only transfer the caller's return address(at) and the _mcount's return address(ra) to us.

move at, ra
jal _mcount

if the function is a leaf, it will no save the return address(ra):

ffffffff80101298 <au1k_wait>:

ffffffff80101298:       67bdfff0        daddiu  sp,sp,-16
ffffffff8010129c:       ffbe0008        sd      s8,8(sp)
ffffffff801012a0:       03a0f02d        move    s8,sp
ffffffff801012a4:       03e0082d        move    at,ra
ffffffff801012a8:       0c042930        jal     ffffffff8010a4c0 <_mcount>
ffffffff801012ac:       00020021        nop

so, we can hijack it directly in _mcount, but if the function is non-leaf, the return address is saved in the stack.

ffffffff80133030 <copy_process>:

ffffffff80133030:       67bdff50        daddiu  sp,sp,-176
ffffffff80133034:       ffbe00a0        sd      s8,160(sp)
ffffffff80133038:       03a0f02d        move    s8,sp
ffffffff8013303c:       ffbf00a8        sd      ra,168(sp)
ffffffff80133040:       ffb70098        sd      s7,152(sp)
ffffffff80133044:       ffb60090        sd      s6,144(sp)
ffffffff80133048:       ffb50088        sd      s5,136(sp)
ffffffff8013304c:       ffb40080        sd      s4,128(sp)
ffffffff80133050:       ffb30078        sd      s3,120(sp)
ffffffff80133054:       ffb20070        sd      s2,112(sp)
ffffffff80133058:       ffb10068        sd      s1,104(sp)
ffffffff8013305c:       ffb00060        sd      s0,96(sp)
ffffffff80133060:       03e0082d        move    at,ra
ffffffff80133064:       0c042930        jal     ffffffff8010a4c0 <_mcount>
ffffffff80133068:       00020021        nop

but we can not get the exact stack address(which saved ra) directly in _mcount, we need to search the content of at register in the stack space or search the "s{d,w} ra, offset(sp)" instruction in the text. 'Cause we can not prove there is only a match in the stack space, so, we search the text instead.

as we can see, if the first instruction above "move at, ra" is "move s8(fp), sp"(only available with -fno-omit-frame-pointer which is enabled by CONFIG_FRAME_POINTER), it is a leaf function, so we hijack the at register directly via putting &return_to_handler into it, otherwise, we search the "s{d,w} ra, offset(sp)" instruction to get the stack offset, and then the stack address. we use the above copy_process() as an example, we at last find "ffbf00a8", 0xa8 is the stack offset, we plus it with s8(fp), that is the stack address, we hijack the content via writing the &return_to_handler in.

(As pajko <[email protected]> recommend, if we enable
PROFILE_BEFORE_PROLOGUE in gcc/config/mips/mips.h, there will be no difference between non-leaf and leaf function, we hope PROFILE_BEFORE_PROLOGUE will be enabled by default in the future version of gcc, so, we can remove ftrace_get_parent_addr() directly. )

---
 arch/mips/Kconfig         |    1 +
 arch/mips/kernel/ftrace.c |   93 +++++++++++++++++++++++++++++++++++++++++++++
 arch/mips/kernel/mcount.S |   47 ++++++++++++++++++++++-
 3 files changed, 140 insertions(+), 1 deletions(-)

index 147fbbc..de690fd 100644
@@ -8,6 +8,7 @@ config MIPS
 	select HAVE_FUNCTION_TRACE_MCOUNT_TEST
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_FTRACE_MCOUNT_RECORD
+	select HAVE_FUNCTION_GRAPH_TRACER
 	# Horrible source of confusion.  Die, die, die ...
 	select EMBEDDED
 	select RTC_LIB if !LEMOTE_FULOONG2E

1.6.2.1

This patch make function graph tracer work with dynamic function tracer.

To share the source code of dynamic function tracer(MCOUNT_SAVE_REGS), and avoid restoring the whole saved registers, we need to restore the ra register from the stack.

---
 arch/mips/kernel/ftrace.c |   21 +++++++++++++++++++++
 arch/mips/kernel/mcount.S |   14 ++++++++++++--
 2 files changed, 33 insertions(+), 2 deletions(-)

index 4cf11f5..1c02e65 100644
@@ -79,6 +79,27 @@ int __init ftrace_dyn_arch_init(void *data)
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 
+#ifdef CONFIG_DYNAMIC_FTRACE
+
+extern void ftrace_graph_call(void);
+#define JMP	0x08000000	/* jump to target directly */
+#define CALL_FTRACE_GRAPH_CALLER \
+	jump_insn_encode(JMP, (unsigned long)(&ftrace_graph_caller))
+#define FTRACE_GRAPH_CALL_IP	((unsigned long)(&ftrace_graph_call))
+
+int ftrace_enable_ftrace_graph_caller(void)
+{
+	return ftrace_modify_code(FTRACE_GRAPH_CALL_IP,
+				  CALL_FTRACE_GRAPH_CALLER);
+}
+
+int ftrace_disable_ftrace_graph_caller(void)
+{
+	return ftrace_modify_code(FTRACE_GRAPH_CALL_IP, ftrace_nop);
+}
+
+#endif				/* !CONFIG_DYNAMIC_FTRACE */
+
 #define S_RA    (0x2fbf << 16)	/* 32bit: afbf, 64bit: ffbf */
 #define MOV_FP_SP       0x03a0f021	/* 32bit: 0x03a0f021, 64bit: 0x03a0f02d */
 #define STACK_OFFSET_MASK	0xfff	/* stack offset range: 0 ~ PT_SIZE(304) */

index a9ba888..260719d 100644
@@ -82,6 +82,13 @@ ftrace_call:
 	nop	/* a placeholder for the call to a real tracing function */
 	nop	/* Do not touch me, I'm in the dealy slot of "jal func" */
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	.globl ftrace_graph_call
+ftrace_graph_call:
+	nop
+	nop
+#endif
+
 	MCOUNT_RESTORE_REGS
 	.globl ftrace_stub
 ftrace_stub:

@@ -129,10 +136,13 @@ ftrace_stub:
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 
 NESTED(ftrace_graph_caller, PT_SIZE, ra)
+#ifdef CONFIG_DYNAMIC_FTRACE
+	PTR_L	a1, PT_R31(sp)	/* load the original ra from the stack */
+#else
 	MCOUNT_SAVE_REGS
-
-	PTR_LA	a0, PT_R1(sp)	/* arg1: &AT -> a0 */
 	move	a1, ra		/* arg2: next ip, selfaddr */
+#endif
+	PTR_LA	a0, PT_R1(sp)	/* arg1: &AT -> a0 */
 	PTR_SUBU a1, MCOUNT_INSN_SIZE
 	move	a2, fp		/* arg3: frame pointer */
 	jal	prepare_ftrace_return

1.6.2.1

Hi,

On Mon, 2009-10-26 at 11:13 -0400, Steven Rostedt wrote:
[...]

Seems that exception handling in an asm is really "awful"(un-readable) and the above ip is what we have got from the ftrace_graph_caller, it should be okay. but if exception handling is necessary, I will send a new patch for the places(including the following one) which need it.

Okay, let's look at this with -mlong-calls,

leaf function:

ffffffff80243cd8 <oops_may_print>:

ffffffff80243cd8:       67bdfff0        daddiu  sp,sp,-16
ffffffff80243cdc:       ffbe0008        sd      s8,8(sp)
ffffffff80243ce0:       03a0f02d        move    s8,sp
ffffffff80243ce4:       3c038021        lui     v1,0x8021
ffffffff80243ce8:       646316b0        daddiu  v1,v1,5808
ffffffff80243cec:       03e0082d        move    at,ra
ffffffff80243cf0:       0060f809        jalr    v1
ffffffff80243cf4:       00020021        nop

non-leaf function:

ffffffff802414c0 <copy_process>:

ffffffff802414c0:       67bdff40        daddiu  sp,sp,-192
ffffffff802414c4:       ffbe00b0        sd      s8,176(sp)
ffffffff802414c8:       03a0f02d        move    s8,sp
ffffffff802414cc:       ffbf00b8        sd      ra,184(sp)
ffffffff802414d0:       ffb700a8        sd      s7,168(sp)
ffffffff802414d4:       ffb600a0        sd      s6,160(sp)
ffffffff802414d8:       ffb50098        sd      s5,152(sp)
ffffffff802414dc:       ffb40090        sd      s4,144(sp)
ffffffff802414e0:       ffb30088        sd      s3,136(sp)
ffffffff802414e4:       ffb20080        sd      s2,128(sp)
ffffffff802414e8:       ffb10078        sd      s1,120(sp)
ffffffff802414ec:       ffb00070        sd      s0,112(sp)
ffffffff802414f0:       3c038021        lui     v1,0x8021
ffffffff802414f4:       646316b0        daddiu  v1,v1,5808
ffffffff802414f8:       03e0082d        move    at,ra
ffffffff802414fc:       0060f809        jalr    v1
ffffffff80241500:       00020021        nop

ip -->

At first, we move to "lui, v1, HI_16BIT_OF_MCOUNT", ip = ip - 12(not 8 when without -mlong-calls, i need to update the source code later).

and then, we check whether there is a "Store" instruction, if it's not a "Store" instruction, the function should be a leaf? otherwise, we continue the searching until finding the "s{d,w} ra, offset(sp)" instruction, get the offset, calculate the stack address, and finish?

So, we just need to replace this:

		if ((code & MOV_FP_SP) == MOV_FP_SP)
			return parent_addr;	

by

#define S_INSN (0xafb0 << 16)

		if ((code & S_INSN) != S_INSN)
			return parent_addr;

We need to really stop before ftrace_push_return_trace to avoid messing with the stack :-) but if we have stopped the tracer, is it important to mess with the stack or not?

Regards,
Wu Zhangjin

Yeah, and probably not as important in the mips world, as it is used more with embedded devices than desktops. We must always take the "paranoid" approach for tracing. At least in PPC and x86, we assume everything is broken ;-) And we want to be as robust as possible. If something goes wrong, we want to detect it ASAP and report it. And keep the system from crashing.

At least with MIPS we don't need to worry about crashing Linus's desktop. With is the #1 priority we have on x86 ... "Don't crash Linus's desktop!".

If Linus sees a warning, he'll bitch at us. If we crash his box, and he was to lose any information, he'll strip out our code!

Yes with -mlong-calls you must jump pass the setting up of the jalr.

Note, you are commenting different than your code. Your code matches more what I want than your comments ;-) You keep saying "if the instruction just after the jump to mcount (and preparation for) is not a store than it is a leaf", where I'm saying (and the code matches), search above the jump to mcount and if we don't find the store of ra, then it is a leaf.

I would be even more paranoid, and make sure each of those stores, store into sp.

The ftrace_push_return_trace does not test if the trace stopped, that is expected to be done by the caller. If you mess with the stack set up, you will crash the box. Remember, before the failure, you could have already replaced return jumps. Those will still be falling back to the return_to_handler. If you mess with the stack, but don't update the return, the other returns will be out of sync and call the wrong return address.

-- Steve

Hi,

[...]

Okay, a new patch for all of the exception handling will go into -v7.

get it :-)

(I need to be more paranoid too, otherwise, Steven will not accept my patches!)

[...]

As you can see, after stopping the function graph tracer(here the function is non-leaf) with ftrace_graph_stop() in ftrace_get_parent_addr(), I return the old parent_addr, this is only the stack address in the stack space of ftrace_graph_caller, which means that, I never touch the real stack address of the non-leaf function, and it will not trap into the return_to_handler hooker 'Cause the non-leaf function will load it's own normal return address from it's own stack, and then just return back normally.
-- This is another trick :-)

Regards,
Wu Zhangjin

Sure I would accept them. I don't know of any MIPS boxes that Linus runs. So I'm not afraid of crashing his boxes with these patches ;-)

But then you should not be calling the push function. That will still push onto the graph stack.

The function graph tracer keeps a separate return stack (current->ret_stack). This is what holds the return addresses.

(normal operation)

func1
jalr _mcount

push ra onto ret_stack
replace ra with return_to_handler

jr ra --> return_to_handler

return_to_handler

pop ret_stack, have original ra
jr original_ra

Now what happens if we fail a call but still push to ret_stack

func1
jalr _mcount

(success)
push ra onto ret_stack
replace ra with return_to_handler

jalr func2

func2
jalr _mcount

(failed)
push ra onto ret_stack <<-- this is wrong! keep original ra

jr ra << does not call tracer function!!!

jr ra << goes to return_to_handler

return_to_handler

pop ra from ret_stack <<--- has func2 ra not func1 ra!!

jr func1_ra

**** CRASH ****

Make sense?

-- Steve

2009/10/25 Wu Zhangjin <[email protected]>:

If you want to enjoy this section, you'd need to tag the mips irq entry functions with "__irq_entry" :)

I guess there is a do_IRQ() in mips that is waiting for that (and probably some others).
The effect is that interrupt areas are cut with a pair of arrows in the trace, so that you more easily spot interrupts in the traces

May be I missed this part in another patch in this series though...

Hi,

ooh, Sorry, only this patch added(I stopped after fixing the compiling errors, no more check! so lazy a guy!).

Just checked the source code of MIPS, the do_IRQ() is defined as a macro, so, I must move the macro to a C file, and also, there is a irq_enter...irq_exit block in a "big" function, I need to split it out.

[...]
/*
* do_IRQ handles all normal device IRQ's (the special
* SMP cross-CPU interrupts have their own specific
* handlers).
*
* Ideally there should be away to get this into kernel/irq/handle.c to
* avoid the overhead of a call for just a tiny function ... */
#define do_IRQ(irq)
\
do {

\
        irq_enter();
\
        __DO_IRQ_SMTC_HOOK(irq);
\
        generic_handle_irq(irq);
\
        irq_exit();

\
} while (0)
[...]

But The comment told us: do not make this tiny function be a standalone function, so???

the same to do_IRQ_no_affinity.

and, about the following function, I need to split the irq_enter()...irq_exit() block out.

void ipi_decode(struct smtc_ipi *pipi)

{
	[...]
        switch (type_copy) {
        case SMTC_CLOCK_TICK:
                irq_enter();
                kstat_incr_irqs_this_cpu(irq, irq_to_desc(irq));
                cd = &per_cpu(mips_clockevent_device, cpu);
                cd->event_handler(cd);
                irq_exit();
                break;

        case LINUX_SMP_IPI:
                switch ((int)arg_copy) {
                case SMP_RESCHEDULE_YOURSELF:
                        ipi_resched_interrupt();
                        break;
                case SMP_CALL_FUNCTION:
                        ipi_call_interrupt();
                        break;
	[...]

Regards,
Wu Zhangjin

2009/10/26 Wu Zhangjin <[email protected]>:

I can't check that currently. But may be the caller of this m

2009/10/27 Frederic Weisbecker <[email protected]>:

Sorry, my message has been sent in the middle. I'm dealing with a strange keyboard where
I am (and also with my strange hands).

So, may be the caller of this macro can take the irqentry tag?

Oh right, this one is more tricky. Well, if that's important for someone, we can deal with that later.

(Add Frederic Weisbecker <[email protected]> to the CC list)

The implementation of function graph tracer for MIPS is a little different from X86.

in MIPS, gcc(with -pg) only transfer the caller's return address(at) and the _mcount's return address(ra) to us.

move at, ra
jal _mcount

if the function is a leaf, it will no save the return address(ra):

ffffffff80101298 <au1k_wait>:

ffffffff80101298:       67bdfff0        daddiu  sp,sp,-16
ffffffff8010129c:       ffbe0008        sd      s8,8(sp)
ffffffff801012a0:       03a0f02d        move    s8,sp
ffffffff801012a4:       03e0082d        move    at,ra
ffffffff801012a8:       0c042930        jal     ffffffff8010a4c0 <_mcount>
ffffffff801012ac:       00020021        nop

so, we can hijack it directly in _mcount, but if the function is non-leaf, the return address is saved in the stack.

ffffffff80133030 <copy_process>:

ffffffff80133030:       67bdff50        daddiu  sp,sp,-176
ffffffff80133034:       ffbe00a0        sd      s8,160(sp)
ffffffff80133038:       03a0f02d        move    s8,sp
ffffffff8013303c:       ffbf00a8        sd      ra,168(sp)
ffffffff80133040:       ffb70098        sd      s7,152(sp)
ffffffff80133044:       ffb60090        sd      s6,144(sp)
ffffffff80133048:       ffb50088        sd      s5,136(sp)
ffffffff8013304c:       ffb40080        sd      s4,128(sp)
ffffffff80133050:       ffb30078        sd      s3,120(sp)
ffffffff80133054:       ffb20070        sd      s2,112(sp)
ffffffff80133058:       ffb10068        sd      s1,104(sp)
ffffffff8013305c:       ffb00060        sd      s0,96(sp)
ffffffff80133060:       03e0082d        move    at,ra
ffffffff80133064:       0c042930        jal     ffffffff8010a4c0 <_mcount>
ffffffff80133068:       00020021        nop

but we can not get the exact stack address(which saved ra) directly in _mcount, we need to search the content of at register in the stack space or search the "s{d,w} ra, offset(sp)" instruction in the text. 'Cause we can not prove there is only a match in the stack space, so, we search the text instead.

as we can see, if the first instruction above "move at, ra" is "move s8(fp), sp"(only available with -fno-omit-frame-pointer which is enabled by CONFIG_FRAME_POINTER), it is a leaf function, so we hijack the at register directly via putting &return_to_handler into it, otherwise, we search the "s{d,w} ra, offset(sp)" instruction to get the stack offset, and then the stack address. we use the above copy_process() as an example, we at last find "ffbf00a8", 0xa8 is the stack offset, we plus it with s8(fp), that is the stack address, we hijack the content via writing the &return_to_handler in.

(As pajko <[email protected]> recommend, if we enable
PROFILE_BEFORE_PROLOGUE in gcc/config/mips/mips.h, there will be no difference between non-leaf and leaf function, we hope PROFILE_BEFORE_PROLOGUE will be enabled by default in the future version of gcc, so, we can remove ftrace_get_parent_addr() directly. )

---
 arch/mips/Kconfig         |    1 +
 arch/mips/kernel/ftrace.c |   93 +++++++++++++++++++++++++++++++++++++++++++++
 arch/mips/kernel/mcount.S |   47 ++++++++++++++++++++++-
 3 files changed, 140 insertions(+), 1 deletions(-)

index 147fbbc..de690fd 100644
@@ -8,6 +8,7 @@ config MIPS
 	select HAVE_FUNCTION_TRACE_MCOUNT_TEST
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_FTRACE_MCOUNT_RECORD
+	select HAVE_FUNCTION_GRAPH_TRACER
 	# Horrible source of confusion.  Die, die, die ...
 	select EMBEDDED
 	select RTC_LIB if !LEMOTE_FULOONG2E

1.6.2.1

2009/10/25 Wu Zhangjin <[email protected]>:

Okay, Will remove it.

Will remove it too.

What about this: __arch_notrace? If the arch need this, define it, otherwise, ignore it! if only graph tracer need it, define it in "#ifdef CONFIG_FUNCTION_GRAPH_TRACER ... #endif".

b/arch/mips/include/asm/ftrace.h
index d5771e8..eeacd51 100644

@@ -31,6 +31,11 @@ static inline unsigned long

ftrace_call_adjust(unsigned long addr)
struct dyn_arch_ftrace {
};
#endif /* CONFIG_DYNAMIC_FTRACE */
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+#define __arch_notrace
+#endif
+
#endif /* __ASSEMBLY__ */
#endif /* CONFIG_FUNCTION_TRACER */
#endif /* _ASM_MIPS_FTRACE_H */

[...]

index 0b4f97d..959c8b3 100644
@@ -511,4 +511,12 @@ static inline void trace_hw_branch_oops(void) {}
 
 #endif /* CONFIG_HW_BRANCH_TRACER */
 
+/* arch specific notrace */
+#ifndef __arch_notrace
+#define __arch_notrace
+#else
+#undef __arch_notrace
+#define __arch_notrace notrace
+#endif
+
 #endif /* _LINUX_FTRACE_H */

[...]

index 9ce9d02..91acdf7 100644
@@ -30,6 +30,7 @@
 #include <linux/sched.h> /* for spin_unlock_irq() using preempt_count()

m68k */
#include <linux/tick.h>
#include <linux/kthread.h>
+#include <linux/ftrace.h>

void timecounter_init(struct timecounter *tc,
const struct cyclecounter *cc,
@@ -52,7 +53,7 @@ EXPORT_SYMBOL(timecounter_init);
* The first call to this function for a new time counter initializes
* the time tracking and returns an undefined result.
*/
-static u64 notrace timecounter_read_delta(struct timecounter *tc) +static u64 __arch_notrace timecounter_read_delta(struct timecounter *tc)

 {
        cycle_t cycle_now, cycle_delta;
        u64 ns_offset;
@@ -72,7 +73,7 @@ static u64 notrace timecounter_read_delta(struct
timecounter *tc)
        return ns_offset;

}

-u64 notrace timecounter_read(struct timecounter *tc) +u64 __arch_notrace timecounter_read(struct timecounter *tc)

 {
        u64 nsec;

Regards,
Wu Zhangjin

Oops, a word has escaped from my above sentence. I wanted to say:

"You don't need to set notrace to inline functions" :)

The problem is that archs may want to disable tracing on different places.
For example mips wants to disable tracing in timecounter_read_delta, but another arch may want to disable tracing somewhere else.

We'll then have several unrelated __arch_notrace. One that is relevant for mips, another that is relevant for arch_foo, but all of them will apply for all arch that have defined a __arch_notrace.

It's true that __mips_notrace is not very elegant as it looks like a specific arch annotation intruder.

But at least that gives us a per arch filter granularity.

If only static ftrace could disappear, we could keep only dynamic ftrace and we would then be able to filter dynamically. But I'm not sure it's a good idea for archs integration.

Hi,

On Mon, 2009-11-02 at 22:43 +0100, Frederic Weisbecker wrote:
[...]

Thanks ;)

I have got your meaning at that time, and have removed them with inline functions.

Got it.

Thanks & Regards,
Wu Zhangjin

Hi,

On Mon, 2009-11-02 at 22:43 +0100, Frederic Weisbecker wrote:
[...]

I think if we use something like __mips_notrace here, we may get lots of __ARCH_notraces here too, 'Cause some other platforms(at least, as I know, Microblaze will do it too) may also need to add one here, it will become:

__mips_notrace __ARCH1_notrace __ARCH2_notrace .... foo() {...}

A little ugly ;)

and If a new platform need it's __ARCH_notrace, they need to touch the common part of ftrace, more side-effects!

but with __arch_notrace, the archs only need to touch it's own part, Although there is a side-effect as you mentioned above ;)

So, what should we do?

Regards,
Wu Zhangjin

Yeah :)
I thought Mips would be the only one to do that.

Why not __time ?
As it's normal that such few functions that are used to read the timecounter have fair chances to be __no_trace on archs like MIPS. Interested archs would just need to override a default stub __time.

Good pointer, will apply it ;)

Regards,
Wu Zhangjin

I agree, that is ugly.

Just do it in the Makefile. We can add __arch_notrace, and then in the Makefile define it with the arch.

ifeq ($(ARCH), MIPS)
CFLAGS_foo.o = -D__arch_notrace=notrace
endif

And we can simply define __arch_notrace in a header:

#ifndef __arch_notrace

# define __arch_notrace
#endif

I much rather uglify the Makefile than the code.

-- Steve

Hi,

On Mon, 2009-11-09 at 07:54 -0500, Steven Rostedt wrote:
[...]

Seems can not totally avoid the problem mentioned by Frederic, that is if there are two many functions in the file, and different platforms care about different functions ;)

what about Frederic's __time, just replace that __arch_notrace by __time_notrace, and only consider the time relative functions currently? Seems this will really make the stuff simpler.

Regards,
Wu Zhangjin

Some patches touch core tracing code, and some are arch specific. Now the question is how do we go. I prefer that we go the path of the tracing tree (easier for me to test). But every patch that touches MIPS arch, needs an Acked-by from the MIPS maintainer. Which I see is Ralf (on the Cc of this patch set.)

Thanks,

-- Steve

Hi,

On Mon, 2009-10-26 at 10:01 -0400, Steven Rostedt wrote:
[...]

Just coped with the feedbacks from Frederic Weisbecker.

I will rebase the whole patches to your git repo(the following one?) and send them out as the -v6 revision:

git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-2.6-trace.git tip/tracing/core

Looking forward to the feedback from Ralf, Seems he is a little busy. and also looking forward to the testing result from the other MIPS developers, so, we can ensure ftrace for MIPS really function!

Welcome to clone this branch and test it:

git://dev.lemote.com/rt4ls.git linux-mips/dev/ftrace-upstream

And this document will tell you how to play with it:
Documentation/trace/ftrace.txt

Thanks & Regards,
Wu Zhangjin

Actually, I always base off of tip itself. Don't use mine. Use this one:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git tracing/core

Then we will stay in sync.

I already have your repo as a remote ;-)

Did you add to it?

Thanks,

-- Steve

Hi,

Okay, pulling it...

Thanks :-)

I have never touched the file, just hope some newbies(like me) can follow it and help to test it :-)

Thanks & Regards,
Wu Zhangjin

2009/10/25 Wu Zhangjin <[email protected]>:

I can't find this one in the series. Did you forget it or am I somehow missing it?

Thanks.