[PATCH 0/3] ftrace: handle kernel code remove

[PATCH 0/3] ftrace: handle kernel code remove

[Steven Rostedt]

The dynamic ftrace feature keeps a table of all the places that call
mcount to either disable them (replacing them with nops) or to enable
them (calling some trace function).

This table of functions is also displayed to the user interface to let
users enable or disable specific functions. This allows users to only
trace some functions within the kernel.

When a module or init sections are removed, the pointers to their locations
still exist in this table.  To protect against faults and writing over
other text, fault handling and code comparing is done. When the code is
update, the code being replaced is calculated and compared to the actual
text that is being replaced, if the code does not match what is expected
to be there, the change is not made.

There is a very small chance that the wrong text (or perhaps a data section)
could match the call to mcount and an inappropriate modification could
be made.

This patch series adds ftrace_release, to allow a module to remove the
pointers to the mcount callers in the module from this table.

Also, __init has "notrace" added to it so that text in the init section
are not traced. The trace currently can not be enabled until after
init anyway, so this should not be a problem.

-- Steve

[PATCH 1/3] ftrace: do not show freed records in available_filter_functions

[Steven Rostedt]

[-- Attachment #1: ftrace-dont-print-freed-recs.patch --]
[-- Type: text/plain, Size: 1243 bytes --]

Seems that freed records can appear in the available_filter_functions list.
This patch fixes that.

CC: Abhishek Sagar <sagar.abhishek@gmail.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
 kernel/trace/ftrace.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

Index: linux-tip.git/kernel/trace/ftrace.c
===================================================================
--- linux-tip.git.orig/kernel/trace/ftrace.c	2008-08-14 22:43:01.000000000 -0400
+++ linux-tip.git/kernel/trace/ftrace.c	2008-08-14 22:43:03.000000000 -0400
@@ -879,15 +879,13 @@ t_next(struct seq_file *m, void *v, loff
 		}
 	} else {
 		rec = &iter->pg->records[iter->idx++];
-		if ((!(iter->flags & FTRACE_ITER_FAILURES) &&
+		if ((rec->flags & FTRACE_FL_FREE) ||
+
+		    (!(iter->flags & FTRACE_ITER_FAILURES) &&
 		     (rec->flags & FTRACE_FL_FAILED)) ||
 
 		    ((iter->flags & FTRACE_ITER_FAILURES) &&
-		     (!(rec->flags & FTRACE_FL_FAILED) ||
-		      (rec->flags & FTRACE_FL_FREE))) ||
-
-		    ((iter->flags & FTRACE_ITER_FILTER) &&
-		     !(rec->flags & FTRACE_FL_FILTER)) ||
+		     !(rec->flags & FTRACE_FL_FAILED)) ||
 
 		    ((iter->flags & FTRACE_ITER_NOTRACE) &&
 		     !(rec->flags & FTRACE_FL_NOTRACE))) {

-- 

[PATCH 2/3] ftrace: move notrace to compiler.h

[Steven Rostedt]

[-- Attachment #1: ftrace-move-notrace-to-compiler.patch --]
[-- Type: text/plain, Size: 1308 bytes --]

The notrace define belongs in compiler.h so that it can be used in
init.h

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
 include/linux/compiler.h |    2 ++
 include/linux/linkage.h  |    2 --
 2 files changed, 2 insertions(+), 2 deletions(-)

Index: linux-tip.git/include/linux/compiler.h
===================================================================
--- linux-tip.git.orig/include/linux/compiler.h	2008-08-14 22:42:59.000000000 -0400
+++ linux-tip.git/include/linux/compiler.h	2008-08-14 22:43:16.000000000 -0400
@@ -44,6 +44,8 @@ extern void __chk_io_ptr(const volatile 
 # error Sorry, your compiler is too old/not recognized.
 #endif
 
+#define notrace __attribute__((no_instrument_function))
+
 /* Intel compiler defines __GNUC__. So we will overwrite implementations
  * coming from above header files here
  */
Index: linux-tip.git/include/linux/linkage.h
===================================================================
--- linux-tip.git.orig/include/linux/linkage.h	2008-08-14 22:42:59.000000000 -0400
+++ linux-tip.git/include/linux/linkage.h	2008-08-14 22:43:16.000000000 -0400
@@ -4,8 +4,6 @@
 #include <linux/compiler.h>
 #include <asm/linkage.h>
 
-#define notrace __attribute__((no_instrument_function))
-
 #ifdef __cplusplus
 #define CPP_ASMLINKAGE extern "C"
 #else

-- 

[PATCH 3/3] ftrace: remove old pointers to mcount

[Steven Rostedt]

[-- Attachment #1: ftrace-release-mcount-recs-by-addr.patch --]
[-- Type: text/plain, Size: 5776 bytes --]

When a mcount pointer is recorded into a table, it is used to add or
remove calls to mcount (replacing them with nops). If the code is removed
via removing a module, the pointers still exist.  At modifying the code
a check is always made to make sure the code being replaced is the code
expected. In-other-words, the code being replaced is compared to what
it is expected to be before being replaced.

There is a very small chance that the code being replaced just happens
to look like code that calls mcount (very small since the call to mcount
is relative). To remove this chance, this patch adds ftrace_release to
allow module unloading to remove the pointers to mcount within the module.

Another change for init calls is made to not trace calls marked with
__init. The tracing can not be started until after init is done anyway.

[
  Rusty, I decided to remove the if statement for you ;-)
]

CC: rusty@rustcorp.com.au
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
 include/linux/ftrace.h |    2 ++
 include/linux/init.h   |    2 +-
 kernel/module.c        |   12 ++++++++----
 kernel/trace/ftrace.c  |   32 ++++++++++++++++++++++++++++++--
 4 files changed, 41 insertions(+), 7 deletions(-)

Index: linux-tip.git/include/linux/ftrace.h
===================================================================
--- linux-tip.git.orig/include/linux/ftrace.h	2008-08-14 22:42:59.000000000 -0400
+++ linux-tip.git/include/linux/ftrace.h	2008-08-14 22:43:33.000000000 -0400
@@ -144,10 +144,12 @@ ftrace_special(unsigned long arg1, unsig
 #ifdef CONFIG_FTRACE_MCOUNT_RECORD
 extern void ftrace_init(void);
 extern void ftrace_init_module(unsigned long *start, unsigned long *end);
+extern void ftrace_release(void *start, unsigned long size);
 #else
 static inline void ftrace_init(void) { }
 static inline void
 ftrace_init_module(unsigned long *start, unsigned long *end) { }
+static inline void ftrace_release(void *start, unsigned long size) { }
 #endif
 
 #endif /* _LINUX_FTRACE_H */
Index: linux-tip.git/kernel/module.c
===================================================================
--- linux-tip.git.orig/kernel/module.c	2008-08-14 22:42:59.000000000 -0400
+++ linux-tip.git/kernel/module.c	2008-08-14 22:43:33.000000000 -0400
@@ -1432,6 +1432,9 @@ static void free_module(struct module *m
 	/* Module unload stuff */
 	module_unload_free(mod);
 
+	/* release any pointers to mcount in this module */
+	ftrace_release(mod->module_core, mod->core_size);
+
 	/* This may be NULL, but that's OK */
 	module_free(mod, mod->module_init);
 	kfree(mod->args);
@@ -1840,6 +1843,7 @@ static struct module *load_module(void _
 	struct module *mod;
 	long err = 0;
 	void *percpu = NULL, *ptr = NULL; /* Stops spurious gcc warning */
+	void *mseg;
 	struct exception_table_entry *extable;
 	mm_segment_t old_fs;
 
@@ -2191,10 +2195,9 @@ static struct module *load_module(void _
 #endif
 	}
 
-	if (mcountindex) {
-		void *mseg = (void *)sechdrs[mcountindex].sh_addr;
-		ftrace_init_module(mseg, mseg + sechdrs[mcountindex].sh_size);
-	}
+	/* sechdrs[0].sh_size is always zero */
+	mseg = (void *)sechdrs[mcountindex].sh_addr;
+	ftrace_init_module(mseg, mseg + sechdrs[mcountindex].sh_size);
 
 	err = module_finalize(hdr, sechdrs, mod);
 	if (err < 0)
@@ -2265,6 +2268,7 @@ static struct module *load_module(void _
  cleanup:
 	kobject_del(&mod->mkobj.kobj);
 	kobject_put(&mod->mkobj.kobj);
+	ftrace_release(mod->module_core, mod->core_size);
  free_unload:
 	module_unload_free(mod);
 	module_free(mod, mod->module_init);
Index: linux-tip.git/kernel/trace/ftrace.c
===================================================================
--- linux-tip.git.orig/kernel/trace/ftrace.c	2008-08-14 22:43:03.000000000 -0400
+++ linux-tip.git/kernel/trace/ftrace.c	2008-08-14 22:43:33.000000000 -0400
@@ -294,13 +294,37 @@ static inline void ftrace_del_hash(struc
 
 static void ftrace_free_rec(struct dyn_ftrace *rec)
 {
-	/* no locking, only called from kstop_machine */
-
 	rec->ip = (unsigned long)ftrace_free_records;
 	ftrace_free_records = rec;
 	rec->flags |= FTRACE_FL_FREE;
 }
 
+void ftrace_release(void *start, unsigned long size)
+{
+	struct dyn_ftrace *rec;
+	struct ftrace_page *pg;
+	unsigned long s = (unsigned long)start;
+	unsigned long e = s + size;
+	int i;
+
+	if (!start)
+		return;
+
+	/* No interrupt should call this */
+	spin_lock(&ftrace_lock);
+
+	for (pg = ftrace_pages_start; pg; pg = pg->next) {
+		for (i = 0; i < pg->index; i++) {
+			rec = &pg->records[i];
+
+			if ((rec->ip >= s) && (rec->ip < e))
+				ftrace_free_rec(rec);
+		}
+	}
+	spin_unlock(&ftrace_lock);
+
+}
+
 static struct dyn_ftrace *ftrace_alloc_dyn_node(unsigned long ip)
 {
 	struct dyn_ftrace *rec;
@@ -1534,7 +1558,9 @@ static int ftrace_convert_nops(unsigned 
 	p = start;
 	while (p < end) {
 		addr = ftrace_call_adjust(*p++);
+		spin_lock(&ftrace_lock);
 		ftrace_record_ip(addr);
+		spin_unlock(&ftrace_lock);
 		ftrace_shutdown_replenish();
 	}
 
@@ -1548,6 +1574,8 @@ static int ftrace_convert_nops(unsigned 
 
 void ftrace_init_module(unsigned long *start, unsigned long *end)
 {
+	if (start == end)
+		return;
 	ftrace_convert_nops(start, end);
 }
 
Index: linux-tip.git/include/linux/init.h
===================================================================
--- linux-tip.git.orig/include/linux/init.h	2008-08-14 22:42:59.000000000 -0400
+++ linux-tip.git/include/linux/init.h	2008-08-14 22:43:33.000000000 -0400
@@ -40,7 +40,7 @@
 
 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init		__section(.init.text) __cold
+#define __init		__section(.init.text) __cold notrace
 #define __initdata	__section(.init.data)
 #define __initconst	__section(.init.rodata)
 #define __exitdata	__section(.exit.data)

-- 

Re: [PATCH 0/3] ftrace: handle kernel code remove

[Ingo Molnar]

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

> The dynamic ftrace feature keeps a table of all the places that call 
> mcount to either disable them (replacing them with nops) or to enable 
> them (calling some trace function).
> 
> This table of functions is also displayed to the user interface to let 
> users enable or disable specific functions. This allows users to only 
> trace some functions within the kernel.
> 
> When a module or init sections are removed, the pointers to their 
> locations still exist in this table.  To protect against faults and 
> writing over other text, fault handling and code comparing is done. 
> When the code is update, the code being replaced is calculated and 
> compared to the actual text that is being replaced, if the code does 
> not match what is expected to be there, the change is not made.
> 
> There is a very small chance that the wrong text (or perhaps a data 
> section) could match the call to mcount and an inappropriate 
> modification could be made.
> 
> This patch series adds ftrace_release, to allow a module to remove the 
> pointers to the mcount callers in the module from this table.
> 
> Also, __init has "notrace" added to it so that text in the init 
> section are not traced. The trace currently can not be enabled until 
> after init anyway, so this should not be a problem.

applied to tip/tracing/ftrace - thanks Steve! I merged it into 
tip/master and started testing it.

	Ingo

Re: [PATCH 0/3] ftrace: handle kernel code remove

[Ingo Molnar]

* Ingo Molnar <mingo@elte.hu> wrote:

> applied to tip/tracing/ftrace - thanks Steve! I merged it into 
> tip/master and started testing it.

hm, massive build failures:

ld: Relocatable linking with relocations from format elf32-i386 (init/.tmp_gl_calibrate.o) to format elf64-x86-64 (init/.tmp_mx_calibrate.o) i  CC      arch/x86/mm/extable.o
objcopy: 'init/.tmp_mx_calibrate.o': No such file
rm: cannot remove `init/.tmp_mx_calibrate.o': No such file or directory
ld: Relocatable linking with relocations from format elf32-i386 (arch/x86/mm/extable.o) to format elf64-x86-64 (arch/x86/mm/.tmp_mx_extable.o) is not supported
mv: cannot stat `arch/x86/mm/.tmp_mx_extable.o': No such file or directory
ld: Relocatable linking with relocations from format elf32-i386 (arch/x86/mm/fault.o) to format elf64-x86-64 (arch/x86/mm/.tmp_mx_fault.o) is not supported

with this config:

  http://redhat.com/~mingo/misc/config-Fri_Aug_15_11_34_53_CEST_2008.bad

	Ingo

Re: [PATCH 0/3] ftrace: handle kernel code remove

[Ingo Molnar]

* Ingo Molnar <mingo@elte.hu> wrote:

> 
> * Ingo Molnar <mingo@elte.hu> wrote:
> 
> > applied to tip/tracing/ftrace - thanks Steve! I merged it into 
> > tip/master and started testing it.
> 
> hm, massive build failures:
> 
> ld: Relocatable linking with relocations from format elf32-i386 (init/.tmp_gl_calibrate.o) to format elf64-x86-64 (init/.tmp_mx_calibrate.o) i  CC      arch/x86/mm/extable.o
> objcopy: 'init/.tmp_mx_calibrate.o': No such file
> rm: cannot remove `init/.tmp_mx_calibrate.o': No such file or directory
> ld: Relocatable linking with relocations from format elf32-i386 (arch/x86/mm/extable.o) to format elf64-x86-64 (arch/x86/mm/.tmp_mx_extable.o) is not supported
> mv: cannot stat `arch/x86/mm/.tmp_mx_extable.o': No such file or directory
> ld: Relocatable linking with relocations from format elf32-i386 (arch/x86/mm/fault.o) to format elf64-x86-64 (arch/x86/mm/.tmp_mx_fault.o) is not supported
> 
> with this config:
> 
>   http://redhat.com/~mingo/misc/config-Fri_Aug_15_11_34_53_CEST_2008.bad

the problem is that i'm building a 32-bit kernel on a 64-bit host, and 
the scripts/recordmcount.pl script does not create the temporary object 
files in the proper (32-bit) output ELF format.

	Ingo

Re: [PATCH 0/3] ftrace: handle kernel code remove

[Ingo Molnar]

* Ingo Molnar <mingo@elte.hu> wrote:

> >   http://redhat.com/~mingo/misc/config-Fri_Aug_15_11_34_53_CEST_2008.bad
> 
> the problem is that i'm building a 32-bit kernel on a 64-bit host, and 
> the scripts/recordmcount.pl script does not create the temporary 
> object files in the proper (32-bit) output ELF format.

the crude hack below got me going for now - but this needs a proper 
solution.

	Ingo

--------------------->
>From 52a4a65bcb5b796b7ad83ad069968c476142706f Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Mon, 9 Jun 2008 20:54:22 +0200
Subject: [PATCH] ftrace: scripts/recordmcount.pl cross-build hack

hack around:

 ld: Relocatable linking with relocations from format elf32-i386 (init/.tmp_gl_calibrate.o) to format elf64-x86-64 (init/.tmp_mx_calibrate.o) i  CC      arch/x86/mm/extable.o
 objcopy: 'init/.tmp_mx_calibrate.o': No such file
 rm: cannot remove `init/.tmp_mx_calibrate.o': No such file or directory
 ld: Relocatable linking with relocations from format elf32-i386 (arch/x86/mm/extable.o) to format elf64-x86-64 (arch/x86/mm/.tmp_mx_extable.o) is not supported
 mv: cannot stat `arch/x86/mm/.tmp_mx_extable.o': No such file or directory
 ld: Relocatable linking with relocations from format elf32-i386 (arch/x86/mm/fault.o) to format elf64-x86-64 (arch/x86/mm/.tmp_mx_fault.o) is not supported

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 scripts/recordmcount.pl |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index 44b4b23..41b55e0 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -108,6 +108,20 @@ if ($#ARGV < 6) {
 
 my ($arch, $objdump, $objcopy, $cc, $ld, $nm, $rm, $mv, $inputfile) = @ARGV;
 
+if ($arch eq "i386") {
+  $ld = "ld -m elf_i386";
+  $objdump = "objdump -M i386";
+  $objcopy = "objcopy -O elf32-i386";
+  $cc = "gcc -m32";
+}
+
+if ($arch eq "x86_64") {
+  $ld = "ld -m elf_x86_64";
+  $objdump = "objdump -M x86-64";
+  $objcopy = "objcopy -O elf64-i386";
+  $cc = "gcc -m64";
+}
+
 $objdump = "objdump" if ((length $objdump) == 0);
 $objcopy = "objcopy" if ((length $objcopy) == 0);
 $cc = "gcc" if ((length $cc) == 0);

Re: [PATCH 0/3] ftrace: handle kernel code remove

[Ingo Molnar]

* Ingo Molnar <mingo@elte.hu> wrote:

> > the problem is that i'm building a 32-bit kernel on a 64-bit host, 
> > and the scripts/recordmcount.pl script does not create the temporary 
> > object files in the proper (32-bit) output ELF format.
> 
> the crude hack below got me going for now - but this needs a proper 
> solution.

updated hack - it now works on 64-bit too.

( Btw., whoever came up with those fantastic variations of BFD, 
  architecture name and ELF format names and sprinkled them around 
  various tools with different command line switches and variants and 
  underscore versus dash names, must not be let near any serious 
  open-source code base again, until the end of his life. )

	Ingo

------------->
>From 9f982af9fb45c438415c2c411cda0d8f1e5f1bb7 Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Mon, 9 Jun 2008 20:54:22 +0200
Subject: [PATCH] ftrace: scripts/recordmcount.pl cross-build hack

hack around:

 ld: Relocatable linking with relocations from format elf32-i386 (init/.tmp_gl_calibrate.o) to format elf64-x86-64 (init/.tmp_mx_calibrate.o) i  CC      arch/x86/mm/extable.o
 objcopy: 'init/.tmp_mx_calibrate.o': No such file
 rm: cannot remove `init/.tmp_mx_calibrate.o': No such file or directory
 ld: Relocatable linking with relocations from format elf32-i386 (arch/x86/mm/extable.o) to format elf64-x86-64 (arch/x86/mm/.tmp_mx_extable.o) is not supported
 mv: cannot stat `arch/x86/mm/.tmp_mx_extable.o': No such file or directory
 ld: Relocatable linking with relocations from format elf32-i386 (arch/x86/mm/fault.o) to format elf64-x86-64 (arch/x86/mm/.tmp_mx_fault.o) is not supported

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 scripts/recordmcount.pl |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/scripts/recordmcount.pl b/scripts/recordmcount.pl
index 44b4b23..e4922a6 100755
--- a/scripts/recordmcount.pl
+++ b/scripts/recordmcount.pl
@@ -108,6 +108,20 @@ if ($#ARGV < 6) {
 
 my ($arch, $objdump, $objcopy, $cc, $ld, $nm, $rm, $mv, $inputfile) = @ARGV;
 
+if ($arch eq "i386") {
+  $ld = "ld -m elf_i386";
+  $objdump = "objdump -M i386";
+  $objcopy = "objcopy -O elf32-i386";
+  $cc = "gcc -m32";
+}
+
+if ($arch eq "x86_64") {
+  $ld = "ld -m elf_x86_64";
+  $objdump = "objdump -M x86-64";
+  $objcopy = "objcopy -O elf64-x86-64";
+  $cc = "gcc -m64";
+}
+
 $objdump = "objdump" if ((length $objdump) == 0);
 $objcopy = "objcopy" if ((length $objcopy) == 0);
 $cc = "gcc" if ((length $cc) == 0);

Re: [PATCH 0/3] ftrace: handle kernel code remove

[Sam Ravnborg]

On Fri, Aug 15, 2008 at 12:06:00PM +0200, Ingo Molnar wrote:
> 
> * Ingo Molnar <mingo@elte.hu> wrote:
> 
> > >   http://redhat.com/~mingo/misc/config-Fri_Aug_15_11_34_53_CEST_2008.bad
> > 
> > the problem is that i'm building a 32-bit kernel on a 64-bit host, and 
> > the scripts/recordmcount.pl script does not create the temporary 
> > object files in the proper (32-bit) output ELF format.
> 
> the crude hack below got me going for now - but this needs a proper 
> solution.

recordmount.pl should use the already define environment variables:
$CC + $CFLAGS
$LD + $LDFLAGS
$OBJCOPY, $OBJCOPYFLAGS
$OBJDUMP

We need to set $OBJCOPYFLAFS to a sensible variable in arch/x86/Makefile
And we should introduce $OBJDUMPFLAGS too.

This would solve all the problems - no?

I am limited in time atm - so relying on one of you to create the patch
and do some testing.

	Sam