[RFC patch] extable and module add object is static

[Mathieu Desnoyers]

* Paul E. McKenney (paulmck@xxxxxxxxxxxxxxxxxx) wrote:
> On Sat, Mar 27, 2010 at 07:20:24PM -0400, Mathieu Desnoyers wrote:
[...]
> > Something close to "object_is_static()" would be "kernel_text_address()", but it
> > only considers the text section addresses. I'd need something that would be
> > broader than that, containing all core kernel and module bss and data sections.
> > 
> > Still looking...
> 
> I was actually feeling pretty good about remembering object_is_on_stack()
> and finding it again.  ;-)
> 
> I am not seeing anything the identifies data or bss, and in any case,
> other situations such as per-CPU, __read_mostly, and who knows what all
> else would also need to be handled.  So in the short term, my guess would
> be that it would be best to provide the three functions (possibly renaming
> them as noted above), but to leave the responsibility for figuring out
> which to invoke with the caller.  Always happy to be proven wrong, of
> course!
> 
> 							Thanx, Paul

I think I found a neat way to do object_is_static(), which is all we need here.
Can you have a look at the following patch ? If you think it's right, I'll add
it to the patchset for the next submission.


extable and module add object is static

Adds an API to extable.c to check if an object is statically defined. This
permits, along with object_is_on_stack(), to figure out is an object is either
statically defined (object_is_static()) or allocated on the stack
(object_is_on_stack()).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
CC: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
CC: David S. Miller <davem@xxxxxxxxxxxxx>
CC: akpm@xxxxxxxxxxxxxxxxxxxx
CC: mingo@xxxxxxx
CC: laijs@xxxxxxxxxxxxxx
CC: dipankar@xxxxxxxxxx
CC: josh@xxxxxxxxxxxxxxxx
CC: dvhltc@xxxxxxxxxx
CC: niv@xxxxxxxxxx
CC: tglx@xxxxxxxxxxxxx
CC: peterz@xxxxxxxxxxxxx
CC: rostedt@xxxxxxxxxxx
CC: Valdis.Kletnieks@xxxxxx
CC: dhowells@xxxxxxxxxx
CC: eric.dumazet@xxxxxxxxx
CC: Alexey Dobriyan <adobriyan@xxxxxxxxx>
---
 include/linux/kernel.h |    2 +
 kernel/extable.c       |   52 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+)

Index: linux.trees.git/include/linux/kernel.h
===================================================================
--- linux.trees.git.orig/include/linux/kernel.h	2010-03-27 19:27:02.000000000 -0400
+++ linux.trees.git/include/linux/kernel.h	2010-03-27 19:28:02.000000000 -0400
@@ -218,6 +218,8 @@ extern int __kernel_text_address(unsigne
 extern int kernel_text_address(unsigned long addr);
 extern int func_ptr_is_kernel_text(void *ptr);
 
+extern int object_is_static(void *obj);
+
 struct pid;
 extern struct pid *session_of_pgrp(struct pid *pgrp);
 
Index: linux.trees.git/kernel/extable.c
===================================================================
--- linux.trees.git.orig/kernel/extable.c	2010-03-27 19:28:06.000000000 -0400
+++ linux.trees.git/kernel/extable.c	2010-03-27 19:54:40.000000000 -0400
@@ -60,6 +60,14 @@ static inline int init_kernel_text(unsig
 	return 0;
 }
 
+static inline int init_kernel_text_or_data(unsigned long addr)
+{
+	if (addr >= (unsigned long)__init_begin &&
+	    addr <= (unsigned long)__init_end)
+		return 1;
+	return 0;
+}
+
 int core_kernel_text(unsigned long addr)
 {
 	if (addr >= (unsigned long)_stext &&
@@ -113,3 +121,47 @@ int func_ptr_is_kernel_text(void *ptr)
 		return 1;
 	return is_module_text_address(addr);
 }
+
+/*
+ * Taking the safe approach to refer to each section individually rather than
+ * just taking a range between _stext and _end, just in case an architecture
+ * would decide to override the standard linker scripts and put a section
+ * outside of this range.
+ *
+ * Should be kept in sync with linux/section.h and asm-generic/vmlinux.lds.h.
+ */
+static int core_object_is_static(void *obj)
+{
+	unsigned long addr = (unsigned long) obj;
+
+	if (addr >= (unsigned long)_sdata &&
+	    addr <= (unsigned long)_edata)
+		return 1;
+	if (addr >= (unsigned long)__bss_start &&
+	    addr <= (unsigned long)__bss_stop)
+		return 1;
+	if (addr >= (unsigned long)__per_cpu_start &&
+	    addr <= (unsigned long)__per_cpu_end)
+		return 1;
+	if (addr >= (unsigned long)__start_rodata &&
+	    addr <= (unsigned long)__end_rodata)
+		return 1;
+	if (system_state == SYSTEM_BOOTING &&
+	    init_kernel_text_or_data(addr))
+		return 1;
+	if (core_kernel_text(addr))
+		return 1;
+	return 0;
+}
+
+/*
+ * object_is_static - returns true is an object is statically defined
+ */
+int object_is_static(void *obj)
+{
+	if (core_object_is_static(obj))
+		return 1;
+	if (is_module_address((unsigned long) obj))
+		return 1;
+	return 0;
+}


-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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