[PATCH 1/3] Kprobes: Make kprobe modules more portable

[Ananth N Mavinakayanahalli <ananth@in.ibm.com>]

From: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

This patch introduces KPROBE_ADDR, a macro that abstracts out the
architecture-specific artefacts of getting the correct text address
given a symbol. While we are at it, also introduce the symbol_name field
in struct kprobe to allow for users to just specify the address to be
probed in terms of the kernel symbol. In-kernel kprobes infrastructure
decodes the actual text address to probe. The symbol resolution happens
only if the kprobe.addr isn't explicitly specified.

---
Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Prasanna S.P <prasanna@in.ibm.com>


---
 include/asm-powerpc/kprobes.h |    2 ++
 include/linux/kprobes.h       |    8 ++++++++
 kernel/kprobes.c              |    4 ++++
 3 files changed, 14 insertions(+)

Index: linux-2.6.18-rc3/include/asm-powerpc/kprobes.h
===================================================================
--- linux-2.6.18-rc3.orig/include/asm-powerpc/kprobes.h
+++ linux-2.6.18-rc3/include/asm-powerpc/kprobes.h
@@ -44,6 +44,8 @@ typedef unsigned int kprobe_opcode_t;
 #define IS_TDI(instr)		(((instr) & 0xfc000000) == 0x08000000)
 #define IS_TWI(instr)		(((instr) & 0xfc000000) == 0x0c000000)
 
+#define KPROBE_ADDR(name) *((kprobe_opcode_t **)(kallsyms_lookup_name(name)))
+
 #define JPROBE_ENTRY(pentry)	(kprobe_opcode_t *)((func_descr_t *)pentry)
 
 #define is_trap(instr)	(IS_TW(instr) || IS_TD(instr) || \
Index: linux-2.6.18-rc3/include/linux/kprobes.h
===================================================================
--- linux-2.6.18-rc3.orig/include/linux/kprobes.h
+++ linux-2.6.18-rc3/include/linux/kprobes.h
@@ -36,6 +36,7 @@
 #include <linux/spinlock.h>
 #include <linux/rcupdate.h>
 #include <linux/mutex.h>
+#include <linux/kallsyms.h>
 
 #ifdef CONFIG_KPROBES
 #include <asm/kprobes.h>
@@ -49,6 +50,10 @@
 /* Attach to insert probes on any functions which should be ignored*/
 #define __kprobes	__attribute__((__section__(".kprobes.text")))
 
+#ifndef KPROBE_ADDR	/* powerpc has its own definition */
+#define KPROBE_ADDR(name) (kprobe_opcode_t *)(kallsyms_lookup_name(name))
+#endif	/* KPROBE_ADDR */
+
 struct kprobe;
 struct pt_regs;
 struct kretprobe;
@@ -77,6 +82,9 @@ struct kprobe {
 	/* location of the probe point */
 	kprobe_opcode_t *addr;
 
+	/* Allow user to indicate symbol name of the probe point */
+	char *symbol_name;
+
 	/* Called before addr is executed. */
 	kprobe_pre_handler_t pre_handler;
 
Index: linux-2.6.18-rc3/kernel/kprobes.c
===================================================================
--- linux-2.6.18-rc3.orig/kernel/kprobes.c
+++ linux-2.6.18-rc3/kernel/kprobes.c
@@ -446,6 +446,10 @@ static int __kprobes __register_kprobe(s
 	struct kprobe *old_p;
 	struct module *probed_mod;
 
+	/* Do the kallsyms lookup only if p->addr == NULL */
+	if (!p->addr && (p->symbol_name))
+		p->addr = KPROBE_ADDR(p->symbol_name);
+
 	if ((!kernel_text_address((unsigned long) p->addr)) ||
 		in_kprobes_functions((unsigned long) p->addr))
 		return -EINVAL;