[PATCH] Kprobes: Make kprobe modules more portable

In an effort to make kprobe modules more portable, here is a patch that:

o Introduces the "symbol_name" field to struct kprobe.
  The symbol->address resolution now happens in the kernel in an
  architecture agnostic manner. 64-bit powerpc users no longer have
  to specify the ".symbols"
o Introduces the "offset" field to struct kprobe to allow a user to
  specify an offset into a symbol.
o The legacy mechanism of specifying the kprobe.addr is still supported.
  However, if both the kprobe.addr and kprobe.symbol_name are specified,
  probe registration fails with an -EINVAL.
o The symbol resolution code uses kallsyms_lookup_name(). So
  CONFIG_KPROBES now depends on CONFIG_KALLSYMS
o Apparantly kprobe modules were the only legitimate out-of-tree user of
  the kallsyms_lookup_name() EXPORT. Now that the symbol resolution
  happens in-kernel, remove the EXPORT as suggested by Christoph Hellwig
o Modify tcp_probe.c that uses the kprobe interface so as to make it
  work on multiple platforms (in its earlier form, the code wouldn't
  work, say, on powerpc)

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 21 insertions, 0 deletions

diff --git a/include/asm-powerpc/kprobes.h b/include/asm-powerpc/kprobes.h
index 34e1f89a5fa0..1ef54be6abfa 100644
--- a/include/asm-powerpc/kprobes.h
+++ b/include/asm-powerpc/kprobes.h
@@ -44,6 +44,21 @@ typedef unsigned int kprobe_opcode_t;
 #define IS_TDI(instr)           (((instr) & 0xfc000000) == 0x08000000)
 #define IS_TWI(instr)           (((instr) & 0xfc000000) == 0x0c000000)
 
+/*
+ * 64bit powerpc uses function descriptors.
+ * Handle cases where:
+ *              - User passes a <.symbol>
+ *              - User passes a <symbol>
+ *              - User passes a non-existant symbol, kallsyms_lookup_name
+ *                returns 0. Don't deref the NULL pointer in that case
+ */
+#define kprobe_lookup_name(name, addr)                                  \
+{                                                                       \
+        addr = (kprobe_opcode_t *)kallsyms_lookup_name(name);           \
+        if (!(name[0] == '.') && addr)                                  \
+                addr = *(kprobe_opcode_t **)addr;                       \
+}
+
 #define JPROBE_ENTRY(pentry)    (kprobe_opcode_t *)((func_descr_t *)pentry)
 
 #define is_trap(instr)  (IS_TW(instr) || IS_TD(instr) || \
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 8bf6702da2a0..a5c5a0cb0d5c 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -77,6 +77,12 @@ struct kprobe {
         /* location of the probe point */
         kprobe_opcode_t *addr;
 
+        /* Allow user to indicate symbol name of the probe point */
+        char *symbol_name;
+
+        /* Offset into the symbol */
+        unsigned int offset;
+
         /* Called before addr is executed. */
         kprobe_pre_handler_t pre_handler;