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SubjectRe: [PATCH 1/3] Kprobes: Make kprobe modules more portable
On Mon, Aug 07, 2006 at 05:25:37PM +0530, Ananth N Mavinakayanahalli wrote:
> 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.

This looks good. A few issues are left:

- the KPROBE_ADDR macro is all uppercase and not exactly very descriptive.
- the symbol name variant should be the default, and no one outside
kprobes.c should know about the KPROBE_ADDR macro
- we should return EINVAL instead of silently discarding things if people
specify a symbol and an address.
- we should have and offset into the symbol specified

The updated patch below does that, aswell as updating the only inkernel
kprobes user (tcp_probe.c) to the new interface (*) and removing the now
obsolete kallsysms_lookup_name export.

(*) tcp_probe.c shows very well how horrible the old interface was, as it's
not portable to ppc64 as-is

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: linux-2.6/include/asm-powerpc/kprobes.h
===================================================================
--- linux-2.6.orig/include/asm-powerpc/kprobes.h 2006-08-08 17:47:22.000000000 +0200
+++ linux-2.6/include/asm-powerpc/kprobes.h 2006-08-08 18:13:57.000000000 +0200
@@ -44,6 +44,9 @@
#define IS_TDI(instr) (((instr) & 0xfc000000) == 0x08000000)
#define IS_TWI(instr) (((instr) & 0xfc000000) == 0x0c000000)

+#define kprobe_lookup_name(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/include/linux/kprobes.h
===================================================================
--- linux-2.6.orig/include/linux/kprobes.h 2006-08-08 17:47:22.000000000 +0200
+++ linux-2.6/include/linux/kprobes.h 2006-08-08 17:47:31.000000000 +0200
@@ -77,6 +77,12 @@
/* 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;

Index: linux-2.6/kernel/kprobes.c
===================================================================
--- linux-2.6.orig/kernel/kprobes.c 2006-08-08 17:47:22.000000000 +0200
+++ linux-2.6/kernel/kprobes.c 2006-08-08 17:47:31.000000000 +0200
@@ -37,6 +37,7 @@
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/moduleloader.h>
+#include <linux/kallsyms.h>
#include <asm-generic/sections.h>
#include <asm/cacheflush.h>
#include <asm/errno.h>
@@ -45,6 +46,16 @@
#define KPROBE_HASH_BITS 6
#define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)

+
+/*
+ * Some oddball architectures like 64bit powerpc have function descriptors
+ * so this must be overridable.
+ */
+#ifndef kprobe_lookup_name
+#define kprobe_lookup_name(name) \
+ ((kprobe_opcode_t *)(kallsyms_lookup_name(name))
+#endif
+
static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
static atomic_t kprobe_count;
@@ -447,6 +458,17 @@
struct kprobe *old_p;
struct module *probed_mod;

+ /*
+ * If we have a symbol_name argument look it up,
+ * and add it to the address. That way the addr
+ * field can either be global or relative to a symbol.
+ */
+ if (p->symbol_name) {
+ if (p->addr)
+ return -EINVAL;
+ p->addr = kprobe_lookup_name(p->symbol_name) + p->offset;
+ }
+
if ((!kernel_text_address((unsigned long) p->addr)) ||
in_kprobes_functions((unsigned long) p->addr))
return -EINVAL;
Index: linux-2.6/kernel/kallsyms.c
===================================================================
--- linux-2.6.orig/kernel/kallsyms.c 2006-08-08 17:13:14.000000000 +0200
+++ linux-2.6/kernel/kallsyms.c 2006-08-08 17:47:39.000000000 +0200
@@ -154,7 +154,6 @@
}
return module_kallsyms_lookup_name(name);
}
-EXPORT_SYMBOL_GPL(kallsyms_lookup_name);

/*
* Lookup an address
Index: linux-2.6/net/ipv4/tcp_probe.c
===================================================================
--- linux-2.6.orig/net/ipv4/tcp_probe.c 2006-08-08 18:13:55.000000000 +0200
+++ linux-2.6/net/ipv4/tcp_probe.c 2006-08-08 18:14:28.000000000 +0200
@@ -99,8 +99,10 @@
}

static struct jprobe tcp_send_probe = {
- .kp = { .addr = (kprobe_opcode_t *) &tcp_sendmsg, },
- .entry = (kprobe_opcode_t *) &jtcp_sendmsg,
+ .kp = {
+ .symbol_name = "tcp_sendmsg",
+ },
+ .entry = JPROBE_ENTRY(jtcp_sendmsg),
};


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