Message-ID: <20060809095111.GC20050@in.ibm.com>
Date:	Wed, 9 Aug 2006 15:21:11 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Christoph Hellwig <hch@...radead.org>,
	linux-kernel@...r.kernel.org, shemminger@...l.org
Subject: Re: [PATCH 1/3] Kprobes: Make kprobe modules more portable

On Tue, Aug 08, 2006 at 05:24:21PM +0100, Christoph Hellwig wrote:
> On Mon, Aug 07, 2006 at 05:25:37PM +0530, Ananth N Mavinakayanahalli wrote:
> > From: Ananth N Mavinakayanahalli <ananth@...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

Agreed.

> 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@....de>

Signed-off-by: Ananth N Mavinakayanahalli <ananth@...ibm.com>

> 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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