linux-kernel - Re: PTRACE_{READ,WRITE}{TEXT,DATA}

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Message-ID: <20080429004405.2c375723@bree.surriel.com>
Date:	Tue, 29 Apr 2008 00:44:05 -0400
From:	Rik van Riel <riel@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	benh@...nel.crashing.org, roland@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: PTRACE_{READ,WRITE}{TEXT,DATA}

On Mon, 28 Apr 2008 21:34:16 -0700 (PDT)
David Miller <davem@...emloft.net> wrote:

> From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Date: Tue, 29 Apr 2008 13:54:08 +1000
> 
> > I noticed kernel/ptrace.c has ptrace_readdata/writedata functions that
> > are only used by sparc and sparc64 which implements the ptrace requests
> > PTRACE_READ_DATA, PTRACE_WRITE_DATA (and _TEXT variants).
> > 
> > Any reason not to make everybody benefit from these and moving the sparc
> > implementation to the generic ptrace_request (&compat) ?
> > 
> > It's more efficient than read/writing one word at a time... I thought
> > about it in the light of some work Rik is doing to make
> > access_process_vm useable on video ram mappings done by the X server...
> 
> It's kind of pointless because what gdb does these days on Linux is
> use the procfs 'mem' file to directly read in parts of the inferior's
> address space.
> 
> See linux_proc_xfer_partial() in gdb/linux-nat.c

Strange, changing access_process_vm on Fedora 9 made gdb able to
see video memory that the X server had mmapped.

Are you sure gdb behaves as you suggest?  

On x86 my patch seems to work as I expected...

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