Re: [RFC v3 3/8] Add basic Linux kernel support

[Philipp Rudo <prudo@linux.vnet.ibm.com>]

Hi Yao,


On Tue, 02 May 2017 12:14:40 +0100
Yao Qi <qiyaoltc@gmail.com> wrote:

> Philipp Rudo <prudo@linux.vnet.ibm.com> writes:
> 
> Hi Philipp,
> 
> > +/* Initialize architecture independent private data.  Must be called
> > +   _after_ symbol tables were initialized.  */
> > +
> > +static void
> > +lk_init_private_data ()
> > +{
> > +  if (LK_PRIVATE->data != NULL)
> > +    htab_empty (LK_PRIVATE->data);
> > +
> > +  LK_DECLARE_FIELD (task_struct, tasks);
> > +  LK_DECLARE_FIELD (task_struct, pid);
> > +  LK_DECLARE_FIELD (task_struct, tgid);
> > +  LK_DECLARE_FIELD (task_struct, thread_group);
> > +  LK_DECLARE_FIELD (task_struct, comm);
> > +  LK_DECLARE_FIELD (task_struct, thread);
> > +
> > +  LK_DECLARE_FIELD (list_head, next);
> > +  LK_DECLARE_FIELD (list_head, prev);
> > +
> > +  LK_DECLARE_FIELD (rq, curr);
> > +
> > +  LK_DECLARE_FIELD (cpumask, bits);
> > +
> > +  LK_DECLARE_ADDR (init_task);
> > +  LK_DECLARE_ADDR (runqueues);
> > +  LK_DECLARE_ADDR (__per_cpu_offset);
> > +  LK_DECLARE_ADDR (init_mm);
> > +
> > +  LK_DECLARE_ADDR_ALIAS (__cpu_online_mask, cpu_online_mask);	/*
> > linux 4.5+ */
> > +  LK_DECLARE_ADDR_ALIAS (cpu_online_bits, cpu_online_mask);	/*
> > linux -4.4 */
> > +  if (LK_ADDR (cpu_online_mask) == -1)
> > +    error (_("Could not find address cpu_online_mask.  Aborting."));
> > +}
> > +  
> 
> > +
> > +/* Initialize linux kernel target.  */
> > +
> > +static void
> > +init_linux_kernel_ops (void)
> > +{
> > +  struct target_ops *t;
> > +
> > +  if (linux_kernel_ops != NULL)
> > +    return;
> > +
> > +  t = XCNEW (struct target_ops);
> > +  t->to_shortname = "linux-kernel";
> > +  t->to_longname = "linux kernel support";
> > +  t->to_doc = "Adds support to debug the Linux kernel";
> > +
> > +  /* set t->to_data = struct lk_private in lk_init_private.  */
> > +
> > +  t->to_open = lk_open;
> > +  t->to_close = lk_close;
> > +  t->to_detach = lk_detach;
> > +  t->to_fetch_registers = lk_fetch_registers;
> > +  t->to_update_thread_list = lk_update_thread_list;
> > +  t->to_pid_to_str = lk_pid_to_str;
> > +  t->to_thread_name = lk_thread_name;
> > +
> > +  t->to_stratum = thread_stratum;
> > +  t->to_magic = OPS_MAGIC;
> > +
> > +  linux_kernel_ops = t;
> > +
> > +  add_target (t);
> > +}
> > +
> > +/* Provide a prototype to silence -Wmissing-prototypes.  */
> > +extern initialize_file_ftype _initialize_linux_kernel;
> > +
> > +void
> > +_initialize_linux_kernel (void)
> > +{
> > +  init_linux_kernel_ops ();
> > +
> > +  observer_attach_new_objfile (lk_observer_new_objfile);
> > +  observer_attach_inferior_created (lk_observer_inferior_created);
> > +}
> > diff --git a/gdb/lk-low.h b/gdb/lk-low.h
> > new file mode 100644
> > index 0000000..292ef97
> > --- /dev/null
> > +++ b/gdb/lk-low.h
> > @@ -0,0 +1,310 @@
> > +/* Basic Linux kernel support, architecture independent.
> > +
> > +   Copyright (C) 2016 Free Software Foundation, Inc.
> > +
> > +   This file is part of GDB.
> > +
> > +   This program is free software; you can redistribute it and/or modify
> > +   it under the terms of the GNU General Public License as published by
> > +   the Free Software Foundation; either version 3 of the License, or
> > +   (at your option) any later version.
> > +
> > +   This program is distributed in the hope that it will be useful,
> > +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > +   GNU General Public License for more details.
> > +
> > +   You should have received a copy of the GNU General Public License
> > +   along with this program.  If not, see <http://www.gnu.org/licenses/>.
> > */ +
> > +#ifndef __LK_LOW_H__
> > +#define __LK_LOW_H__
> > +
> > +#include "target.h"
> > +
> > +extern struct target_ops *linux_kernel_ops;
> > +
> > +/* Copy constants defined in Linux kernel.  */
> > +#define LK_TASK_COMM_LEN 16
> > +#define LK_BITS_PER_BYTE 8
> > +
> > +/* Definitions used in linux kernel target.  */
> > +#define LK_CPU_INVAL -1U
> > +
> > +/* Private data structs for this target.  */
> > +/* Forward declarations.  */
> > +struct lk_private_hooks;
> > +struct lk_ptid_map;
> > +
> > +/* Short hand access to private data.  */
> > +#define LK_PRIVATE ((struct lk_private *) linux_kernel_ops->to_data)
> > +#define LK_HOOK (LK_PRIVATE->hooks)
> > +
> > +struct lk_private  
> 
> "private" here is a little confusing.  How about rename it to "linux_kernel"?

I called it "private" as it is the targets private data stored in its to_data
hook.  But I don't mind renaming it.  Especially ...
 
> > +{
> > +  /* Hashtab for needed addresses, structs and fields.  */
> > +  htab_t data;
> > +
> > +  /* Linked list to map between cpu number and original ptid from target
> > +     beneath.  */
> > +  struct lk_ptid_map *old_ptid;
> > +
> > +  /* Hooks for architecture dependent functions.  */
> > +  struct lk_private_hooks *hooks;
> > +};
> > +  
> 
> Secondly, can we change it to a class and function pointers in
> lk_private_hooks become virtual functions.  gdbarch_lk_init_private
> returns a pointer to an instance of sub-class of "linux_kernel".
> 
> lk_init_private_data can be put the constructor of base class, to add
> entries to "data", and sub-class (in each gdbarch) can add their own
> specific stuff.

... when classifying the struct, which already is on my long ToDo-list.  This
struct is a left over from when I started working on the project shortly before
gdb-7.12 was released.  I didn't think that the C++-yfication would kick off
that fast and started with plain C ...

Thanks
Philipp

> > +
> > +/* Functions to initialize private data.  Do not use directly, use the
> > +   macros below instead.  */
> > +
> > +extern struct lk_private_data *lk_init_addr (const char *name,
> > +					     const char *alias, int
> > silent); +extern struct lk_private_data *lk_init_struct (const char *name,
> > +					       const char *alias, int
> > silent);  
> 
> > +
> > +/* Definitions for architecture dependent hooks.  */
> > +/* Hook to read registers from the target and supply their content
> > +   to the regcache.  */
> > +typedef void (*lk_hook_get_registers) (CORE_ADDR task,
> > +				       struct target_ops *target,
> > +				       struct regcache *regcache,
> > +				       int regnum);
> > +
> > +/* Hook to return the per_cpu_offset of cpu CPU.  Only architectures that
> > +   do not use the __per_cpu_offset array to determin the offset have to
> > +   supply this hook.  */
> > +typedef CORE_ADDR (*lk_hook_get_percpu_offset) (unsigned int cpu);
> > +
> > +/* Hook to map a running task to a logical CPU.  Required if the target
> > +   beneath uses a different PID as struct rq.  */
> > +typedef unsigned int (*lk_hook_map_running_task_to_cpu) (struct
> > thread_info *ti); +
> > +struct lk_private_hooks
> > +{
> > +  /* required */
> > +  lk_hook_get_registers get_registers;
> > +
> > +  /* optional, required if __per_cpu_offset array is not used to determine
> > +     offset.  */
> > +  lk_hook_get_percpu_offset get_percpu_offset;
> > +
> > +  /* optional, required if the target beneath uses a different PID as
> > struct
> > +     rq.  */
> > +  lk_hook_map_running_task_to_cpu map_running_task_to_cpu;
> > +};  
>