Re: [PATCH 06/10] Replace breakpoint_reinsert_addr by get_next_pcs operation in GDBServer.

[Antoine Tremblay <antoine.tremblay@ericsson.com>]

On 11/04/2015 01:48 PM, Pedro Alves wrote:
> On 10/29/2015 05:09 PM, Antoine Tremblay wrote:
>> This patch in preparation for software single step support on ARM. It refactors
>> breakpoint_reinsert_addr into get_next_pcs so that multiple location can be
>> returned.
>>
>> When software single stepping there can be multiple possible next addresses
>> because we're stepping over a branch instruction for example.
>
> ITYM mean a _conditional_ branch instruction.
>

Yes, fixed.

>>
>> The operation get_next_pcs handles that by returning a vector of all the
>> possible next addresses.
>>
>> Software breakpoints are installed at each location returned.
>>
>> No regressions, tested on ubuntu 14.04 ARMv7 and x86.
>> With gdbserver-{native,extended} / { -marm -mthumb }
>>
>> gdb/ChangeLog:
>>
>> 	* common/get-next-pcs.h: New file.
>> 	* common/gdb_vecs.h: Add CORE_ADDR vect.
>> 	* symtab.h: Move CORE_ADDR vect to gdb_vecs.h
>
> Missing period in last line.  (Pedantically, AFAICS, in this patch,
> nothing in gdb includes common/get-next-pcs.h, and nothing
> in gdbserver includes symtab.h.  So seems like putting the VEC
> in common/gdb_vecs.h here is premature.)
>

Yes I could do another patch with just that change since I really wanted 
it to be out of the big 08/10 Support software single step on ARM in 
GDBServer patch, but that would kinda remove some context and it would 
still be premature in the same way.

Same applies to 07/10 Share some ARM target dependant code from GDB with 
GDBServer...

I'm keeping it there in the context that this is a preparatory patch 
unless there's an objection.

>>
>> gdb/gdbserver/ChangeLog:
>> 	* linux-aarch64-low.c (struct linux_target_ops): Rename
>> 	breakpoint_reinsert_addr to get_next_pcs.
>> 	* linux-arm-low.c (struct linux_target_ops): Likewise.
>> 	* linux-bfin-low.c (struct linux_target_ops): Likewise.
>> 	* linux-cris-low.c (struct linux_target_ops): Likewise.
>> 	* linux-crisv32-low.c (struct linux_target_ops): Likewise.
>> 	* linux-low.c (can_software_single_step): Likewise.
>> 	(install_software_single_step_breakpoints): New function.
>> 	(start_step_over): Use isntall_software_single_step_breakpoints.
>> 	* linux-low.h: Rename breakpoint_reinsert_addr to
>> 	get_next_pcs.
>> 	* linux-mips-low.c (struct linux_target_ops): Likewise.
>> 	* linux-nios2-low.c (struct linux_target_ops): Likewise.
>> 	* linux-sparc-low.c (struct linux_target_ops): Likewise.
>
>
> This LGTM.  Some nits below.
>
>> +++ b/gdb/common/get-next-pcs.h
>> @@ -0,0 +1,34 @@
>> +/* Common code for software single stepping support.
>> +
>> +   Copyright (C) 2015 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 GET_NEXT_PCS_H
>> +#define GET_NEXT_PCS_H 1
>> +
>> +#include "gdb_vecs.h"
>> +
>> +struct get_next_pcs
>
> There should be an intro comment mentioning the purpose of
> this structure.
>
Done as :

/* This structure contains the shared context of a get_next_pcs call, as
    used in linux target operation "get_next_pcs" in GDBServer and the
    software_single_step architecture dependent function in GDB.  */

>> +{
>> +  /* Resulting vector of possible next addresses.  */
>> +  VEC (CORE_ADDR) *result;
>> +  /* Base PC from which to get the next pcs.  */
>> +  CORE_ADDR pc;
>> +  struct regcache* regcache;
>
> This field should be documented too.
>

Done.

>> @@ -3876,6 +3877,29 @@ enqueue_pending_signal (struct lwp_info *lwp, int signal, siginfo_t *info)
>>     lwp->pending_signals = p_sig;
>>   }
>>
>> +/* Install breakpoints for software single stepping.  */
>> +
>> +static void
>> +install_software_single_step_breakpoints (struct lwp_info *lwp)
>> +{
>> +  struct get_next_pcs next_pcs;
>> +  int i;
>> +  CORE_ADDR pc;
>> +
>> +  struct regcache *regcache = get_thread_regcache (current_thread, 1);
>
> Formatting.  Variable should be declared in the declaration block
> along with the others, and then there should be a line break.
>

Done thanks,

>> +  next_pcs.pc = get_pc (lwp);
>> +  next_pcs.regcache = regcache;
>> +  next_pcs.result = VEC_alloc (CORE_ADDR, 1);
>
> Is there a reason to allocate upfront instead of setting it to NULL?
>

No that was a mistake, fixed.

>> +  (*the_low_target.get_next_pcs) (&next_pcs);
>> +
>> +  for (i = 0; VEC_iterate (CORE_ADDR, next_pcs.result, i, pc); ++i)
>> +    {
>> +      set_reinsert_breakpoint (pc);
>> +    }
>
> At some point we should do a pass and rename "reinsert breakpoint"
> to "software single-step breakpoint" throughout.  It's no longer
> just about reinserting a breakpoint that we step over.
>

Ok, noted.

Thanks,
Antoine Tremblay