[PATCH/gdbserver] Remove current_inferior's save/restore when call get_thread_regcache.

[PATCH/gdbserver] Remove current_inferior's save/restore when call get_thread_regcache.

[Yao Qi]

Hi,
The current_inferior is saved and restored inside get_thread_regcache,
so it is not necessary to save and restore current_inferior out side
of it.

Regression tested on x86_64-linux.  OK to apply?

gdb/gdbserver:

2012-05-04  Yao Qi  <yao@codesourcery.com>

	* linux-low.c (get_pc, linux_wait_for_lwp): Don't save and restore
	current_inferior when call get_thread_cache.
	* proc-service.c (ps_lgetregs): Likewise.
---
 gdb/gdbserver/linux-low.c    |   12 ++----------
 gdb/gdbserver/proc-service.c |    7 +------
 2 files changed, 3 insertions(+), 16 deletions(-)

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 751867b..64d314c 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -503,23 +503,18 @@ handle_extended_wait (struct lwp_info *event_child, int wstat)
 static CORE_ADDR
 get_pc (struct lwp_info *lwp)
 {
-  struct thread_info *saved_inferior;
   struct regcache *regcache;
   CORE_ADDR pc;
 
   if (the_low_target.get_pc == NULL)
     return 0;
 
-  saved_inferior = current_inferior;
-  current_inferior = get_lwp_thread (lwp);
-
-  regcache = get_thread_regcache (current_inferior, 1);
+  regcache = get_thread_regcache (get_lwp_thread (lwp), 1);
   pc = (*the_low_target.get_pc) (regcache);
 
   if (debug_threads)
     fprintf (stderr, "pc is 0x%lx\n", (long) pc);
 
-  current_inferior = saved_inferior;
   return pc;
 }
 
@@ -1425,15 +1420,12 @@ retry:
       && WIFSTOPPED (*wstatp)
       && the_low_target.get_pc != NULL)
     {
-      struct thread_info *saved_inferior = current_inferior;
       struct regcache *regcache;
       CORE_ADDR pc;
 
-      current_inferior = get_lwp_thread (child);
-      regcache = get_thread_regcache (current_inferior, 1);
+      regcache = get_thread_regcache (get_lwp_thread (child), 1);
       pc = (*the_low_target.get_pc) (regcache);
       fprintf (stderr, "linux_wait_for_lwp: pc is 0x%lx\n", (long) pc);
-      current_inferior = saved_inferior;
     }
 
   return child;
diff --git a/gdb/gdbserver/proc-service.c b/gdb/gdbserver/proc-service.c
index 5584dab..d4c17a2 100644
--- a/gdb/gdbserver/proc-service.c
+++ b/gdb/gdbserver/proc-service.c
@@ -99,20 +99,15 @@ ps_lgetregs (gdb_ps_prochandle_t ph, lwpid_t lwpid, prgregset_t gregset)
 {
 #ifdef HAVE_REGSETS
   struct lwp_info *lwp;
-  struct thread_info *reg_inferior, *save_inferior;
   struct regcache *regcache;
 
   lwp = find_lwp_pid (pid_to_ptid (lwpid));
   if (lwp == NULL)
     return PS_ERR;
 
-  reg_inferior = get_lwp_thread (lwp);
-  save_inferior = current_inferior;
-  current_inferior = reg_inferior;
-  regcache = get_thread_regcache (current_inferior, 1);
+  regcache = get_thread_regcache (get_lwp_thread (lwp), 1);
   gregset_info ()->fill_function (regcache, gregset);
 
-  current_inferior = save_inferior;
   return PS_OK;
 #else
   return PS_ERR;
-- 
1.7.0.4

Re: [PATCH/gdbserver] Remove current_inferior's save/restore when call get_thread_regcache.

[Pedro Alves]

On 05/04/2012 11:51 AM, Yao Qi wrote:

> Hi,
> The current_inferior is saved and restored inside get_thread_regcache,
> so it is not necessary to save and restore current_inferior out side
> of it.
> 
> Regression tested on x86_64-linux.  OK to apply?

>

> 
> gdb/gdbserver:
> 
> 2012-05-04  Yao Qi  <yao@codesourcery.com>
> 
> 	* linux-low.c (get_pc, linux_wait_for_lwp): Don't save and restore
> 	current_inferior when call get_thread_cache.
> 	* proc-service.c (ps_lgetregs): Likewise.
> ---
>  gdb/gdbserver/linux-low.c    |   12 ++----------
>  gdb/gdbserver/proc-service.c |    7 +------
>  2 files changed, 3 insertions(+), 16 deletions(-)
> 
> diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
> index 751867b..64d314c 100644
> --- a/gdb/gdbserver/linux-low.c
> +++ b/gdb/gdbserver/linux-low.c
> @@ -503,23 +503,18 @@ handle_extended_wait (struct lwp_info *event_child, int wstat)
>  static CORE_ADDR
>  get_pc (struct lwp_info *lwp)
>  {
> -  struct thread_info *saved_inferior;
>    struct regcache *regcache;
>    CORE_ADDR pc;
>  
>    if (the_low_target.get_pc == NULL)
>      return 0;
>  
> -  saved_inferior = current_inferior;
> -  current_inferior = get_lwp_thread (lwp);
> -
> -  regcache = get_thread_regcache (current_inferior, 1);
> +  regcache = get_thread_regcache (get_lwp_thread (lwp), 1);
>    pc = (*the_low_target.get_pc) (regcache);


No, the_low_target.get_pc also needs to go to the right inferior.

>  
>    if (debug_threads)
>      fprintf (stderr, "pc is 0x%lx\n", (long) pc);
>  
> -  current_inferior = saved_inferior;
>    return pc;
>  }
>  
> @@ -1425,15 +1420,12 @@ retry:
>        && WIFSTOPPED (*wstatp)
>        && the_low_target.get_pc != NULL)
>      {
> -      struct thread_info *saved_inferior = current_inferior;
>        struct regcache *regcache;
>        CORE_ADDR pc;
>  
> -      current_inferior = get_lwp_thread (child);
> -      regcache = get_thread_regcache (current_inferior, 1);
> +      regcache = get_thread_regcache (get_lwp_thread (child), 1);
>        pc = (*the_low_target.get_pc) (regcache);


Ditto.

>        fprintf (stderr, "linux_wait_for_lwp: pc is 0x%lx\n", (long) pc);

> -      current_inferior = saved_inferior;
>      }
>  
>    return child;
> diff --git a/gdb/gdbserver/proc-service.c b/gdb/gdbserver/proc-service.c
> index 5584dab..d4c17a2 100644
> --- a/gdb/gdbserver/proc-service.c
> +++ b/gdb/gdbserver/proc-service.c
> @@ -99,20 +99,15 @@ ps_lgetregs (gdb_ps_prochandle_t ph, lwpid_t lwpid, prgregset_t gregset)
>  {
>  #ifdef HAVE_REGSETS
>    struct lwp_info *lwp;
> -  struct thread_info *reg_inferior, *save_inferior;
>    struct regcache *regcache;
>  
>    lwp = find_lwp_pid (pid_to_ptid (lwpid));
>    if (lwp == NULL)
>      return PS_ERR;
>  
> -  reg_inferior = get_lwp_thread (lwp);
> -  save_inferior = current_inferior;
> -  current_inferior = reg_inferior;
> -  regcache = get_thread_regcache (current_inferior, 1);
> +  regcache = get_thread_regcache (get_lwp_thread (lwp), 1);
>    gregset_info ()->fill_function (regcache, gregset);


Ditto the whole gregset_info ()->fill_function line, particularly
after my multi-process/multi-arch series, while the fill_function
depends on inferior.

>  
> -  current_inferior = save_inferior;
>    return PS_OK;
>  #else
>    return PS_ERR;



-- 
Pedro Alves

Re: [PATCH/gdbserver] Remove current_inferior's save/restore when call get_thread_regcache.

[Yao Qi]

On 05/04/2012 08:31 PM, Pedro Alves wrote:
>> > -  regcache = get_thread_regcache (current_inferior, 1);
>> > +  regcache = get_thread_regcache (get_lwp_thread (lwp), 1);
>> >    pc = (*the_low_target.get_pc) (regcache);
> 
> No, the_low_target.get_pc also needs to go to the right inferior.
> 

I thought the_low_target.get_pc is to extract value of pc from regcache,
so inferior is not needed.  I examined linux-foo-low.c files again, and
find only ppc_get_pc needs the right inferior, sigh.

>> >  
>> >    return child;
>> > diff --git a/gdb/gdbserver/proc-service.c b/gdb/gdbserver/proc-service.c
>> > index 5584dab..d4c17a2 100644
>> > --- a/gdb/gdbserver/proc-service.c
>> > +++ b/gdb/gdbserver/proc-service.c
>> > @@ -99,20 +99,15 @@ ps_lgetregs (gdb_ps_prochandle_t ph, lwpid_t lwpid, prgregset_t gregset)
>> >  {
>> >  #ifdef HAVE_REGSETS
>> >    struct lwp_info *lwp;
>> > -  struct thread_info *reg_inferior, *save_inferior;
>> >    struct regcache *regcache;
>> >  
>> >    lwp = find_lwp_pid (pid_to_ptid (lwpid));
>> >    if (lwp == NULL)
>> >      return PS_ERR;
>> >  
>> > -  reg_inferior = get_lwp_thread (lwp);
>> > -  save_inferior = current_inferior;
>> > -  current_inferior = reg_inferior;
>> > -  regcache = get_thread_regcache (current_inferior, 1);
>> > +  regcache = get_thread_regcache (get_lwp_thread (lwp), 1);
>> >    gregset_info ()->fill_function (regcache, gregset);
> 
> Ditto the whole gregset_info ()->fill_function line, particularly
> after my multi-process/multi-arch series, while the fill_function
> depends on inferior.
> 

So any code needs inferior should be wrapped in the follow manner?

save_inferior = current_inferior;
current_inferior = reg_inferior;
....
....
current_inferior = save_inferior;

The following question is what functions need inferior?  AFAICS, all the
methods in the_low_target and functions in `struct regset_info' need
inferior.  Anything else?

If methods in the_low_target may need inferior, all the usage of
the_low_target methods should be wrapped by the block above.  Is it
correct?  I hope I am wrong :)

-- 
Yao (齐尧)

Re: [PATCH/gdbserver] Remove current_inferior's save/restore when call get_thread_regcache.

[Pedro Alves]

On 05/04/2012 02:08 PM, Yao Qi wrote:

> So any code needs inferior should be wrapped in the follow manner?

Almost.  The exception is code that takes an explicit thread argument
(current_inferior is a thread pointer).  So when you call:

void foo (struct thread_info *thread)

you don't have to care to swap the current_inferior global.  `foo' will do
it internally if necessary.

-- 
Pedro Alves