PATCH : allow to set length of hw watchpoints (e.g. for Valgrind gdbserver)

PATCH : allow to set length of hw watchpoints (e.g. for Valgrind gdbserver)

[Philippe Waroquiers]

[-- Attachment #1: Type: text/plain, Size: 4864 bytes --]

(copy of the below text also put in an attachment, as my mailer seems
to eat e.g. the tab characters of the ChangeLog).

A gdbserver has been integrated in Valgrind svn version.
(see https://bugs.kde.org/show_bug.cgi?id=214909 for details).

This gdbserver can provide 'unlimited' watchpoint length
using the Valgrind memcheck machinery. Such watchpoints
are slower than hardware watchpoints, but are faster
that gdb software watchpoints.
However, gdb remote.c hardcodes the length of a remote
watchpoint to 4 bytes (which looks like a bug).
The attached patch fixes this by adding a new variable
and the related commands to set/show it.
This follows the principles of similar variables
configuring e.g. the nr of remote watchpoints.

With the last svn Valgrind, and this patch, the following
watchpoint will be handled at a reasonable (i.e. "valgrind")
speed:
In the program being debugged:
  char s[1000];

in gdb:
  awatch s

as the hardware watchpoint will be accepted by the valgrind
gdbserver, and implemented using Valgrind validity bits
mechanism.


The change is small, so no paper signing might be needed.
But if deemed necessary, I can sign the needed papers.


Here is the change log entry for this change.

2011-05-14  Philippe Waroquiers <philippe.waroquiers@skynet.be>
 * remote.c (remote_region_ok_for_hw_watchpoint): New function.
 (remote_hw_watchpoint_length_limit): New variable.
 (_initialize_remote) add set,show cmds for this new variable.
 gdb.texinfo: document these new commands.

Index: gdb/remote.c
===================================================================
RCS file: /cvs/src/src/gdb/remote.c,v
retrieving revision 1.446
diff -c -p -r1.446 remote.c
*** gdb/remote.c 12 May 2011 12:09:16 -0000 1.446
--- gdb/remote.c 14 May 2011 14:40:08 -0000
*************** remote_remove_watchpoint (CORE_ADDR addr
*** 7756,7764 ****
--- 7756,7778 ----
  
  
  int remote_hw_watchpoint_limit = -1;
+ int remote_hw_watchpoint_length_limit = -1;
  int remote_hw_breakpoint_limit = -1;
  
  static int
+ remote_region_ok_for_hw_watchpoint (CORE_ADDR addr, int len)
+ {
+   if (remote_hw_watchpoint_length_limit == 0)
+     return 0;
+   else if (remote_hw_watchpoint_length_limit < 0)
+     return 1;
+   else if (len <= remote_hw_watchpoint_length_limit)
+     return 1;
+   else
+     return 0;
+ }
+ 
+ static int
  remote_check_watch_resources (int type, int cnt, int ot)
  {
    if (type == bp_hardware_breakpoint)
*************** Specify the serial device it is connecte
*** 10326,10331 ****
--- 10340,10347 ----
    remote_ops.to_can_use_hw_breakpoint = remote_check_watch_resources;
    remote_ops.to_insert_hw_breakpoint = remote_insert_hw_breakpoint;
    remote_ops.to_remove_hw_breakpoint = remote_remove_hw_breakpoint;
+   remote_ops.to_region_ok_for_hw_watchpoint
+      = remote_region_ok_for_hw_watchpoint;
    remote_ops.to_insert_watchpoint = remote_insert_watchpoint;
    remote_ops.to_remove_watchpoint = remote_remove_watchpoint;
    remote_ops.to_kill = remote_kill;
*************** Specify a negative limit for unlimited."
*** 10735,10740 ****
--- 10751,10763 ----
          number of target hardware
          watchpoints is %s.  */
         &remote_set_cmdlist, &remote_show_cmdlist);
+   add_setshow_zinteger_cmd ("hardware-watchpoint-length-limit", no_class,
+        &remote_hw_watchpoint_length_limit, _("\
+ Set the maximum length of a target hardware watchpoint."), _("\
+ Show the maximum length of a target hardware watchpoint."), _("\
+ Specify a negative limit for unlimited."),
+        NULL, NULL, /* FIXME: i18n: The maximum length of a target hardware watchpoint is %s.  */
+        &remote_set_cmdlist, &remote_show_cmdlist);
    add_setshow_zinteger_cmd ("hardware-breakpoint-limit", no_class,
         &remote_hw_breakpoint_limit, _("\
  Set the maximum number of target hardware breakpoints."), _("\
Index: gdb/doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.838
diff -c -p -r1.838 gdb.texinfo
*** gdb/doc/gdb.texinfo 13 May 2011 22:36:07 -0000 1.838
--- gdb/doc/gdb.texinfo 14 May 2011 14:40:33 -0000
*************** responses.
*** 16578,16583 ****
--- 16578,16591 ----
  Restrict @value{GDBN} to using @var{limit} remote hardware breakpoint or
  watchpoints.  A limit of -1, the default, is treated as unlimited.
  
+ @cindex limit hardware watchpoints length
+ @cindex remote target, limit watchpoints length
+ @anchor{set remote hardware-watchpoint-length-limit}
+ @item set remote hardware-watchpoint-length-limit @var{limit}
+ Restrict @value{GDBN} to using @var{limit} for the maximum length of
+ remote hardware watchpoints.  A limit of -1, the default, is treated
+ as unlimited.
+ 
  @item set remote exec-file @var{filename}
  @itemx show remote exec-file
  @anchor{set remote exec-file}

[-- Attachment #2: set-length-limit-desc.txt --]
[-- Type: text/plain, Size: 4869 bytes --]


A gdbserver has been integrated in Valgrind svn version.
(see https://bugs.kde.org/show_bug.cgi?id=214909 for details).

This gdbserver can provide 'unlimited' watchpoint length
using the Valgrind memcheck machinery. Such watchpoints
are slower than hardware watchpoints, but are faster
that gdb software watchpoints.
However, gdb remote.c hardcodes the length of a remote
watchpoint to 4 bytes (which looks like a bug).
The attached patch fixes this by adding a new variable
and the related commands to set/show it.
This follows the principles of similar variables
configuring e.g. the nr of remote watchpoints.

With the last svn Valgrind, and this patch, the following
watchpoint will be handled at a reasonable (i.e. "valgrind")
speed:
In the program being debugged:
  char s[1000];

in gdb:
  awatch s

as the hardware watchpoint will be accepted by the valgrind
gdbserver, and implemented using Valgrind validity bits
mechanism.


The change is small, so no paper signing might be needed.
But if deemed necessary, I can sign the needed papers.


Here is the change log entry for this change.

2011-05-14  Philippe Waroquiers <philippe.waroquiers@skynet.be>
	* remote.c (remote_region_ok_for_hw_watchpoint): New function.
	(remote_hw_watchpoint_length_limit): New variable.
	(_initialize_remote) add set,show cmds for this new variable.
	gdb.texinfo: document these new commands.

Index: gdb/remote.c
===================================================================
RCS file: /cvs/src/src/gdb/remote.c,v
retrieving revision 1.446
diff -c -p -r1.446 remote.c
*** gdb/remote.c	12 May 2011 12:09:16 -0000	1.446
--- gdb/remote.c	14 May 2011 14:40:08 -0000
*************** remote_remove_watchpoint (CORE_ADDR addr
*** 7756,7764 ****
--- 7756,7778 ----
  
  
  int remote_hw_watchpoint_limit = -1;
+ int remote_hw_watchpoint_length_limit = -1;
  int remote_hw_breakpoint_limit = -1;
  
  static int
+ remote_region_ok_for_hw_watchpoint (CORE_ADDR addr, int len)
+ {
+   if (remote_hw_watchpoint_length_limit == 0)
+     return 0;
+   else if (remote_hw_watchpoint_length_limit < 0)
+     return 1;
+   else if (len <= remote_hw_watchpoint_length_limit)
+     return 1;
+   else
+     return 0;
+ }
+ 
+ static int
  remote_check_watch_resources (int type, int cnt, int ot)
  {
    if (type == bp_hardware_breakpoint)
*************** Specify the serial device it is connecte
*** 10326,10331 ****
--- 10340,10347 ----
    remote_ops.to_can_use_hw_breakpoint = remote_check_watch_resources;
    remote_ops.to_insert_hw_breakpoint = remote_insert_hw_breakpoint;
    remote_ops.to_remove_hw_breakpoint = remote_remove_hw_breakpoint;
+   remote_ops.to_region_ok_for_hw_watchpoint
+      = remote_region_ok_for_hw_watchpoint;
    remote_ops.to_insert_watchpoint = remote_insert_watchpoint;
    remote_ops.to_remove_watchpoint = remote_remove_watchpoint;
    remote_ops.to_kill = remote_kill;
*************** Specify a negative limit for unlimited."
*** 10735,10740 ****
--- 10751,10763 ----
  					   number of target hardware
  					   watchpoints is %s.  */
  			    &remote_set_cmdlist, &remote_show_cmdlist);
+   add_setshow_zinteger_cmd ("hardware-watchpoint-length-limit", no_class,
+ 			    &remote_hw_watchpoint_length_limit, _("\
+ Set the maximum length of a target hardware watchpoint."), _("\
+ Show the maximum length of a target hardware watchpoint."), _("\
+ Specify a negative limit for unlimited."),
+ 			    NULL, NULL, /* FIXME: i18n: The maximum length of a target hardware watchpoint is %s.  */
+ 			    &remote_set_cmdlist, &remote_show_cmdlist);
    add_setshow_zinteger_cmd ("hardware-breakpoint-limit", no_class,
  			    &remote_hw_breakpoint_limit, _("\
  Set the maximum number of target hardware breakpoints."), _("\
Index: gdb/doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.838
diff -c -p -r1.838 gdb.texinfo
*** gdb/doc/gdb.texinfo	13 May 2011 22:36:07 -0000	1.838
--- gdb/doc/gdb.texinfo	14 May 2011 14:40:33 -0000
*************** responses.
*** 16578,16583 ****
--- 16578,16591 ----
  Restrict @value{GDBN} to using @var{limit} remote hardware breakpoint or
  watchpoints.  A limit of -1, the default, is treated as unlimited.
  
+ @cindex limit hardware watchpoints length
+ @cindex remote target, limit watchpoints length
+ @anchor{set remote hardware-watchpoint-length-limit}
+ @item set remote hardware-watchpoint-length-limit @var{limit}
+ Restrict @value{GDBN} to using @var{limit} for the maximum length of
+ remote hardware watchpoints.  A limit of -1, the default, is treated
+ as unlimited.
+ 
  @item set remote exec-file @var{filename}
  @itemx show remote exec-file
  @anchor{set remote exec-file}

Re: PATCH : allow to set length of hw watchpoints (e.g. for Valgrind gdbserver)

[Eli Zaretskii]

> From: "Philippe Waroquiers" <philippe.waroquiers@skynet.be>
> Date: Sun, 15 May 2011 19:38:44 +0200
> 
> With the last svn Valgrind, and this patch, the following
> watchpoint will be handled at a reasonable (i.e. "valgrind")
> speed:
> In the program being debugged:
>   char s[1000];
> 
> in gdb:
>   awatch s
> 
> as the hardware watchpoint will be accepted by the valgrind
> gdbserver, and implemented using Valgrind validity bits
> mechanism.

If this is accepted, I think this is NEWS worthy.

A few comments to the documentation part:

> + @item set remote hardware-watchpoint-length-limit @var{limit}
> + Restrict @value{GDBN} to using @var{limit} for the maximum length of
> + remote hardware watchpoints.  A limit of -1, the default, is treated
> + as unlimited.

I think we should tell explicitly that the limit is in bytes.  (Btw,
why the corresponding data types are `int' and not `ssize_t'?)

Also, I think we also document the "show" counterpart of each "set"
command.

Thanks.

Re: PATCH : allow to set length of hw watchpoints (e.g. for Valgrind gdbserver)

[Philippe Waroquiers]

[-- Attachment #1: Type: text/plain, Size: 5625 bytes --]

Thanks for the quick review.
Find below a new version of the patch (also in attachment).

> If this is accepted, I think this is NEWS worthy.
Added a paragraph to describe this. 

> I think we should tell explicitly that the limit is in bytes.  (Btw,
> why the corresponding data types are `int' and not `ssize_t'?)
Added 'in bytes' in the doc and in the on-line command description.
Note that I have kept 'int' as all other similar variables are int, and an int
will be large enough for any reasonable watchpoint.

> Also, I think we also document the "show" counterpart of each "set"
> command.
Done.

2011-05-14  Philippe Waroquiers <philippe.waroquiers@skynet.be>
 * remote.c (remote_region_ok_for_hw_watchpoint): New function.
 (remote_hw_watchpoint_length_limit): New variable.
 (_initialize_remote) add set,show cmds for this new variable.
 gdb.texinfo: document these new commands.
 NEWS: document the change.

Index: gdb/NEWS
===================================================================
RCS file: /cvs/src/src/gdb/NEWS,v
retrieving revision 1.441
diff -c -p -r1.441 NEWS
*** gdb/NEWS 13 May 2011 22:36:06 -0000 1.441
--- gdb/NEWS 15 May 2011 19:51:54 -0000
***************
*** 3,8 ****
--- 3,18 ----
  
  *** Changes since GDB 7.3
  
+ * GDB has two new commands: "set remote hardware-watchpoint-length-limit"
+   and "show remote hardware-watchpoint-length-limit". These allows to
+   set or show the maximum length limit (in bytes) of a remote
+   target hardware watchpoint.
+ 
+   This allows e.g. to use "unlimited" hardware watchpoints with the
+   gdbserver integrated in Valgrind version >= 3.7.0. Such Valgrind
+   watchpoints are slower than real hardware watchpoints but are
+   significantly faster than gdb software watchpoints.
+ 
  * libthread-db-search-path now supports two special values: $sdir and $pdir.
    $sdir specifies the default system locations of shared libraries.
    $pdir specifies the directory where the libpthread used by the application
Index: gdb/remote.c
===================================================================
RCS file: /cvs/src/src/gdb/remote.c,v
retrieving revision 1.446
diff -c -p -r1.446 remote.c
*** gdb/remote.c 12 May 2011 12:09:16 -0000 1.446
--- gdb/remote.c 15 May 2011 19:52:00 -0000
*************** remote_remove_watchpoint (CORE_ADDR addr
*** 7756,7764 ****
--- 7756,7778 ----
  
  
  int remote_hw_watchpoint_limit = -1;
+ int remote_hw_watchpoint_length_limit = -1;
  int remote_hw_breakpoint_limit = -1;
  
  static int
+ remote_region_ok_for_hw_watchpoint (CORE_ADDR addr, int len)
+ {
+   if (remote_hw_watchpoint_length_limit == 0)
+     return 0;
+   else if (remote_hw_watchpoint_length_limit < 0)
+     return 1;
+   else if (len <= remote_hw_watchpoint_length_limit)
+     return 1;
+   else
+     return 0;
+ }
+ 
+ static int
  remote_check_watch_resources (int type, int cnt, int ot)
  {
    if (type == bp_hardware_breakpoint)
*************** Specify the serial device it is connecte
*** 10326,10331 ****
--- 10340,10347 ----
    remote_ops.to_can_use_hw_breakpoint = remote_check_watch_resources;
    remote_ops.to_insert_hw_breakpoint = remote_insert_hw_breakpoint;
    remote_ops.to_remove_hw_breakpoint = remote_remove_hw_breakpoint;
+   remote_ops.to_region_ok_for_hw_watchpoint
+      = remote_region_ok_for_hw_watchpoint;
    remote_ops.to_insert_watchpoint = remote_insert_watchpoint;
    remote_ops.to_remove_watchpoint = remote_remove_watchpoint;
    remote_ops.to_kill = remote_kill;
*************** Specify a negative limit for unlimited."
*** 10735,10740 ****
--- 10751,10765 ----
          number of target hardware
          watchpoints is %s.  */
         &remote_set_cmdlist, &remote_show_cmdlist);
+   add_setshow_zinteger_cmd ("hardware-watchpoint-length-limit", no_class,
+        &remote_hw_watchpoint_length_limit, _("\
+ Set the maximum length (in bytes) of a target hardware watchpoint."), _("\
+ Show the maximum length (in bytes) of a target hardware watchpoint."), _("\
+ Specify a negative limit for unlimited."),
+        NULL, NULL, /* FIXME: i18n: The maximum
+                                            length (in bytes) of a target
+                                            hardware watchpoint is %s.  */
+        &remote_set_cmdlist, &remote_show_cmdlist);
    add_setshow_zinteger_cmd ("hardware-breakpoint-limit", no_class,
         &remote_hw_breakpoint_limit, _("\
  Set the maximum number of target hardware breakpoints."), _("\
Index: gdb/doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.838
diff -c -p -r1.838 gdb.texinfo
*** gdb/doc/gdb.texinfo 13 May 2011 22:36:07 -0000 1.838
--- gdb/doc/gdb.texinfo 15 May 2011 19:52:25 -0000
*************** responses.
*** 16578,16583 ****
--- 16578,16595 ----
  Restrict @value{GDBN} to using @var{limit} remote hardware breakpoint or
  watchpoints.  A limit of -1, the default, is treated as unlimited.
  
+ @cindex limit hardware watchpoints length
+ @cindex remote target, limit watchpoints length
+ @anchor{set remote hardware-watchpoint-length-limit}
+ @item set remote hardware-watchpoint-length-limit @var{limit}
+ Restrict @value{GDBN} to using @var{limit} bytes for the maximum length of
+ a remote hardware watchpoint.  A limit of -1, the default, is treated
+ as unlimited.
+ 
+ @item show remote hardware-watchpoint-length-limit
+ Show the current limit (in bytes) of the maximum length of
+ a remote hardware watchpoint.
+ 
  @item set remote exec-file @var{filename}
  @itemx show remote exec-file
  @anchor{set remote exec-file}

[-- Attachment #2: set-length-limit-3.desc.txt --]
[-- Type: text/plain, Size: 5144 bytes --]

2011-05-14  Philippe Waroquiers <philippe.waroquiers@skynet.be>
	* remote.c (remote_region_ok_for_hw_watchpoint): New function.
	(remote_hw_watchpoint_length_limit): New variable.
	(_initialize_remote) add set,show cmds for this new variable.
	gdb.texinfo: document these new commands.
	NEWS: document the change.

Index: gdb/NEWS
===================================================================
RCS file: /cvs/src/src/gdb/NEWS,v
retrieving revision 1.441
diff -c -p -r1.441 NEWS
*** gdb/NEWS	13 May 2011 22:36:06 -0000	1.441
--- gdb/NEWS	15 May 2011 19:51:54 -0000
***************
*** 3,8 ****
--- 3,18 ----
  
  *** Changes since GDB 7.3
  
+ * GDB has two new commands: "set remote hardware-watchpoint-length-limit"
+   and "show remote hardware-watchpoint-length-limit". These allows to
+   set or show the maximum length limit (in bytes) of a remote
+   target hardware watchpoint.
+ 
+   This allows e.g. to use "unlimited" hardware watchpoints with the
+   gdbserver integrated in Valgrind version >= 3.7.0. Such Valgrind
+   watchpoints are slower than real hardware watchpoints but are
+   significantly faster than gdb software watchpoints.
+ 
  * libthread-db-search-path now supports two special values: $sdir and $pdir.
    $sdir specifies the default system locations of shared libraries.
    $pdir specifies the directory where the libpthread used by the application
Index: gdb/remote.c
===================================================================
RCS file: /cvs/src/src/gdb/remote.c,v
retrieving revision 1.446
diff -c -p -r1.446 remote.c
*** gdb/remote.c	12 May 2011 12:09:16 -0000	1.446
--- gdb/remote.c	15 May 2011 19:52:00 -0000
*************** remote_remove_watchpoint (CORE_ADDR addr
*** 7756,7764 ****
--- 7756,7778 ----
  
  
  int remote_hw_watchpoint_limit = -1;
+ int remote_hw_watchpoint_length_limit = -1;
  int remote_hw_breakpoint_limit = -1;
  
  static int
+ remote_region_ok_for_hw_watchpoint (CORE_ADDR addr, int len)
+ {
+   if (remote_hw_watchpoint_length_limit == 0)
+     return 0;
+   else if (remote_hw_watchpoint_length_limit < 0)
+     return 1;
+   else if (len <= remote_hw_watchpoint_length_limit)
+     return 1;
+   else
+     return 0;
+ }
+ 
+ static int
  remote_check_watch_resources (int type, int cnt, int ot)
  {
    if (type == bp_hardware_breakpoint)
*************** Specify the serial device it is connecte
*** 10326,10331 ****
--- 10340,10347 ----
    remote_ops.to_can_use_hw_breakpoint = remote_check_watch_resources;
    remote_ops.to_insert_hw_breakpoint = remote_insert_hw_breakpoint;
    remote_ops.to_remove_hw_breakpoint = remote_remove_hw_breakpoint;
+   remote_ops.to_region_ok_for_hw_watchpoint
+      = remote_region_ok_for_hw_watchpoint;
    remote_ops.to_insert_watchpoint = remote_insert_watchpoint;
    remote_ops.to_remove_watchpoint = remote_remove_watchpoint;
    remote_ops.to_kill = remote_kill;
*************** Specify a negative limit for unlimited."
*** 10735,10740 ****
--- 10751,10765 ----
  					   number of target hardware
  					   watchpoints is %s.  */
  			    &remote_set_cmdlist, &remote_show_cmdlist);
+   add_setshow_zinteger_cmd ("hardware-watchpoint-length-limit", no_class,
+ 			    &remote_hw_watchpoint_length_limit, _("\
+ Set the maximum length (in bytes) of a target hardware watchpoint."), _("\
+ Show the maximum length (in bytes) of a target hardware watchpoint."), _("\
+ Specify a negative limit for unlimited."),
+ 			    NULL, NULL, /* FIXME: i18n: The maximum
+                                            length (in bytes) of a target
+                                            hardware watchpoint is %s.  */
+ 			    &remote_set_cmdlist, &remote_show_cmdlist);
    add_setshow_zinteger_cmd ("hardware-breakpoint-limit", no_class,
  			    &remote_hw_breakpoint_limit, _("\
  Set the maximum number of target hardware breakpoints."), _("\
Index: gdb/doc/gdb.texinfo
===================================================================
RCS file: /cvs/src/src/gdb/doc/gdb.texinfo,v
retrieving revision 1.838
diff -c -p -r1.838 gdb.texinfo
*** gdb/doc/gdb.texinfo	13 May 2011 22:36:07 -0000	1.838
--- gdb/doc/gdb.texinfo	15 May 2011 19:52:25 -0000
*************** responses.
*** 16578,16583 ****
--- 16578,16595 ----
  Restrict @value{GDBN} to using @var{limit} remote hardware breakpoint or
  watchpoints.  A limit of -1, the default, is treated as unlimited.
  
+ @cindex limit hardware watchpoints length
+ @cindex remote target, limit watchpoints length
+ @anchor{set remote hardware-watchpoint-length-limit}
+ @item set remote hardware-watchpoint-length-limit @var{limit}
+ Restrict @value{GDBN} to using @var{limit} bytes for the maximum length of
+ a remote hardware watchpoint.  A limit of -1, the default, is treated
+ as unlimited.
+ 
+ @item show remote hardware-watchpoint-length-limit
+ Show the current limit (in bytes) of the maximum length of
+ a remote hardware watchpoint.
+ 
  @item set remote exec-file @var{filename}
  @itemx show remote exec-file
  @anchor{set remote exec-file}

Re: PATCH : allow to set length of hw watchpoints (e.g. for Valgrind gdbserver)

[Eli Zaretskii]

> From: "Philippe Waroquiers" <philippe.waroquiers@skynet.be>
> Cc: <gdb-patches@sourceware.org>
> Date: Sun, 15 May 2011 22:11:54 +0200
> 
> Note that I have kept 'int' as all other similar variables are int, and an int
> will be large enough for any reasonable watchpoint.

I'm not convinced, but I'll let others speak up.

>  gdb.texinfo: document these new commands.
>  NEWS: document the change.

These are fine, but please leave 2 spaces between sentences in the
NEWS entry.

Re: PATCH : allow to set length of hw watchpoints (e.g. for Valgrind gdbserver)

[Philippe Waroquiers]

>> Note that I have kept 'int' as all other similar variables are int, and an int
>> will be large enough for any reasonable watchpoint.
> 
> I'm not convinced, but I'll let others speak up.
I was also (initially) convinced to go for ssize_t.
But the reason given above +  the fact that I could not find the equivalent 
of add_setshow_zinteger_cmd for an ssize_t made me believe an int was
good enough.
For sure, if such an equivalent exists, it will be trivial to change to ssize_t.
Without such an equivalent, there will be some more work
to define e.g. add_setshow_zssize_t_cmd.

> These are fine, but please leave 2 spaces between sentences in the
> NEWS entry.
I assume there will be some other comments (maybe related to ssize_t).
I will update NEWS together with handling the other comments.

Thanks again for the review.

Philippe