[PATCH v2 0/3] Check for zpoint support when handling watchpoints

[PATCH v2 0/3] Check for zpoint support when handling watchpoints

[Mohamed Bouhaouel]

Hi all,

Many thanks Guinevere Larsen for your feedback, I updated this patch
series accordingly.

V1 of this series can be found here:
https://sourceware.org/pipermail/gdb-patches/2023-March/198371.html

Changes since V1:
* Updated the commit message of the first patch
* Added a NEWS entry.
* Updated the 'qSupported' features in the remote protocol documentation.

Regards,
Mohamed

Mohamed Bouhaouel (3):
  gdb, gdbserver, zpoint: report z_point support
  gdb, breakpoint: add a breakpoint type converter
  gdb, zpoint: check for target hardware breakpoint support

 gdb/NEWS               |  3 +++
 gdb/breakpoint.c       | 20 ++++++++++++++++++++
 gdb/breakpoint.h       |  3 +++
 gdb/doc/gdb.texinfo    | 30 ++++++++++++++++++++++++++++++
 gdb/remote.c           | 41 ++++++++++++++++++++++++++++++++++++++---
 gdbserver/mem-break.cc |  2 +-
 gdbserver/mem-break.h  |  4 ++++
 gdbserver/server.cc    |  7 +++++++
 8 files changed, 106 insertions(+), 4 deletions(-)

-- 
2.25.1

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

[PATCH v2 1/3] gdb, gdbserver, zpoint: report z_point support

[Mohamed Bouhaouel]

Make gdbserver report which types of breakpoints and watchpoints
are supported when exchanging features.  This is done by replying with
Z<type>+ (Supported) or Z<type>- (unsupported)
---
 gdb/NEWS               |  4 ++++
 gdb/doc/gdb.texinfo    | 32 ++++++++++++++++++++++++++++++++
 gdb/remote.c           | 16 ++++++++++++++++
 gdbserver/mem-break.cc |  2 +-
 gdbserver/mem-break.h  |  4 ++++
 gdbserver/server.cc    |  7 +++++++
 6 files changed, 64 insertions(+), 1 deletion(-)

diff --git a/gdb/NEWS b/gdb/NEWS
index 682def44ce0..8146f695df3 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -49,6 +49,10 @@ QThreadOptions in qSupported
   QThreadOptions packet, and the qSupported response can contain the
   set of thread options the remote stub supports.
 
+qSupported
+  Gdbserver now reports which types of breakpoints and watchpoints
+  are supported when exchanging features using Z<type>+, Z<type>-.
+
 *** Changes in GDB 14
 
 * GDB now supports the AArch64 Scalable Matrix Extension 2 (SME2), which
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index e4c00143fd1..20f1906be97 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -44631,6 +44631,31 @@ These are the currently defined stub features and their properties:
 @tab @samp{-}
 @tab No
 
+@item @samp{Z0}
+@tab No
+@tab @samp{-}
+@tab No
+
+@item @samp{Z1}
+@tab No
+@tab @samp{-}
+@tab No
+
+@item @samp{Z2}
+@tab No
+@tab @samp{-}
+@tab No
+
+@item @samp{Z3}
+@tab No
+@tab @samp{-}
+@tab No
+
+@item @samp{Z4}
+@tab No
+@tab @samp{-}
+@tab No
+
 @end multitable
 
 These are the currently defined stub features, in more detail:
@@ -44858,6 +44883,13 @@ The remote stub supports and implements the required memory tagging
 functionality and understands the @samp{qMemTags} (@pxref{qMemTags}) and
 @samp{QMemTags} (@pxref{QMemTags}) packets.
 
+@item Z@var{type}
+The remote stub reports which types of breakpoints and watchpoints are
+supported.  This is done using flags, @samp{Z}@var{type}@samp{+} for supported
+and @samp{Z}@var{type}@samp{-} for unsupported, where @var{type} is one of
+@samp{0}, @samp{1}, @samp{2}, @samp{3}, @samp{4}
+(@pxref{insert breakpoint or watchpoint packet}).
+
 For AArch64 GNU/Linux systems, this feature also requires access to the
 @file{/proc/@var{pid}/smaps} file so memory mapping page flags can be inspected.
 This is done via the @samp{vFile} requests.
diff --git a/gdb/remote.c b/gdb/remote.c
index ce5addade6f..7aa380a5989 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -808,6 +808,10 @@ class remote_target : public process_stratum_target
   int insert_watchpoint (CORE_ADDR, int, enum target_hw_bp_type,
 			 struct expression *) override;
 
+  /* Returns true if GDB Z breakpoint type TYPE is supported,
+     false otherwise.  */
+  bool supports_z_point_type (int type);
+
   int remove_watchpoint (CORE_ADDR, int, enum target_hw_bp_type,
 			 struct expression *) override;
 
@@ -5717,6 +5721,11 @@ static const struct protocol_feature remote_protocol_features[] = {
   { "no-resumed", PACKET_DISABLE, remote_supported_packet, PACKET_no_resumed },
   { "memory-tagging", PACKET_DISABLE, remote_supported_packet,
     PACKET_memory_tagging_feature },
+  { "Z0", PACKET_SUPPORT_UNKNOWN, remote_supported_packet, PACKET_Z0 },
+  { "Z1", PACKET_SUPPORT_UNKNOWN, remote_supported_packet, PACKET_Z1 },
+  { "Z2", PACKET_SUPPORT_UNKNOWN, remote_supported_packet, PACKET_Z2 },
+  { "Z3", PACKET_SUPPORT_UNKNOWN, remote_supported_packet, PACKET_Z3 },
+  { "Z4", PACKET_SUPPORT_UNKNOWN, remote_supported_packet, PACKET_Z4 },
 };
 
 static char *remote_support_xml;
@@ -10991,6 +11000,13 @@ watchpoint_to_Z_packet (int type)
     }
 }
 
+bool
+remote_target::supports_z_point_type (int type)
+{
+  Z_packet_type packet = watchpoint_to_Z_packet (type);
+  return (m_features.packet_support (PACKET_Z0 + packet) != PACKET_DISABLE);
+}
+
 int
 remote_target::insert_watchpoint (CORE_ADDR addr, int len,
 				  enum target_hw_bp_type type, struct expression *cond)
diff --git a/gdbserver/mem-break.cc b/gdbserver/mem-break.cc
index 3bee8bc8990..7c3a1d1d47e 100644
--- a/gdbserver/mem-break.cc
+++ b/gdbserver/mem-break.cc
@@ -998,7 +998,7 @@ find_gdb_breakpoint (char z_type, CORE_ADDR addr, int kind)
   return NULL;
 }
 
-static int
+int
 z_type_supported (char z_type)
 {
   return (z_type >= '0' && z_type <= '4'
diff --git a/gdbserver/mem-break.h b/gdbserver/mem-break.h
index 9bf7aa84932..b27f0a23ac2 100644
--- a/gdbserver/mem-break.h
+++ b/gdbserver/mem-break.h
@@ -276,4 +276,8 @@ int remove_memory_breakpoint (struct raw_breakpoint *bp);
 void clone_all_breakpoints (struct thread_info *child_thread,
 			    const struct thread_info *parent_thread);
 
+
+/* Returns true if Z_TYPE is supported by the target.  */
+
+int z_type_supported (char z_type);
 #endif /* GDBSERVER_MEM_BREAK_H */
diff --git a/gdbserver/server.cc b/gdbserver/server.cc
index a8e23561dcb..e727973ad45 100644
--- a/gdbserver/server.cc
+++ b/gdbserver/server.cc
@@ -2613,6 +2613,13 @@ handle_query (char *own_buf, int packet_len, int *new_packet_len_p)
       if (target_supports_memory_tagging ())
 	strcat (own_buf, ";memory-tagging+");
 
+      /* Z points support.  */
+      strcat (own_buf, z_type_supported ('0') ? ";Z0+" : ";Z0-");
+      strcat (own_buf, z_type_supported ('1') ? ";Z1+" : ";Z1-");
+      strcat (own_buf, z_type_supported ('2') ? ";Z2+" : ";Z2-");
+      strcat (own_buf, z_type_supported ('3') ? ";Z3+" : ";Z3-");
+      strcat (own_buf, z_type_supported ('4') ? ";Z4+" : ";Z4-");
+
       /* Reinitialize components as needed for the new connection.  */
       hostio_handle_new_gdb_connection ();
       target_handle_new_gdb_connection ();
-- 
2.25.1

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

[PATCH v2 2/3] gdb, breakpoint: add a breakpoint type converter

[Mohamed Bouhaouel]

Add a new function 'bptype_to_target_hw_bp_type' to perform
the translation from 'bptype' to 'target_hw_bp_type'.

Reviewed-By: Guinevere Larsen <blarsen@redhat.com>
---
 gdb/breakpoint.c | 20 ++++++++++++++++++++
 gdb/breakpoint.h |  3 +++
 2 files changed, 23 insertions(+)

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index fe09dbcbeee..13eaff79789 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -9827,6 +9827,26 @@ watchpoint::~watchpoint ()
   bpt->related_breakpoint = this->related_breakpoint;
 }
 
+/* See breakpoint.h.  */
+
+target_hw_bp_type
+bptype_to_target_hw_bp_type (bptype type)
+{
+  switch (type)
+    {
+    case bp_hardware_watchpoint:
+      return hw_write;
+    case bp_read_watchpoint:
+      return hw_read;
+    case bp_access_watchpoint:
+      return hw_access;
+    case bp_hardware_breakpoint:
+      return hw_execute;
+    default:
+      error (_ ("Bad breakpoint type: bptype %d."), type);
+    }
+}
+
 /*  Return non-zero if EXP is verified as constant.  Returned zero
     means EXP is variable.  Also the constant detection may fail for
     some constant expressions and in such case still falsely return
diff --git a/gdb/breakpoint.h b/gdb/breakpoint.h
index e75efc90495..cc9a1ebc184 100644
--- a/gdb/breakpoint.h
+++ b/gdb/breakpoint.h
@@ -2029,4 +2029,7 @@ extern void enable_disable_bp_location (bp_location *loc, bool enable);
 
 extern void notify_breakpoint_modified (breakpoint *b);
 
+/* Translate BPTYPE to TARGET_HW_BP_TYPE.  */
+
+extern target_hw_bp_type bptype_to_target_hw_bp_type (bptype type);
 #endif /* !defined (BREAKPOINT_H) */
-- 
2.25.1

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

[PATCH v2 3/3] gdb, zpoint: check for target hardware breakpoint support

[Mohamed Bouhaouel]

In 'can_use_hw_breakpoint', check if the target supports
hardware-assisted breakpoints.  This will prevent GDB
from trying to insert the hardware breakpoint in case
it is not supported.

Reviewed-By: Guinevere Larsen <blarsen@redhat.com>
---
 gdb/remote.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/gdb/remote.c b/gdb/remote.c
index 7aa380a5989..10504696a57 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -10982,7 +10982,7 @@ remote_target::remove_breakpoint (struct gdbarch *gdbarch,
 }
 
 static enum Z_packet_type
-watchpoint_to_Z_packet (int type)
+hw_bp_to_Z_packet (int type)
 {
   switch (type)
     {
@@ -10995,6 +10995,9 @@ watchpoint_to_Z_packet (int type)
     case hw_access:
       return Z_PACKET_ACCESS_WP;
       break;
+    case hw_execute:
+      return Z_PACKET_HARDWARE_BP;
+      break;
     default:
       internal_error (_("hw_bp_to_z: bad watchpoint type %d"), type);
     }
@@ -11003,7 +11006,7 @@ watchpoint_to_Z_packet (int type)
 bool
 remote_target::supports_z_point_type (int type)
 {
-  Z_packet_type packet = watchpoint_to_Z_packet (type);
+  Z_packet_type packet = hw_bp_to_Z_packet (type);
   return (m_features.packet_support (PACKET_Z0 + packet) != PACKET_DISABLE);
 }
 
@@ -11014,7 +11017,7 @@ remote_target::insert_watchpoint (CORE_ADDR addr, int len,
   struct remote_state *rs = get_remote_state ();
   char *endbuf = rs->buf.data () + get_remote_packet_size ();
   char *p;
-  enum Z_packet_type packet = watchpoint_to_Z_packet (type);
+  enum Z_packet_type packet = hw_bp_to_Z_packet (type);
 
   if (m_features.packet_support ((to_underlying (PACKET_Z0)
 				  + to_underlying (packet))) == PACKET_DISABLE)
@@ -11064,7 +11067,7 @@ remote_target::remove_watchpoint (CORE_ADDR addr, int len,
   struct remote_state *rs = get_remote_state ();
   char *endbuf = rs->buf.data () + get_remote_packet_size ();
   char *p;
-  enum Z_packet_type packet = watchpoint_to_Z_packet (type);
+  enum Z_packet_type packet = hw_bp_to_Z_packet (type);
 
   if (m_features.packet_support ((to_underlying (PACKET_Z0)
 				  + to_underlying (packet))) == PACKET_DISABLE)
@@ -11118,6 +11121,11 @@ remote_target::can_use_hw_breakpoint (enum bptype type, int cnt, int ot)
 {
   if (type == bp_hardware_breakpoint)
     {
+      /* Check if the target supports hardware-assisted breakpoints.
+	 Return 0 if not.  */
+      if (!supports_z_point_type (bptype_to_target_hw_bp_type (type)))
+	return 0;
+
       if (remote_hw_breakpoint_limit == 0)
 	return 0;
       else if (remote_hw_breakpoint_limit < 0)
@@ -11127,6 +11135,18 @@ remote_target::can_use_hw_breakpoint (enum bptype type, int cnt, int ot)
     }
   else
     {
+      /* Check if the target supports the hardware watchpoint type.
+	 Return 0 if not.  */
+      if (!supports_z_point_type (bptype_to_target_hw_bp_type (type)))
+	{
+	  /* If hw read watchpoints are not supported while hw access are,
+	     GDB will try to insert the watchpoint as hw access.  */
+	  bool access_support = supports_z_point_type (
+	    bptype_to_target_hw_bp_type (bp_access_watchpoint));
+	  if (!(type == bp_read_watchpoint && access_support))
+	    return 0;
+	}
+
       if (remote_hw_watchpoint_limit == 0)
 	return 0;
       else if (remote_hw_watchpoint_limit < 0)
-- 
2.25.1

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

Re: [PATCH v2 1/3] gdb, gdbserver, zpoint: report z_point support

[Eli Zaretskii]

> From: Mohamed Bouhaouel <mohamed.bouhaouel@intel.com>
> Cc: blarsen@redhat.com,
> 	mohamed.bouhaouel@intel.com
> Date: Tue, 14 Nov 2023 10:20:27 +0100
> 
> Make gdbserver report which types of breakpoints and watchpoints
> are supported when exchanging features.  This is done by replying with
> Z<type>+ (Supported) or Z<type>- (unsupported)
> ---
>  gdb/NEWS               |  4 ++++
>  gdb/doc/gdb.texinfo    | 32 ++++++++++++++++++++++++++++++++
>  gdb/remote.c           | 16 ++++++++++++++++
>  gdbserver/mem-break.cc |  2 +-
>  gdbserver/mem-break.h  |  4 ++++
>  gdbserver/server.cc    |  7 +++++++
>  6 files changed, 64 insertions(+), 1 deletion(-)

Thanks.

> diff --git a/gdb/NEWS b/gdb/NEWS
> index 682def44ce0..8146f695df3 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -49,6 +49,10 @@ QThreadOptions in qSupported
>    QThreadOptions packet, and the qSupported response can contain the
>    set of thread options the remote stub supports.
>  
> +qSupported
> +  Gdbserver now reports which types of breakpoints and watchpoints
> +  are supported when exchanging features using Z<type>+, Z<type>-.
> +
>  *** Changes in GDB 14

This part is OK.

> +@item Z@var{type}
> +The remote stub reports which types of breakpoints and watchpoints are
> +supported.  This is done using flags, @samp{Z}@var{type}@samp{+} for supported
                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^
This should be @samp{Z@var{type}+}.  IOW, @var can be nested inside @samp.

> +and @samp{Z}@var{type}@samp{-} for unsupported, where @var{type} is one of
       ^^^^^^^^^^^^^^^^^^^^^^^^^^
Same here.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>