[PATCH v3 1/1] gdb: avoid conversion of SIGSEGV to SIGTRAP on user breakpoints

[Klaus Gerlicher <klaus.gerlicher@intel.com>]

From: "Gerlicher, Klaus" <klaus.gerlicher@intel.com>

GDB converts signals GDB_SIGNAL_ILL, GDB_SIGNAL_SEGV and GDB_SIGNAL_EMT to
GDB_SIGNAL_SEGV if a breakpoint is inserted at the fault location.  If, due
to imprecise page fault reporting, a breakpoint is at the same address as
the fault address, this signal would always be reported as GDB_SIGNAL_TRAP.

Add a new gdbarch function that allows the signal conversion from SIGNAL_SEGV
to SIGNAL_TRAP to be skipped for an architecture.
---
 gdb/gdbarch-gen.c         | 22 ++++++++++++++++++++++
 gdb/gdbarch-gen.h         |  7 +++++++
 gdb/gdbarch_components.py | 12 ++++++++++++
 gdb/infrun.c              |  4 +++-
 4 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/gdb/gdbarch-gen.c b/gdb/gdbarch-gen.c
index d05c7a3cbdf..255f851ffa3 100644
--- a/gdb/gdbarch-gen.c
+++ b/gdb/gdbarch-gen.c
@@ -260,6 +260,7 @@ struct gdbarch
   gdbarch_get_pc_address_flags_ftype *get_pc_address_flags = default_get_pc_address_flags;
   gdbarch_read_core_file_mappings_ftype *read_core_file_mappings = default_read_core_file_mappings;
   gdbarch_use_target_description_from_corefile_notes_ftype *use_target_description_from_corefile_notes = default_use_target_description_from_corefile_notes;
+  gdbarch_imprecise_pagefault_reporting_ftype *imprecise_pagefault_reporting = [] () -> bool {return false;};
 };
 
 /* Create a new ``struct gdbarch'' based on information provided by
@@ -531,6 +532,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* Skip verify of get_pc_address_flags, invalid_p == 0.  */
   /* Skip verify of read_core_file_mappings, invalid_p == 0.  */
   /* Skip verify of use_target_description_from_corefile_notes, invalid_p == 0.  */
+  /* Skip verify of imprecise_pagefault_reporting, invalid_p == 0.  */
   if (!log.empty ())
     internal_error (_("verify_gdbarch: the following are invalid ...%s"),
 		    log.c_str ());
@@ -1396,6 +1398,9 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
   gdb_printf (file,
 	      "gdbarch_dump: use_target_description_from_corefile_notes = <%s>\n",
 	      host_address_to_string (gdbarch->use_target_description_from_corefile_notes));
+  gdb_printf (file,
+	      "gdbarch_dump: imprecise_pagefault_reporting = <%s>\n",
+	      host_address_to_string (gdbarch->imprecise_pagefault_reporting));
   if (gdbarch->dump_tdep != NULL)
     gdbarch->dump_tdep (gdbarch, file);
 }
@@ -5507,3 +5512,20 @@ set_gdbarch_use_target_description_from_corefile_notes (struct gdbarch *gdbarch,
 {
   gdbarch->use_target_description_from_corefile_notes = use_target_description_from_corefile_notes;
 }
+
+bool
+gdbarch_imprecise_pagefault_reporting (struct gdbarch *gdbarch)
+{
+  gdb_assert (gdbarch != NULL);
+  gdb_assert (gdbarch->imprecise_pagefault_reporting != NULL);
+  if (gdbarch_debug >= 2)
+    gdb_printf (gdb_stdlog, "gdbarch_imprecise_pagefault_reporting called\n");
+  return gdbarch->imprecise_pagefault_reporting ();
+}
+
+void
+set_gdbarch_imprecise_pagefault_reporting (struct gdbarch *gdbarch,
+					   gdbarch_imprecise_pagefault_reporting_ftype imprecise_pagefault_reporting)
+{
+  gdbarch->imprecise_pagefault_reporting = imprecise_pagefault_reporting;
+}
diff --git a/gdb/gdbarch-gen.h b/gdb/gdbarch-gen.h
index 9fda85f860f..e2ca6e59680 100644
--- a/gdb/gdbarch-gen.h
+++ b/gdb/gdbarch-gen.h
@@ -1778,3 +1778,10 @@ extern void set_gdbarch_read_core_file_mappings (struct gdbarch *gdbarch, gdbarc
 typedef bool (gdbarch_use_target_description_from_corefile_notes_ftype) (struct gdbarch *gdbarch, struct bfd *corefile_bfd);
 extern bool gdbarch_use_target_description_from_corefile_notes (struct gdbarch *gdbarch, struct bfd *corefile_bfd);
 extern void set_gdbarch_use_target_description_from_corefile_notes (struct gdbarch *gdbarch, gdbarch_use_target_description_from_corefile_notes_ftype *use_target_description_from_corefile_notes);
+
+/* Returns true if architecture has imprecise pagefault reporting.  This is
+   used in conversion of SIGSEGV to SIGTRAP for an architecture. */
+
+typedef bool (gdbarch_imprecise_pagefault_reporting_ftype) ();
+extern bool gdbarch_imprecise_pagefault_reporting (struct gdbarch *gdbarch);
+extern void set_gdbarch_imprecise_pagefault_reporting (struct gdbarch *gdbarch, gdbarch_imprecise_pagefault_reporting_ftype *imprecise_pagefault_reporting);
diff --git a/gdb/gdbarch_components.py b/gdb/gdbarch_components.py
index cc7c6d8677b..8f518e1052a 100644
--- a/gdb/gdbarch_components.py
+++ b/gdb/gdbarch_components.py
@@ -2815,3 +2815,15 @@ The corefile's bfd is passed through COREFILE_BFD.
     predefault="default_use_target_description_from_corefile_notes",
     invalid=False,
 )
+
+Function(
+    comment="""
+Returns true if architecture has imprecise pagefault reporting.  This is
+used in conversion of SIGSEGV to SIGTRAP for an architecture.
+""",
+    type="bool",
+    name="imprecise_pagefault_reporting",
+    params=[],
+    predefault="[] () -> bool {return false;}",
+    invalid=False
+)
diff --git a/gdb/infrun.c b/gdb/infrun.c
index 43eca814e29..eb34aed09e0 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -6138,7 +6138,9 @@ handle_inferior_event (struct execution_control_state *ecs)
      stack.  */
   if (ecs->ws.kind () == TARGET_WAITKIND_STOPPED
       && (ecs->ws.sig () == GDB_SIGNAL_ILL
-	  || ecs->ws.sig () == GDB_SIGNAL_SEGV
+	  || (ecs->ws.sig () == GDB_SIGNAL_SEGV
+	      && !gdbarch_imprecise_pagefault_reporting
+	        (current_inferior ()->arch ()))
 	  || ecs->ws.sig () == GDB_SIGNAL_EMT))
     {
       struct regcache *regcache = get_thread_regcache (ecs->event_thread);
-- 
2.34.1

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