[PATCH v4 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_TRAP 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, imprecise_pagefault_reporting, that allows the
signal conversion from GDB_SIGNAL_SEGV to GDB_SIGNAL_TRAP to be skipped for
an architecture.  The default is false (conversion enabled), preserving
existing behavior.
---
 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 f424fa2a86e..d9bb3e7078c 100644
--- a/gdb/gdbarch-gen.c
+++ b/gdb/gdbarch-gen.c
@@ -253,6 +253,7 @@ struct gdbarch
   gdbarch_core_parse_exec_context_ftype *core_parse_exec_context = default_core_parse_exec_context;
   gdbarch_shadow_stack_push_ftype *shadow_stack_push = nullptr;
   gdbarch_get_shadow_stack_pointer_ftype *get_shadow_stack_pointer = default_get_shadow_stack_pointer;
+  gdbarch_imprecise_pagefault_reporting_ftype *imprecise_pagefault_reporting = [] () -> bool {return false;};
 };
 
 /* Create a new ``struct gdbarch'' based on information provided by
@@ -513,6 +514,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* Skip verify of core_parse_exec_context, invalid_p == 0.  */
   /* Skip verify of shadow_stack_push, has predicate.  */
   /* Skip verify of get_shadow_stack_pointer, 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 ());
@@ -1339,6 +1341,9 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
   gdb_printf (file,
 	      "gdbarch_dump: get_shadow_stack_pointer = <%s>\n",
 	      host_address_to_string (gdbarch->get_shadow_stack_pointer));
+  gdb_printf (file,
+	      "gdbarch_dump: imprecise_pagefault_reporting = <%s>\n",
+	      host_address_to_string (gdbarch->imprecise_pagefault_reporting));
   if (gdbarch->dump_tdep != nullptr)
     gdbarch->dump_tdep (gdbarch, file);
 }
@@ -5286,3 +5291,20 @@ set_gdbarch_get_shadow_stack_pointer (struct gdbarch *gdbarch,
 {
   gdbarch->get_shadow_stack_pointer = get_shadow_stack_pointer;
 }
+
+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 678b308fba5..bb95df25eb6 100644
--- a/gdb/gdbarch-gen.h
+++ b/gdb/gdbarch-gen.h
@@ -1752,3 +1752,10 @@ void set_gdbarch_shadow_stack_push (struct gdbarch *gdbarch, gdbarch_shadow_stac
 using gdbarch_get_shadow_stack_pointer_ftype = std::optional<CORE_ADDR> (struct gdbarch *gdbarch, regcache *regcache, bool &shadow_stack_enabled);
 std::optional<CORE_ADDR> gdbarch_get_shadow_stack_pointer (struct gdbarch *gdbarch, regcache *regcache, bool &shadow_stack_enabled);
 void set_gdbarch_get_shadow_stack_pointer (struct gdbarch *gdbarch, gdbarch_get_shadow_stack_pointer_ftype *get_shadow_stack_pointer);
+
+/* 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 b9304d3036d..d903446435f 100644
--- a/gdb/gdbarch_components.py
+++ b/gdb/gdbarch_components.py
@@ -2781,3 +2781,15 @@ SHADOW_STACK_ENABLED to false.
     predefault="default_get_shadow_stack_pointer",
     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 c0767e7f764..25ed7e7523f 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -6331,7 +6331,9 @@ 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
+		  (target_thread_architecture (ecs->event_thread->ptid)))
 	  || ecs->ws.sig () == GDB_SIGNAL_EMT))
     {
       struct regcache *regcache = get_thread_regcache (ecs->event_thread);
-- 
2.34.1

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