[PATCH v5 1/5] gdb: make gdbarch store a vector of frame unwinders

[Guinevere Larsen <guinevere@redhat.com>]

From: Guinevere Larsen <blarsen@redhat.com>

Before this commit, all frame unwinders would be stored in the obstack
of a gdbarch and accessed by using the registry system. This made for
unwieldy code, and unnecessarily complex logic in the frame_unwinder
implementation, along with making frame_unwind structs be unable to have
non-trivial destructors.

Seeing as a future patch of this series wants to refactor the
frame_unwind struct to use inheritance, and we'd like to not restrict
the future derived classes on what destructors are allowed. In
preparation for that change, this commit adds an std::vector to gdbarch
to store the unwinders in.

There should be no user-visible changes.
---
 gdb/arch-utils.c   |   8 ++++
 gdb/frame-unwind.c | 113 +++++++++++++++++----------------------------
 gdb/gdbarch-gen.c  |   6 +++
 gdb/gdbarch.h      |   5 ++
 gdb/gdbarch.py     |   6 +++
 5 files changed, 67 insertions(+), 71 deletions(-)

diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
index 6ffa4109765..5a4ed097321 100644
--- a/gdb/arch-utils.c
+++ b/gdb/arch-utils.c
@@ -1225,6 +1225,14 @@ obstack *gdbarch_obstack (gdbarch *arch)
 
 /* See gdbarch.h.  */
 
+std::vector<const frame_unwind *> &
+gdbarch_unwinder_list (struct gdbarch *arch)
+{
+  return arch->unwinders;
+}
+
+/* See gdbarch.h.  */
+
 char *
 gdbarch_obstack_strdup (struct gdbarch *arch, const char *string)
 {
diff --git a/gdb/frame-unwind.c b/gdb/frame-unwind.c
index e5f108d3257..b69ae8596a2 100644
--- a/gdb/frame-unwind.c
+++ b/gdb/frame-unwind.c
@@ -31,62 +31,46 @@
 #include "cli/cli-cmds.h"
 #include "inferior.h"
 
-struct frame_unwind_table_entry
+/* Default sniffers, that must always be the first in the unwinder list,
+   no matter the architecture.  */
+static constexpr auto standard_unwinders =
 {
-  const struct frame_unwind *unwinder;
-  struct frame_unwind_table_entry *next;
-};
+  &dummy_frame_unwind,
+  /* The DWARF tailcall sniffer must come before the inline sniffer.
+     Otherwise, we can end up in a situation where a DWARF frame finds
+     tailcall information, but then the inline sniffer claims a frame
+     before the tailcall sniffer, resulting in confusion.  This is
+     safe to do always because the tailcall sniffer can only ever be
+     activated if the newer frame was created using the DWARF
+     unwinder, and it also found tailcall information.  */
+  &dwarf2_tailcall_frame_unwind,
+  &inline_frame_unwind,
 
-struct frame_unwind_table
-{
-  struct frame_unwind_table_entry *list = nullptr;
-  /* The head of the OSABI part of the search list.  */
-  struct frame_unwind_table_entry **osabi_head = nullptr;
 };
 
-static const registry<gdbarch>::key<struct frame_unwind_table>
-     frame_unwind_data;
+/* If an unwinder should be prepended to the list, this is the
+   index in which it should be inserted.  */
+static constexpr int prepend_unwinder_index = standard_unwinders.size ();
 
-/* A helper function to add an unwinder to a list.  LINK says where to
-   install the new unwinder.  The new link is returned.  */
-
-static struct frame_unwind_table_entry **
-add_unwinder (struct obstack *obstack, const struct frame_unwind *unwinder,
-	      struct frame_unwind_table_entry **link)
+/* Start the table out with a few default sniffers.  OSABI code
+   can't override this.  */
+static void
+initialize_frame_unwind_table (std::vector<const frame_unwind *>& table)
 {
-  *link = OBSTACK_ZALLOC (obstack, struct frame_unwind_table_entry);
-  (*link)->unwinder = unwinder;
-  return &(*link)->next;
+  gdb_assert (table.empty ());
+
+  table.insert(table.begin (), standard_unwinders.begin (), standard_unwinders.end ());
 }
 
-static struct frame_unwind_table *
+/* This function call retrieves the list of frame unwinders available in
+   GDBARCH.  If this list is empty, it is initialized before being
+   returned.  */
+static std::vector<const frame_unwind *> &
 get_frame_unwind_table (struct gdbarch *gdbarch)
 {
-  struct frame_unwind_table *table = frame_unwind_data.get (gdbarch);
-  if (table != nullptr)
-    return table;
-
-  table = new frame_unwind_table;
-
-  /* Start the table out with a few default sniffers.  OSABI code
-     can't override this.  */
-  struct frame_unwind_table_entry **link = &table->list;
-
-  struct obstack *obstack = gdbarch_obstack (gdbarch);
-  link = add_unwinder (obstack, &dummy_frame_unwind, link);
-  /* The DWARF tailcall sniffer must come before the inline sniffer.
-     Otherwise, we can end up in a situation where a DWARF frame finds
-     tailcall information, but then the inline sniffer claims a frame
-     before the tailcall sniffer, resulting in confusion.  This is
-     safe to do always because the tailcall sniffer can only ever be
-     activated if the newer frame was created using the DWARF
-     unwinder, and it also found tailcall information.  */
-  link = add_unwinder (obstack, &dwarf2_tailcall_frame_unwind, link);
-  link = add_unwinder (obstack, &inline_frame_unwind, link);
-
-  /* The insertion point for OSABI sniffers.  */
-  table->osabi_head = link;
-  frame_unwind_data.set (gdbarch, table);
+  std::vector<const frame_unwind *> &table = gdbarch_unwinder_list (gdbarch);
+  if (table.size () == 0)
+    initialize_frame_unwind_table (table);
 
   return table;
 }
@@ -95,27 +79,16 @@ void
 frame_unwind_prepend_unwinder (struct gdbarch *gdbarch,
 				const struct frame_unwind *unwinder)
 {
-  struct frame_unwind_table *table = get_frame_unwind_table (gdbarch);
-  struct frame_unwind_table_entry *entry;
-
-  /* Insert the new entry at the start of the list.  */
-  entry = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct frame_unwind_table_entry);
-  entry->unwinder = unwinder;
-  entry->next = (*table->osabi_head);
-  (*table->osabi_head) = entry;
+  std::vector<const frame_unwind *> &table = get_frame_unwind_table (gdbarch);
+
+  table.insert (table.begin () + prepend_unwinder_index, unwinder);
 }
 
 void
 frame_unwind_append_unwinder (struct gdbarch *gdbarch,
 			      const struct frame_unwind *unwinder)
 {
-  struct frame_unwind_table *table = get_frame_unwind_table (gdbarch);
-  struct frame_unwind_table_entry **ip;
-
-  /* Find the end of the list and insert the new entry there.  */
-  for (ip = table->osabi_head; (*ip) != NULL; ip = &(*ip)->next);
-  (*ip) = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct frame_unwind_table_entry);
-  (*ip)->unwinder = unwinder;
+  get_frame_unwind_table (gdbarch).push_back (unwinder);
 }
 
 /* Call SNIFFER from UNWINDER.  If it succeeded set UNWINDER for
@@ -188,9 +161,6 @@ frame_unwind_find_by_frame (const frame_info_ptr &this_frame, void **this_cache)
   FRAME_SCOPED_DEBUG_ENTER_EXIT;
   frame_debug_printf ("this_frame=%d", frame_relative_level (this_frame));
 
-  struct gdbarch *gdbarch = get_frame_arch (this_frame);
-  struct frame_unwind_table *table = get_frame_unwind_table (gdbarch);
-  struct frame_unwind_table_entry *entry;
   const struct frame_unwind *unwinder_from_target;
 
   unwinder_from_target = target_get_unwinder ();
@@ -205,8 +175,10 @@ frame_unwind_find_by_frame (const frame_info_ptr &this_frame, void **this_cache)
 				   unwinder_from_target))
     return;
 
-  for (entry = table->list; entry != NULL; entry = entry->next)
-    if (frame_unwind_try_unwinder (this_frame, this_cache, entry->unwinder))
+  struct gdbarch *gdbarch = get_frame_arch (this_frame);
+  std::vector<const frame_unwind *> &table = get_frame_unwind_table (gdbarch);
+  for (auto unwinder : table)
+    if (frame_unwind_try_unwinder (this_frame, this_cache, unwinder))
       return;
 
   internal_error (_("frame_unwind_find_by_frame failed"));
@@ -347,7 +319,7 @@ static void
 maintenance_info_frame_unwinders (const char *args, int from_tty)
 {
   gdbarch *gdbarch = current_inferior ()->arch ();
-  struct frame_unwind_table *table = get_frame_unwind_table (gdbarch);
+  std::vector<const frame_unwind *> &table = get_frame_unwind_table (gdbarch);
 
   ui_out *uiout = current_uiout;
   ui_out_emit_table table_emitter (uiout, 2, -1, "FrameUnwinders");
@@ -355,11 +327,10 @@ maintenance_info_frame_unwinders (const char *args, int from_tty)
   uiout->table_header (25, ui_left, "type", "Type");
   uiout->table_body ();
 
-  for (struct frame_unwind_table_entry *entry = table->list; entry != NULL;
-       entry = entry->next)
+  for (auto unwinder : table)
     {
-      const char *name = entry->unwinder->name;
-      const char *type = frame_type_str (entry->unwinder->type);
+      const char *name = unwinder->name;
+      const char *type = frame_type_str (unwinder->type);
 
       ui_out_emit_list tuple_emitter (uiout, nullptr);
       uiout->field_string ("name", name);
diff --git a/gdb/gdbarch-gen.c b/gdb/gdbarch-gen.c
index 0d00cd7c993..03894b19bd6 100644
--- a/gdb/gdbarch-gen.c
+++ b/gdb/gdbarch-gen.c
@@ -27,6 +27,8 @@
 
 /* Maintain the struct gdbarch object.  */
 
+#include <vector>
+
 struct gdbarch
 {
   /* Has this architecture been fully initialized?  */
@@ -34,9 +36,13 @@ struct gdbarch
 
   /* An obstack bound to the lifetime of the architecture.  */
   auto_obstack obstack;
+
   /* Registry.  */
   registry<gdbarch> registry_fields;
 
+  /* List of frame unwinders.  */
+  std::vector<const frame_unwind *> unwinders;
+
   /* basic architectural information.  */
   const struct bfd_arch_info * bfd_arch_info;
   enum bfd_endian byte_order;
diff --git a/gdb/gdbarch.h b/gdb/gdbarch.h
index 60a0f60df39..d729b16f7cb 100644
--- a/gdb/gdbarch.h
+++ b/gdb/gdbarch.h
@@ -30,6 +30,7 @@
 #include "displaced-stepping.h"
 #include "gdbsupport/gdb-checked-static-cast.h"
 #include "registry.h"
+#include "frame-unwind.h"
 
 struct floatformat;
 struct ui_file;
@@ -310,6 +311,10 @@ extern obstack *gdbarch_obstack (gdbarch *arch);
 
 #define GDBARCH_OBSTACK_ZALLOC(GDBARCH, TYPE)   obstack_zalloc<TYPE> (gdbarch_obstack ((GDBARCH)))
 
+/* Return the vector of unwinders stored in a gdbarch object.  */
+
+std::vector<const frame_unwind*> &gdbarch_unwinder_list (struct gdbarch *arch);
+
 /* Duplicate STRING, returning an equivalent string that's allocated on the
    obstack associated with GDBARCH.  The string is freed when the corresponding
    architecture is also freed.  */
diff --git a/gdb/gdbarch.py b/gdb/gdbarch.py
index dd1658d5274..274be3ab0d7 100755
--- a/gdb/gdbarch.py
+++ b/gdb/gdbarch.py
@@ -125,6 +125,8 @@ with open("gdbarch-gen.c", "w") as f:
     print(file=f)
     print("/* Maintain the struct gdbarch object.  */", file=f)
     print(file=f)
+    print("#include <vector>", file=f)
+    print(file=f)
     #
     # The struct definition body.
     #
@@ -135,9 +137,13 @@ with open("gdbarch-gen.c", "w") as f:
     print(file=f)
     print("  /* An obstack bound to the lifetime of the architecture.  */", file=f)
     print("  auto_obstack obstack;", file=f)
+    print(file=f)
     print("  /* Registry.  */", file=f)
     print("  registry<gdbarch> registry_fields;", file=f)
     print(file=f)
+    print("  /* List of frame unwinders.  */", file=f)
+    print("  std::vector<const frame_unwind *> unwinders;", file=f)
+    print(file=f)
     print("  /* basic architectural information.  */", file=f)
     for c in filter(info, components):
         print(f"  {c.type} {c.name};", file=f)
-- 
2.46.2