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

Guinevere Larsen
2024-10-01T18:43:50Z

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