[PATCH v5 11/12] gdb, gdbarch: Introduce gdbarch method to get the shadow stack pointer.

Christina Schimpe
2025-06-28T08:36:37Z

This patch is required by the following commit
"gdb: Enable displaced stepping with shadow stack on amd64 linux."

Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Reviewed-By: Luis Machado <luis.machado@arm.com>
---
gdb/arch-utils.c | 10 ++++++++++
gdb/arch-utils.h | 5 +++++
gdb/gdbarch-gen.c | 22 ++++++++++++++++++++++
gdb/gdbarch-gen.h | 12 +++++++++++-
gdb/gdbarch_components.py | 17 ++++++++++++++++-
5 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
index f320d3d7365..c396e9e3840 100644
--- a/gdb/arch-utils.c
+++ b/gdb/arch-utils.c
@@ -1218,6 +1218,16 @@ default_gdbarch_return_value
readbuf, writebuf);
}

+/* See arch-utils.h. */
+
+std::optional<CORE_ADDR>
+default_get_shadow_stack_pointer (gdbarch *gdbarch, regcache *regcache,
+ bool &shadow_stack_enabled)
+{
+ shadow_stack_enabled = false;
+ return {};
+}
+
obstack *gdbarch_obstack (gdbarch *arch)
{
return &arch->obstack;
diff --git a/gdb/arch-utils.h b/gdb/arch-utils.h
index 1509cb7441e..14a84b74733 100644
--- a/gdb/arch-utils.h
+++ b/gdb/arch-utils.h
@@ -414,4 +414,9 @@ extern enum return_value_convention default_gdbarch_return_value
struct regcache *regcache, struct value **read_value,
const gdb_byte *writebuf);

+/* Default implementation of gdbarch default_get_shadow_stack_pointer
+ method. */
+extern std::optional<CORE_ADDR> default_get_shadow_stack_pointer
+ (gdbarch *gdbarch, regcache *regcache, bool &shadow_stack_enabled);
+
#endif /* GDB_ARCH_UTILS_H */
diff --git a/gdb/gdbarch-gen.c b/gdb/gdbarch-gen.c
index a4b72793fd8..caeda3cefae 100644
--- a/gdb/gdbarch-gen.c
+++ b/gdb/gdbarch-gen.c
@@ -263,6 +263,7 @@ struct gdbarch
gdbarch_use_target_description_from_corefile_notes_ftype *use_target_description_from_corefile_notes = default_use_target_description_from_corefile_notes;
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;
};

/* Create a new ``struct gdbarch'' based on information provided by
@@ -537,6 +538,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
/* Skip verify of use_target_description_from_corefile_notes, invalid_p == 0. */
/* 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. */
if (!log.empty ())
internal_error (_("verify_gdbarch: the following are invalid ...%s"),
log.c_str ());
@@ -1414,6 +1416,9 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
gdb_printf (file,
"gdbarch_dump: shadow_stack_push = <%s>\n",
host_address_to_string (gdbarch->shadow_stack_push));
+ gdb_printf (file,
+ "gdbarch_dump: get_shadow_stack_pointer = <%s>\n",
+ host_address_to_string (gdbarch->get_shadow_stack_pointer));
if (gdbarch->dump_tdep != NULL)
gdbarch->dump_tdep (gdbarch, file);
}
@@ -5583,3 +5588,20 @@ set_gdbarch_shadow_stack_push (struct gdbarch *gdbarch,
{
gdbarch->shadow_stack_push = shadow_stack_push;
}
+
+std::optional<CORE_ADDR>
+gdbarch_get_shadow_stack_pointer (struct gdbarch *gdbarch, regcache *regcache, bool &shadow_stack_enabled)
+{
+ gdb_assert (gdbarch != NULL);
+ gdb_assert (gdbarch->get_shadow_stack_pointer != NULL);
+ if (gdbarch_debug >= 2)
+ gdb_printf (gdb_stdlog, "gdbarch_get_shadow_stack_pointer called\n");
+ return gdbarch->get_shadow_stack_pointer (gdbarch, regcache, shadow_stack_enabled);
+}
+
+void
+set_gdbarch_get_shadow_stack_pointer (struct gdbarch *gdbarch,
+ gdbarch_get_shadow_stack_pointer_ftype get_shadow_stack_pointer)
+{
+ gdbarch->get_shadow_stack_pointer = get_shadow_stack_pointer;
+}
diff --git a/gdb/gdbarch-gen.h b/gdb/gdbarch-gen.h
index 71142332540..c36171b089e 100644
--- a/gdb/gdbarch-gen.h
+++ b/gdb/gdbarch-gen.h
@@ -1807,7 +1807,8 @@ extern void set_gdbarch_core_parse_exec_context (struct gdbarch *gdbarch, gdbarc
technologies. For example, the Intel Control-Flow Enforcement Technology
(Intel CET) on x86 provides a shadow stack and indirect branch tracking.
To enable shadow stack support for inferior calls the shadow_stack_push
- gdbarch hook has to be provided.
+ gdbarch hook has to be provided. The get_shadow_stack_pointer gdbarch
+ hook has to be provided to enable displaced stepping.

Push NEW_ADDR to the shadow stack and update the shadow stack pointer. */

@@ -1816,3 +1817,12 @@ extern bool gdbarch_shadow_stack_push_p (struct gdbarch *gdbarch);
typedef void (gdbarch_shadow_stack_push_ftype) (struct gdbarch *gdbarch, CORE_ADDR new_addr, regcache *regcache);
extern void gdbarch_shadow_stack_push (struct gdbarch *gdbarch, CORE_ADDR new_addr, regcache *regcache);
extern void set_gdbarch_shadow_stack_push (struct gdbarch *gdbarch, gdbarch_shadow_stack_push_ftype *shadow_stack_push);
+
+/* If possible, return the shadow stack pointer. On some architectures, the
+ shadow stack pointer is available even if the feature is disabled. To
+ return the feature's enablement state configure SHADOW_STACK_ENABLED.
+ Set it to true in case the shadow stack is enabled. */
+
+typedef std::optional<CORE_ADDR> (gdbarch_get_shadow_stack_pointer_ftype) (struct gdbarch *gdbarch, regcache *regcache, bool &shadow_stack_enabled);
+extern std::optional<CORE_ADDR> gdbarch_get_shadow_stack_pointer (struct gdbarch *gdbarch, regcache *regcache, bool &shadow_stack_enabled);
+extern void set_gdbarch_get_shadow_stack_pointer (struct gdbarch *gdbarch, gdbarch_get_shadow_stack_pointer_ftype *get_shadow_stack_pointer);
diff --git a/gdb/gdbarch_components.py b/gdb/gdbarch_components.py
index abc79588473..73459064170 100644
--- a/gdb/gdbarch_components.py
+++ b/gdb/gdbarch_components.py
@@ -2855,7 +2855,8 @@ Some targets support special hardware-assisted control-flow protection
technologies. For example, the Intel Control-Flow Enforcement Technology
(Intel CET) on x86 provides a shadow stack and indirect branch tracking.
To enable shadow stack support for inferior calls the shadow_stack_push
-gdbarch hook has to be provided.
+gdbarch hook has to be provided. The get_shadow_stack_pointer gdbarch
+hook has to be provided to enable displaced stepping.

Push NEW_ADDR to the shadow stack and update the shadow stack pointer.
""",
@@ -2864,3 +2865,17 @@ Push NEW_ADDR to the shadow stack and update the shadow stack pointer.
params=[("CORE_ADDR", "new_addr"), ("regcache *", "regcache")],
predicate=True,
)
+
+Method(
+ comment="""
+If possible, return the shadow stack pointer. On some architectures, the
+shadow stack pointer is available even if the feature is disabled. To
+return the feature's enablement state configure SHADOW_STACK_ENABLED.
+Set it to true in case the shadow stack is enabled.
+""",
+ type="std::optional<CORE_ADDR>",
+ name="get_shadow_stack_pointer",
+ params=[("regcache *", "regcache"), ("bool &", "shadow_stack_enabled")],
+ predefault="default_get_shadow_stack_pointer",
+ invalid=False,
+)
--
2.43.0