Re: [PATCH v4 10/11] gdb, gdbarch: Introduce gdbarch method to get the shadow stack pointer.

Luis Machado
2025-06-19T09:28:46Z

On 6/17/25 13:11, Christina Schimpe wrote:
> This patch is required by the following commit.

What particular entry in the series uses this? The displaced stepping one?

If so, we should make it more explicit.

>
> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
> ---
> gdb/arch-utils.c | 10 ++++++++++
> gdb/arch-utils.h | 5 +++++
> gdb/gdbarch-gen.c | 22 ++++++++++++++++++++++
> gdb/gdbarch-gen.h | 10 ++++++++++
> gdb/gdbarch_components.py | 15 +++++++++++++++
> 5 files changed, 62 insertions(+)
>
> diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
> index be0494fba1e..c86df72a6d8 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 3ca19c427a3..4490d53a940 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 c276cd66d71..b8d1df94f59 100644
> --- a/gdb/gdbarch-gen.h
> +++ b/gdb/gdbarch-gen.h
> @@ -1806,6 +1806,8 @@ 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 inferior calls the function shadow_stack_push has to be provided.
> + The method get_shadow_stack_pointer has to be provided to enable displaced
> + stepping.
>
> Push the address NEW_ADDR on the shadow stack and update the shadow stack
> pointer. */
> @@ -1815,3 +1817,11 @@ 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 shadow stack enablement state configure SHADOW_STACK_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 ab685b14ec7..ccbdcaf07c9 100644
> --- a/gdb/gdbarch_components.py
> +++ b/gdb/gdbarch_components.py
> @@ -2855,6 +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 inferior calls the function shadow_stack_push has to be provided.
> +The method get_shadow_stack_pointer has to be provided to enable displaced

Maybe...

"The get_shadow_stack_pointer gdbarch hook has to be..."

> +stepping.
>
> Push the address NEW_ADDR on the shadow stack and update the shadow stack
> pointer.
> @@ -2864,3 +2866,16 @@ 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 shadow stack enablement state configure SHADOW_STACK_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,
> +)

Otherwise looks OK.

Reviewed-By: Luis Machado <luis.machado@arm.com>