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

[Luis Machado <luis.machado@arm.com>]

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>