Re: [PATCH v4 01/23] aarch64: Add -mbranch-protection=gcs option

[Jonathan Wakely <jwakely@redhat.com>]

On 14/11/24 12:36 +0000, Yury Khrustalev wrote:
>From: Szabolcs Nagy <szabolcs.nagy@arm.com>
>
>This enables Guarded Control Stack (GCS) compatible code generation.
>
>The "standard" branch-protection type enables it, and the default
>depends on the compiler default.
>
>gcc/ChangeLog:
>
>	* config/aarch64/aarch64-protos.h (aarch_gcs_enabled): Declare.
>	* config/aarch64/aarch64.cc (aarch_gcs_enabled): Define.
>	(aarch_handle_no_branch_protection): Handle gcs.
>	(aarch_handle_standard_branch_protection): Handle gcs.
>	(aarch_handle_gcs_protection): New.
>	* config/aarch64/aarch64.opt: Add aarch_enable_gcs.
>	* configure: Regenerate.
>	* configure.ac: Handle gcs in --enable-standard-branch-protection.
>	* doc/invoke.texi: Document -mbranch-protection=gcs.
>---
> gcc/config/aarch64/aarch64-protos.h |  2 ++
> gcc/config/aarch64/aarch64.cc       | 24 ++++++++++++++++++++++++
> gcc/config/aarch64/aarch64.opt      |  3 +++
> gcc/configure                       |  2 +-
> gcc/configure.ac                    |  6 +++---
> gcc/doc/invoke.texi                 |  5 +++--
> 6 files changed, 36 insertions(+), 6 deletions(-)
>
>diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
>index 05d3258abf7..481907422e8 100644
>--- a/gcc/config/aarch64/aarch64-protos.h
>+++ b/gcc/config/aarch64/aarch64-protos.h
>@@ -1206,4 +1206,6 @@ extern void aarch64_adjust_reg_alloc_order ();
> bool aarch64_optimize_mode_switching (aarch64_mode_entity);
> void aarch64_restore_za (rtx);
>
>+extern bool aarch64_gcs_enabled ();
>+
> #endif /* GCC_AARCH64_PROTOS_H */
>diff --git a/gcc/config/aarch64/aarch64.cc b/gcc/config/aarch64/aarch64.cc
>index 00bcf18ae97..68230e1f4c2 100644
>--- a/gcc/config/aarch64/aarch64.cc
>+++ b/gcc/config/aarch64/aarch64.cc
>@@ -8562,6 +8562,13 @@ aarch_bti_j_insn_p (rtx_insn *insn)
>   return GET_CODE (pat) == UNSPEC_VOLATILE && XINT (pat, 1) == UNSPECV_BTI_J;
> }
>
>+/* Return TRUE if Guarded Control Stack is enabled.  */
>+bool
>+aarch64_gcs_enabled (void)
>+{
>+  return (aarch64_enable_gcs == 1);
>+}
>+
> /* Check if X (or any sub-rtx of X) is a PACIASP/PACIBSP instruction.  */
> bool
> aarch_pac_insn_p (rtx x)
>@@ -18981,6 +18988,7 @@ aarch64_handle_no_branch_protection (void)
> {
>   aarch_ra_sign_scope = AARCH_FUNCTION_NONE;
>   aarch_enable_bti = 0;
>+  aarch64_enable_gcs = 0;
> }
>
> static void
>@@ -18989,6 +18997,7 @@ aarch64_handle_standard_branch_protection (void)
>   aarch_ra_sign_scope = AARCH_FUNCTION_NON_LEAF;
>   aarch64_ra_sign_key = AARCH64_KEY_A;
>   aarch_enable_bti = 1;
>+  aarch64_enable_gcs = 1;
> }
>
> static void
>@@ -19015,6 +19024,11 @@ aarch64_handle_bti_protection (void)
> {
>   aarch_enable_bti = 1;
> }
>+static void
>+aarch64_handle_gcs_protection (void)
>+{
>+  aarch64_enable_gcs = 1;
>+}
>
> static const struct aarch_branch_protect_type aarch64_pac_ret_subtypes[] = {
>   { "leaf", false, aarch64_handle_pac_ret_leaf, NULL, 0 },
>@@ -19029,6 +19043,7 @@ static const struct aarch_branch_protect_type aarch64_branch_protect_types[] =
>   { "pac-ret", false, aarch64_handle_pac_ret_protection,
>     aarch64_pac_ret_subtypes, ARRAY_SIZE (aarch64_pac_ret_subtypes) },
>   { "bti", false, aarch64_handle_bti_protection, NULL, 0 },
>+  { "gcs", false, aarch64_handle_gcs_protection, NULL, 0 },
>   { NULL, false, NULL, NULL, 0 }
> };
>
>@@ -19128,6 +19143,15 @@ aarch64_override_options (void)
> #endif
>     }
>
>+  if (aarch64_enable_gcs == 2)
>+    {
>+#ifdef TARGET_ENABLE_GCS
>+      aarch64_enable_gcs = 1;
>+#else
>+      aarch64_enable_gcs = 0;
>+#endif
>+    }
>+
>   /* Return address signing is currently not supported for ILP32 targets.  For
>      LP64 targets use the configured option in the absence of a command-line
>      option for -mbranch-protection.  */
>diff --git a/gcc/config/aarch64/aarch64.opt b/gcc/config/aarch64/aarch64.opt
>index c2c9965b062..36bc719b822 100644
>--- a/gcc/config/aarch64/aarch64.opt
>+++ b/gcc/config/aarch64/aarch64.opt
>@@ -45,6 +45,9 @@ uint64_t aarch64_isa_flags_1 = 0
> TargetVariable
> unsigned aarch_enable_bti = 2
>
>+TargetVariable
>+unsigned aarch64_enable_gcs = 2
>+
> TargetVariable
> enum aarch64_key_type aarch64_ra_sign_key = AARCH64_KEY_A
>
>diff --git a/gcc/configure b/gcc/configure
>index 150ab616414..df64af3af57 100755
>--- a/gcc/configure
>+++ b/gcc/configure
>@@ -28093,7 +28093,7 @@ if test "${enable_standard_branch_protection+set}" = set; then :
>   enableval=$enable_standard_branch_protection;
>         case $enableval in
>           yes)
>-            tm_defines="${tm_defines} TARGET_ENABLE_BTI=1 TARGET_ENABLE_PAC_RET=1"
>+            tm_defines="${tm_defines} TARGET_ENABLE_BTI=1 TARGET_ENABLE_PAC_RET=1 TARGET_ENABLE_GCS=1"
>             ;;
>           no)
>             ;;

This file was not correctly regenerated.


>diff --git a/gcc/configure.ac b/gcc/configure.ac
>index bdb22d53e2c..bdd8cb0002f 100644
>--- a/gcc/configure.ac
>+++ b/gcc/configure.ac
>@@ -4402,14 +4402,14 @@ case "$target" in
>     AC_ARG_ENABLE(standard-branch-protection,
>     [
> AS_HELP_STRING([--enable-standard-branch-protection],
>-        [enable Branch Target Identification Mechanism and Return Address Signing by default for AArch64])
>+        [enable Branch Target Identification Mechanism, Return Address Signing, and Guarded Control Stack by default for AArch64])
> AS_HELP_STRING([--disable-standard-branch-protection],
>-        [disable Branch Target Identification Mechanism and Return Address Signing by default for AArch64])
>+        [disable Branch Target Identification Mechanism, Return Address Signing, and Guarded Control Stack by default for AArch64])
>     ],
>       [
>         case $enableval in
>           yes)
>-            tm_defines="${tm_defines} TARGET_ENABLE_BTI=1 TARGET_ENABLE_PAC_RET=1"
>+            tm_defines="${tm_defines} TARGET_ENABLE_BTI=1 TARGET_ENABLE_PAC_RET=1 TARGET_ENABLE_GCS=1"
>             ;;
>           no)
>             ;;
>diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
>index aa979c3c2fd..ccf34dc28ce 100644
>--- a/gcc/doc/invoke.texi
>+++ b/gcc/doc/invoke.texi
>@@ -814,7 +814,7 @@ Objective-C and Objective-C++ Dialects}.
> -mpc-relative-literal-loads
> -msign-return-address=@var{scope}
> -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}
>-+@var{b-key}]|@var{bti}
>++@var{b-key}]|@var{bti}|@var{gcs}
> -mharden-sls=@var{opts}
> -march=@var{name}  -mcpu=@var{name}  -mtune=@var{name}
> -moverride=@var{string}  -mverbose-cost-dump
>@@ -21591,7 +21591,7 @@ default value is @samp{none}. This option has been deprecated by
> -mbranch-protection.
>
> @opindex mbranch-protection
>-@item -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}+@var{b-key}]|@var{bti}
>+@item -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}+@var{b-key}]|@var{bti}|@var{gcs}
> Select the branch protection features to use.
> @samp{none} is the default and turns off all types of branch protection.
> @samp{standard} turns on all types of branch protection features.  If a feature
>@@ -21604,6 +21604,7 @@ argument @samp{leaf} can be used to extend the signing to include leaf
> functions.  The optional argument @samp{b-key} can be used to sign the functions
> with the B-key instead of the A-key.
> @samp{bti} turns on branch target identification mechanism.
>+@samp{gcs} turns on guarded control stack compatible code generation.
>
> @opindex mharden-sls
> @item -mharden-sls=@var{opts}
>-- 
>2.39.5
>