Add option -{m,mno}-forced-sw-shadow-stack

Author: Yeting Kuo

clang/docs/ShadowCallStack.rst

@@ -59,7 +59,9 @@ and destruction would need to be intercepted by the application.
 
 The instrumentation makes use of the platform register ``x18`` on AArch64,
 ``x3`` (``gp``) on RISC-V with software shadow stack and ``ssp`` on RISC-V with
-hardware shadow stack, which needs `Zicfiss`_ and ``-mllvm -riscv-hardware-shadow-stack``.
+hardware shadow stack, which needs `Zicfiss`_ and ``-mno-forced-sw-shadow-stack``
+(default option). ``-mforced-sw-shadow-stack`` make risc-v backend generate
+software shadow stack with `Zicfiss`_ when shadow stack enabled.
 For simplicity we will refer to this as the ``SCSReg``. On some platforms,
 ``SCSReg`` is reserved, and on others, it is designated as a scratch register.
 This generally means that any code that may run on the same thread as code compiled with ShadowCallStack must either target

clang/include/clang/Driver/Options.td

@@ -4578,6 +4578,10 @@ def msave_restore : Flag<["-"], "msave-restore">, Group<m_riscv_Features_Group>,
   HelpText<"Enable using library calls for save and restore">;
 def mno_save_restore : Flag<["-"], "mno-save-restore">, Group<m_riscv_Features_Group>,
   HelpText<"Disable using library calls for save and restore">;
+def mforced_sw_shadow_stack : Flag<["-"], "mforced-sw-shadow-stack">, Group<m_riscv_Features_Group>,
+  HelpText<"Force using software shadow stack when shadow-stack enabled">;
+def mno_forced_sw_shadow_stack : Flag<["-"], "mno-forced-sw-shadow-stack">, Group<m_riscv_Features_Group>,
+  HelpText<"Not force using software shadow stack when shadow-stack enabled">;
 } // let Flags = [TargetSpecific]
 let Flags = [TargetSpecific] in {
 def menable_experimental_extensions : Flag<["-"], "menable-experimental-extensions">, Group<m_Group>,

clang/test/Driver/riscv-features.c

@@ -27,6 +27,11 @@
 // DEFAULT-NOT: "-target-feature" "-save-restore"
 // DEFAULT-NOT: "-target-feature" "+save-restore"
 
+// RUN: %clang --target=riscv32-unknown-elf -### %s -mforced-sw-shadow-stack 2>&1 | FileCheck %s -check-prefix=FORCE-SW-SCS
+// RUN: %clang --target=riscv32-unknown-elf -### %s -mno-forced-sw-shadow-stack 2>&1 | FileCheck %s -check-prefix=NO-FORCE-SW-SCS
+// FORCE-SW-SCS: "-target-feature" "+forced-sw-shadow-stack"
+// NO-FORCE-SW-SCS: "-target-feature" "-forced-sw-shadow-stack"
+
 // RUN: %clang --target=riscv32-unknown-elf -### %s -munaligned-access 2>&1 | FileCheck %s -check-prefix=FAST-UNALIGNED-ACCESS
 // RUN: %clang --target=riscv32-unknown-elf -### %s -mno-unaligned-access 2>&1 | FileCheck %s -check-prefix=NO-FAST-UNALIGNED-ACCESS
 // RUN: %clang --target=riscv32-unknown-elf -### %s -mno-strict-align 2>&1 | FileCheck %s -check-prefix=FAST-UNALIGNED-ACCESS