[x86][CET] Introduce _get_ssp, _inc_ssp intrinsics

[GBuella]

Summary

The _get_ssp intrinsic can be used to retrieve the
shadow stack pointer, independent of the current arch -- in
contract with the rdsspd and the rdsspq intrinsics.
Also, this intrinsic returns zero on CPUs which don't
support CET. The rdssp[d|q] instruction is decoded as nop,
essentially just returning the input operand, which is zero.
Example result of compilation:

xorl    %eax, %eax
movl    %eax, %ecx
rdsspq  %rcx         # NOP when CET is not supported
movq    %rcx, %rax   # return zero

[craig.topper]

lib/Headers/cetintrin.h

44

Start a new #ifdef x86_64 here that is just for your new intrinsics. That way it doesn't look weird that the #else contains fewer functions than the #if.

45

Where is the zeroing behavior for older CPUs coming from? This implementation looks identical to _incsspq?

65

same comments as above.

[GBuella]

lib/Headers/cetintrin.h

45

Do we need some zeroing behaviour for _inc_ssp?
I know we need it for _get_ssp.

[craig.topper]

LGTM

lib/Headers/cetintrin.h

45

Nevermind. I mixed up the instructions, and didn't realize that we already modeled rdsspq/rdsspd as taking a value as input. I assumed we would have to do more work. Should have looked more closely. Sorry.

lib/Headers/cetintrin.h

 }
 #endif /* __x86_64__ */
 
+#ifdef __x86_64__
+static __inline__ void __DEFAULT_FN_ATTRS _inc_ssp(unsigned int __a) {
+  __builtin_ia32_incsspq(__a);
+}
+#else /* __x86_64__ */
+static __inline__ void __DEFAULT_FN_ATTRS _inc_ssp(unsigned int __a) {
+  __builtin_ia32_incsspd((int)__a);
+}
+#endif /* __x86_64__ */
+
 static __inline__ unsigned int __DEFAULT_FN_ATTRS _rdsspd(unsigned int __a) {
   return __builtin_ia32_rdsspd(__a);
 }

 }
 #endif /* __x86_64__ */
 
+#ifdef __x86_64__
+static __inline__ unsigned long long __DEFAULT_FN_ATTRS _get_ssp(void) {
+  return __builtin_ia32_rdsspq(0);
+}
+#else /* __x86_64__ */
+static __inline__ unsigned int __DEFAULT_FN_ATTRS _get_ssp(void) {
+  return __builtin_ia32_rdsspd(0);
+}
+#endif /* __x86_64__ */
+
 static __inline__ void __DEFAULT_FN_ATTRS _saveprevssp() {
   __builtin_ia32_saveprevssp();
 }

test/CodeGen/cetintrin.c

-// RUN: %clang_cc1 -ffreestanding %s -triple=i386-apple-darwin -target-feature +shstk -emit-llvm -o - -Wall -Werror | FileCheck %s
-// RUN: %clang_cc1 -ffreestanding %s -triple=x86_64-apple-darwin -target-feature +shstk  -emit-llvm -o - -Wall -Werror | FileCheck %s --check-prefix=X86_64
+// RUN: %clang_cc1 -ffreestanding %s -triple=i386-apple-darwin -target-feature +shstk -emit-llvm -o - -Wall -Werror | FileCheck %s --check-prefix=I386 --check-prefix=CHECK
+// RUN: %clang_cc1 -ffreestanding %s -triple=x86_64-apple-darwin -target-feature +shstk  -emit-llvm -o - -Wall -Werror | FileCheck %s --check-prefix=X86_64  --check-prefix=CHECK
 
 #include <immintrin.h>
 

   // X86_64:       call void @llvm.x86.incsspq(i64 %{{[a-z0-9.]+}})
   _incsspq(a);
 }
+
+void test_inc_ssp(unsigned int a) {
+  // X86_64-LABEL: @test_inc_ssp
+  // X86_64:       call void @llvm.x86.incsspq(i64 %{{[a-z0-9.]+}})
+  _inc_ssp(a);
+}
+#else
+
+void test_inc_ssp(unsigned int a) {
+  // I386-LABEL: @test_inc_ssp
+  // I386:       call void @llvm.x86.incsspd(i32 %{{[0-9]+}})
+  _inc_ssp(a);
+}
+
 #endif
 
 unsigned int test_rdsspd(unsigned int a) {

   // X86_64:       call i64 @llvm.x86.rdsspq(i64 %{{[a-z0-9.]+}})
   return _rdsspq(a);
 }
+
+unsigned long long test_get_ssp(void) {
+  // X86_64-LABEL: @test_get_ssp
+  // X86_64:       call i64 @llvm.x86.rdsspq(i64 0)
+  return _get_ssp();
+}
+
+#else
+
+unsigned int test_get_ssp(void) {
+  // I386-LABEL: @test_get_ssp
+  // I386:       call i32 @llvm.x86.rdsspd(i32 0)
+  return _get_ssp();
+}
+
 #endif
 
 void  test_saveprevssp() {