[LLVM][rtsan] Add sanitize_realtime attribute for the realtime sanitizer (#100596)

Add a new "sanitize_realtime" attribute, which will correspond to the
nonblocking function effect in clang. This is used in the realtime
sanitizer transform.

Please see the [reviewer support
document](https://github.com/realtime-sanitizer/radsan/blob/doc/review-support/doc/review.md)
for what our next steps are. The original discourse thread can be found
[here](https://discourse.llvm.org/t/rfc-nolock-and-noalloc-attributes/76837)

Author: cjappl

llvm/docs/LangRef.rst

@@ -2309,6 +2309,10 @@ example:
     This attribute indicates that MemTagSanitizer checks
     (dynamic address safety analysis based on Armv8 MTE) are enabled for
     this function.
+``sanitize_realtime``
+    This attribute indicates that RealtimeSanitizer checks
+    (realtime safety analysis - no allocations, syscalls or exceptions) are enabled
+    for this function.
 ``speculative_load_hardening``
     This attribute indicates that
     `Speculative Load Hardening <https://llvm.org/docs/SpeculativeLoadHardening.html>`_

llvm/include/llvm/Bitcode/LLVMBitCodes.h

@@ -758,6 +758,7 @@ enum AttributeKindCodes {
   ATTR_KIND_SANITIZE_NUMERICAL_STABILITY = 93,
   ATTR_KIND_INITIALIZES = 94,
   ATTR_KIND_HYBRID_PATCHABLE = 95,
+  ATTR_KIND_SANITIZE_REALTIME = 96,
 };
 
 enum ComdatSelectionKindCodes {

llvm/include/llvm/IR/Attributes.td

@@ -297,6 +297,9 @@ def SanitizeMemTag : EnumAttr<"sanitize_memtag", [FnAttr]>;
 /// NumericalStabilitySanitizer is on.
 def SanitizeNumericalStability : EnumAttr<"sanitize_numerical_stability", [FnAttr]>;
 
+/// RealtimeSanitizer is on.
+def SanitizeRealtime : EnumAttr<"sanitize_realtime", [FnAttr]>;
+
 /// Speculative Load Hardening is enabled.
 ///
 /// Note that this uses the default compatibility (always compatible during
@@ -385,6 +388,7 @@ def : CompatRule<"isEqual<SanitizeMemoryAttr>">;
 def : CompatRule<"isEqual<SanitizeHWAddressAttr>">;
 def : CompatRule<"isEqual<SanitizeMemTagAttr>">;
 def : CompatRule<"isEqual<SanitizeNumericalStabilityAttr>">;
+def : CompatRule<"isEqual<SanitizeRealtimeAttr>">;
 def : CompatRule<"isEqual<SafeStackAttr>">;
 def : CompatRule<"isEqual<ShadowCallStackAttr>">;
 def : CompatRule<"isEqual<UseSampleProfileAttr>">;

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -2141,6 +2141,8 @@ static Attribute::AttrKind getAttrFromCode(uint64_t Code) {
     return Attribute::SanitizeMemory;
   case bitc::ATTR_KIND_SANITIZE_NUMERICAL_STABILITY:
     return Attribute::SanitizeNumericalStability;
+  case bitc::ATTR_KIND_SANITIZE_REALTIME:
+    return Attribute::SanitizeRealtime;
   case bitc::ATTR_KIND_SPECULATIVE_LOAD_HARDENING:
     return Attribute::SpeculativeLoadHardening;
   case bitc::ATTR_KIND_SWIFT_ERROR:

llvm/lib/Bitcode/Writer/BitcodeWriter.cpp

@@ -843,6 +843,8 @@ static uint64_t getAttrKindEncoding(Attribute::AttrKind Kind) {
     return bitc::ATTR_KIND_SANITIZE_MEMORY;
   case Attribute::SanitizeNumericalStability:
     return bitc::ATTR_KIND_SANITIZE_NUMERICAL_STABILITY;
+  case Attribute::SanitizeRealtime:
+    return bitc::ATTR_KIND_SANITIZE_REALTIME;
   case Attribute::SpeculativeLoadHardening:
     return bitc::ATTR_KIND_SPECULATIVE_LOAD_HARDENING;
   case Attribute::SwiftError:

llvm/lib/Transforms/Utils/CodeExtractor.cpp

@@ -959,6 +959,7 @@ Function *CodeExtractor::constructFunction(const ValueSet &inputs,
       case Attribute::SanitizeThread:
       case Attribute::SanitizeHWAddress:
       case Attribute::SanitizeMemTag:
+      case Attribute::SanitizeRealtime:
       case Attribute::SpeculativeLoadHardening:
       case Attribute::StackProtect:
       case Attribute::StackProtectReq:

llvm/test/Bitcode/attributes.ll

@@ -505,6 +505,12 @@ define void @f86() nosanitize_bounds
         ret void;
 }
 
+; CHECK: define void @f92() #53
+define void @f92() sanitize_realtime
+{
+        ret void;
+}
+
 ; CHECK: define void @f87() [[FNRETTHUNKEXTERN:#[0-9]+]]
 define void @f87() fn_ret_thunk_extern { ret void }
 
@@ -599,6 +605,7 @@ define void @initializes(ptr initializes((-4, 0), (4, 8)) %a) {
 ; CHECK: attributes #50 = { disable_sanitizer_instrumentation }
 ; CHECK: attributes #51 = { uwtable(sync) }
 ; CHECK: attributes #52 = { nosanitize_bounds }
+; CHECK: attributes #53 = { sanitize_realtime }
 ; CHECK: attributes [[FNRETTHUNKEXTERN]] = { fn_ret_thunk_extern }
 ; CHECK: attributes [[SKIPPROFILE]] = { skipprofile }
 ; CHECK: attributes [[OPTDEBUG]] = { optdebug }

llvm/test/Bitcode/compatibility.ll

@@ -1562,7 +1562,7 @@ exit:
   ; CHECK: select <2 x i1> <i1 true, i1 false>, <2 x i8> <i8 2, i8 3>, <2 x i8> <i8 3, i8 2>
 
   call void @f.nobuiltin() builtin
-  ; CHECK: call void @f.nobuiltin() #52
+  ; CHECK: call void @f.nobuiltin() #53
 
   call fastcc noalias ptr @f.noalias() noinline
   ; CHECK: call fastcc noalias ptr @f.noalias() #12
@@ -1989,6 +1989,9 @@ declare void @f.allockind() allockind("alloc,uninitialized")
 declare void @f.sanitize_numerical_stability() sanitize_numerical_stability
 ; CHECK: declare void @f.sanitize_numerical_stability() #51
 
+declare void @f.sanitize_realtime() sanitize_realtime
+; CHECK: declare void @f.sanitize_realtime() #52
+
 ; CHECK: declare nofpclass(snan) float @nofpclass_snan(float nofpclass(snan))
 declare nofpclass(snan) float @nofpclass_snan(float nofpclass(snan))
 
@@ -2111,7 +2114,8 @@ define float @nofpclass_callsites(float %arg) {
 ; CHECK: attributes #49 = { nosanitize_bounds }
 ; CHECK: attributes #50 = { allockind("alloc,uninitialized") }
 ; CHECK: attributes #51 = { sanitize_numerical_stability }
-; CHECK: attributes #52 = { builtin }
+; CHECK: attributes #52 = { sanitize_realtime }
+; CHECK: attributes #53 = { builtin }
 
 ;; Metadata