[AArch64] Add command-line option for SSBS

Summary:
SSBS (Speculative Store Bypass Safe) is only mandatory from 8.5
onwards but is optional from Armv8.0-A. This patch adds a command
line option to enable SSBS, as it was previously only possible to
enable by selecting -march=armv8.5-a.

Similar patch upstream in GNU binutils:
https://sourceware.org/ml/binutils/2018-09/msg00274.html

Reviewers: olista01, samparker, aemerson

Reviewed By: samparker

Subscribers: javed.absar, kristof.beyls, kristina, llvm-commits

Differential Revision: https://reviews.llvm.org/D54629

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@348137 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/AArch64TargetParser.def

@@ -72,6 +72,7 @@ AARCH64_ARCH_EXT_NAME("sve",      AArch64::AEK_SVE,      "+sve",  "-sve")
 AARCH64_ARCH_EXT_NAME("rcpc",     AArch64::AEK_RCPC,     "+rcpc", "-rcpc")
 AARCH64_ARCH_EXT_NAME("rng",      AArch64::AEK_RAND,     "+rand",  "-rand")
 AARCH64_ARCH_EXT_NAME("memtag",   AArch64::AEK_MTE,      "+mte",   "-mte")
+AARCH64_ARCH_EXT_NAME("ssbs",     AArch64::AEK_SSBS,     "+ssbs",  "-ssbs")
 #undef AARCH64_ARCH_EXT_NAME
 
 #ifndef AARCH64_CPU_NAME

include/llvm/Support/AArch64TargetParser.h

@@ -47,6 +47,7 @@ enum ArchExtKind : unsigned {
   AEK_FP16FML =     1 << 17,
   AEK_RAND =        1 << 18,
   AEK_MTE =         1 << 19,
+  AEK_SSBS =        1 << 20,
 };
 
 enum class ArchKind {

lib/Target/AArch64/AArch64.td

@@ -306,6 +306,9 @@ def FeatureFRInt3264 : SubtargetFeature<"fptoint", "HasFRInt3264", "true",
 def FeatureSpecRestrict : SubtargetFeature<"specrestrict", "HasSpecRestrict",
   "true", "Enable architectural speculation restriction" >;
 
+def FeatureSSBS : SubtargetFeature<"ssbs", "HasSSBS",
+  "true", "Enable Speculative Store Bypass Safe bit" >;
+
 def FeatureSpecCtrl : SubtargetFeature<"specctrl", "HasSpecCtrl", "true",
   "Enable speculation control barrier" >;
 
@@ -349,7 +352,7 @@ def HasV8_4aOps : SubtargetFeature<"v8.4a", "HasV8_4aOps", "true",
 def HasV8_5aOps : SubtargetFeature<
   "v8.5a", "HasV8_5aOps", "true", "Support ARM v8.5a instructions",
   [HasV8_4aOps, FeatureAltFPCmp, FeatureFRInt3264, FeatureSpecRestrict,
-   FeatureSpecCtrl, FeaturePredCtrl, FeatureCacheDeepPersist,
+   FeatureSSBS, FeatureSpecCtrl, FeaturePredCtrl, FeatureCacheDeepPersist,
    FeatureBranchTargetId]
 >;
 

lib/Target/AArch64/AArch64Subtarget.h

@@ -127,6 +127,7 @@ protected:
   bool HasFRInt3264 = false;
   bool HasSpecRestrict = false;
   bool HasSpecCtrl = false;
+  bool HasSSBS = false;
   bool HasPredCtrl = false;
   bool HasCCDP = false;
   bool HasBTI = false;
@@ -355,6 +356,7 @@ public:
   bool hasFRInt3264() const { return HasFRInt3264; }
   bool hasSpecRestrict() const { return HasSpecRestrict; }
   bool hasSpecCtrl() const { return HasSpecCtrl; }
+  bool hasSSBS() const { return HasSSBS; }
   bool hasPredCtrl() const { return HasPredCtrl; }
   bool hasCCDP() const { return HasCCDP; }
   bool hasBTI() const { return HasBTI; }

lib/Target/AArch64/AArch64SystemOperands.td

@@ -343,7 +343,7 @@ def : PState<"UAO",     0b00011>;
 let Requires = [{ {AArch64::FeatureDIT} }] in
 def : PState<"DIT",     0b11010>;
 // v8.5a Spectre Mitigation
-let Requires = [{ {AArch64::FeatureSpecRestrict} }] in
+let Requires = [{ {AArch64::FeatureSSBS} }] in
 def : PState<"SSBS",    0b11001>;
 // v8.5a Memory Tagging Extension
 let Requires = [{ {AArch64::FeatureMTE} }] in
@@ -1444,7 +1444,7 @@ def : RWSysReg<"ZCR_EL12",         0b11, 0b101, 0b0001, 0b0010, 0b000>;
 
 // V8.5a Spectre mitigation SSBS register
 //                     Op0   Op1    CRn     CRm     Op2
-let Requires = [{ {AArch64::FeatureSpecRestrict} }] in
+let Requires = [{ {AArch64::FeatureSSBS} }] in
 def : RWSysReg<"SSBS", 0b11, 0b011, 0b0100, 0b0010, 0b110>;
 
 // v8.5a Memory Tagging Extension

test/MC/AArch64/armv8.5a-specrestrict.s

@@ -51,19 +51,3 @@ msr SCXTNUM_EL12, x4
 // NOSPECID-NEXT: {{scxtnum_el3|SCXTNUM_EL3}}
 // NOSPECID:      error: expected writable system register
 // NOSPECID-NEXT: {{scxtnum_el12|SCXTNUM_EL12}}
-
-mrs x2, SSBS
-
-// CHECK:         mrs x2, {{ssbs|SSBS}} // encoding: [0xc2,0x42,0x3b,0xd5]
-// NOSPECID:      error: expected readable system register
-// NOSPECID-NEXT: mrs x2, {{ssbs|SSBS}}
-
-msr SSBS, x3
-msr SSBS, #1
-
-// CHECK:         msr {{ssbs|SSBS}}, x3 // encoding: [0xc3,0x42,0x1b,0xd5]
-// CHECK:         msr {{ssbs|SSBS}}, #1 // encoding: [0x3f,0x41,0x03,0xd5]
-// NOSPECID:      error: expected writable system register or pstate
-// NOSPECID-NEXT: msr {{ssbs|SSBS}}, x3
-// NOSPECID:      error: expected writable system register or pstate
-// NOSPECID-NEXT: msr {{ssbs|SSBS}}, #1

test/MC/AArch64/armv8.5a-specrestrict-error.s → test/MC/AArch64/armv8.5a-ssbs-error.s

@@ -1,6 +1,6 @@
-// RUN: not llvm-mc -triple aarch64 -show-encoding -mattr=+specrestrict < %s 2>&1 | FileCheck %s
-// RUN: not llvm-mc -triple aarch64 -show-encoding -mattr=+v8.5a        < %s 2>&1 | FileCheck %s
-// RUN: not llvm-mc -triple aarch64 -show-encoding -mattr=-specrestrict < %s 2>&1 | FileCheck %s --check-prefix=NOSPECID
+// RUN: not llvm-mc -triple aarch64 -show-encoding -mattr=+ssbs  < %s 2>&1 | FileCheck %s
+// RUN: not llvm-mc -triple aarch64 -show-encoding -mattr=+v8.5a < %s 2>&1 | FileCheck %s
+// RUN: not llvm-mc -triple aarch64 -show-encoding -mattr=-ssbs  < %s 2>&1 | FileCheck %s --check-prefix=NOSPECID
 
 msr SSBS, #2
 

test/MC/AArch64/armv8.5a-ssbs.s

@@ -0,0 +1,19 @@
+// RUN:     llvm-mc -triple aarch64 -show-encoding -mattr=+ssbs  < %s      | FileCheck %s
+// RUN:     llvm-mc -triple aarch64 -show-encoding -mattr=+v8.5a < %s      | FileCheck %s
+// RUN: not llvm-mc -triple aarch64 -show-encoding -mattr=-ssbs  < %s 2>&1 | FileCheck %s --check-prefix=NOSPECID
+
+mrs x2, SSBS
+
+// CHECK:         mrs x2, {{ssbs|SSBS}} // encoding: [0xc2,0x42,0x3b,0xd5]
+// NOSPECID:      error: expected readable system register
+// NOSPECID-NEXT: mrs x2, {{ssbs|SSBS}}
+
+msr SSBS, x3
+msr SSBS, #1
+
+// CHECK:         msr {{ssbs|SSBS}}, x3 // encoding: [0xc3,0x42,0x1b,0xd5]
+// CHECK:         msr {{ssbs|SSBS}}, #1 // encoding: [0x3f,0x41,0x03,0xd5]
+// NOSPECID:      error: expected writable system register or pstate
+// NOSPECID-NEXT: msr {{ssbs|SSBS}}, x3
+// NOSPECID:      error: expected writable system register or pstate
+// NOSPECID-NEXT: msr {{ssbs|SSBS}}, #1

test/MC/Disassembler/AArch64/armv8.5a-specrestrict.txt

@@ -40,13 +40,3 @@
 # NOSPECID: msr S3_4_C13_C0_7, x6
 # NOSPECID: msr S3_6_C13_C0_7, x5
 # NOSPECID: msr S3_5_C13_C0_7, x4
-
-[0x3f 0x41 0x03 0xd5]
-[0xc3 0x42 0x1b 0xd5]
-[0xc2 0x42 0x3b 0xd5]
-# CHECK:    msr SSBS, #1
-# CHECK:    msr SSBS, x3
-# CHECK:    mrs x2, SSBS
-# NOSPECID: msr S0_3_C4_C1_1, xzr
-# NOSPECID: msr S3_3_C4_C2_6, x3
-# NOSPECID: mrs x2, S3_3_C4_C2_6

test/MC/Disassembler/AArch64/armv8.5a-ssbs.txt

@@ -0,0 +1,13 @@
+# RUN: llvm-mc -triple=aarch64 -mattr=+ssbs  -disassemble < %s | FileCheck %s
+# RUN: llvm-mc -triple=aarch64 -mattr=+v8.5a -disassemble < %s | FileCheck %s
+# RUN: llvm-mc -triple=aarch64 -mattr=-ssbs  -disassemble < %s | FileCheck %s --check-prefix=NOSPECID
+
+[0x3f 0x41 0x03 0xd5]
+[0xc3 0x42 0x1b 0xd5]
+[0xc2 0x42 0x3b 0xd5]
+# CHECK:    msr SSBS, #1
+# CHECK:    msr SSBS, x3
+# CHECK:    mrs x2, SSBS
+# NOSPECID: msr S0_3_C4_C1_1, xzr
+# NOSPECID: msr S3_3_C4_C2_6, x3
+# NOSPECID: mrs x2, S3_3_C4_C2_6

unittests/Support/TargetParserTest.cpp

@@ -508,7 +508,7 @@ TEST(TargetParserTest, testARMExtension) {
 }
 
 TEST(TargetParserTest, ARMFPUVersion) {
-  for (ARM::FPUKind FK = static_cast<ARM::FPUKind>(0); 
+  for (ARM::FPUKind FK = static_cast<ARM::FPUKind>(0);
        FK <= ARM::FPUKind::FK_LAST;
        FK = static_cast<ARM::FPUKind>(static_cast<unsigned>(FK) + 1))
     if (FK == ARM::FK_LAST || ARM::getFPUName(FK) == "invalid" ||
@@ -992,7 +992,8 @@ TEST(TargetParserTest, AArch64ArchExtFeature) {
                               {"dotprod", "nodotprod", "+dotprod", "-dotprod"},
                               {"rcpc", "norcpc", "+rcpc", "-rcpc" },
                               {"rng", "norng", "+rand", "-rand"},
-                              {"memtag", "nomemtag", "+mte", "-mte"}};
+                              {"memtag", "nomemtag", "+mte", "-mte"},
+                              {"ssbs", "nossbs", "+ssbs", "-ssbs"}};
 
   for (unsigned i = 0; i < array_lengthof(ArchExt); i++) {
     EXPECT_EQ(StringRef(ArchExt[i][2]),