[RISCV] Support RISCV Atomics ABI attributes (#84597)

This patch adds support for the `atomic_abi` attribute, specifid in

https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc#tag_riscv_atomic_abi-14-uleb128version.

The atomics_abi tag merging is conducted as follows:

- UNKNOWN is safe to merge with all other values.
- A6C is compatible with A6S, and results in the A6C ABI.
- A6C is incompatible with A7, and results in an error.
- A6S and A7 are compatible, and merging results in the A7 ABI.

Note: the A7 is not yet supported in either LLVM or in any current
hardware,
and is therefore ommited from attribute generation in
RISCVTargetStreamer.

Author: ilovepi

lld/ELF/Arch/RISCV.cpp

@@ -1084,10 +1084,62 @@ static void mergeArch(RISCVISAInfo::OrderedExtensionMap &mergedExts,
   }
 }
 
+static void mergeAtomic(DenseMap<unsigned, unsigned>::iterator it,
+                        const InputSectionBase *oldSection,
+                        const InputSectionBase *newSection, unsigned int oldTag,
+                        unsigned int newTag) {
+  using RISCVAttrs::RISCVAtomicAbiTag::AtomicABI;
+  // Same tags stay the same, and UNKNOWN is compatible with anything
+  if (oldTag == newTag || newTag == AtomicABI::UNKNOWN)
+    return;
+
+  switch (oldTag) {
+  case AtomicABI::UNKNOWN:
+    it->getSecond() = newTag;
+    return;
+  case AtomicABI::A6C:
+    switch (newTag) {
+    case AtomicABI::A6S:
+      it->getSecond() = AtomicABI::A6C;
+      return;
+    case AtomicABI::A7:
+      error(toString(oldSection) + " has atomic_abi=" + Twine(oldTag) +
+            " but " + toString(newSection) +
+            " has atomic_abi=" + Twine(newTag));
+      return;
+    };
+
+  case AtomicABI::A6S:
+    switch (newTag) {
+    case AtomicABI::A6C:
+      it->getSecond() = AtomicABI::A6C;
+      return;
+    case AtomicABI::A7:
+      it->getSecond() = AtomicABI::A7;
+      return;
+    };
+
+  case AtomicABI::A7:
+    switch (newTag) {
+    case AtomicABI::A6S:
+      it->getSecond() = AtomicABI::A7;
+      return;
+    case AtomicABI::A6C:
+      error(toString(oldSection) + " has atomic_abi=" + Twine(oldTag) +
+            " but " + toString(newSection) +
+            " has atomic_abi=" + Twine(newTag));
+      return;
+    };
+  default:
+    llvm_unreachable("unknown AtomicABI");
+  };
+}
+
 static RISCVAttributesSection *
 mergeAttributesSection(const SmallVector<InputSectionBase *, 0> &sections) {
   RISCVISAInfo::OrderedExtensionMap exts;
   const InputSectionBase *firstStackAlign = nullptr;
+  const InputSectionBase *firstAtomicAbi = nullptr;
   unsigned firstStackAlignValue = 0, xlen = 0;
   bool hasArch = false;
 
@@ -1134,6 +1186,17 @@ mergeAttributesSection(const SmallVector<InputSectionBase *, 0> &sections) {
       case RISCVAttrs::PRIV_SPEC_MINOR:
       case RISCVAttrs::PRIV_SPEC_REVISION:
         break;
+
+      case llvm::RISCVAttrs::AttrType::ATOMIC_ABI:
+        if (auto i = parser.getAttributeValue(tag.attr)) {
+          auto r = merged.intAttr.try_emplace(tag.attr, *i);
+          if (r.second) {
+            firstAtomicAbi = sec;
+          } else {
+            mergeAtomic(r.first, firstAtomicAbi, sec, r.first->getSecond(), *i);
+          }
+        }
+        continue;
       }
 
       // Fallback for deprecated priv_spec* and other unknown attributes: retain

lld/test/ELF/riscv-attributes.s

@@ -44,6 +44,39 @@
 # RUN: not ld.lld a.o b.o c.o diff_stack_align.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=STACK_ALIGN --implicit-check-not=error:
 # STACK_ALIGN: error: diff_stack_align.o:(.riscv.attributes) has stack_align=32 but a.o:(.riscv.attributes) has stack_align=16
 
+## merging atomic_abi values for A6C and A7 lead to an error.
+# RUN: llvm-mc -filetype=obj -triple=riscv64  atomic_abi_A6C.s -o atomic_abi_A6C.o
+# RUN: llvm-mc -filetype=obj -triple=riscv64  atomic_abi_A7.s -o atomic_abi_A7.o
+# RUN: not ld.lld atomic_abi_A6C.o atomic_abi_A7.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=ATOMIC_ABI_ERROR --implicit-check-not=error:
+# ATOMIC_ABI_ERROR: error: atomic_abi_A6C.o:(.riscv.attributes) has atomic_abi=1 but atomic_abi_A7.o:(.riscv.attributes) has atomic_abi=3
+
+
+# RUN: llvm-mc -filetype=obj -triple=riscv64  atomic_abi_A6S.s -o atomic_abi_A6S.o
+# RUN: ld.lld atomic_abi_A6S.o atomic_abi_A6C.o -o atomic_abi_A6C_A6S
+# RUN: llvm-readobj -A atomic_abi_A6C_A6S | FileCheck %s --check-prefix=A6C_A6S
+
+# RUN: ld.lld atomic_abi_A6S.o atomic_abi_A7.o -o atomic_abi_A6S_A7
+# RUN: llvm-readobj -A atomic_abi_A6S_A7 | FileCheck %s --check-prefix=A6S_A7
+
+# RUN: llvm-mc -filetype=obj -triple=riscv64  atomic_abi_unknown.s -o atomic_abi_unknown.o
+# RUN: ld.lld atomic_abi_unknown.o atomic_abi_A6C.o -o atomic_abi_A6C_unknown
+# RUN: llvm-readobj -A atomic_abi_A6C_unknown | FileCheck %s --check-prefixes=UNKNOWN_A6C
+
+# RUN: ld.lld atomic_abi_unknown.o diff_stack_align.o -o atomic_abi_none_unknown
+# RUN: llvm-readobj -A atomic_abi_none_unknown | FileCheck %s --check-prefixes=UNKNOWN_NONE
+
+# RUN: ld.lld diff_stack_align.o atomic_abi_A6C.o -o atomic_abi_A6C_none
+# RUN: llvm-readobj -A atomic_abi_A6C_none | FileCheck %s --check-prefixes=NONE_A6C
+
+# RUN: ld.lld atomic_abi_unknown.o atomic_abi_A6S.o -o atomic_abi_A6S_unknown
+# RUN: llvm-readobj -A atomic_abi_A6S_unknown | FileCheck %s --check-prefix=UNKNOWN_A6S
+
+# RUN: ld.lld atomic_abi_unknown.o atomic_abi_A7.o -o atomic_abi_A7_unknown
+# RUN: llvm-readobj -A atomic_abi_A7_unknown | FileCheck %s --check-prefix=UNKNOWN_A7
+
+# RUN: ld.lld diff_stack_align.o atomic_abi_A7.o -o atomic_abi_A7_none
+# RUN: llvm-readobj -A atomic_abi_A7_none | FileCheck %s --check-prefix=NONE_A7
+
 ## The deprecated priv_spec is not handled as GNU ld does.
 ## Differing priv_spec attributes lead to an absent attribute.
 # RUN: llvm-mc -filetype=obj -triple=riscv64 diff_priv_spec.s -o diff_priv_spec.o
@@ -286,6 +319,175 @@
 .attribute priv_spec, 3
 .attribute priv_spec_minor, 3
 
+#--- atomic_abi_unknown.s
+.attribute atomic_abi, 0
+
+#--- atomic_abi_A6C.s
+.attribute atomic_abi, 1
+
+#--- atomic_abi_A6S.s
+.attribute atomic_abi, 2
+
+#--- atomic_abi_A7.s
+.attribute atomic_abi, 3
+
+#      UNKNOWN_NONE: BuildAttributes {
+# UNKNOWN_NONE-NEXT:   FormatVersion: 0x41
+# UNKNOWN_NONE-NEXT:   Section 1 {
+# UNKNOWN_NONE-NEXT:     SectionLength: 17
+# UNKNOWN_NONE-NEXT:     Vendor: riscv
+# UNKNOWN_NONE-NEXT:     Tag: Tag_File (0x1)
+# UNKNOWN_NONE-NEXT:     Size: 7
+# UNKNOWN_NONE-NEXT:     FileAttributes {
+# UNKNOWN_NONE-NEXT:       Attribute {
+# UNKNOWN_NONE-NEXT:         Tag: 4
+# UNKNOWN_NONE-NEXT:         Value: 32
+# UNKNOWN_NONE-NEXT:         TagName: stack_align
+# UNKNOWN_NONE-NEXT:         Description: Stack alignment is 32-bytes
+# UNKNOWN_NONE-NEXT:       }
+# UNKNOWN_NONE-NEXT:     }
+# UNKNOWN_NONE-NEXT:   }
+# UNKNOWN_NONE-NEXT: }
+
+#      NONE_A6C: BuildAttributes {
+# NONE_A6C-NEXT:   FormatVersion: 0x41
+# NONE_A6C-NEXT:   Section 1 {
+# NONE_A6C-NEXT:     SectionLength: 19
+# NONE_A6C-NEXT:     Vendor: riscv
+# NONE_A6C-NEXT:     Tag: Tag_File (0x1)
+# NONE_A6C-NEXT:     Size: 9
+# NONE_A6C-NEXT:     FileAttributes {
+# NONE_A6C-NEXT:       Attribute {
+# NONE_A6C-NEXT:         Tag: 14
+# NONE_A6C-NEXT:         Value: 1
+# NONE_A6C-NEXT:         TagName: atomic_abi
+# NONE_A6C-NEXT:         Description: Atomic ABI is 1
+# NONE_A6C-NEXT:       }
+# NONE_A6C-NEXT:       Attribute {
+# NONE_A6C-NEXT:         Tag: 4
+# NONE_A6C-NEXT:         Value: 32
+# NONE_A6C-NEXT:         TagName: stack_align
+# NONE_A6C-NEXT:         Description: Stack alignment is 32-bytes
+# NONE_A6C-NEXT:       }
+# NONE_A6C-NEXT:     }
+# NONE_A6C-NEXT:   }
+# NONE_A6C-NEXT: }
+
+#      UNKNOWN_A6C: BuildAttributes {
+# UNKNOWN_A6C-NEXT:   FormatVersion: 0x41
+# UNKNOWN_A6C-NEXT:   Section 1 {
+# UNKNOWN_A6C-NEXT:     SectionLength: 17
+# UNKNOWN_A6C-NEXT:     Vendor: riscv
+# UNKNOWN_A6C-NEXT:     Tag: Tag_File (0x1)
+# UNKNOWN_A6C-NEXT:     Size: 7
+# UNKNOWN_A6C-NEXT:     FileAttributes {
+# UNKNOWN_A6C-NEXT:       Attribute {
+# UNKNOWN_A6C-NEXT:         Tag: 14
+# UNKNOWN_A6C-NEXT:         Value: 1
+# UNKNOWN_A6C-NEXT:         TagName: atomic_abi
+# UNKNOWN_A6C-NEXT:         Description: Atomic ABI is 1
+# UNKNOWN_A6C-NEXT:       }
+# UNKNOWN_A6C-NEXT:     }
+# UNKNOWN_A6C-NEXT:   }
+# UNKNOWN_A6C-NEXT: }
+
+#      UNKNOWN_A6S: BuildAttributes {
+# UNKNOWN_A6S-NEXT:   FormatVersion: 0x41
+# UNKNOWN_A6S-NEXT:   Section 1 {
+# UNKNOWN_A6S-NEXT:     SectionLength:
+# UNKNOWN_A6S-NEXT:     Vendor: riscv
+# UNKNOWN_A6S-NEXT:     Tag: Tag_File (0x1)
+# UNKNOWN_A6S-NEXT:     Size: 7
+# UNKNOWN_A6S-NEXT:     FileAttributes {
+# UNKNOWN_A6S-NEXT:       Attribute {
+# UNKNOWN_A6S-NEXT:         Tag: 14
+# UNKNOWN_A6S-NEXT:         Value: 2
+# UNKNOWN_A6S-NEXT:         TagName: atomic_abi
+# UNKNOWN_A6S-NEXT:         Description: Atomic ABI is 2
+# UNKNOWN_A6S-NEXT:       }
+# UNKNOWN_A6S-NEXT:     }
+# UNKNOWN_A6S-NEXT:   }
+# UNKNOWN_A6S-NEXT: }
+
+#      NONE_A7: BuildAttributes {
+# NONE_A7-NEXT:   FormatVersion: 0x41
+# NONE_A7-NEXT:   Section 1 {
+# NONE_A7-NEXT:     SectionLength: 19
+# NONE_A7-NEXT:     Vendor: riscv
+# NONE_A7-NEXT:     Tag: Tag_File (0x1)
+# NONE_A7-NEXT:     Size: 9
+# NONE_A7-NEXT:     FileAttributes {
+# NONE_A7-NEXT:       Attribute {
+# NONE_A7-NEXT:         Tag: 14
+# NONE_A7-NEXT:         Value: 3
+# NONE_A7-NEXT:         TagName: atomic_abi
+# NONE_A7-NEXT:         Description: Atomic ABI is 3
+# NONE_A7-NEXT:       }
+# NONE_A7-NEXT:       Attribute {
+# NONE_A7-NEXT:         Tag: 4
+# NONE_A7-NEXT:         Value: 32
+# NONE_A7-NEXT:         TagName: stack_align
+# NONE_A7-NEXT:         Description: Stack alignment is 32-bytes
+# NONE_A7-NEXT:       }
+# NONE_A7-NEXT:     }
+# NONE_A7-NEXT:   }
+# NONE_A7-NEXT: }
+
+
+#      UNKNOWN_A7: BuildAttributes {
+# UNKNOWN_A7-NEXT:   FormatVersion: 0x41
+# UNKNOWN_A7-NEXT:   Section 1 {
+# UNKNOWN_A7-NEXT:     SectionLength: 17
+# UNKNOWN_A7-NEXT:     Vendor: riscv
+# UNKNOWN_A7-NEXT:     Tag: Tag_File (0x1)
+# UNKNOWN_A7-NEXT:     Size: 7
+# UNKNOWN_A7-NEXT:     FileAttributes {
+# UNKNOWN_A7-NEXT:       Attribute {
+# UNKNOWN_A7-NEXT:         Tag: 14
+# UNKNOWN_A7-NEXT:         Value: 3
+# UNKNOWN_A7-NEXT:         TagName: atomic_abi
+# UNKNOWN_A7-NEXT:         Description: Atomic ABI is 3
+# UNKNOWN_A7-NEXT:       }
+# UNKNOWN_A7-NEXT:     }
+# UNKNOWN_A7-NEXT:   }
+# UNKNOWN_A7-NEXT: }
+
+#      A6C_A6S: BuildAttributes {
+# A6C_A6S-NEXT:   FormatVersion: 0x41
+# A6C_A6S-NEXT:   Section 1 {
+# A6C_A6S-NEXT:     SectionLength: 17
+# A6C_A6S-NEXT:     Vendor: riscv
+# A6C_A6S-NEXT:     Tag: Tag_File (0x1)
+# A6C_A6S-NEXT:     Size: 7
+# A6C_A6S-NEXT:     FileAttributes {
+# A6C_A6S-NEXT:       Attribute {
+# A6C_A6S-NEXT:         Tag: 14
+# A6C_A6S-NEXT:         Value: 1
+# A6C_A6S-NEXT:         TagName: atomic_abi
+# A6C_A6S-NEXT:         Description: Atomic ABI is 1
+# A6C_A6S-NEXT:       }
+# A6C_A6S-NEXT:     }
+# A6C_A6S-NEXT:   }
+# A6C_A6S-NEXT: }
+
+#      A6S_A7: BuildAttributes {
+# A6S_A7-NEXT:   FormatVersion: 0x41
+# A6S_A7-NEXT:   Section 1 {
+# A6S_A7-NEXT:     SectionLength: 17
+# A6S_A7-NEXT:     Vendor: riscv
+# A6S_A7-NEXT:     Tag: Tag_File (0x1)
+# A6S_A7-NEXT:     Size: 7
+# A6S_A7-NEXT:     FileAttributes {
+# A6S_A7-NEXT:       Attribute {
+# A6S_A7-NEXT:         Tag: 14
+# A6S_A7-NEXT:         Value: 3
+# A6S_A7-NEXT:         TagName: atomic_abi
+# A6S_A7-NEXT:         Description: Atomic ABI is 3
+# A6S_A7-NEXT:       }
+# A6S_A7-NEXT:     }
+# A6S_A7-NEXT:   }
+# A6S_A7-NEXT: }
+
 #--- unknown13.s
 .attribute 13, "0"
 #--- unknown13a.s

llvm/include/llvm/Support/RISCVAttributeParser.h

@@ -24,6 +24,7 @@ class RISCVAttributeParser : public ELFAttributeParser {
 
   Error unalignedAccess(unsigned tag);
   Error stackAlign(unsigned tag);
+  Error atomicAbi(unsigned tag);
 
 public:
   RISCVAttributeParser(ScopedPrinter *sw)

llvm/include/llvm/Support/RISCVAttributes.h

@@ -32,8 +32,21 @@ enum AttrType : unsigned {
   PRIV_SPEC = 8,
   PRIV_SPEC_MINOR = 10,
   PRIV_SPEC_REVISION = 12,
+  ATOMIC_ABI = 14,
 };
 
+namespace RISCVAtomicAbiTag {
+enum AtomicABI : unsigned {
+  // Values for Tag_RISCV_atomic_abi
+  // Defined at
+  // https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-elf.adoc#tag_riscv_atomic_abi-14-uleb128version
+  UNKNOWN = 0,
+  A6C = 1,
+  A6S = 2,
+  A7 = 3,
+};
+} // namespace RISCVAtomicAbiTag
+
 enum { NOT_ALLOWED = 0, ALLOWED = 1 };
 
 } // namespace RISCVAttrs

llvm/lib/Support/RISCVAttributeParser.cpp

@@ -36,7 +36,18 @@ const RISCVAttributeParser::DisplayHandler
         {
             RISCVAttrs::UNALIGNED_ACCESS,
             &RISCVAttributeParser::unalignedAccess,
-        }};
+        },
+        {
+            RISCVAttrs::ATOMIC_ABI,
+            &RISCVAttributeParser::atomicAbi,
+        },
+};
+
+Error RISCVAttributeParser::atomicAbi(unsigned Tag) {
+  uint64_t Value = de.getULEB128(cursor);
+  printAttribute(Tag, Value, "Atomic ABI is " + utostr(Value));
+  return Error::success();
+}
 
 Error RISCVAttributeParser::unalignedAccess(unsigned tag) {
   static const char *strings[] = {"No unaligned access", "Unaligned access"};

llvm/lib/Support/RISCVAttributes.cpp

@@ -18,6 +18,7 @@ static constexpr TagNameItem tagData[] = {
     {PRIV_SPEC, "Tag_priv_spec"},
     {PRIV_SPEC_MINOR, "Tag_priv_spec_minor"},
     {PRIV_SPEC_REVISION, "Tag_priv_spec_revision"},
+    {ATOMIC_ABI, "Tag_atomic_abi"},
 };
 
 constexpr TagNameMap RISCVAttributeTags{tagData};

llvm/lib/Target/RISCV/MCTargetDesc/RISCVTargetStreamer.cpp

@@ -75,6 +75,13 @@ void RISCVTargetStreamer::emitTargetAttributes(const MCSubtargetInfo &STI,
     auto &ISAInfo = *ParseResult;
     emitTextAttribute(RISCVAttrs::ARCH, ISAInfo->toString());
   }
+
+  if (STI.hasFeature(RISCV::FeatureStdExtA)) {
+    unsigned AtomicABITag = STI.hasFeature(RISCV::FeatureTrailingSeqCstFence)
+                                ? RISCVAttrs::RISCVAtomicAbiTag::AtomicABI::A6S
+                                : RISCVAttrs::RISCVAtomicAbiTag::AtomicABI::A6C;
+    emitAttribute(RISCVAttrs::ATOMIC_ABI, AtomicABITag);
+  }
 }
 
 // This part is for ascii assembly output

llvm/test/CodeGen/RISCV/attributes.ll

@@ -129,7 +129,8 @@
 ; RUN: llc -mtriple=riscv64 -mattr=+m %s -o - | FileCheck --check-prefixes=CHECK,RV64M %s
 ; RUN: llc -mtriple=riscv64 -mattr=+zmmul %s -o - | FileCheck --check-prefixes=CHECK,RV64ZMMUL %s
 ; RUN: llc -mtriple=riscv64 -mattr=+m,+zmmul %s -o - | FileCheck --check-prefixes=CHECK,RV64MZMMUL %s
-; RUN: llc -mtriple=riscv64 -mattr=+a %s -o - | FileCheck --check-prefixes=CHECK,RV64A %s
+; RUN: llc -mtriple=riscv64 -mattr=+a %s -o - | FileCheck --check-prefixes=CHECK,RV64A,A6C %s
+; RUN: llc -mtriple=riscv64 -mattr=+a,+seq-cst-trailing-fence %s -o - | FileCheck --check-prefixes=CHECK,RV64A,A6S %s
 ; RUN: llc -mtriple=riscv64 -mattr=+f %s -o - | FileCheck --check-prefixes=CHECK,RV64F %s
 ; RUN: llc -mtriple=riscv64 -mattr=+d %s -o - | FileCheck --check-prefixes=CHECK,RV64D %s
 ; RUN: llc -mtriple=riscv64 -mattr=+c %s -o - | FileCheck --check-prefixes=CHECK,RV64C %s
@@ -516,3 +517,10 @@ define i32 @addi(i32 %a) {
   %1 = add i32 %a, 1
   ret i32 %1
 }
+
+define i8 @atomic_load_i8_seq_cst(ptr %a) nounwind {
+  %1 = load atomic i8, ptr %a seq_cst, align 1
+  ret i8 %1
+; A6S: .attribute 14, 2
+; A6C: .attribute 14, 1
+}

llvm/test/MC/RISCV/attribute.s

@@ -24,3 +24,6 @@
 
 .attribute priv_spec_revision, 0
 # CHECK: attribute      12, 0
+
+.attribute atomic_abi, 0
+# CHECK: attribute      14, 0