[lld][AArch64][Build Attributes] Add support for AArch64 Build Attributes #144082

sivan-shani · 2025-06-13T14:19:35Z

This patch enables lld to read AArch64 Build Attributes and convert them into GNU Properties.

Changes:

Parses AArch64 Build Attributes from input object files.
Converts known attributes into corresponding GNU Properties.
Merges attributes when linking multiple objects.

Spec reference:
https://github.com/ARM-software/abi-aa/pull/230/files

…utes This patch enables lld to read AArch64 Build Attributes and convert them into GNU Properties. Changes: - Parses AArch64 Build Attributes from input object files. - Converts known attributes into corresponding GNU Properties. - Merges attributes when linking multiple objects. Spec reference: https://github.com/ARM-software/abi-aa/pull/230/files#r1030

sivan-shani · 2025-06-16T13:45:49Z

This PR is the second step, based on #141920 We would appreciate as many eyes as possible on this PR to ensure it is solid and aligns with project expectations.

smithp35

Please can you mention in the description that this change does not include support for outputting build attributes for relocatable links. This will come in a follow up patch.

lld/test/ELF/aarch64-feature-pac-replace.s

lld/test/ELF/Inputs/aarch64-func3-pac-replace.s

lld/test/ELF/Inputs/aarch64-pac1-replace.s

lld/test/ELF/aarch64-build-attributes-be.s

lld/test/ELF/aarch64-build-attributes-mixed.s

lld/test/ELF/aarch64-build-attributes.s

lld/test/ELF/aarch64-feature-pac-replace.s

sivan-shani · 2025-06-23T16:11:46Z

Review comments on test files addressed.

smithp35

I don't have any more comments on the draft. Happy for it to move forward for wider review.

llvmbot · 2025-06-24T13:48:44Z

@llvm/pr-subscribers-lld

@llvm/pr-subscribers-llvm-support

Author: SivanShani-Arm (sivan-shani)

Changes

This patch enables lld to read AArch64 Build Attributes and convert them into GNU Properties.

Changes:

Parses AArch64 Build Attributes from input object files.
Converts known attributes into corresponding GNU Properties.
Merges attributes when linking multiple objects.

Spec reference:
https://github.com/ARM-software/abi-aa/pull/230/files

Patch is 22.16 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/144082.diff

10 Files Affected:

(modified) lld/ELF/InputFiles.cpp (+103-10)
(modified) lld/ELF/InputFiles.h (+5)
(added) lld/test/ELF/aarch64-build-attributes-be.s (+29)
(added) lld/test/ELF/aarch64-build-attributes-err.s (+35)
(added) lld/test/ELF/aarch64-build-attributes-invalid.s (+18)
(added) lld/test/ELF/aarch64-build-attributes-malformed.s (+18)
(added) lld/test/ELF/aarch64-build-attributes-mixed.s (+67)
(modified) lld/test/ELF/aarch64-build-attributes.s (+41-17)
(modified) llvm/include/llvm/Support/AArch64AttributeParser.h (+11)
(modified) llvm/lib/Support/AArch64AttributeParser.cpp (+27)

diff --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
index 71e72e7184b9f..55a04c43056c4 100644
--- a/lld/ELF/InputFiles.cpp
+++ b/lld/ELF/InputFiles.cpp
@@ -21,6 +21,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/LTO/LTO.h"
 #include "llvm/Object/IRObjectFile.h"
+#include "llvm/Support/AArch64AttributeParser.h"
 #include "llvm/Support/ARMAttributeParser.h"
 #include "llvm/Support/ARMBuildAttributes.h"
 #include "llvm/Support/Endian.h"
@@ -537,6 +538,52 @@ uint32_t ObjFile<ELFT>::getSectionIndex(const Elf_Sym &sym) const {
       this);
 }
 
+template <class ELFT>
+static void
+handleAArch64BAAndGnuProperties(ObjFile<ELFT> *file, Ctx &ctx, bool hasGP,
+                                const AArch64BuildAttrSubsections &baInfo,
+                                const GnuPropertiesInfo &gpInfo) {
+  if (hasGP) {
+    // Check for data mismatch
+    if (gpInfo.pauthAbiCoreInfo) {
+      if (baInfo.Pauth.TagPlatform != gpInfo.pauthAbiCoreInfo->platform ||
+          baInfo.Pauth.TagSchema != gpInfo.pauthAbiCoreInfo->version)
+        Err(ctx)
+            << file
+            << " Pauth Data mismatch: file contains both GNU properties and "
+               "AArch64 build attributes sections with different Pauth data";
+    }
+    if (baInfo.AndFeatures != gpInfo.andFeatures)
+      Err(ctx) << file
+               << " Features Data mismatch: file contains both GNU "
+                  "properties and AArch64 build attributes sections with "
+                  "different And Features data";
+  } else {
+    // Write missing data
+    // We can only know when Pauth is missing.
+    // Unlike AArch64 Build Attributes, GNU properties does not give a way to
+    // distinguish between no-value given to value of '0' given.
+    if (baInfo.Pauth.TagPlatform || baInfo.Pauth.TagSchema) {
+      // According to the BuildAttributes specification Build Attributes
+      // default to a value of 0 when not present. A (TagPlatform, TagSchema) of
+      // (0, 0) maps to 'no PAuth property present'. A (TagPlatform, TagSchema)
+      // of (0, 1) maps to an explicit PAuth property of platform = 0, version =
+      // 0 ('Invalid').
+      if (baInfo.Pauth.TagPlatform == 0 && baInfo.Pauth.TagSchema == 1) {
+        file->aarch64PauthAbiCoreInfo = {0, 0};
+      } else {
+        file->aarch64PauthAbiCoreInfo = {baInfo.Pauth.TagPlatform,
+                                         baInfo.Pauth.TagSchema};
+      }
+    }
+    file->andFeatures = baInfo.AndFeatures;
+  }
+}
+
+template <typename ELFT>
+static GnuPropertiesInfo readGnuProperty(Ctx &, const InputSection &,
+                                         ObjFile<ELFT> &);
+
 template <class ELFT> void ObjFile<ELFT>::parse(bool ignoreComdats) {
   object::ELFFile<ELFT> obj = this->getObj();
   // Read a section table. justSymbols is usually false.
@@ -552,8 +599,31 @@ template <class ELFT> void ObjFile<ELFT>::parse(bool ignoreComdats) {
   StringRef shstrtab = CHECK2(obj.getSectionStringTable(objSections), this);
   uint64_t size = objSections.size();
   sections.resize(size);
+
+  // For handling AArch64 Build attributes and GNU properties
+  AArch64BuildAttrSubsections aarch64BAsubSections;
+  GnuPropertiesInfo gnuProperty;
+  bool hasAArch64BuildAttributes = false;
+  bool hasGNUProperties = false;
+
   for (size_t i = 0; i != size; ++i) {
     const Elf_Shdr &sec = objSections[i];
+    // Object files that use processor features such as Intel Control-Flow
+    // Enforcement (CET) or AArch64 Branch Target Identification BTI, use a
+    // .note.gnu.property section containing a bitfield of feature bits like the
+    // GNU_PROPERTY_X86_FEATURE_1_IBT flag. Read a bitmap containing the flag.
+    if (check(obj.getSectionName(sec, shstrtab)) == ".note.gnu.property") {
+      gnuProperty = readGnuProperty(
+          ctx,
+          InputSection(*this, sec, check(obj.getSectionName(sec, shstrtab))),
+          *this);
+      hasGNUProperties = true;
+      // Since we merge bitmaps from multiple object files to create a new
+      // .note.gnu.property containing a single AND'ed bitmap, we discard an
+      // input file's .note.gnu.property section.
+      sections[i] = &InputSection::discarded;
+    }
+
     if (LLVM_LIKELY(sec.sh_type == SHT_PROGBITS))
       continue;
     if (LLVM_LIKELY(sec.sh_type == SHT_GROUP)) {
@@ -637,13 +707,27 @@ template <class ELFT> void ObjFile<ELFT>::parse(bool ignoreComdats) {
       }
       break;
     case EM_AARCH64:
-      // FIXME: BuildAttributes have been implemented in llvm, but not yet in
-      // lld. Remove the section so that it does not accumulate in the output
-      // file. When support is implemented we expect not to output a build
-      // attributes section in files of type ET_EXEC or ET_SHARED, but ld -r
-      // ouptut will need a single merged attributes section.
-      if (sec.sh_type == SHT_AARCH64_ATTRIBUTES)
+      // At this stage AArch64 Build Attributes does not replace GNU Properties.
+      // When both exists, their values must match.
+      // When both exists and contain different attributes, they complement each
+      // other. Currently attributes are represented in the linked object file
+      // as GNU properties, which are already supported by the Linux kernel and
+      // the dynamic loader. In the future, when relocatable linking (`-r` flag)
+      // is performed, a single merged AArch64 Build Attributes section will be
+      // emitted.
+      if (sec.sh_type == SHT_AARCH64_ATTRIBUTES) {
+        ArrayRef<uint8_t> contents = check(obj.getSectionContents(sec));
+        AArch64AttributeParser attributes;
+        StringRef name = check(obj.getSectionName(sec, shstrtab));
+        InputSection isec(*this, sec, name);
+        if (Error e = attributes.parse(contents, ELFT::Endianness)) {
+          Warn(ctx) << &isec << ": " << std::move(e);
+        } else {
+          aarch64BAsubSections = extractBuildAttributesSubsections(attributes);
+          hasAArch64BuildAttributes = true;
+        }
         sections[i] = &InputSection::discarded;
+      }
       // Producing a static binary with MTE globals is not currently supported,
       // remove all SHT_AARCH64_MEMTAG_GLOBALS_STATIC sections as they're unused
       // medatada, and we don't want them to end up in the output file for
@@ -655,6 +739,14 @@ template <class ELFT> void ObjFile<ELFT>::parse(bool ignoreComdats) {
     }
   }
 
+  if (hasAArch64BuildAttributes) {
+    // Handle AArch64 Build Attributes and GNU properties:
+    // - Err on mismatched values.
+    // - Store missing values as GNU properties.
+    handleAArch64BAAndGnuProperties<ELFT>(this, ctx, hasGNUProperties,
+                                          aarch64BAsubSections, gnuProperty);
+  }
+
   // Read a symbol table.
   initializeSymbols(obj);
 }
@@ -974,8 +1066,8 @@ static void parseGnuPropertyNote(Ctx &ctx, ELFFileBase &f,
 //   hardware-assisted call flow control;
 // - AArch64 PAuth ABI core info (16 bytes).
 template <class ELFT>
-static void readGnuProperty(Ctx &ctx, const InputSection &sec,
-                            ObjFile<ELFT> &f) {
+static GnuPropertiesInfo readGnuProperty(Ctx &ctx, const InputSection &sec,
+                                         ObjFile<ELFT> &f) {
   using Elf_Nhdr = typename ELFT::Nhdr;
   using Elf_Note = typename ELFT::Note;
 
@@ -992,7 +1084,7 @@ static void readGnuProperty(Ctx &ctx, const InputSection &sec,
     featureAndType = GNU_PROPERTY_RISCV_FEATURE_1_AND;
     break;
   default:
-    return;
+    return GnuPropertiesInfo{};
   }
 
   ArrayRef<uint8_t> data = sec.content();
@@ -1007,7 +1099,7 @@ static void readGnuProperty(Ctx &ctx, const InputSection &sec,
     auto *nhdr = reinterpret_cast<const Elf_Nhdr *>(data.data());
     if (data.size() < sizeof(Elf_Nhdr) ||
         data.size() < nhdr->getSize(sec.addralign))
-      return void(err(data.data()) << "data is too short");
+      return (err(data.data()) << "data is too short", GnuPropertiesInfo{});
 
     Elf_Note note(*nhdr);
     if (nhdr->n_type != NT_GNU_PROPERTY_TYPE_0 || note.getName() != "GNU") {
@@ -1023,6 +1115,7 @@ static void readGnuProperty(Ctx &ctx, const InputSection &sec,
     // Go to next NOTE record to look for more FEATURE_1_AND descriptions.
     data = data.slice(nhdr->getSize(sec.addralign));
   }
+  return GnuPropertiesInfo{f.andFeatures, f.aarch64PauthAbiCoreInfo};
 }
 
 template <class ELFT>
diff --git a/lld/ELF/InputFiles.h b/lld/ELF/InputFiles.h
index ba844ad18f637..9d40030f22fcc 100644
--- a/lld/ELF/InputFiles.h
+++ b/lld/ELF/InputFiles.h
@@ -244,6 +244,11 @@ class ELFFileBase : public InputFile {
   std::optional<AArch64PauthAbiCoreInfo> aarch64PauthAbiCoreInfo;
 };
 
+struct GnuPropertiesInfo {
+  uint32_t andFeatures = 0;
+  std::optional<AArch64PauthAbiCoreInfo> pauthAbiCoreInfo;
+};
+
 // .o file.
 template <class ELFT> class ObjFile : public ELFFileBase {
   LLVM_ELF_IMPORT_TYPES_ELFT(ELFT)
diff --git a/lld/test/ELF/aarch64-build-attributes-be.s b/lld/test/ELF/aarch64-build-attributes-be.s
new file mode 100644
index 0000000000000..8ae9ce5d7f60b
--- /dev/null
+++ b/lld/test/ELF/aarch64-build-attributes-be.s
@@ -0,0 +1,29 @@
+// REQUIRES: aarch64
+// RUN: llvm-mc -triple=aarch64_be %s -filetype=obj -o %t.o
+// RUN: ld.lld %t.o --shared -o %t.so
+// RUN: llvm-readelf -n %t.so | FileCheck %s --check-prefix=NOTE
+
+// RUN: llvm-mc -triple=aarch64_be %s -filetype=obj -o %t.o
+// RUN: ld.lld %t.o --shared -o %t.so
+// RUN: llvm-readelf -n %t.so | FileCheck %s --check-prefix=NOTE
+// RUN: ld.lld %t.o -o %t
+// RUN: llvm-readelf -n %t.so | FileCheck %s --check-prefix=NOTE
+// RUN: ld.lld -r %t.o -o %t2.o
+// RUN: llvm-readelf -n %t.so | FileCheck %s --check-prefix=NOTE
+
+/// Test that lld can read big-endian build-attributes.
+
+// NOTE: Displaying notes found in: .note.gnu.property
+// NOTE-NEXT: Owner Data size Description
+// NOTE-NEXT: GNU 0x00000028 NT_GNU_PROPERTY_TYPE_0 (property note)
+// NOTE-NEXT: Properties: aarch64 feature: BTI, PAC, GCS
+// NOTE-NEXT: AArch64 PAuth ABI core info: platform 0x89abcdef (unknown), version 0x89abcdef
+
+
+.aeabi_subsection aeabi_pauthabi, required, uleb128
+.aeabi_attribute Tag_PAuth_Platform, 0x123456789ABCDEF
+.aeabi_attribute Tag_PAuth_Schema, 0x123456789ABCDEF
+.aeabi_subsection aeabi_feature_and_bits, optional, uleb128
+.aeabi_attribute Tag_Feature_BTI, 1
+.aeabi_attribute Tag_Feature_PAC, 1
+.aeabi_attribute Tag_Feature_GCS, 1
diff --git a/lld/test/ELF/aarch64-build-attributes-err.s b/lld/test/ELF/aarch64-build-attributes-err.s
new file mode 100644
index 0000000000000..029cb1a68a5e7
--- /dev/null
+++ b/lld/test/ELF/aarch64-build-attributes-err.s
@@ -0,0 +1,35 @@
+// REQUIRES: aarch64
+
+// RUN: llvm-mc -triple=aarch64 %s -filetype=obj -o %t.o
+// RUN: not ld.lld %t.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=ERR
+
+// ERR: Pauth Data mismatch: file contains both GNU properties and AArch64 build attributes sections with different Pauth data
+// ERR-NEXT: Features Data mismatch: file contains both GNU properties and AArch64 build attributes sections with different And Features data
+
+.aeabi_subsection aeabi_pauthabi, required, uleb128
+.aeabi_attribute Tag_PAuth_Platform, 5
+.aeabi_attribute Tag_PAuth_Schema, 5
+.aeabi_subsection aeabi_feature_and_bits, optional, uleb128
+.aeabi_attribute Tag_Feature_BTI, 1
+.aeabi_attribute Tag_Feature_PAC, 1
+.aeabi_attribute Tag_Feature_GCS, 1
+
+.section ".note.gnu.property", "a"
+.long 0x4
+.long 0x10
+.long 0x5
+.asciz "GNU"
+.long 0xc0000000 // GNU_PROPERTY_AARCH64_FEATURE_1_AND
+.long 0x4
+.long 0x2          // GNU_PROPERTY_AARCH64_FEATURE_1_PAC
+.long 0x0
+
+.section ".note.gnu.property", "a"
+.long 0x4
+.long 0x18
+.long 0x5
+.asciz "GNU"
+.long 0xc0000001
+.long 0x10
+.quad 0x12345678 // platform
+.quad 0x87654321  // version
diff --git a/lld/test/ELF/aarch64-build-attributes-invalid.s b/lld/test/ELF/aarch64-build-attributes-invalid.s
new file mode 100644
index 0000000000000..7cd4723087de2
--- /dev/null
+++ b/lld/test/ELF/aarch64-build-attributes-invalid.s
@@ -0,0 +1,18 @@
+// REQUIRES: aarch64
+
+// RUN: llvm-mc -triple=aarch64 -filetype=obj %s -o %t.o
+// RUN: ld.lld -r %t.o -o %t.invalid.o
+// RUN: llvm-readelf -n %t.invalid.o | FileCheck %s
+
+/// According to the BuildAttributes specification Build Attributes
+/// A (TagPlatform, TagSchema)of (0, 1) maps to an explicit PAuth property 
+/// of platform = 0, version = 0 ('Invalid').
+
+// CHECK:      Displaying notes found in: .note.gnu.property
+// CHECK-NEXT:  Owner                Data size 	Description
+// CHECK-NEXT:  GNU                  0x00000018	NT_GNU_PROPERTY_TYPE_0 (property note)
+// CHECK-NEXT:    Properties:        AArch64 PAuth ABI core info: platform 0x0 (invalid), version 0x0
+
+.aeabi_subsection aeabi_pauthabi, required, uleb128
+.aeabi_attribute Tag_PAuth_Platform, 0
+.aeabi_attribute Tag_PAuth_Schema, 1
diff --git a/lld/test/ELF/aarch64-build-attributes-malformed.s b/lld/test/ELF/aarch64-build-attributes-malformed.s
new file mode 100644
index 0000000000000..f40da1ab7e8a1
--- /dev/null
+++ b/lld/test/ELF/aarch64-build-attributes-malformed.s
@@ -0,0 +1,18 @@
+# REQUIRES: aarch64
+
+# RUN: llvm-mc -triple=aarch64 -filetype=obj %s -o %t.o
+# RUN: ld.lld %t.o /dev/null 2>&1 | FileCheck %s
+
+# CHECK: (.ARM.attributes): unexpected end of data at offset 0x3f while reading [0x3d, 0x41)
+
+.section .ARM.attributes,"",%0x70000003
+.byte 0x41                               // Tag 'A' (format version)
+.long 0x00000019                         // Subsection length
+.asciz "aeabi_pauthabi"                  // Subsection name
+.byte 0x00, 0x00                         // Optionality and Type
+.byte 0x01, 0x01, 0x02, 0x01             // PAuth_Platform and PAuth_Schema
+.long 0x00000023                         // Subsection length
+.asciz "aeabi_feature_and_bits"          // Subsection name
+.byte 0x01, 0x00                         // Optionality and Type
+.byte 0x00, 0x01, 0x01, 0x01, 0x02, 0x01 // BTI, PAC, GCS
+.byte 0x00, 0x00                         // This is the malformation, data is too long.
diff --git a/lld/test/ELF/aarch64-build-attributes-mixed.s b/lld/test/ELF/aarch64-build-attributes-mixed.s
new file mode 100644
index 0000000000000..68e9a1fbffda5
--- /dev/null
+++ b/lld/test/ELF/aarch64-build-attributes-mixed.s
@@ -0,0 +1,67 @@
+// REQUIRES: aarch64
+
+// RUN: rm -rf %t && split-file %s %t && cd %t
+
+// RUN: llvm-mc -triple=aarch64 -filetype=obj %s -o %t11.o
+// RUN: llvm-mc -triple=aarch64 -filetype=obj merged-property.s -o %t12.o
+// RUN: llvm-mc -triple=aarch64 -filetype=obj merged-property2.s -o %t13.o
+// RUN: ld.lld -r %t11.o %t12.o %t13.o -o %t.merged1.o
+// RUN: llvm-readelf -n %t.merged1.o | FileCheck %s --check-prefix=NOTE-MIXED
+
+/// This test verifies merging of AArch64 build attributes and GNU property notes.
+/// Three object files are combined: one with build attributes (PAuth information, BTI, PAC, GCS),
+/// and two with GNU property notes encoding the same feature bits. 
+/// PAuth ABI info is provided in one of the files and it is expected to be preserved in the merged output.
+
+// NOTE-MIXED: Displaying notes found in: .note.gnu.property
+// NOTE-MIXED-NEXT:   Owner                Data size 	Description
+// NOTE-MIXED-NEXT:   GNU                  0x00000028	NT_GNU_PROPERTY_TYPE_0 (property note)
+// NOTE-MIXED-NEXT:     Properties:    aarch64 feature: BTI, PAC
+// NOTE-MIXED-NEXT:         AArch64 PAuth ABI core info: platform 0x31 (unknown), version 0x13
+
+// CHECK: .note.gnu.property
+// CHECK-NOT: .ARM.attributes
+
+.aeabi_subsection aeabi_pauthabi, required, uleb128
+.aeabi_attribute Tag_PAuth_Platform, 49
+.aeabi_attribute Tag_PAuth_Schema, 19
+.aeabi_subsection aeabi_feature_and_bits, optional, uleb128
+.aeabi_attribute Tag_Feature_BTI, 1
+.aeabi_attribute Tag_Feature_PAC, 1
+.aeabi_attribute Tag_Feature_GCS, 1
+
+
+//--- merged-property.s
+.section ".note.gnu.property", "a"
+  .long 0x4           // Name length is always 4 ("GNU")
+  .long end - begin   // Data length
+  .long 0x5           // Type: NT_GNU_PROPERTY_TYPE_0
+  .asciz "GNU"        // Name
+  .p2align 0x3
+begin:
+  .long 0xc0000000    // GNU_PROPERTY_AARCH64_FEATURE_1_AND
+  .long 0x4
+  .long 0x7           // pr_data: BTI (1), PAC (2), GCS (4) = 0b111 = 7
+  .long 0x0
+  // PAuth ABI property note
+  .long 0xc0000001    // GNU_PROPERTY_AARCH64_FEATURE_PAUTH
+  .long 0x10          // Data length
+  .quad 0x31          // PAuth ABI platform
+  .quad 0x13          // PAuth ABI version
+  .p2align 0x3        // Align to 8 byte for 64 bit
+end:
+
+//--- merged-property2.s
+.section .note.gnu.property, "a"
+  .align 0x4
+  .long 0x4           // Name length is always 4 ("GNU")
+  .long end2 - begin2 // Data length
+  .long 0x5           // Type: NT_GNU_PROPERTY_TYPE_0
+  .asciz "GNU"        // Name
+begin2:
+  .align 0x4
+  .long 0xc0000000    // Type: GNU_PROPERTY_AARCH64_FEATURE_1_AND
+  .long 0x4           // Data length
+  .long 0x7           // pr_data: BTI (1), PAC (2), GCS (4) = 0b111 = 7
+  .long 0x0
+end2:
diff --git a/lld/test/ELF/aarch64-build-attributes.s b/lld/test/ELF/aarch64-build-attributes.s
index 24e15f94e3d4a..f2d542150897e 100644
--- a/lld/test/ELF/aarch64-build-attributes.s
+++ b/lld/test/ELF/aarch64-build-attributes.s
@@ -1,26 +1,50 @@
 // REQUIRES: aarch64
-// RUN: llvm-mc -triple=aarch64 %s -filetype=obj -o %t.o
-// RUN: ld.lld %t.o --shared -o %t.so
-// RUN: llvm-readelf --sections %t.so | FileCheck %s
-// RUN: ld.lld %t.o -o %t
-// RUN: llvm-readelf --sections %t | FileCheck %s
-// RUN: ld.lld -r %t.o -o %t2.o
-// RUN: llvm-readelf --sections %t2.o | FileCheck %s
-
-/// File has a Build attributes section. This should not appear in
-/// ET_EXEC or ET_SHARED files as there is no requirement for it to
-/// do so. FIXME, the ld -r (relocatable link) should output a single
-/// merged build attributes section. When full support is added in
-/// ld.lld this test should be updated.
+// RUN: rm -rf %t && split-file %s %t && cd %t
 
+// RUN: llvm-mc -triple=aarch64 -filetype=obj %s -o %t1.o
+// RUN: llvm-mc -triple=aarch64 -filetype=obj pauth-bti-gcs.s -o %t2.o
+// RUN: llvm-mc -triple=aarch64 -filetype=obj pauth-bti-pac.s -o %t3.o
+// RUN: ld.lld -r %t1.o %t2.o %t3.o -o %t.merged.o
+// RUN: llvm-readelf -n %t.merged.o | FileCheck %s --check-prefix=NOTE
+
+/// This test merges three object files with AArch64 build attributes.
+/// All contain identical PAuth ABI info (platform/version), which must be preserved.
+/// Only BTI is common across all three in the AND feature set, so the merged output
+/// must show BTI only. PAC and GCS are present in subsets and should not appear.
+
+// NOTE: Displaying notes found in: .note.gnu.property
+// NOTE-NEXT:  Owner                Data size 	Description
+// NOTE-NEXT:  GNU                  0x00000028	NT_GNU_PROPERTY_TYPE_0 (property note)
+// NOTE-NEXT:    Properties:    aarch64 feature: BTI
+// NOTE-NEXT:        AArch64 PAuth ABI core info: platform 0x31 (unknown), version 0x13
+
+// CHECK: .note.gnu.property
 // CHECK-NOT: .ARM.attributes
 
+.aeabi_subsection aeabi_pauthabi, required, uleb128
+.aeabi_attribute Tag_PAuth_Platform, 49
+.aeabi_attribute Tag_PAuth_Schema, 19
 .aeabi_subsection aeabi_feature_and_bits, optional, uleb128
 .aeabi_attribute Tag_Feature_BTI, 1
 .aeabi_attribute Tag_Feature_PAC, 1
 .aeabi_attribute Tag_Feature_GCS, 1
 
-.global _start
-.type _start, %function
-_start:
-ret
+
+//--- pauth-bti-gcs.s
+.aeabi_subsection aeabi_pauthabi, required, uleb128
+.aeabi_attribute Tag_PAuth_Platform, 49
+.aeabi_attribute Tag_PAuth_Schema, 19
+.aeabi_subsection aeabi_feature_and_bits, optional, uleb128
+.aeabi_attribute Tag_Feature_BTI, 1
+.aeabi_attribute Tag_Feature_PAC, 0
+.aeabi_attribute Tag_Feature_GCS, 1
+
+
+//--- pauth-bti-pac.s
+.aeabi_subsection aeabi_pauthabi, required, uleb128
+.aeabi_attribute Tag_PAuth_Platform, 49
+.aeabi_attribute Tag_PAuth_Schema, 19
+.aeabi_subsection aeabi_feature_and_bits, optional, uleb128
+.aeabi_attribute Tag_Feature_BTI, 1
+.aeabi_attribute Tag_Feature_PAC, 1
+.aeabi_attribute Tag_Feature_GCS, 0
diff --git a/llvm/include/llvm/Support/AArch64AttributeParser.h b/llvm/include/llvm/Support/AArch64AttributeParser.h
index aa82ca13668d5..796dbfd6f4162 100644
--- a/llvm/include/llvm/Support/AArch64AttributeParser.h
+++ b/llvm/include/llvm/Support/AArch64AttributeParser.h
@@ -25,6 +25,17 @@ class AArch64AttributeParser : public ELFExtendedAttrParser ...
[truncated]

sivan-shani force-pushed the BAlld_RefMerged branch from 4d25945 to d9ec4f9 Compare June 16, 2025 13:26

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sivan-shani force-pushed the BAlld_RefMerged branch from f8882c6 to cbc512f Compare June 23, 2025 16:09

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sivan-shani marked this pull request as ready for review June 24, 2025 13:48

llvmbot added lld lld:ELF llvm:support labels Jun 24, 2025

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[lld][AArch64][Build Attributes] Add support for AArch64 Build Attributes #144082

[lld][AArch64][Build Attributes] Add support for AArch64 Build Attributes #144082

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[lld][AArch64][Build Attributes] Add support for AArch64 Build Attributes #144082

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