[AARCH64][ELF][llvm-readobj] Support for AArch64 .note.gnu.property

[peter.smith]

Summary

ELF for the 64-bit Arm Architecture defines a processor specific property type GNU_PROPERTY_AARCH64_FEATURE_1_AND as GNU_PROPERTY_LOPROC. This property works in a similar way to the existing X86 processor specific property GNU_PROPERTY_GNU_X86_FEATURE_1_AND.

Two feature bits are defined for GNU_PROPERTY_AARCH64_FEATURE_1_AND:

• GNU_PROPERTY_AARCH64_FEATURE_1_BTI 0x1
• GNU_PROPERTY_AARCH64_FEATURE_1_PAC 0x2

This patch defines the property, feature bits and implements support for printing in llvm-readobj.

The overall destination is support for BTI and PAC in LLD.

The ELF for the 64-bit Arm Architecture spec with the above features defined can be found at: https://developer.arm.com/docs/ihi0056/latest/elf-for-the-arm-64-bit-architecture-aarch64-abi-2019q1-documentation

[grimar]

tools/llvm-readobj/ELFDumper.cpp

3748

Seems you should be able to share the logic with GNU_PROPERTY_X86_FEATURE_1_AND?

i.e.

case GNU_PROPERTY_X86_FEATURE_1_AND:
case GNU_PROPERTY_AARCH64_FEATURE_1_AND:
....

OS << (Type == GNU_PROPERTY_AARCH64_FEATURE_1_AND) ?
  "aarch64 feature: " : "x86 feature: ";
...

and so on. Will it be better?

[peter.smith]

Updated diff to share more of the code with the GNU_PROPERTY_GNU_X86_FEATURE_1_AND. The processor specific feature bits will overlap so these need to be protected. I think this is better than the previous version as we are sharing the parsing code.

[grimar]

LGTM

test/tools/llvm-readobj/aarch64-note-gnu-property.s

4

nit: I think we use llvm-readobj and llvm-readelf usually instead of specifying -elf-output-style explicitly.

[MaskRay]

test/tools/llvm-readobj/aarch64-note-gnu-property.s

1

This line is not needed. llvm-readobj doesn't use any llvm/lib/Target/AArch64 code (I guess that is what aarch64-registered-target is about)

Also consider moving the test under the AArch64 directory since it is there?

[grimar]

test/tools/llvm-readobj/aarch64-note-gnu-property.s

1

I think this is for llvm-mc call below..
We can avoid it with using yaml instead, but perhaps it is not that really valuable.

[peter.smith]

Thanks for the reviews, I'll move the test to the AArch64 dir and lose the top line. Will do that on Monday as I'll be out of office tomorrow.

include/llvm/BinaryFormat/ELF.h

enum {
   NT_GNU_GOLD_VERSION = 4,
   NT_GNU_PROPERTY_TYPE_0 = 5,
 };
 
 // Property types used in GNU_PROPERTY_TYPE_0 notes.
 enum : unsigned {
   GNU_PROPERTY_STACK_SIZE = 1,
   GNU_PROPERTY_NO_COPY_ON_PROTECTED = 2,
+  GNU_PROPERTY_AARCH64_FEATURE_1_AND = 0xc0000000,
   GNU_PROPERTY_X86_FEATURE_1_AND = 0xc0000002,
   GNU_PROPERTY_X86_ISA_1_NEEDED = 0xc0008000,
   GNU_PROPERTY_X86_FEATURE_2_NEEDED = 0xc0008001,
   GNU_PROPERTY_X86_ISA_1_USED = 0xc0010000,
   GNU_PROPERTY_X86_FEATURE_2_USED = 0xc0010001,
 };
 
+// aarch64 processor feature bits.
+enum : unsigned {
+  GNU_PROPERTY_AARCH64_FEATURE_1_BTI = 1 << 0,
+  GNU_PROPERTY_AARCH64_FEATURE_1_PAC = 1 << 1,
+};
+
 // x86 processor feature bits.
 enum : unsigned {
   GNU_PROPERTY_X86_FEATURE_1_IBT = 1 << 0,
   GNU_PROPERTY_X86_FEATURE_1_SHSTK = 1 << 1,
 
   GNU_PROPERTY_X86_ISA_1_CMOV = 1 << 0,
   GNU_PROPERTY_X86_ISA_1_SSE = 1 << 1,
   GNU_PROPERTY_X86_ISA_1_SSE2 = 1 << 2,

test/tools/llvm-readobj/aarch64-note-gnu-property.s

+// REQUIRES: aarch64-registered-target
+// RUN: llvm-mc -filetype=obj -triple aarch64-linux-gnu %s -o %t
+// RUN: llvm-readobj -elf-output-style GNU --notes %t | FileCheck %s --check-prefix=GNU
+// RUN: llvm-readobj -elf-output-style LLVM --notes %t | FileCheck %s --check-prefix=LLVM
+
+// GNU: Displaying notes found at file offset 0x00000040 with length 0x00000020:
+// GNU-NEXT:   Owner                 Data size  Description
+// GNU-NEXT:   GNU                   0x00000010 NT_GNU_PROPERTY_TYPE_0 (property note)
+// GNU-NEXT:     Properties:    aarch64 feature: BTI, PAC
+
+// LLVM:      Notes [
+// LLVM-NEXT:   NoteSection {
+// LLVM-NEXT:     Offset: 0x40
+// LLVM-NEXT:     Size: 0x20
+// LLVM-NEXT:     Note {
+// LLVM-NEXT:       Owner: GNU
+// LLVM-NEXT:       Data size: 0x10
+// LLVM-NEXT:       Type: NT_GNU_PROPERTY_TYPE_0 (property note)
+// LLVM-NEXT:       Property [
+// LLVM-NEXT:         aarch64 feature: BTI, PAC
+// LLVM-NEXT:       ]
+// LLVM-NEXT:     }
+// LLVM-NEXT:   }
+// LLVM-NEXT: ]
+
+.section ".note.gnu.property", "a"
+.align 4
+  .long 4           /* Name length is always 4 ("GNU") */
+  .long end - begin /* Data length */
+  .long 5           /* Type: NT_GNU_PROPERTY_TYPE_0 */
+  .asciz "GNU"      /* Name */
+  .p2align 3
+begin:
+  /* BTI and PAC property note */
+  .long 0xc0000000  /* Type: GNU_PROPERTY_AARCH64_FEATURE_1_AND */
+  .long 4           /* Data size */
+  .long 3           /* BTI and PAC */
+  .p2align 3        /* Align to 8 byte for 64 bit */
+end:

tools/llvm-readobj/ELFDumper.cpp

else
       OS << format("<corrupt length: 0x%x>", DataSize);
     return OS.str();
   }
   case GNU_PROPERTY_NO_COPY_ON_PROTECTED:
     OS << "no copy on protected";
     if (DataSize)
       OS << format(" <corrupt length: 0x%x>", DataSize);
     return OS.str();
+  case GNU_PROPERTY_AARCH64_FEATURE_1_AND:
   case GNU_PROPERTY_X86_FEATURE_1_AND:
-    OS << "x86 feature: ";
+    OS << ((Type == GNU_PROPERTY_AARCH64_FEATURE_1_AND) ? "aarch64 feature: "
+                                                        : "x86 feature: ");
     if (DataSize != 4) {
       OS << format("<corrupt length: 0x%x>", DataSize);
       return OS.str();
     }
     PrData = support::endian::read32<ELFT::TargetEndianness>(Data.data());
     if (PrData == 0) {
       OS << "<None>";
       return OS.str();
     }
+    if (Type == GNU_PROPERTY_AARCH64_FEATURE_1_AND) {
+      DumpBit(GNU_PROPERTY_AARCH64_FEATURE_1_BTI, "BTI");
+      DumpBit(GNU_PROPERTY_AARCH64_FEATURE_1_PAC, "PAC");
+    } else {
       DumpBit(GNU_PROPERTY_X86_FEATURE_1_IBT, "IBT");
       DumpBit(GNU_PROPERTY_X86_FEATURE_1_SHSTK, "SHSTK");
+    }
     if (PrData)
       OS << format("<unknown flags: 0x%x>", PrData);
     return OS.str();
   case GNU_PROPERTY_X86_ISA_1_NEEDED:
   case GNU_PROPERTY_X86_ISA_1_USED:
     OS << "x86 ISA "
        << (Type == GNU_PROPERTY_X86_ISA_1_NEEDED ? "needed: " : "used: ");
     if (DataSize != 4) {