[llvm-objdump] Support PLT decoding for aarch64_be

[jhenderson]

Not being experienced with AARCH64, what does the endianness impact? Does it affect the encoding of instructions, because if so, I'm surprised that the .plt section disassembles fine in this case.

llvm/test/tools/llvm-objdump/ELF/AArch64/plt.test

9–11

Any particular reason you've removed the new line? The line is getting a little long here.

[MaskRay]

In D96211#2547988, @jhenderson wrote:

Not being experienced with AARCH64, what does the endianness impact? Does it affect the encoding of instructions, because if so, I'm surprised that the .plt section disassembles fine in this case.

Instructions use little-endian. Data is big-endian, but it is unrelated.

[MaskRay]

llvm/test/tools/llvm-objdump/ELF/AArch64/plt.test

9–11

86 bytes... which is fine

[jhenderson]

In D96211#2547998, @MaskRay wrote:

In D96211#2547988, @jhenderson wrote:

Not being experienced with AARCH64, what does the endianness impact? Does it affect the encoding of instructions, because if so, I'm surprised that the .plt section disassembles fine in this case.

Instructions use little-endian. Data is big-endian, but it is unrelated.

Okay, thanks. LGTM.

[peter.smith]

LGTM too, thanks for updating for BE.

llvm/lib/Object/ELFObjectFile.cpp

ELFObjectFileBase::getPltAddresses() const {
   switch (Triple.getArch()) {
     case Triple::x86:
       JumpSlotReloc = ELF::R_386_JUMP_SLOT;
       break;
     case Triple::x86_64:
       JumpSlotReloc = ELF::R_X86_64_JUMP_SLOT;
       break;
     case Triple::aarch64:
+    case Triple::aarch64_be:
       JumpSlotReloc = ELF::R_AARCH64_JUMP_SLOT;
       break;
     default:
       return {};
   }
   std::unique_ptr<const MCInstrInfo> MII(T->createMCInstrInfo());
   std::unique_ptr<const MCInstrAnalysis> MIA(
       T->createMCInstrAnalysis(MII.get()));

llvm/test/tools/llvm-objdump/ELF/AArch64/plt.test

 # RUN: llvm-objdump -d %p/Inputs/cfi.elf-aarch64 | FileCheck %s
 
 # CHECK: Disassembly of section .plt:
 # CHECK: <__cfi_slowpath@plt>:
 # CHECK-NEXT: adrp      x16, {{.*}}
 # CHECK: bl {{.*}} <__cfi_slowpath@plt>
 
 # RUN: yaml2obj %s -o %t.aarch64
-# RUN: llvm-objdump -d --mattr=+bti %t.aarch64 | \
-# RUN:   FileCheck --check-prefix=CHECK-BTI %s
+# RUN: llvm-objdump -d --mattr=+bti %t.aarch64 | FileCheck --check-prefix=CHECK-BTI %s
+# RUN: yaml2obj -DENDIAN=MSB %s -o %t.aarch64_be
+# RUN: llvm-objdump -d --mattr=+bti %t.aarch64_be | FileCheck --check-prefix=CHECK-BTI %s
 # CHECK-BTI: bl {{.*}} <f1@plt>
 # CHECK-BTI: bl {{.*}} <f2@plt>
 # CHECK-BTI: Disassembly of section .plt:
 # CHECK-BTI: <f1@plt>:
 # CHECK-BTI-NEXT: bti   c
 # CHECK-BTI-NEXT: adrp  x16, {{.*}}
 # CHECK-BTI: <f2@plt>:
 # CHECK-BTI-NEXT: bti   c

 
 # INVALID_ST_NAME:      warning: '[[FILE]]': st_name (0x1234) is past the end of the string table of size 0x7
 # INVALID_ST_NAME-NEXT: warning: '[[FILE]]': PLT entry at 0x210030 references an invalid symbol{{$}}
 # INVALID_ST_NAME:      Disassembly of section .text:
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
-  Data:    ELFDATA2LSB
+  Data:    ELFDATA2[[ENDIAN=LSB]]
   Type:    ET_EXEC
   Machine: EM_AARCH64
 Sections:
   - Name:    .rela.plt
     Type:    SHT_RELA
     Flags:   [ SHF_ALLOC ]
     EntSize: 0x0000000000000018
     Info:    .got.plt
- Name:    .text
     Content: 0C00009411000094C0035FD6
   - Name:    .plt
     Type:    SHT_PROGBITS
     Flags:   [ SHF_ALLOC, SHF_EXECINSTR ]
     Address: 0x0000000000210010
     Content: 5F2403D5F07BBFA910010090110A40F91042009120021FD61F2003D51F2003D55F2403D510010090110E40F9106200919F2103D520021FD65F2403D510010090111240F9108200919F2103D520021FD6
   - Name:    .got.plt
     Type:    SHT_PROGBITS
+## The content is in little-endian, but it does not affect aarch64_be PLT decoding.
     Content: '000000000000000000000000000000000000000000000000100021000000000010002100000000001000210000000000'
 Symbols:
   - Name:    f1
     StName:  [[ST_NAME=<none>]]
     Type:    STT_FUNC
     Binding: STB_GLOBAL
   - Name:    f2
     Type:    STT_FUNC
     Binding: STB_GLOBAL
 ...