[llvm] [AArch64, ELF] Allow implicit $d/$x at section beginning (PR #99718)

[Peter Smith via llvm-commits]

================
@@ -0,0 +1,45 @@
+# REQUIRES: aarch64
+# RUN: llvm-mc -filetype=obj -triple=aarch64 -implicit-mapsyms %s -o %t.o
+# RUN: ld.lld %t.o -z keep-text-section-prefix -o %t
+# RUN: llvm-objdump -d --no-print-imm-hex --show-all-symbols %t | FileCheck %s
+
+# CHECK:      <_start>:
+# CHECK-NEXT:   nop
+# CHECK-EMPTY:
+# CHECK-NEXT: <$d>:
+# CHECK-NEXT:   .word   0x0000002a
+# CHECK-EMPTY:
+# CHECK-NEXT: <$x>:
+# CHECK-NEXT:   nop
+# CHECK-EMPTY:
+# CHECK-NEXT: Disassembly of section .text.hot:
+# CHECK-EMPTY:
+# CHECK-NEXT: <.text.hot>:
+# CHECK-NEXT:   nop
+# CHECK-EMPTY:
+# CHECK-NEXT: <$d>:
+# CHECK-NEXT:   .word   0x0000002a
+# CHECK-EMPTY:
+# CHECK-NEXT: <$d>:
+# CHECK-NEXT: <$x>:
+# CHECK-NEXT:   udf     #42
----------------
smithp35 wrote:

This points at an issue in llvm-objdump. It could be sorting symbols at the same address by name.

Looking at `llvm-readelf --symbols` for 0x201134 I can see $x before $d as we would expect, however llvm-objdump has put the $d before $x.
```
Symbol table '.symtab' contains 8 entries:
   Num:    Value          Size Type    Bind   Vis       Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT   UND
     1: 0000000000210124     0 NOTYPE  LOCAL  DEFAULT     1 $d
     2: 0000000000210128     0 NOTYPE  LOCAL  DEFAULT     1 $x
     3: 0000000000210130     0 NOTYPE  LOCAL  DEFAULT     2 $d
     4: 0000000000210134     0 NOTYPE  LOCAL  DEFAULT     2 $x
     5: 0000000000210134     0 NOTYPE  LOCAL  DEFAULT     2 $d
     6: 0000000000210138     0 NOTYPE  LOCAL  DEFAULT     2 $x
     7: 0000000000210120     0 NOTYPE  GLOBAL DEFAULT     1 _start
```
This is unfortunate as it means every trailing `$x` is going to result in an incorrect disassembly when there's a leading `$d`.



https://github.com/llvm/llvm-project/pull/99718