[LLD][ELF][AArch64] Guard --fix-cortex-a53-843419 against --just-syms

[peter.smith]

Summary

If --just-syms is used the mapping symbols from the ELF file will be absolute symbols with no section. The code to process mapping symbols in --fix-cortex-a53-843419 assumes that these symbols have a defining section so a crash will result when --just-syms is used. The simple fix is to not
process the symbol when it doesn't have a section (there is no section to search for errata).

I'm a little surprised that --just-syms imports local symbols, as they are in theory not accessible from other objects.

Fixes PR37971 (https://bugs.llvm.org/show_bug.cgi?id=37971)

[ruiu]

LGTM

[ruiu]

As to importing local symbols, I think we don't do anything special for --just-symbols. When you pass an object file as an argument for --just-symbols, we ignore section contents, but all symbols are handled normally.

lld/trunk/ELF/AArch64ErrataFix.cpp

void AArch64Err843419Patcher::init() {
   for (InputFile *File : ObjectFiles) {
     auto *F = cast<ObjFile<ELF64LE>>(File);
     for (Symbol *B : F->getLocalSymbols()) {
       auto *Def = dyn_cast<Defined>(B);
       if (!Def)
         continue;
       if (!IsCodeMapSymbol(Def) && !IsDataMapSymbol(Def))
         continue;
-      if (auto *Sec = dyn_cast<InputSection>(Def->Section))
+      if (auto *Sec = dyn_cast_or_null<InputSection>(Def->Section))
         if (Sec->Flags & SHF_EXECINSTR)
           SectionMap[Sec].push_back(Def);
     }
   }
   // For each InputSection make sure the mapping symbols are in sorted in
   // ascending order and free from consecutive runs of mapping symbols with
   // the same type. For example we must remove the redundant $d.1 from $x.0
   // $d.0 $d.1 $x.1.

lld/trunk/test/ELF/aarch64-cortex-a53-843419-abs-mapsyms.s

+// REQUIRES: aarch64
+// RUN: llvm-mc -filetype=obj -triple=aarch64-linux-gnu %s -o %t
+// RUN: ld.lld --just-symbols %t -fix-cortex-a53-843419 -o %t.axf
+// RUN: llvm-readobj --symbols %t.axf | FileCheck %s
+
+// Check that we can gracefully handle --just-symbols, which gives a local
+// absolute mapping symbol (with no Section). Previously we assumed that all
+// mapping symbols were defined relative to a section and assert failed.
+
+        .text
+        .global _start
+        .type _start, %function
+_start: ret
+
+// CHECK:     Name: $x.0
+// CHECK-NEXT:     Value: 0x0
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Local (0x0)
+// CHECK-NEXT:     Type: None (0x0)
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: Absolute (0xFFF1)
+// CHECK-NEXT:   }