Re-apply "[ELF] Allow getErrPlace() to work before Out::bufferStart is set"

This time with a fix for the UBSAN failure.

Differential Revision: https://reviews.llvm.org/D70659

Author: arichardson

lld/ELF/Target.cpp

@@ -28,6 +28,7 @@
 #include "OutputSections.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
+#include "SyntheticSections.h"
 #include "lld/Common/ErrorHandler.h"
 #include "llvm/Object/ELF.h"
 
@@ -91,15 +92,20 @@ TargetInfo *getTarget() {
 }
 
 template <class ELFT> static ErrorPlace getErrPlace(const uint8_t *loc) {
-  if (!Out::bufferStart)
-    return {};
-
+  assert(loc != nullptr);
   for (InputSectionBase *d : inputSections) {
     auto *isec = cast<InputSection>(d);
     if (!isec->getParent())
       continue;
 
-    uint8_t *isecLoc = Out::bufferStart + isec->getParent()->offset + isec->outSecOff;
+    const uint8_t *isecLoc =
+        Out::bufferStart
+            ? (Out::bufferStart + isec->getParent()->offset + isec->outSecOff)
+            : isec->data().data();
+    if (isecLoc == nullptr) {
+      assert(isa<SyntheticSection>(isec) && "No data but not synthetic?");
+      continue;
+    }
     if (isecLoc <= loc && loc < isecLoc + isec->getSize())
       return {isec, isec->template getLocation<ELFT>(loc - isecLoc) + ": "};
   }

lld/test/ELF/mips-jalr-non-functions.s

@@ -15,13 +15,13 @@ test:
 .Ltmp1:
   jr  $t9
   nop
-# WARNING-MESSAGE: warning: found R_MIPS_JALR relocation against non-function symbol tls_obj. This is invalid and most likely a compiler bug.
+# WARNING-MESSAGE: warning: {{.+}}.tmp.o:(.text+0x0): found R_MIPS_JALR relocation against non-function symbol tls_obj. This is invalid and most likely a compiler bug.
 
   .reloc .Ltmp2, R_MIPS_JALR, reg_obj
 .Ltmp2:
   jr  $t9
   nop
-# WARNING-MESSAGE: warning: found R_MIPS_JALR relocation against non-function symbol reg_obj. This is invalid and most likely a compiler bug.
+# WARNING-MESSAGE: warning: {{.+}}.tmp.o:(.text+0x8): found R_MIPS_JALR relocation against non-function symbol reg_obj. This is invalid and most likely a compiler bug.
 
   .reloc .Ltmp3, R_MIPS_JALR, untyped
 .Ltmp3: