[LLD] [COFF] Fix crashes when writing a PDB after adding thunks.

[mstorsjo]

Summary

When writing a PDB, the OutputSection of all chunks need to be set. The thunks are added directly to OutputSection after the normal machinery that sets it for all other chunks.

This fixes part of PR40467.

[ruiu]

LGTM

lld/trunk/COFF/Writer.cpp

 // instead of creating a new thunk. All range checks are done with the
 // specified margin, to make sure that relocations that originally are in
 // range, but only barely, also get thunks - in case other added thunks makes
 // the target go out of range.
 //
 // After adding thunks, we verify that all relocations are in range (with
 // no extra margin requirements). If this failed, we restart (throwing away
 // the previously created thunks) and retry with a wider margin.
-static bool createThunks(std::vector<Chunk *> &Chunks, int Margin) {
+static bool createThunks(OutputSection *OS, int Margin) {
   bool AddressesChanged = false;
   DenseMap<uint64_t, Defined *> LastThunks;
   size_t ThunksSize = 0;
   // Recheck Chunks.size() each iteration, since we can insert more
   // elements into it.
-  for (size_t I = 0; I != Chunks.size(); ++I) {
-    SectionChunk *SC = dyn_cast_or_null<SectionChunk>(Chunks[I]);
+  for (size_t I = 0; I != OS->Chunks.size(); ++I) {
+    SectionChunk *SC = dyn_cast_or_null<SectionChunk>(OS->Chunks[I]);
     if (!SC)
       continue;
     size_t ThunkInsertionSpot = I + 1;
 
     // Try to get a good enough estimate of where new thunks will be placed.
     // Offset this by the size of the new thunks added so far, to make the
     // estimate slightly better.
     size_t ThunkInsertionRVA = SC->getRVA() + SC->getSize() + ThunksSize;
for (size_t J = 0, E = SC->Relocs.size(); J < E; ++J) {
       // thunk.
       Defined *Thunk;
       bool WasNew;
       std::tie(Thunk, WasNew) = getThunk(LastThunks, Sym, P, Rel.Type, Margin);
       if (WasNew) {
         Chunk *ThunkChunk = Thunk->getChunk();
         ThunkChunk->setRVA(
             ThunkInsertionRVA); // Estimate of where it will be located.
-        Chunks.insert(Chunks.begin() + ThunkInsertionSpot, ThunkChunk);
+        ThunkChunk->setOutputSection(OS);
+        OS->Chunks.insert(OS->Chunks.begin() + ThunkInsertionSpot, ThunkChunk);
         ThunkInsertionSpot++;
         ThunksSize += ThunkChunk->getSize();
         ThunkInsertionRVA += ThunkChunk->getSize();
         AddressesChanged = true;
       }
       RelocTarget = Thunk;
     }
   }
if (Pass > 0) {
       }
       Margin *= 2;
     }
 
     // Try adding thunks everywhere where it is needed, with a margin
     // to avoid things going out of range due to the added thunks.
     bool AddressesChanged = false;
     for (OutputSection *Sec : OutputSections)
-      AddressesChanged |= createThunks(Sec->Chunks, Margin);
+      AddressesChanged |= createThunks(Sec, Margin);
     // If the verification above thought we needed thunks, we should have
     // added some.
     assert(AddressesChanged);
 
     // Recalculate the layout for the whole image (and verify the ranges at
     // the start of the next round).
     assignAddresses();
 

lld/trunk/test/COFF/arm-thumb-thunks-pdb.s

+// REQUIRES: arm
+// RUN: llvm-mc -filetype=obj -triple=thumbv7-windows %s -o %t.obj
+// RUN: lld-link -entry:main -subsystem:console %t.obj -out:%t.exe -debug -pdb:%t.pdb -verbose 2>&1 | FileCheck %s --check-prefix=VERBOSE
+
+// VERBOSE: Added 1 thunks with margin {{.*}} in {{.*}} passes
+
+    .syntax unified
+    .globl main
+    .globl func1
+    .text
+main:
+    bne func1
+    bx lr
+    .section .text$a, "xr"
+    .space 0x100000
+    .section .text$b, "xr"
+func1:
+    bx lr