[PATCH] D124653: [ELF] Fix ThunkSection distance computation

[Fangrui Song via Phabricator via llvm-commits]

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Similar to D117734 <https://reviews.llvm.org/D117734>. Take AArch64 as an example when the branch range is +-0x8000000.

getISDThunkSec returns `ts` when `src-0x8000000-r_addend <= tsBase < src-0x8000000`
and the new thunk will be placed in `ts` (`ts->addThunk(t)`). However, the new
thunk (at the end of ts) may be unreachable from src. The bug is extremely rare
but I have observed it in one test with a sufficiently large r_addend (47664):
there are initially 245 Thunk's, then in each iteration 14 Thunk's cannot be reached and
get appended to the unreachable ThunkSection. After 15 iterations lld fails with
`thunk creation not converged`.

---

Still figuring out a test


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D124653

Files:
  lld/ELF/Relocations.cpp


Index: lld/ELF/Relocations.cpp
===================================================================
--- lld/ELF/Relocations.cpp
+++ lld/ELF/Relocations.cpp
@@ -1872,8 +1872,8 @@
                                            uint64_t src) {
   for (std::pair<ThunkSection *, uint32_t> tp : isd->thunkSections) {
     ThunkSection *ts = tp.first;
-    uint64_t tsBase = os->addr + ts->outSecOff + rel.addend;
-    uint64_t tsLimit = tsBase + ts->getSize() + rel.addend;
+    uint64_t tsBase = os->addr + ts->outSecOff;
+    uint64_t tsLimit = tsBase + ts->getSize();
     if (target->inBranchRange(rel.type, src,
                               (src > tsLimit) ? tsBase : tsLimit))
       return ts;


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