[PATCH] D108897: [lld/mac] Set branchRange a bit more carefully

[Nico Weber via Phabricator via llvm-commits]

thakis created this revision.
thakis added a reviewer: lld-macho.
Herald added a reviewer: gkm.
Herald added a project: lld-macho.
thakis requested review of this revision.

- Don't subtract thunkSize from branchRange. Most places care about the actual maximal branch range. Subtract thunkSize in the one place that wants to leave room for a thunk.
- Set it to 0x800_0000 instead of 0xFF_FFFF
- Subtract 4 for the positive branch direction since it's a two's complement 24bit number sign-extended mutiplied by 4, so its range is -0x800_0000..+0x7FF_FFFC
- Make boundary checks include the boundary values

This doesn't make a huge difference in practice. It's preparation
for a "real" fix for PR51578 -- but it also lets the repro in comment 0
in that bug place one more thunk before hitting the TODO.


https://reviews.llvm.org/D108897

Files:
  lld/MachO/Arch/ARM64.cpp
  lld/MachO/ConcatOutputSection.cpp


Index: lld/MachO/ConcatOutputSection.cpp
===================================================================
--- lld/MachO/ConcatOutputSection.cpp
+++ lld/MachO/ConcatOutputSection.cpp
@@ -225,8 +225,8 @@
     assert(isec->isFinal);
     uint64_t isecVA = isec->getVA();
     // Assign addresses up-to the forward branch-range limit
-    while (finalIdx < endIdx &&
-           isecAddr + inputs[finalIdx]->getSize() < isecVA + branchRange)
+    while (finalIdx < endIdx && isecAddr + inputs[finalIdx]->getSize() <
+                                    isecVA + branchRange - thunkSize)
       finalizeOne(inputs[finalIdx++]);
     if (isec->callSiteCount == 0)
       continue;
@@ -255,7 +255,7 @@
       // Calculate branch reachability boundaries
       uint64_t callVA = isecVA + r.offset;
       uint64_t lowVA = branchRange < callVA ? callVA - branchRange : 0;
-      uint64_t highVA = callVA + branchRange;
+      uint64_t highVA = callVA + branchRange - 4;
       // Calculate our call referent address
       auto *funcSym = r.referent.get<Symbol *>();
       ThunkInfo &thunkInfo = thunkMap[funcSym];
@@ -267,7 +267,7 @@
       }
       uint64_t funcVA = funcSym->resolveBranchVA();
       ++thunkInfo.callSitesUsed;
-      if (lowVA < funcVA && funcVA < highVA) {
+      if (lowVA <= funcVA && funcVA <= highVA) {
         // The referent is reachable with a simple call instruction.
         continue;
       }
@@ -276,7 +276,7 @@
       // If an existing thunk is reachable, use it ...
       if (thunkInfo.sym) {
         uint64_t thunkVA = thunkInfo.isec->getVA();
-        if (lowVA < thunkVA && thunkVA < highVA) {
+        if (lowVA <= thunkVA && thunkVA <= highVA) {
           r.referent = thunkInfo.sym;
           continue;
         }
Index: lld/MachO/Arch/ARM64.cpp
===================================================================
--- lld/MachO/Arch/ARM64.cpp
+++ lld/MachO/Arch/ARM64.cpp
@@ -134,7 +134,7 @@
 
   stubSize = sizeof(stubCode);
   thunkSize = sizeof(thunkCode);
-  branchRange = maxIntN(28) - thunkSize;
+  branchRange = 128 * 1024 * 1024;
   stubHelperHeaderSize = sizeof(stubHelperHeaderCode);
   stubHelperEntrySize = sizeof(stubHelperEntryCode);
 }


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