[llvm] 6957c00 - [RuntimeDyld][ELF][AArch64] Fix resolveAArch64ShortBranch. (#92245)

[via llvm-commits]

Author: Alastair Houghton
Date: 2024-05-29T09:27:30+01:00
New Revision: 6957c00a8ccd36d990ebeb3b672621ba237bd9d8

URL: https://github.com/llvm/llvm-project/commit/6957c00a8ccd36d990ebeb3b672621ba237bd9d8
DIFF: https://github.com/llvm/llvm-project/commit/6957c00a8ccd36d990ebeb3b672621ba237bd9d8.diff

LOG: [RuntimeDyld][ELF][AArch64] Fix resolveAArch64ShortBranch. (#92245)

We don't know the load addresses when this function is called, so it
shouldn't be trying to use them to determine whether or not the branch
is short. Notably, this will fail in the case where the code is being
loaded into a target in such a way that the section offsets differ
between the process generating the code and the target process.

rdar://127673408

Added: 
    llvm/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_xsec_branch.s

Modified: 
    llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp
index eaf8c35142def..0046220611203 100644
--- a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp
+++ b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldELF.cpp
@@ -1129,7 +1129,8 @@ uint32_t RuntimeDyldELF::getMatchingLoRelocation(uint32_t RelType,
 bool RuntimeDyldELF::resolveAArch64ShortBranch(
     unsigned SectionID, relocation_iterator RelI,
     const RelocationValueRef &Value) {
-  uint64_t Address;
+  uint64_t TargetOffset;
+  unsigned TargetSectionID;
   if (Value.SymbolName) {
     auto Loc = GlobalSymbolTable.find(Value.SymbolName);
 
@@ -1138,23 +1139,32 @@ bool RuntimeDyldELF::resolveAArch64ShortBranch(
       return false;
 
     const auto &SymInfo = Loc->second;
-    Address =
-        uint64_t(Sections[SymInfo.getSectionID()].getLoadAddressWithOffset(
-            SymInfo.getOffset()));
+
+    TargetSectionID = SymInfo.getSectionID();
+    TargetOffset = SymInfo.getOffset();
   } else {
-    Address = uint64_t(Sections[Value.SectionID].getLoadAddress());
+    TargetSectionID = Value.SectionID;
+    TargetOffset = 0;
   }
-  uint64_t Offset = RelI->getOffset();
-  uint64_t SourceAddress = Sections[SectionID].getLoadAddressWithOffset(Offset);
+
+  // We don't actually know the load addresses at this point, so if the
+  // branch is cross-section, we don't know exactly how far away it is.
+  if (TargetSectionID != SectionID)
+    return false;
+
+  uint64_t SourceOffset = RelI->getOffset();
 
   // R_AARCH64_CALL26 requires immediate to be in range -2^27 <= imm < 2^27
   // If distance between source and target is out of range then we should
   // create thunk.
-  if (!isInt<28>(Address + Value.Addend - SourceAddress))
+  if (!isInt<28>(TargetOffset + Value.Addend - SourceOffset))
     return false;
 
-  resolveRelocation(Sections[SectionID], Offset, Address, RelI->getType(),
-                    Value.Addend);
+  RelocationEntry RE(SectionID, SourceOffset, RelI->getType(), Value.Addend);
+  if (Value.SymbolName)
+    addRelocationForSymbol(RE, Value.SymbolName);
+  else
+    addRelocationForSection(RE, Value.SectionID);
 
   return true;
 }

diff  --git a/llvm/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_xsec_branch.s b/llvm/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_xsec_branch.s
new file mode 100644
index 0000000000000..fd04f569526b9
--- /dev/null
+++ b/llvm/test/ExecutionEngine/RuntimeDyld/AArch64/ELF_ARM64_xsec_branch.s
@@ -0,0 +1,20 @@
+# RUN: llvm-mc -triple=arm64-none-linux-gnu -filetype=obj -o %t %s
+# RUN: llvm-rtdyld -triple=arm64-none-linux-gnu -verify -check=%s %t
+
+.globl _main
+.weak _label1
+
+.section .text.label1,"ax"
+_label1:
+        nop
+
+.section .text.main,"ax"
+_main:
+        b _label1
+
+# Branch must be to stub in .text.main, *not* back to _label1, because
+# in general sections could be loaded at arbitrary addresses in target memory,
+# and when initially processing locations and generating stubs we don't know
+# the final layout yet, so we can't tell if the branch offset is within range.
+
+# rtdyld-check: *{4}(_main) = 0x14000001