ARM: Resolve thumb_bl fixup in same MCFragment.

In Thumb1 mode, bl instruction might be selected for branches between
basic blocks in the function if the offset is greater than 2KB.
However, this might cause SEGV because the destination symbol
is not marked as thumb function and the execution mode will be reset
to ARM mode.

Since we are sure that these symbols are in the same data fragment, we
can simply resolve these local symbols, and don't emit any relocation
information for this bl instruction.

llvm-svn: 200842

1 files changed, 8 insertions, 1 deletions

diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
index 7db700472cb..698487980c3 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -565,11 +565,18 @@ void ARMAsmBackend::processFixupValue(const MCAssembler &Asm,
         Value |= 1;
     }
   }
+  // For Thumb1 BL instruction, it is possible to be a long jump between
+  // the basic blocks of the same function.  Thus, we would like to resolve
+  // the offset when the destination has the same MCFragment.
+  if (A && (unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_bl) {
+    const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
+    MCSymbolData &SymData = Asm.getSymbolData(Sym);
+    IsResolved = (SymData.getFragment() == DF);
+  }
   // We must always generate a relocation for BL/BLX instructions if we have
   // a symbol to reference, as the linker relies on knowing the destination
   // symbol's thumb-ness to get interworking right.
   if (A && ((unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_blx ||
-            (unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_bl ||
             (unsigned)Fixup.getKind() == ARM::fixup_arm_blx ||
             (unsigned)Fixup.getKind() == ARM::fixup_arm_uncondbl ||
             (unsigned)Fixup.getKind() == ARM::fixup_arm_condbl))