[ARM] Create relocations for Thumb functions calling ARM fns in ELF.

Summary:
Without using a fixup in this case, BL will be used instead of BLX to
call internal ARM functions from Thumb functions.

Reviewers: rafael, t.p.northover, peter.smith, kristof.beyls

Reviewed By: peter.smith

Subscribers: srhines, echristo, aemerson, rengolin, javed.absar, llvm-commits

Differential Revision: https://reviews.llvm.org/D33436

llvm-svn: 304413

1 files changed, 9 insertions, 0 deletions

diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
index 40bf545e832..b0d1d3fb9ef 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -729,6 +729,15 @@ void ARMAsmBackend::processFixupValue(const MCAssembler &Asm,
     // linker can handle it. GNU AS produces an error in this case.
     if (Sym->isExternal() || Value >= 0x400004)
       IsResolved = false;
+    // When an ARM function is called from a Thumb function, produce a
+    // relocation so the linker will use the correct branch instruction for ELF
+    // binaries.
+    if (Sym->isELF()) {
+      unsigned Type = dyn_cast<MCSymbolELF>(Sym)->getType();
+      if ((Type == ELF::STT_FUNC || Type == ELF::STT_GNU_IFUNC) &&
+          !Asm.isThumbFunc(Sym))
+        IsResolved = false;
+    }
   }
   // 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