[ARM] Create relocations for unconditional branches.

Summary:
Relocations are required for unconditional branches to function symbols with
different execution mode. Without this patch, incorrect branches are
generated for tail calls between functions with different execution
mode.


Reviewers: peter.smith, rafael, echristo, kristof.beyls

Reviewed By: peter.smith

Subscribers: aemerson, javed.absar, llvm-commits

Differential Revision: https://reviews.llvm.org/D33898

llvm-svn: 304882

llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp

@@ -748,13 +748,18 @@ 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))
+  }
+  // Create relocations for unconditional branches to function symbols with
+  // different execution mode in ELF binaries.
+  if (Sym && Sym->isELF()) {
+    unsigned Type = dyn_cast<MCSymbolELF>(Sym)->getType();
+    if ((Type == ELF::STT_FUNC || Type == ELF::STT_GNU_IFUNC)) {
+      unsigned FixupKind = Fixup.getKind() ;
+      if (Asm.isThumbFunc(Sym) && (FixupKind == ARM::fixup_arm_uncondbranch))
+        IsResolved = false;
+      if (!Asm.isThumbFunc(Sym) && (FixupKind == ARM::fixup_arm_thumb_br ||
+                                    FixupKind == ARM::fixup_arm_thumb_bl ||
+                                    FixupKind == ARM::fixup_t2_uncondbranch))
         IsResolved = false;
     }
   }

llvm/test/MC/ARM/arm-thumb-tail-call.ll

+; RUN: llc -O0 < %s -mtriple armv7-linux-gnueabi -o - \
+; RUN:   | llvm-mc -triple armv7-linux-gnueabi -filetype=obj -o - \
+; RUN:    | llvm-readobj -r | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "armv7--linux-gnueabihf"
+
+define internal i32 @arm_fn() #1 {
+  %1 = tail call i32 @thumb_fn()
+  ret i32 %1
+}
+
+define internal i32 @thumb_fn() #2 {
+  %1 = tail call i32 @arm_fn()
+  ret i32 %1
+}
+
+attributes #1 = { "target-features"="-thumb-mode" }
+attributes #2 = { "target-features"="+thumb-mode" }
+
+; CHECK: Relocations [
+; CHECK-NEXT: Section (3) .rel.text {
+; CHECK-NEXT: 0x0 R_ARM_JUMP24 thumb_fn 0x0
+; CHECK-NEXT: 0x4 R_ARM_THM_JUMP24 arm_fn 0x0
+; CHECK-NEXT: }