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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200842 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp b/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
index 7db700472cb00d9d36e40a43cec4fcc433ef8d3c..698487980c37a076ad15936ffe5232b029257380 100644 (file)
--- a/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ b/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -565,11 +565,18 @@ void ARMAsmBackend::processFixupValue(const MCAssembler &Asm,
         Value |= 1;
     }
   }
         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 ||
   // 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))
             (unsigned)Fixup.getKind() == ARM::fixup_arm_blx ||
             (unsigned)Fixup.getKind() == ARM::fixup_arm_uncondbl ||
             (unsigned)Fixup.getKind() == ARM::fixup_arm_condbl))

diff --git a/test/MC/ARM/thumb-far-jump.s b/test/MC/ARM/thumb-far-jump.s
new file mode 100644 (file)
index 0000000..2fd2c56
--- /dev/null
+++ b/test/MC/ARM/thumb-far-jump.s
@@ -0,0 +1,26 @@
+@ RUN: llvm-mc < %s -triple thumbv5-linux-gnueabi -filetype=obj -o - \
+@ RUN:   | llvm-readobj -r | FileCheck %s
+       .syntax unified
+
+       .text
+       .align  2
+       .globl  main
+       .type   main,%function
+       .thumb_func
+main:
+       bl      end
+       .space 8192
+end:
+       bl      main2
+       bx      lr
+
+       .text
+       .align  2
+       .globl  main2
+       .type   main2,%function
+       .thumb_func
+main2:
+       bx      lr
+
+@ CHECK-NOT: 0x0 R_ARM_THM_CALL end 0x0
+@ CHECK: 0x2004 R_ARM_THM_CALL main2 0x0