[lld] r233798 - [ARM] Enhance checks for entry point

[Denis Protivensky]

The second case reflects programmer's mistake and cannot happen because of wrong input, while the first one is possible. I'll change the first to report fatal error instead.

On 04/02/2015 12:59 AM, Rui Ueyama wrote:
On Wed, Apr 1, 2015 at 4:36 AM, Denis Protivensky <dprotivensky at accesssoftek.com<mailto:dprotivensky at accesssoftek.com>> wrote:
Author: denis-protivensky
Date: Wed Apr  1 06:36:58 2015
New Revision: 233798

URL: http://llvm.org/viewvc/llvm-project?rev=233798&view=rev
Log:
[ARM] Enhance checks for entry point

Modified:
    lld/trunk/lib/ReaderWriter/ELF/ARM/ARMExecutableWriter.h

Modified: lld/trunk/lib/ReaderWriter/ELF/ARM/ARMExecutableWriter.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/lib/ReaderWriter/ELF/ARM/ARMExecutableWriter.h?rev=233798&r1=233797&r2=233798&view=diff
==============================================================================
--- lld/trunk/lib/ReaderWriter/ELF/ARM/ARMExecutableWriter.h (original)
+++ lld/trunk/lib/ReaderWriter/ELF/ARM/ARMExecutableWriter.h Wed Apr  1 06:36:58 2015
@@ -101,12 +101,22 @@ std::error_code ARMExecutableWriter<ELFT
   if (std::error_code ec = ExecutableWriter<ELFT>::setELFHeader())
     return ec;

-  // Fixup entry point for Thumb code.
   StringRef entryName = _ctx.entrySymbolName();
   if (const AtomLayout *al = _armLayout.findAtomLayoutByName(entryName)) {
-    const auto *ea = dyn_cast<DefinedAtom>(al->_atom);
-    if (ea && ea->codeModel() == DefinedAtom::codeARMThumb)
-      this->_elfHeader->e_entry(al->_virtualAddr | 0x1);
+    if (const auto *ea = dyn_cast<DefinedAtom>(al->_atom)) {
+      switch (ea->codeModel()) {
+      case DefinedAtom::codeNA:
+        if (al->_virtualAddr & 0x3)
+          llvm_unreachable("Two least bits must be zero for ARM entry point");
+      break;
+      case DefinedAtom::codeARMThumb:
+        // Fixup entry point for Thumb code.
+        this->_elfHeader->e_entry(al->_virtualAddr | 0x1);
+      break;
+      default:
+        llvm_unreachable("Wrong code model of entry point atom");
+      }
+    }
   }

Are these statements really unreachable, assuming there's no bug in the code, or they might be reachable if we give broken object files or something to the linker? I don't know which is the case, but if the latter is the case, you may want to use llvm::report_fatal_error instead of llvm_unreachable because llvm_unreachable may be expanded to __builtin_unreachable (so it may not print out error messages).

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