Add missing nullptr check before getSection() to AArch64MachObjectWriter::recordRelocation

[paquette]

Summary

There was a missing nullptr check in AArch64MachObjectWriter::recordRelocation which would cause a segfault in code like the attached test.

This patch adds the missing check and ensures that we get an error message instead of a crash.

[t.p.northover]

LGTM.

[paquette]

Committed in r329716.

[alekseyshl]

arm64-no-section.ll fails at our bot:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap/builds/5009/steps/check-llvm%20asan/logs/stdio

[davezarzycki]

FYI – This test fails on my machine (Release+Assert):

FAIL: LLVM :: MC/AArch64/arm64-no-section.ll (28812 of 38754)
******************** TEST 'LLVM :: MC/AArch64/arm64-no-section.ll' FAILED ********************
Script:
--
/tmp/_update_lc_t/bin/llc -mtriple=aarch64-darwin-- -filetype=obj /home/dave/s/lc/test/MC/AArch64/arm64-no-section.ll -o -
--
Exit Code: 134

Command Output (stderr):
--
This constant variable should have been expanded during evaluation
UNREACHABLE executed at /home/dave/s/lc/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp:358!
#0 0x0000000002033b7f llvm::sys::PrintStackTrace(llvm::raw_ostream&) (/tmp/_update_lc_t/bin/llc+0x2033b7f)
#1 0x0000000002033e86 SignalHandler(int) (/tmp/_update_lc_t/bin/llc+0x2033e86)
#2 0x00007ff9049d0fb0 __restore_rt (/lib64/libpthread.so.0+0x11fb0)
#3 0x00007ff903346f4b __GI_raise (/lib64/libc.so.6+0x36f4b)
#4 0x00007ff903331591 __GI_abort (/lib64/libc.so.6+0x21591)
#5 0x0000000001fde378 (/tmp/_update_lc_t/bin/llc+0x1fde378)
#6 0x00000000013869aa (anonymous namespace)::AArch64MachObjectWriter::recordRelocation(llvm::MachObjectWriter*, llvm::MCAssembler&, llvm::MCAsmLayout const&, llvm::MCFragment const*, llvm::MCFixup const&, llvm::MCValue, unsigned long&) (/tmp/_update_lc_t/bin/llc+0x13869aa)
#7 0x0000000001b23223 llvm::MachObjectWriter::recordRelocation(llvm::MCAssembler&, llvm::MCAsmLayout const&, llvm::MCFragment const*, llvm::MCFixup const&, llvm::MCValue, unsigned long&) (/tmp/_update_lc_t/bin/llc+0x1b23223)
#8 0x0000000001aed865 llvm::MCAssembler::layout(llvm::MCAsmLayout&) (/tmp/_update_lc_t/bin/llc+0x1aed865)
#9 0x0000000001aedb4b llvm::MCAssembler::Finish() (/tmp/_update_lc_t/bin/llc+0x1aedb4b)
#10 0x0000000001b0cd2f (anonymous namespace)::MCMachOStreamer::FinishImpl() (/tmp/_update_lc_t/bin/llc+0x1b0cd2f)
#11 0x00000000015c8394 llvm::AsmPrinter::doFinalization(llvm::Module&) (/tmp/_update_lc_t/bin/llc+0x15c8394)
#12 0x0000000001a7086f llvm::FPPassManager::doFinalization(llvm::Module&) (/tmp/_update_lc_t/bin/llc+0x1a7086f)
#13 0x0000000001a70de0 llvm::legacy::PassManagerImpl::run(llvm::Module&) (/tmp/_update_lc_t/bin/llc+0x1a70de0)
#14 0x0000000000ff99d7 compileModule(char**, llvm::LLVMContext&) (/tmp/_update_lc_t/bin/llc+0xff99d7)
#15 0x0000000000ff70bb main (/tmp/_update_lc_t/bin/llc+0xff70bb)
#16 0x00007ff9033331bb __libc_start_main (/lib64/libc.so.6+0x231bb)
#17 0x0000000000ff602a _start (/tmp/_update_lc_t/bin/llc+0xff602a)
Stack dump:
0.      Program arguments: /tmp/_update_lc_t/bin/llc -mtriple=aarch64-darwin-- -filetype=obj /home/dave/s/lc/test/MC/AArch64/arm64-no-section.ll -o - 
/tmp/_update_lc_t/test/MC/AArch64/Output/arm64-no-section.ll.script: line 1: 274231 Aborted                 /tmp/_update_lc_t/bin/llc -mtriple=aarch64-darwin-- -filetype=obj /home/dave/s/lc/test/MC/AArch64/arm64-no-section.ll -o -

--

[paquette]

Currently looking into it.

I think I can have a fix up in a few minutes. If not I’ll revert.

• Jessica

[paquette]

I think (hope) r329723 should fix it…

• Jessica

lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp

if (Target.isAbsolute()) { // constant
     Type = MachO::ARM64_RELOC_SUBTRACTOR;
   } else { // A + constant
     const MCSymbol *Symbol = &Target.getSymA()->getSymbol();
     const MCSectionMachO &Section =
         static_cast<const MCSectionMachO &>(*Fragment->getParent());
 
     bool CanUseLocalRelocation =
         canUseLocalRelocation(Section, *Symbol, Log2Size);
-    if (Symbol->isTemporary() && (Value || !CanUseLocalRelocation)) {
+    if (Symbol->isTemporary() && Symbol->isInSection() &&
+        (Value || !CanUseLocalRelocation)) {
       const MCSection &Sec = Symbol->getSection();
       if (!Asm.getContext().getAsmInfo()->isSectionAtomizableBySymbols(Sec))
         Symbol->setUsedInReloc();
     }
 
     const MCSymbol *Base = Asm.getAtom(*Symbol);
     // If the symbol is a variable it can either be in a section and
     // we have a base or it is absolute and should have been expanded.

test/MC/AArch64/arm64-no-section.ll

+; RUN: llc -mtriple=aarch64-darwin-- -filetype=obj %s -o -
+; CHECK: <inline asm>:1:2: error: unsupported relocation of local symbol
+; CHECK-SAME: 'L_foo_end'. Must have non-local symbol earlier in section.
+
+; Make sure that we emit an error when we try to reference something that
+; doesn't belong to a section.
+define void @foo() local_unnamed_addr {
+  tail call void asm sideeffect "b L_foo_end\0A", ""()
+  ret void
+}