[PATCH] COFF: Handle references from LTO object to lazy symbols correctly.

[Peter Collingbourne]

Hi ruiu,

The code generator may create references to runtime library symbols such as
__chkstk which were not visible via LTOModule. Handle these cases by loading
the object file from the library, but abort if we end up having loaded any
bitcode objects.

Because loading the object file may have introduced new undefined references,
call reportRemainingUndefines again to detect and report them.

http://reviews.llvm.org/D10332

Files:
  COFF/SymbolTable.cpp
  test/COFF/Inputs/lto-chkstk-chkstk.s
  test/COFF/Inputs/lto-chkstk-foo.s
  test/COFF/lto-chkstk.ll

Index: COFF/SymbolTable.cpp
===================================================================
--- COFF/SymbolTable.cpp
+++ COFF/SymbolTable.cpp
@@ -307,8 +307,27 @@
         return make_error_code(LLDError::BrokenFile);
       }
     }
+
+    // We may see new references to runtime library symbols such as __chkstk
+    // here. These symbols must be wholly defined in non-bitcode files.
+    if (auto *B = dyn_cast<Lazy>(Sym->Body)) {
+      unsigned NumBitcodeFiles = BitcodeFiles.size();
+      auto EC = addMemberFile(B);
+      if (EC)
+        return EC;
+      if (BitcodeFiles.size() != NumBitcodeFiles) {
+        llvm::errs()
+            << "LTO: late loaded symbol created new bitcode reference: " << Name
+            << "\n";
+        return make_error_code(LLDError::BrokenFile);
+      }
+    }
   }
 
+  // New runtime library symbol references may have created undefined references.
+  if (reportRemainingUndefines())
+    return make_error_code(LLDError::BrokenFile);
+
   return std::error_code();
 }
 
Index: test/COFF/Inputs/lto-chkstk-chkstk.s
===================================================================
--- /dev/null
+++ test/COFF/Inputs/lto-chkstk-chkstk.s
@@ -0,0 +1,3 @@
+.globl __chkstk
+__chkstk:
+ret
Index: test/COFF/Inputs/lto-chkstk-foo.s
===================================================================
--- /dev/null
+++ test/COFF/Inputs/lto-chkstk-foo.s
@@ -0,0 +1,3 @@
+.globl foo
+foo:
+ret
Index: test/COFF/lto-chkstk.ll
===================================================================
--- /dev/null
+++ test/COFF/lto-chkstk.ll
@@ -0,0 +1,17 @@
+; RUN: llvm-as -o %t.obj %s
+; RUN: llvm-mc -triple=x86_64-pc-windows-msvc -filetype=obj -o %T/lto-chkstk-foo.obj %S/Inputs/lto-chkstk-foo.s
+; RUN: llvm-mc -triple=x86_64-pc-windows-msvc -filetype=obj -o %T/lto-chkstk-chkstk.obj %S/Inputs/lto-chkstk-chkstk.s
+; RUN: llvm-ar cru %t.lib %T/lto-chkstk-chkstk.obj
+; RUN: lld -flavor link2 /out:%t.exe /entry:main /subsystem:console %t.obj %T/lto-chkstk-foo.obj %t.lib
+
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc"
+
+define void @main() {
+entry:
+  %array4096 = alloca [4096 x i8]
+  call void @foo([4096 x i8]* %array4096)
+  ret void
+}
+
+declare void @foo([4096 x i8]*)

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