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

[Rui Ueyama]

__chkstk is a special symbol. Does the code generator introduce arbitrary
symbols? If not (if it could introduce only a limited set of symbols), we
may want to resolve them unconditionally as if they were specified with
/include.
2015/06/08 午後6:00 "Peter Collingbourne" <peter at pcc.me.uk>:

> 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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