[llvm-bugs] [Bug 31372] New: llvm-lib (and `lld-link /lib`) should error out on cl.exe LTCG obj files

via llvm-bugs llvm-bugs at lists.llvm.org
Wed Dec 14 07:32:28 PST 2016


            Bug ID: 31372
           Summary: llvm-lib (and `lld-link /lib`) should error out on
                    cl.exe LTCG obj files
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: COFF
          Assignee: unassignedbugs at nondot.org
          Reporter: nicolasweber at gmx.de
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

In https://crbug.com/672229 we accidentally built some of our object files with
cl.exe /GL (which activates their link-time codegen, so .obj files are some
kind of IR, not a real .obj file).

C:\src\llvm-build-2015-mt>type a.cc
void f();
int main() {

C:\src\llvm-build-2015-mt>type b.cc
void f() {

C:\src\llvm-build-2015-mt>bin\clang-cl.exe /c a.cc

C:\src\llvm-build-2015-mt>cl /c b.cc /GL /nologo

In general, lld-link copes well with this:

C:\src\llvm-build-2015-mt>bin\lld-link.exe a.obj b.obj
error: b.obj: is not a native COFF file. Recompile without /GL

C:\src\llvm-build-2015-mt>lib /out:blib.lib b.obj /nologo /ltcg

C:\src\llvm-build-2015-mt>bin\lld-link.exe a.obj blib.lib
error: unknown file type: blib.lib

However, llvm-lib silently produces an empty lib file, which then leads to
confusing error messages with both lld-link.exe and link.exe:

C:\src\llvm-build-2015-mt>lld-link.exe /lib b.obj /out:blib2.lib

C:\src\llvm-build-2015-mt>bin\lld-link.exe a.obj blib2.lib
a.obj: undefined symbol: ?f@@YAXXZ
error: link failed

C:\src\llvm-build-2015-mt>link.exe a.obj blib2.lib /nologo
blib2.lib : warning LNK4003: invalid library format; library ignored
a.obj : error LNK2019: unresolved external symbol "void __cdecl f(void)"
(?f@@YAXXZ) referenced in function main
a.exe : fatal error LNK1120: 1 unresolved externals

llvm-lib should print some error and fail when fed LTCG'd obj files instead of
silently doing the wrong thing.

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