[llvm-bugs] [Bug 42536] New: lld-link reporting undefined symbol with lto

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=42536

            Bug ID: 42536
           Summary: lld-link reporting undefined symbol with lto
           Product: lld
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: COFF
          Assignee: unassignedbugs at nondot.org
          Reporter: russell_gallop at sn.scee.net
                CC: llvm-bugs at lists.llvm.org

Created attachment 22205
  --> https://bugs.llvm.org/attachment.cgi?id=22205&action=edit
Reproducible

lld-link 8.0.0 crashes when reporting an undefined symbol (still present at
r364942).

(note that the test case below wouldn't link successfully with the bug fixed
due to the undefined symbols).

--- library.cpp
struct S {
  virtual void foo() {}
};
void a() { S b; }

--- main.cpp
struct __declspec(dllimport) S {
  virtual void foo();
};
struct a {
  a();
};
struct {
  a b;
  S c;
} d;

> clang-cl /c /nologo /O2 /MT /TP -m64 -flto library.cpp
> llvm-lib /OUT:library.lib /NOLOGO library.obj
> clang-cl /c /nologo /O2 /MT /TP -m64 -flto main.cpp
>lld-link /OUT:test.exe "library.lib" "main.obj" /MACHINE:X64 /INCREMENTAL:NO /SUBSYSTEM:CONSOLE /ERRORREPORT:PROMPT /NOLOGO /NODEFAULTLIB
lld-link: error: <root>: undefined symbol: mainCRTStartup
Stack dump:
0.      Program arguments: lld-link /OUT:test.exe library.lib main.obj
/MACHINE:X64 /INCREMENTAL:NO /SUBSYSTEM:CONSOLE /ERRORREPORT:PROMPT /NOLOGO
/NODEFAULTLIB
 #0 0x00007ff6b77886d3 lld::coff::getSymbol
F:\git\llvm-project\lld\COFF\SymbolTable.cpp:72:0
 #1 0x00007ff6b7787c0c lld::coff::getSymbolLocations(class lld::coff::ObjFile
*,unsigned int) F:\git\llvm-project\lld\COFF\SymbolTable.cpp:102:0
 #2 0x00007ff6b778bcaf lld::coff::reportUndefinedSymbol
F:\git\llvm-project\lld\COFF\SymbolTable.cpp:147:0
 #3 0x00007ff6b778b498 lld::coff::SymbolTable::reportRemainingUndefines(void)
F:\git\llvm-project\lld\COFF\SymbolTable.cpp:331:0
 #4 0x00007ff6b76f0437 lld::coff::LinkerDriver::link(class llvm::ArrayRef<char
const *>) F:\git\llvm-project\lld\COFF\Driver.cpp:1761:0
 #5 0x00007ff6b76e89e1 lld::coff::link(class llvm::ArrayRef<char const
*>,bool,class llvm::raw_ostream &) F:\git\llvm-project\lld\COFF\Driver.cpp:78:0
 #6 0x00007ff6b76b1227 main F:\git\llvm-project\lld\tools\lld\lld.cpp:155:0
 #7 0x00007ff6b95fbc94 __scrt_common_main_seh
d:\agent\_work\1\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl:288:0
 #8 0x00007ffe2d414034 (C:\WINDOWS\System32\KERNEL32.DLL+0x14034)
 #9 0x00007ffe2e553691 (C:\WINDOWS\SYSTEM32\ntdll.dll+0x73691)

Without -flto this reports:
lld-link: error: <root>: undefined symbol: mainCRTStartup
lld-link: error: undefined symbol: public: __cdecl a::a(void)
>>> referenced by main.obj:(_GLOBAL__sub_I_main.cpp)

lld-link: error: undefined symbol: const type_info::`vftable'
>>> referenced by main.obj:(struct S `RTTI Type Descriptor')
>>> referenced by library.lib(library.obj)

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