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lld-link: Several tweaks to default entry point selection. 

Three related changes:

1. link.exe uses the presence of main and wmain to decide if it should call
   mainCRTStartup or wmainCRTStartup, even if /nodefaultlib is passed. For
   compatibility, remove FindMain logic.

2. Default to the non-wide entrypoint if main is not found. This has two effects:

2a. In normal links, lld-link now prints

        lld-link: error: undefined symbol: _main
        >>> referenced by f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:78
        >>>               libcmt.lib(exe_main.obj):("int __cdecl invoke_main(void)" (?invoke_main@@YAHXZ))
        >>> referenced by f:\dd\vctools\crt\vcstartup\src\startup\exe_common.inl:283
        >>>               libcmt.lib(exe_main.obj):("int __cdecl __scrt_common_main_seh(void)" (?__scrt_common_main_seh@@YAHXZ))

    instead of

        lld-link: error: entry point must be defined

    This is arguably a better error message, since it now mentions that _main is
    missing. (This matches link.exe's diagnostic in this case.)

2b. With /nodefautlib, we now default to mainCRTStartup if no main() is
    present, again matching link.exe. This makes r337407 obsolete.

This means if you have a cc file containing both mainCRTStartup and
wmainCRTStartup and you pass /nodefaultlib /subsystem:console, lld-link will
now call mainCRTStartup, matching link.exe

3. Print a warning if both main and wmain are present, similar to link.exe's
   LNK4067.

Differential Revision: https://reviews.llvm.org/D52832

llvm-svn: 343698
This commit is contained in:
Nico Weber 2018-10-03 17:01:39 +00:00
parent 2c59475c06
commit d377826277
3 changed files with 39 additions and 17 deletions
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24
lld/COFF/Driver.cpp
View File

@ -430,26 +430,28 @@ StringRef LinkerDriver::findDefaultEntry() {
assert(Config->Subsystem != IMAGE_SUBSYSTEM_UNKNOWN &&
"must handle /subsystem before calling this");
// As a special case, if /nodefaultlib is given, we directly look for an
// entry point. This is because, if no default library is linked, users
// need to define an entry point instead of a "main".
bool FindMain = !Config->NoDefaultLibAll;
if (Config->Subsystem == IMAGE_SUBSYSTEM_WINDOWS_GUI) {
if (findUnderscoreMangle(FindMain ? "WinMain" : "WinMainCRTStartup"))
return mangle("WinMainCRTStartup");
if (findUnderscoreMangle(FindMain ? "wWinMain" : "wWinMainCRTStartup"))
if (findUnderscoreMangle("wWinMain")) {
if (!findUnderscoreMangle("WinMain"))
return mangle("wWinMainCRTStartup");
warn("found both wWinMain and WinMain; using latter");
}
if (findUnderscoreMangle(FindMain ? "main" : "mainCRTStartup"))
return mangle("mainCRTStartup");
if (findUnderscoreMangle(FindMain ? "wmain" : "wmainCRTStartup"))
return mangle("WinMainCRTStartup");
}
if (findUnderscoreMangle("wmain")) {
if (!findUnderscoreMangle("main"))
return mangle("wmainCRTStartup");
return "";
warn("found both wmain and main; using latter");
}
return mangle("mainCRTStartup");
}
WindowsSubsystem LinkerDriver::inferSubsystem() {
if (Config->DLL)
return IMAGE_SUBSYSTEM_WINDOWS_GUI;
// Note that link.exe infers the subsystem from the presence of these
// functions even if /entry: or /nodefaultlib are passed which causes them
// to not be called.
bool HaveMain = findUnderscoreMangle("main");
bool HaveWMain = findUnderscoreMangle("wmain");
bool HaveWinMain = findUnderscoreMangle("WinMain");

8
lld/test/COFF/entry-inference.test
View File

@ -1,18 +1,26 @@
# RUN: sed -e s/ENTRYNAME/main/ %s | yaml2obj > %t.obj
# RUN: not lld-link /out:%t.exe %t.obj > %t.log 2>&1
# RUN: FileCheck -check-prefix=MAIN %s < %t.log
# RUN: not lld-link /nodefaultlib /out:%t.exe %t.obj > %t.log 2>&1
# RUN: FileCheck -check-prefix=MAIN %s < %t.log
# RUN: sed s/ENTRYNAME/wmain/ %s | yaml2obj > %t.obj
# RUN: not lld-link /out:%t.exe %t.obj > %t.log 2>&1
# RUN: FileCheck -check-prefix=WMAIN %s < %t.log
# RUN: not lld-link /nodefaultlib /out:%t.exe %t.obj > %t.log 2>&1
# RUN: FileCheck -check-prefix=WMAIN %s < %t.log
# RUN: sed s/ENTRYNAME/WinMain/ %s | yaml2obj > %t.obj
# RUN: not lld-link /out:%t.exe %t.obj > %t.log 2>&1
# RUN: FileCheck -check-prefix=WINMAIN %s < %t.log
# RUN: not lld-link /nodefaultlib /out:%t.exe %t.obj > %t.log 2>&1
# RUN: FileCheck -check-prefix=WINMAIN %s < %t.log
# RUN: sed s/ENTRYNAME/wWinMain/ %s | yaml2obj > %t.obj
# RUN: not lld-link /out:%t.exe %t.obj > %t.log 2>&1
# RUN: FileCheck -check-prefix=WWINMAIN %s < %t.log
# RUN: not lld-link /nodefaultlib /out:%t.exe %t.obj > %t.log 2>&1
# RUN: FileCheck -check-prefix=WWINMAIN %s < %t.log
# MAIN: error: <root>: undefined symbol: mainCRTStartup
# WMAIN: error: <root>: undefined symbol: wmainCRTStartup

12
lld/test/COFF/entry-inference4.test
View File

@ -14,10 +14,22 @@
# RUN: not lld-link /subsystem:console /out:%t.exe %t.obj > %t.log 2>&1
# RUN: FileCheck -check-prefix=WMAIN %s < %t.log
# RUN: sed 's/ENTRY1/wmain/;s/ENTRY2/main/' %s | yaml2obj > %t.obj
# RUN: not lld-link /out:%t.exe %t.obj > %t.log 2>&1
# RUN: FileCheck -check-prefix=MAINWMAIN %s < %t.log
# RUN: sed 's/ENTRY1/wWinMain/;s/ENTRY2/WinMain/' %s | yaml2obj > %t.obj
# RUN: not lld-link /out:%t.exe %t.obj > %t.log 2>&1
# RUN: FileCheck -check-prefix=WINMAINWWINMAIN %s < %t.log
# MAIN: error: <root>: undefined symbol: mainCRTStartup
# WMAIN: error: <root>: undefined symbol: wmainCRTStartup
# MAINWMAIN: warning: found both wmain and main; using latter
# MAINWMAIN: error: <root>: undefined symbol: mainCRTStartup
# WINMAIN: error: <root>: undefined symbol: WinMainCRTStartup
# WWINMAIN: error: <root>: undefined symbol: wWinMainCRTStartup
# WINMAINWWINMAIN: warning: found both wWinMain and WinMain; using latter
# WINMAINWWINMAIN: error: <root>: undefined symbol: WinMainCRTStartup
--- !COFF
header: