[LLD] [COFF] Make -export-all-symbols work as intended for EXEs

[mstorsjo]

Summary

If some symbols are marked with dllexport, we still want to export
all symbols if -export-all-symbols is specified. Previously, this
only worked as it should for DLL output, not for EXE.

This should fix downstream bug
https://github.com/msys2/MINGW-packages/issues/9163.

[jeremyd2019]

This allowed postgres to link its modules successfully. LGTM, for what that's worth.

[mstorsjo]

In D106245#2886333, @jeremyd2019 wrote:

This allowed postgres to link its modules successfully. LGTM, for what that's worth.

Marking the patch as accepted with this comment as approval - the patch itself is fairly trivial too. I'll go ahead and land it in today/tomorrow/soonish.

[mati865]

LGTM sorry for the delay.

lld/COFF/Driver.cpp

 
 // In MinGW, if no symbols are chosen to be exported, then all symbols are
 // automatically exported by default. This behavior can be forced by the
 // -export-all-symbols option, so that it happens even when exports are
 // explicitly specified. The automatic behavior can be disabled using the
 // -exclude-all-symbols option, so that lld-link behaves like link.exe rather
 // than MinGW in the case that nothing is explicitly exported.
 void LinkerDriver::maybeExportMinGWSymbols(const opt::InputArgList &args) {
+  if (!args.hasArg(OPT_export_all_symbols)) {
     if (!config->dll)
       return;
 
-  if (!args.hasArg(OPT_export_all_symbols)) {
     if (!config->exports.empty())
       return;
     if (args.hasArg(OPT_exclude_all_symbols))
       return;
   }
 
   AutoExporter exporter;
 

lld/test/COFF/export-all.s

 # dllexport directive for some of the symbols.
 
 # RUN: yaml2obj %p/Inputs/export.yaml -o %t.obj
 #
 # RUN: lld-link -safeseh:no -out:%t.dll -dll %t.obj -lldmingw -export-all-symbols -output-def:%t.def
 # RUN: llvm-readobj --coff-exports %t.dll | FileCheck -check-prefix=CHECK2 %s
 # RUN: cat %t.def | FileCheck -check-prefix=CHECK2-DEF %s
 
+# RUN: lld-link -safeseh:no -out:%t.exe %t.obj -lldmingw -export-all-symbols -output-def:%t.def -entry:_DllMainCRTStartup
+# RUN: llvm-readobj --coff-exports %t.exe | FileCheck -check-prefix=CHECK2 %s
+# RUN: cat %t.def | FileCheck -check-prefix=CHECK2-DEF %s
+
 # Note, this will actually export _DllMainCRTStartup as well, since
 # it uses the standard spelling in this object file, not the MinGW one.
 
 # CHECK2: Name: exportfn1
 # CHECK2: Name: exportfn2
 # CHECK2: Name: exportfn3
 
 # CHECK2-DEF: EXPORTS