[llvm] [llvm-dlltool] Use EXPORTAS name type for renamed imports on ARM64EC. (PR #99346)

[Jacek Caban via llvm-commits]

https://github.com/cjacek created https://github.com/llvm/llvm-project/pull/99346

As discussed in #98229, renamed entries are more tricky on ARM64EC due to additional symbols (we need `__imp_aux_*` in addition to `__imp_*` and both mangled and unmangled symbol thunks). While we could extend weak aliases to add them, it seems cleaner to just always use EXPORTAS name type on ARM64EC targets. Unlike other targets, linkers supporting ARM64EC need to support EXPORTAS, so there is no compatibility problem with that.

Compared to weak aliases, there is a small difference for linked binaries. If both original and aliased names are referenced, this solution will create separate import entries with the same name. I don't think it's a problem in practice. Both MSVC and LLD (from my WIP branch) are fine with it and such binaries run fine on Windows.

>From 7799bc571abea5fd507b47c6c7d03822ffd07d33 Mon Sep 17 00:00:00 2001
From: Jacek Caban <jacek at codeweavers.com>
Date: Wed, 17 Jul 2024 17:25:05 +0200
Subject: [PATCH] [llvm-dlltool] Use EXPORTAS name type for renamed imports on
 ARM64EC.

---
 llvm/lib/Object/COFFImportFile.cpp        |  5 ++++-
 llvm/test/tools/llvm-dlltool/arm64ec.test | 18 ++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Object/COFFImportFile.cpp b/llvm/lib/Object/COFFImportFile.cpp
index 2458a53cb6d54..e67b02405a3a1 100644
--- a/llvm/lib/Object/COFFImportFile.cpp
+++ b/llvm/lib/Object/COFFImportFile.cpp
@@ -729,7 +729,10 @@ Error writeImportLibrary(StringRef ImportName, StringRef Path,
         else if (Machine == IMAGE_FILE_MACHINE_I386 &&
                  applyNameType(IMPORT_NAME_NOPREFIX, Name) == E.ImportName)
           NameType = IMPORT_NAME_NOPREFIX;
-        else if (Name == E.ImportName)
+        else if (isArm64EC(M)) {
+          NameType = IMPORT_NAME_EXPORTAS;
+          ExportName = E.ImportName;
+        } else if (Name == E.ImportName)
           NameType = IMPORT_NAME;
         else {
           Deferred D;
diff --git a/llvm/test/tools/llvm-dlltool/arm64ec.test b/llvm/test/tools/llvm-dlltool/arm64ec.test
index b03b4eaf7b2d0..7b0590d3625b7 100644
--- a/llvm/test/tools/llvm-dlltool/arm64ec.test
+++ b/llvm/test/tools/llvm-dlltool/arm64ec.test
@@ -44,6 +44,19 @@ RUN: llvm-nm --print-armap test3.lib | FileCheck --check-prefix=ARMAP2 %s
 RUN: not llvm-dlltool -m arm64 -d test.def -N test2.def -l test4.lib 2>&1 | FileCheck --check-prefix=ERR %s
 ERR: native .def file is supported only on arm64ec target
 
+RUN: llvm-dlltool -m arm64ec -d test.def -l test3.lib
+RUN: llvm-readobj test3.lib | FileCheck --check-prefix=ALIAS %s
+
+ALIAS:      File: test.dll
+ALIAS-NEXT: Format: COFF-import-file-ARM64EC
+ALIAS-NEXT: Type: code
+ALIAS-NEXT: Name type: export as
+ALIAS-NEXT: Export name: func
+ALIAS-NEXT: Symbol: __imp_func
+ALIAS-NEXT: Symbol: func
+ALIAS-NEXT: Symbol: __imp_aux_func
+ALIAS-NEXT: Symbol: #func
+
 #--- test.def
 LIBRARY test.dll
 EXPORTS
@@ -53,3 +66,8 @@ EXPORTS
 LIBRARY test.dll
 EXPORTS
     otherfunc
+
+#--- test3.def
+LIBRARY test.dll
+EXPORTS
+    func == efunc