[clang] [flang][Driver] Let the linker fail on multiple definitions of main() (PR #73124)

[Michael Klemm via cfe-commits]

https://github.com/mjklemm updated https://github.com/llvm/llvm-project/pull/73124

>From ba38aec7ac04c63fd5167908fe7f91d6ac7bceed Mon Sep 17 00:00:00 2001
From: Michael Klemm <michael.klemm at amd.com>
Date: Wed, 22 Nov 2023 14:22:20 +0100
Subject: [PATCH 1/2] Let the linker fail on multiple definitions of main()

---
 clang/lib/Driver/ToolChains/CommonArgs.cpp | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 5d2cd1959b06925..30c249d05677ce5 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -1018,7 +1018,20 @@ void tools::addFortranRuntimeLibs(const ToolChain &TC, const ArgList &Args,
       break;
     }
   } else {
+    // --whole-archive needs to be part of the link line to make sure
+    // that the main() function from Fortran_main.a is pulled in by
+    // the linker.
+    //
+    // We are using this --whole-archive/--no-whole-archive bracket w/o
+    // any further checks, because -Wl,--whole-archive at the flang-new new
+    // line will not sucessfully complete, unless the user correctly specified
+    // -Wl,--no-whole-archive (e.g., -Wl,--whole-archive -ldummy
+    // -Wl,--no-whole-archive).
+    CmdArgs.push_back("--whole-archive");
     CmdArgs.push_back("-lFortran_main");
+    CmdArgs.push_back("--no-whole-archive");
+
+    // Perform regular linkage of the remaining runtime libraries.
     CmdArgs.push_back("-lFortranRuntime");
     CmdArgs.push_back("-lFortranDecimal");
   }
@@ -1029,7 +1042,7 @@ void tools::addFortranRuntimeLibraryPath(const ToolChain &TC,
                                          ArgStringList &CmdArgs) {
   // Default to the <driver-path>/../lib directory. This works fine on the
   // platforms that we have tested so far. We will probably have to re-fine
-  // this in the future. In particular, on some platforms, we may need to use
+  // this in the future. In particular, on some platforms, we may need to useq
   // lib64 instead of lib.
   SmallString<256> DefaultLibPath =
       llvm::sys::path::parent_path(TC.getDriver().Dir);

>From 7d1180b11ed02cedf1c9fea56bf2ff329274c066 Mon Sep 17 00:00:00 2001
From: Michael Klemm <michael.klemm at amd.com>
Date: Wed, 22 Nov 2023 15:18:51 +0100
Subject: [PATCH 2/2] Improve comments and remove accidental typo

---
 clang/lib/Driver/ToolChains/CommonArgs.cpp | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 30c249d05677ce5..12e3ce184898250 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -1023,10 +1023,10 @@ void tools::addFortranRuntimeLibs(const ToolChain &TC, const ArgList &Args,
     // the linker.
     //
     // We are using this --whole-archive/--no-whole-archive bracket w/o
-    // any further checks, because -Wl,--whole-archive at the flang-new new
-    // line will not sucessfully complete, unless the user correctly specified
-    // -Wl,--no-whole-archive (e.g., -Wl,--whole-archive -ldummy
-    // -Wl,--no-whole-archive).
+    // any further checks, because -Wl,--whole-archive at the flang
+    // driver's link line will not sucessfully complete, unless the user
+    // correctly specified -Wl,--whole-archive/-Wl,--no-whole-archive
+    // (e.g., -Wl,--whole-archive -ldummy -Wl,--no-whole-archive).
     CmdArgs.push_back("--whole-archive");
     CmdArgs.push_back("-lFortran_main");
     CmdArgs.push_back("--no-whole-archive");
@@ -1042,7 +1042,7 @@ void tools::addFortranRuntimeLibraryPath(const ToolChain &TC,
                                          ArgStringList &CmdArgs) {
   // Default to the <driver-path>/../lib directory. This works fine on the
   // platforms that we have tested so far. We will probably have to re-fine
-  // this in the future. In particular, on some platforms, we may need to useq
+  // this in the future. In particular, on some platforms, we may need to use
   // lib64 instead of lib.
   SmallString<256> DefaultLibPath =
       llvm::sys::path::parent_path(TC.getDriver().Dir);