https://github.com/mjklemm created
https://github.com/llvm/llvm-project/pull/73124
The flang driver was silently ignoring the `main()` function in
`Fortran_main.a` for entry into the Fortran program unit if an external
`main()` as supplied (e.g., via cross-language linkage with Fortran and C/C++).
This PR fixes this by making sure that the linker always pulls in the `main()`
definition from `Fortran_main.a` and consequently fails due to multiple
definitions of the same symbol if another object file also has a definition of
`main()`.
>From ba38aec7ac04c63fd5167908fe7f91d6ac7bceed Mon Sep 17 00:00:00 2001
From: Michael Klemm <michael.kl...@amd.com>
Date: Wed, 22 Nov 2023 14:22:20 +0100
Subject: [PATCH] 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);
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