[llvm-branch-commits] [clang] release/21.x: [Driver][MinGW] Always put libc argument last, even if non-standard (#149434) (PR #151933)

[Tobias Hieta via llvm-branch-commits]

https://github.com/tru updated https://github.com/llvm/llvm-project/pull/151933

>From 1d46440e9f8232950de632102c56e85397b92fcb Mon Sep 17 00:00:00 2001
From: Keno Fischer <keno at juliahub.com>
Date: Wed, 30 Jul 2025 01:09:27 -0400
Subject: [PATCH] [Driver][MinGW] Always put libc argument last, even if
 non-standard (#149434)

I was attempting to build openblas with clang in msys2's `ucrt64`
environment (I'm aware of the `clang64` environment, but I wanted
libstdc++). The openblas link failed with the following:

```
clang -march=native -mtune=native -m64  -O2 -fno-asynchronous-unwind-tables -O2 -DSMALL_MATRIX_OPT -DMS_ABI -DMAX_STACK_ALLOC=2048 -Wall -m64 -DF_INTERFACE_GFORT -DDYNAMIC_ARCH -DSMP_SERVER -DNO_WARMUP -DMAX_CPU_NUMBER=512 -DMAX_PARALLEL_NUMBER=1 -DBUILD_SINGLE=1 -DBUILD_DOUBLE=1 -DBUILD_COMPLEX=1 -DBUILD_COMPLEX16=1 -DVERSION=\"0.3.29\" -UASMNAME -UASMFNAME -UNAME -UCNAME -UCHAR_NAME -UCHAR_CNAME -DASMNAME= -DASMFNAME=_ -DNAME=_ -DCNAME= -DCHAR_NAME=\"_\" -DCHAR_CNAME=\"\" -DNO_AFFINITY -I..  libopenblas64_.def dllinit.obj \
-shared -o ../libopenblas64_.dll -Wl,--out-implib,../libopenblas64_.dll.a \
-Wl,--whole-archive ../libopenblas64_p-r0.3.29.a -Wl,--no-whole-archive -LC:/msys64/ucrt64/bin/../lib/gcc/x86_64-w64-mingw32/15.1.0 -LC:/msys64/ucrt64/bin/../lib/gcc -LC:/msys64/ucrt64/bin/../lib/gcc/x86_64-w64-mingw32/15.1.0/../../../../x86_64-w64-mingw32/lib/../lib -LC:/msys64/ucrt64/bin/../lib/gcc/x86_64-w64-mingw32/15.1.0/../../../../lib -LC:/msys64/ucrt64/bin/../lib/gcc/x86_64-w64-mingw32/15.1.0/../../../../x86_64-w64-mingw32/lib -LC:/msys64/ucrt64/bin/../lib/gcc/x86_64-w64-mingw32/15.1.0/../../..  -lgfortran -lmingwex -lmsvcrt -lquadmath -lm -lpthread -lmingwex -lmsvcrt  -defaultlib:advapi32 -lgfortran -defaultlib:advapi32 -lgfortran

C:/msys64/ucrt64/bin/ld: C:/msys64/ucrt64/bin/../lib/gcc/x86_64-w64-mingw32/15.1.0/../../../../lib/libmingw32.a(lib64_libmingw32_a-pseudo-reloc.o): in function `__report_error':
D:/W/B/src/mingw-w64/mingw-w64-crt/crt/pseudo-reloc.c:157:(.text+0x59): undefined reference to `abort'
C:/msys64/ucrt64/bin/ld: C:/msys64/ucrt64/bin/../lib/gcc/x86_64-w64-mingw32/15.1.0/../../../../lib/libmingw32.a(lib64_libmingw32_a-tlsthrd.o): in function `___w64_mingwthr_add_key_dtor':
D:/W/B/src/mingw-w64/mingw-w64-crt/crt/tlsthrd.c:48:(.text+0xa5): undefined reference to `calloc'
C:/msys64/ucrt64/bin/ld: C:/msys64/ucrt64/bin/../lib/gcc/x86_64-w64-mingw32/15.1.0/../../../../lib/libmingw32.a(lib64_libmingw32_a-pesect.o): in function `_FindPESectionByName':
D:/W/B/src/mingw-w64/mingw-w64-crt/crt/pesect.c:79:(.text+0xfd): undefined reference to `strncmp'
```

These symbols come from the `-lmingw32` dep that the driver added and
are ordinarily found in `-lmsvcrt`, which got skipped here, because
openblas passed `-lmsvcrt` explicitly earlier in the link line. Since we
always add these libraries at the end here, I think that clang is "at
fault" (as opposed to a user or packaging mistake) and should have added
some crt here.

To preserve the intent of letting the user override which crt is chosen,
duplicate the (first) user chosen crt `-l` into this position, although
we should perhaps consider an explicit `-mcrtdll` like gcc has as well.

(cherry picked from commit 7f470586e10543aa12efc7e04d4d4ac814eaca35)
---
 clang/lib/Driver/ToolChains/MinGW.cpp | 11 +++++++++--
 clang/test/Driver/mingw-msvcrt.c      |  8 ++++----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/clang/lib/Driver/ToolChains/MinGW.cpp b/clang/lib/Driver/ToolChains/MinGW.cpp
index b2e36ae6f97c3..4894e6a52e93d 100644
--- a/clang/lib/Driver/ToolChains/MinGW.cpp
+++ b/clang/lib/Driver/ToolChains/MinGW.cpp
@@ -85,11 +85,18 @@ void tools::MinGW::Linker::AddLibGCC(const ArgList &Args,
 
   CmdArgs.push_back("-lmoldname");
   CmdArgs.push_back("-lmingwex");
-  for (auto Lib : Args.getAllArgValues(options::OPT_l))
+  for (auto Lib : Args.getAllArgValues(options::OPT_l)) {
     if (StringRef(Lib).starts_with("msvcr") ||
         StringRef(Lib).starts_with("ucrt") ||
-        StringRef(Lib).starts_with("crtdll"))
+        StringRef(Lib).starts_with("crtdll")) {
+      std::string CRTLib = (llvm::Twine("-l") + Lib).str();
+      // Respect the user's chosen crt variant, but still provide it
+      // again as the last linker argument, because some of the libraries
+      // we added above may depend on it.
+      CmdArgs.push_back(Args.MakeArgStringRef(CRTLib));
       return;
+    }
+  }
   CmdArgs.push_back("-lmsvcrt");
 }
 
diff --git a/clang/test/Driver/mingw-msvcrt.c b/clang/test/Driver/mingw-msvcrt.c
index 340ce1f57b0f8..e1648630476a0 100644
--- a/clang/test/Driver/mingw-msvcrt.c
+++ b/clang/test/Driver/mingw-msvcrt.c
@@ -7,10 +7,10 @@
 // CHECK_DEFAULT: "-lmingwex" "-lmsvcrt" "-ladvapi32"
 // CHECK_DEFAULT-SAME: "-lmsvcrt" "-lkernel32" "{{.*}}crtend.o"
 // CHECK_MSVCR120: "-lmsvcr120"
-// CHECK_MSVCR120-SAME: "-lmingwex" "-ladvapi32"
+// CHECK_MSVCR120-SAME: "-lmingwex" "-lmsvcr120" "-ladvapi32"
 // CHECK_UCRTBASE: "-lucrtbase"
-// CHECK_UCRTBASE-SAME: "-lmingwex" "-ladvapi32"
+// CHECK_UCRTBASE-SAME: "-lmingwex" "-lucrtbase" "-ladvapi32"
 // CHECK_UCRT: "-lucrt"
-// CHECK_UCRT-SAME: "-lmingwex" "-ladvapi32"
+// CHECK_UCRT-SAME: "-lmingwex" "-lucrt" "-ladvapi32"
 // CHECK_CRTDLL: "-lcrtdll"
-// CHECK_CRTDLL-SAME: "-lmingwex" "-ladvapi32"
+// CHECK_CRTDLL-SAME: "-lmingwex" "-lcrtdll" "-ladvapi32"