# /home/anton/tmp/robsd/src-llvm-ubsan.diff

commit d3a6aff1880a334ddf75aa7e037dc00f054d9d75
Author: Anton Lindqvist <anton@basename.se>
Date:   Tue Sep 30 20:36:43 2025 +0200

    UBSan and execute-only are mutually exclusive
    
    -fsanitize=function implied by UBSan sanitizes indirect function calls in which
    a destination is only considered valid if preceded by a well known sequence
    (0xc105cafe). This of course requires being able to read the text segment,
    making it incompatible with execute-only.

diff --git gnu/llvm/clang/lib/Driver/ToolChains/OpenBSD.cpp gnu/llvm/clang/lib/Driver/ToolChains/OpenBSD.cpp
index 3770471bae7c..2a076df1905d 100644
--- gnu/llvm/clang/lib/Driver/ToolChains/OpenBSD.cpp
+++ gnu/llvm/clang/lib/Driver/ToolChains/OpenBSD.cpp
@@ -288,6 +288,19 @@ void openbsd::Linker::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(crtend)));
   }
 
+  auto hasNoExecuteOnly = [&Args]() {
+    for (const Arg *A : Args) {
+      if (A->getOption().matches(options::OPT_Wl_COMMA) &&
+          A->containsValue("--no-execute-only"))
+        return true;
+    }
+    return false;
+  };
+  if (ToolChain.getSanitizerArgs(Args).needsUbsanRt() && !hasNoExecuteOnly()) {
+    D.Diag(diag::err_drv_argument_only_allowed_with)
+        << "-fsanitize=undefined" << "-Wl,--no-execute-only";
+  }
+
   ToolChain.addProfileRTLibs(Args, CmdArgs);
 
   const char *Exec = Args.MakeArgString(ToolChain.GetLinkerPath());