From 32dcc62c24264edb7072a9d627c07b097a5c5acc Mon Sep 17 00:00:00 2001
From: Demetrius Kanios <demetrius@kanios.net>
Date: Wed, 24 Jun 2026 13:54:25 -0700
Subject: [PATCH] Add LDC-specific DRuntime changes.

---
 runtime/CMakeLists.txt                      |  5 ++-
 runtime/druntime/src/core/thread/osthread.d | 26 +++++++++++++++
 runtime/druntime/src/ldc/eh_wasm.d          | 35 +++++++++++++++++++++
 runtime/druntime/src/ldc/intrinsics.di      |  5 +++
 runtime/druntime/src/rt/sections_ldc.d      |  1 +
 5 files changed, 71 insertions(+), 1 deletion(-)
 create mode 100644 runtime/druntime/src/ldc/eh_wasm.d

diff --git a/runtime/CMakeLists.txt b/runtime/CMakeLists.txt
index a203e1c56b0..ba5fe6b759f 100644
--- a/runtime/CMakeLists.txt
+++ b/runtime/CMakeLists.txt
@@ -181,11 +181,12 @@ file(GLOB_RECURSE DRUNTIME_D_OPENBSD ${RUNTIME_DIR}/src/core/sys/openbsd/*.d)
 file(GLOB_RECURSE DRUNTIME_D_POSIX   ${RUNTIME_DIR}/src/core/sys/posix/*.d)
 file(GLOB_RECURSE DRUNTIME_D_SOLARIS ${RUNTIME_DIR}/src/core/sys/solaris/*.d)
 file(GLOB_RECURSE DRUNTIME_D_WINDOWS ${RUNTIME_DIR}/src/core/sys/windows/*.d)
+file(GLOB_RECURSE DRUNTIME_D_WASI ${RUNTIME_DIR}/src/core/sys/wasi/*.d)
 list(REMOVE_ITEM DRUNTIME_D
     ${DRUNTIME_D_BIONIC}  ${DRUNTIME_D_DARWIN}  ${DRUNTIME_D_DRAGONFLYBSD}
     ${DRUNTIME_D_FREEBSD} ${DRUNTIME_D_LINUX}   ${DRUNTIME_D_NETBSD}
     ${DRUNTIME_D_OPENBSD} ${DRUNTIME_D_POSIX}   ${DRUNTIME_D_SOLARIS}
-    ${DRUNTIME_D_WINDOWS}
+    ${DRUNTIME_D_WINDOWS} ${DRUNTIME_D_WASI}
 )
 if("${TARGET_SYSTEM}" MATCHES "Windows")
     list(APPEND DRUNTIME_D ${DRUNTIME_D_WINDOWS})
@@ -206,6 +207,8 @@ elseif("${TARGET_SYSTEM}" MATCHES "UNIX")
         list(APPEND DRUNTIME_D ${DRUNTIME_D_OPENBSD})
     elseif("${TARGET_SYSTEM}" MATCHES "SunOS")
         list(APPEND DRUNTIME_D ${DRUNTIME_D_SOLARIS})
+    elseif("${TARGET_SYSTEM}" MATCHES "WASI")
+        list(APPEND DRUNTIME_D ${DRUNTIME_D_WASI})
     endif()
 endif()
 
diff --git a/runtime/druntime/src/core/thread/osthread.d b/runtime/druntime/src/core/thread/osthread.d
index 73e5adb4d9b..493ff22ccb2 100644
--- a/runtime/druntime/src/core/thread/osthread.d
+++ b/runtime/druntime/src/core/thread/osthread.d
@@ -1831,6 +1831,24 @@ version (LDC)
                 static assert(0);
         }
     }
+    else version (WebAssembly)
+    {
+        /* Must NOT be naked, but is safe to inline.
+         *
+         * The function prologue is what loads the `__stack_pointer` global
+         * into a fake "physical" register (which becomes a Wasm local).
+         * Manipulation of the stack is done with the local, and only synced
+         * back out to `__stack_pointer` across function boundaries.
+         *
+         * `llvm_stackaddress` gives us access to this fake register
+         * and allows for better optimization than inline asm would.
+         */
+        private extern(D) void* getStackTop() nothrow @nogc
+        {
+            import ldc.intrinsics;
+            return llvm_stackaddress();
+        }
+    }
     else
     {
         /* The use of intrinsic llvm_frameaddress is a reasonable default for
@@ -1874,6 +1892,14 @@ version (LDC_Windows)
             static assert(false, "Architecture not supported.");
     }
 }
+else version (WebAssembly)
+{
+    private extern(C) extern void* __stack_low;
+    private extern(D) void* getStackBottom() nothrow @nogc
+    {
+        return __stack_low;
+    }
+}
 else
 private extern(D) void* getStackBottom() nothrow @nogc
 {
diff --git a/runtime/druntime/src/ldc/eh_wasm.d b/runtime/druntime/src/ldc/eh_wasm.d
new file mode 100644
index 00000000000..59dd74f4ee8
--- /dev/null
+++ b/runtime/druntime/src/ldc/eh_wasm.d
@@ -0,0 +1,35 @@
+/**
+ * This module implements the runtime-part of LDC exceptions
+ * on WebAssembly (Wasm EH)
+ */
+
+module ldc.eh_wasm;
+
+version (WebAssembly):
+
+extern (C) void _d_throw_exception(Throwable t) {
+    import core.stdc.stdio : fwrite, stdout, putc;
+    import ldc.intrinsics : llvm_trap;
+
+    auto msg = t.toString();
+    fwrite(msg.ptr, msg.length, 1, stdout);
+    putc('\n', stdout);
+
+    llvm_trap();
+}
+
+extern (C) void _Unwind_Resume(void*) {
+    import core.stdc.stdio : puts;
+    import ldc.intrinsics : llvm_trap;
+
+    puts("Cannot EH unwind on Wasm (yet).");
+    llvm_trap();
+}
+
+extern (C) void _d_eh_enter_catch(void*) {
+    import core.stdc.stdio : puts;
+    import ldc.intrinsics : llvm_trap;
+
+    puts("Cannot EH catch on Wasm (yet).");
+    llvm_trap();
+}
diff --git a/runtime/druntime/src/ldc/intrinsics.di b/runtime/druntime/src/ldc/intrinsics.di
index 96256e5e871..5bac20af473 100644
--- a/runtime/druntime/src/ldc/intrinsics.di
+++ b/runtime/druntime/src/ldc/intrinsics.di
@@ -54,6 +54,11 @@ pragma(LDC_intrinsic, "llvm.returnaddress")
 pragma(LDC_intrinsic, "llvm.frameaddress.p0")
     void* llvm_frameaddress(uint level);
 
+/// The 'llvm.stackaddress' intrinsic returns the starting address of the stack
+// region that may be used by called functions.
+pragma(LDC_intrinsic, "llvm.stackaddress.p0")
+    void* llvm_stackaddress();
+
 /// The 'llvm.stacksave' intrinsic is used to remember the current state of the
 /// function stack, for use with llvm.stackrestore. This is useful for
 /// implementing language features like scoped automatic variable sized arrays
diff --git a/runtime/druntime/src/rt/sections_ldc.d b/runtime/druntime/src/rt/sections_ldc.d
index 8d42a109527..828cceb046c 100644
--- a/runtime/druntime/src/rt/sections_ldc.d
+++ b/runtime/druntime/src/rt/sections_ldc.d
@@ -32,6 +32,7 @@ else version (DragonFlyBSD) {}
 else version (NetBSD) {}
 else version (OpenBSD) {}
 else version (Windows) {}
+else version (WebAssembly) {}
 else version (LDC):
 
 import rt.minfo;