[libunwind] [libunwind] Enable wasm target for exceptions (PR #168449)

[Yerzhan Zhamashev via cfe-commits]

https://github.com/yerzham created https://github.com/llvm/llvm-project/pull/168449

Most minimal changes to enable libunwind to build for wasm by excluding `__wasm__` from the Windows-style __declspec path in config.h and by recognizing wasm in assembly.h to skip the unsupported-target error. This unblocks building an exceptions-enabled wasi-sdk sysroot (see https://github.com/WebAssembly/wasi-sdk/issues/565) and builds on prior attempts including [yamt’s gist](https://gist.github.com/yamt/b699eb2604d2598810a2876ff2ffc8d8), https://github.com/llvm/llvm-project/pull/79667, and https://github.com/llvm/llvm-project/pull/140365.

>From be1d7651c263c62fbaad0bc2d30985283c1bfefd Mon Sep 17 00:00:00 2001
From: Yerzhan Zhamashev <yerzhan at novel.systems>
Date: Mon, 17 Nov 2025 23:26:51 +0200
Subject: [PATCH 1/2] libunwind: clang-format config.h

---
 libunwind/src/config.h | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/libunwind/src/config.h b/libunwind/src/config.h
index f017403fa2234..41cc63eac358c 100644
--- a/libunwind/src/config.h
+++ b/libunwind/src/config.h
@@ -75,13 +75,13 @@
   #define _LIBUNWIND_EXPORT
   #define _LIBUNWIND_HIDDEN
 #else
-  #if !defined(__ELF__) && !defined(__MACH__) && !defined(_AIX)
-    #define _LIBUNWIND_EXPORT __declspec(dllexport)
-    #define _LIBUNWIND_HIDDEN
-  #else
-    #define _LIBUNWIND_EXPORT __attribute__((visibility("default")))
-    #define _LIBUNWIND_HIDDEN __attribute__((visibility("hidden")))
-  #endif
+#if !defined(__ELF__) && !defined(__MACH__) && !defined(_AIX)
+#define _LIBUNWIND_EXPORT __declspec(dllexport)
+#define _LIBUNWIND_HIDDEN
+#else
+#define _LIBUNWIND_EXPORT __attribute__((visibility("default")))
+#define _LIBUNWIND_HIDDEN __attribute__((visibility("hidden")))
+#endif
 #endif
 
 #define STR(a) #a

>From 8baec647c9f3c3d6ae7269ed0b5b28405ca44646 Mon Sep 17 00:00:00 2001
From: Yerzhan Zhamashev <yerzhan at novel.systems>
Date: Mon, 17 Nov 2025 23:29:14 +0200
Subject: [PATCH 2/2] libunwind: fix wasm build

---
 libunwind/src/assembly.h | 2 ++
 libunwind/src/config.h   | 3 ++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/libunwind/src/assembly.h b/libunwind/src/assembly.h
index 84c9d526f1d75..9c35b6050a2bf 100644
--- a/libunwind/src/assembly.h
+++ b/libunwind/src/assembly.h
@@ -254,6 +254,8 @@ aliasname:                                                                     \
 #define NO_EXEC_STACK_DIRECTIVE
 
 // clang-format on
+#elif defined(__wasm__)
+
 #else
 
 #error Unsupported target
diff --git a/libunwind/src/config.h b/libunwind/src/config.h
index 41cc63eac358c..73162995f9293 100644
--- a/libunwind/src/config.h
+++ b/libunwind/src/config.h
@@ -75,7 +75,8 @@
   #define _LIBUNWIND_EXPORT
   #define _LIBUNWIND_HIDDEN
 #else
-#if !defined(__ELF__) && !defined(__MACH__) && !defined(_AIX)
+#if !defined(__ELF__) && !defined(__MACH__) && !defined(_AIX) &&               \
+    !defined(__wasm__)
 #define _LIBUNWIND_EXPORT __declspec(dllexport)
 #define _LIBUNWIND_HIDDEN
 #else