From 80da515cf77860bf47cb61d46e67e33db57e7bec Mon Sep 17 00:00:00 2001
From: Johannes Stoelp <johannes.stoelp@gmail.com>
Date: Tue, 23 Apr 2024 22:34:04 +0200
Subject: fn: fix fn_t, add static asserts for glibc

---
 fn_hook.cc | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/fn_hook.cc b/fn_hook.cc
index 1c70eab..bf6d8f2 100644
--- a/fn_hook.cc
+++ b/fn_hook.cc
@@ -28,10 +28,7 @@ struct hook;
 template <typename Derived, typename Ret, typename... Args, bool IsNoexcept>
 struct hook<Derived, Ret (*)(Args...) noexcept(IsNoexcept)> {
   // Function pointer type.
-  using fn_t = Ret (*)(Args...);
-
-  // Remember whether this hook was noexcept, to be used for the outer wrapper.
-  static constexpr bool is_noexcept = IsNoexcept;
+  using fn_t = Ret (*)(Args...) noexcept(IsNoexcept);
 
   constexpr hook() noexcept = default;
 
@@ -52,6 +49,11 @@ struct hook<Derived, Ret (*)(Args...) noexcept(IsNoexcept)> {
     ptr = reinterpret_cast<fn_t>(::dlsym(RTLD_NEXT, Derived::sym));
   }
 
+  // Remember whether this hook was noexcept, to be used for the outer wrapper.
+  static constexpr bool is_noexcept() {
+    return IsNoexcept;
+  }
+
 private:
   fn_t ptr = nullptr;
 };
@@ -74,7 +76,7 @@ private:
   } fn;                                                                  \
   }                                                                      \
                                                                          \
-  extern "C" ret fn(__VA_ARGS__) noexcept(detail::hook_##fn::is_noexcept)
+  extern "C" ret fn(__VA_ARGS__) noexcept(detail::hook_##fn::is_noexcept())
 
 // -- EXAMPLE ------------------------------------------------------------------
 
@@ -85,11 +87,15 @@ WRAP(ssize_t, write, int fd, const void* buf, size_t sz) {
   puts("wrapper write(..)");
   return detail::write(fd, buf, sz);
 }
+// glibc: write is not marked noexcept, as it is a cancellation point.
+static_assert(!detail::hook_write::is_noexcept());
 
 WRAP(pid_t, getpid) {
   puts("wrapper getpid()");
   return detail::getpid();
 }
+// glibc: getpid is marked noexcept.
+static_assert(detail::hook_getpid::is_noexcept());
 
 int main() {
   const char msg[] = "hello moose\n";
-- 
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