From 75311e2f9aabd1e4775176e9adff5cd5f1fe42aa Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Fri, 19 Apr 2024 15:44:36 -0400
Subject: config: Check for max_align_t

---
 config/header.mk     |  1 +
 config/max-align-t.c |  8 ++++++++
 src/prelude.h        | 19 +++++++++++++++----
 3 files changed, 24 insertions(+), 4 deletions(-)
 create mode 100644 config/max-align-t.c

diff --git a/config/header.mk b/config/header.mk
index 86a4dc5..bba03ef 100644
--- a/config/header.mk
+++ b/config/header.mk
@@ -18,6 +18,7 @@ HEADERS := \
     ${GEN}/getdents64-syscall.h \
     ${GEN}/getprogname.h \
     ${GEN}/getprogname-gnu.h \
+    ${GEN}/max-align-t.h \
     ${GEN}/pipe2.h \
     ${GEN}/posix-spawn-addfchdir.h \
     ${GEN}/posix-spawn-addfchdir-np.h \
diff --git a/config/max-align-t.c b/config/max-align-t.c
new file mode 100644
index 0000000..96165ce
--- /dev/null
+++ b/config/max-align-t.c
@@ -0,0 +1,8 @@
+// Copyright © Tavian Barnes <tavianator@tavianator.com>
+// SPDX-License-Identifier: 0BSD
+
+#include <stddef.h>
+
+int main(void) {
+	return _Alignof(max_align_t);
+}
diff --git a/src/prelude.h b/src/prelude.h
index a23b167..390666b 100644
--- a/src/prelude.h
+++ b/src/prelude.h
@@ -181,15 +181,26 @@ extern const char bfs_version[];
 #  define TRUE_SHARING_SIZE 64
 #endif
 
+/**
+ * Polyfill max_align_t if we don't already have it.
+ */
+#if !BFS_HAS_MAX_ALIGN_T
+typedef union {
+#  ifdef __BIGGEST_ALIGNMENT__
+	alignas(__BIGGEST_ALIGNMENT__) char c;
+#  else
+	long double ld;
+	long long ll;
+	void *ptr;
+#  endif
+} max_align_t;
+#endif
+
 /**
  * Alignment specifier that avoids false sharing.
  */
 #define cache_align alignas(FALSE_SHARING_SIZE)
 
-#if __COSMOPOLITAN__
-typedef long double max_align_t;
-#endif
-
 // Wrappers for attributes
 
 /**
-- 
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