From 26eddd713bdac79382e315b5296d0281ec81a0ab Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Thu, 23 Apr 2026 21:49:01 +0300
Subject: [PATCH] thirdparty: fix Cross-compiling from amd64 to arm64 double
 definition C error (fixes #26534)

---
 thirdparty/stdatomic/nix/atomic.h      |  9 +--------
 vlib/sync/stdatomic/1.declarations.c.v |  1 -
 vlib/v/builder/cc_test.v               | 25 +++++++++++++++++++++++++
 3 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/thirdparty/stdatomic/nix/atomic.h b/thirdparty/stdatomic/nix/atomic.h
index 3622d85ef..ddd5c1963 100644
--- a/thirdparty/stdatomic/nix/atomic.h
+++ b/thirdparty/stdatomic/nix/atomic.h
@@ -54,17 +54,10 @@ typedef volatile uintptr_t atomic_uintptr_t;
 extern void atomic_thread_fence (int memory_order);
 extern void __atomic_thread_fence (int memory_order);
 
-// workaround for tcc/aarch64; Note: latest prebuilt tcc works, and does not need this hack:
+// TinyCC relies on its runtime atomics support for thread fences.
 #if !defined(__APPLE__)
-#if (defined(__aarch64__) || defined(_M_ARM64))
-    // `_V_atomic_thread_fence` is defined in `atomic.S`
-    extern void _V_atomic_thread_fence(int memory_order);
-    #define atomic_thread_fence(order) _V_atomic_thread_fence(order)
-    #define __atomic_thread_fence(order) _V_atomic_thread_fence(order)
-#else
     #define atomic_thread_fence(order) __atomic_thread_fence(order)
 #endif
-#endif
 
 // use functions for 64, 32 and 8 bit from libatomic directly
 // since tcc is not capible to use "generic" C functions
diff --git a/vlib/sync/stdatomic/1.declarations.c.v b/vlib/sync/stdatomic/1.declarations.c.v
index 9a8760c21..a0d39e5ec 100644
--- a/vlib/sync/stdatomic/1.declarations.c.v
+++ b/vlib/sync/stdatomic/1.declarations.c.v
@@ -63,7 +63,6 @@ $if linux {
 				// Alpine:
 				#flag $when_first_existing('/usr/lib/libatomic.so','/usr/lib/gcc/aarch64-pc-linux-musl/6/libatomic.so','/usr/lib/gcc/aarch64-pc-linux-musl/7/libatomic.so','/usr/lib/gcc/aarch64-pc-linux-musl/8/libatomic.so','/usr/lib/gcc/aarch64-pc-linux-musl/9/libatomic.so','/usr/lib/gcc/aarch64-pc-linux-musl/10/libatomic.so','/usr/lib/gcc/aarch64-pc-linux-musl/11/libatomic.so','/usr/lib/gcc/aarch64-pc-linux-musl/12/libatomic.so','/usr/lib/gcc/aarch64-pc-linux-musl/13/libatomic.so','/usr/lib/gcc/aarch64-pc-linux-musl/14/libatomic.so')
 			}
-			#flag @VEXEROOT/thirdparty/stdatomic/nix/atomic.S
 		}
 	}
 }
diff --git a/vlib/v/builder/cc_test.v b/vlib/v/builder/cc_test.v
index 2c1bb7cfb..0433b9749 100644
--- a/vlib/v/builder/cc_test.v
+++ b/vlib/v/builder/cc_test.v
@@ -379,6 +379,31 @@ fn test_thirdparty_cross_compile_config_for_freebsd_matches_target() {
 	]
 }
 
+fn test_linux_tcc_arm64_stdatomic_does_not_add_atomic_s() {
+	$if !linux {
+		return
+	}
+	test_dir := os.join_path(os.vtmp_dir(), 'v_builder_stdatomic_tcc_arm64_${os.getpid()}')
+	os.mkdir_all(test_dir) or { panic(err) }
+	defer {
+		os.rmdir_all(test_dir) or {}
+	}
+	src_file := os.join_path(test_dir, 'main.v')
+	os.write_file(src_file, 'import sync.stdatomic
+fn main() {
+	mut x := u64(0)
+	stdatomic.store_u64(&x, 1)
+}
+') or {
+		panic(err)
+	}
+	res :=
+		os.execute('${os.quoted_path(@VEXE)} -dump-c-flags - -cc tcc -arch arm64 ${os.quoted_path(src_file)}')
+	assert res.exit_code == 0, res.output
+	assert !res.output.contains('thirdparty/stdatomic/nix/atomic.S')
+	assert res.output.contains('libatomic.so')
+}
+
 fn test_live_windows_main_linker_args_export_host_symbols() {
 	linker_args := builder_linker_args([
 		'-os',
-- 
2.39.5