From a5e45bf44de100b9d8fc1781e9fe09837161e202 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Thu, 23 Apr 2026 19:34:13 +0300
Subject: [PATCH] builtin: fix [ARM64] - failed to build (fixes #26267)

---
 vlib/builtin/array.v                          | 20 ++++++++++++-------
 vlib/builtin/array_d_gcboehm_opt.v            |  4 ++--
 ...array_data_header_size_runtime.c.must_have |  4 ++++
 .../array_data_header_size_runtime.vv         |  3 +++
 4 files changed, 22 insertions(+), 9 deletions(-)
 create mode 100644 vlib/v/gen/c/testdata/array_data_header_size_runtime.c.must_have
 create mode 100644 vlib/v/gen/c/testdata/array_data_header_size_runtime.vv

diff --git a/vlib/builtin/array.v b/vlib/builtin/array.v
index 39aeac228..e435415f5 100644
--- a/vlib/builtin/array.v
+++ b/vlib/builtin/array.v
@@ -39,17 +39,23 @@ mut:
 
 // Must be aligned to at least the maximum fundamental type alignment (pointer size)
 // so that the array data following the header is properly aligned.
-const array_data_header_size = int(sizeof(voidptr))
+//
+// Keep this as a function, not a const. When V bootstraps from generated C, a const
+// would bake in the snapshot generator's pointer size instead of the target C ABI.
+@[inline]
+fn array_data_header_size() int {
+	return int(sizeof(voidptr))
+}
 
 @[inline]
 fn array_data_allocation_size(total_size u64) u64 {
-	return u64(array_data_header_size) + __at_least_one(total_size)
+	return u64(array_data_header_size()) + __at_least_one(total_size)
 }
 
 @[inline]
 fn alloc_array_data(total_size u64) voidptr {
 	raw := vcalloc(array_data_allocation_size(total_size))
-	return unsafe { &u8(raw) + array_data_header_size }
+	return unsafe { &u8(raw) + array_data_header_size() }
 }
 
 @[inline]
@@ -57,7 +63,7 @@ fn alloc_array_data_uninit(total_size u64) voidptr {
 	raw := unsafe { malloc_uninit(array_data_allocation_size(total_size)) }
 	unsafe {
 		(&ArrayDataHeader(raw)).has_slices = false
-		return &u8(raw) + array_data_header_size
+		return &u8(raw) + array_data_header_size()
 	}
 }
 
@@ -92,7 +98,7 @@ fn (a array) data_header() &ArrayDataHeader {
 		return unsafe { nil }
 	}
 	base_data := unsafe { &u8(a.data) - u64(a.offset) }
-	return unsafe { &ArrayDataHeader(base_data - array_data_header_size) }
+	return unsafe { &ArrayDataHeader(base_data - array_data_header_size()) }
 }
 
 @[inline]
@@ -372,7 +378,7 @@ pub fn (mut a array) ensure_cap(required int) {
 		if a.flags.has(.noslices) && !a.flags.has(.is_slice) && !a.buffer_has_slices() {
 			unsafe {
 				if a.flags.has(.managed) {
-					free(&u8(a.data) - u64(array_data_header_size))
+					free(&u8(a.data) - u64(array_data_header_size()))
 				} else {
 					free(a.data)
 				}
@@ -1150,7 +1156,7 @@ pub fn (a &array) free() {
 	if mblock_ptr != unsafe { nil } {
 		unsafe {
 			if a.flags.has(.managed) {
-				free(mblock_ptr - array_data_header_size)
+				free(mblock_ptr - array_data_header_size())
 			} else {
 				free(mblock_ptr)
 			}
diff --git a/vlib/builtin/array_d_gcboehm_opt.v b/vlib/builtin/array_d_gcboehm_opt.v
index 4a44128b0..812b1bd30 100644
--- a/vlib/builtin/array_d_gcboehm_opt.v
+++ b/vlib/builtin/array_d_gcboehm_opt.v
@@ -8,7 +8,7 @@ module builtin
 @[inline]
 fn alloc_array_data_noscan(total_size u64) voidptr {
 	raw := vcalloc_noscan(array_data_allocation_size(total_size))
-	return unsafe { &u8(raw) + array_data_header_size }
+	return unsafe { &u8(raw) + array_data_header_size() }
 }
 
 @[inline]
@@ -16,7 +16,7 @@ fn alloc_array_data_noscan_uninit(total_size u64) voidptr {
 	raw := unsafe { malloc_noscan_uninit(array_data_allocation_size(total_size)) }
 	unsafe {
 		(&ArrayDataHeader(raw)).has_slices = false
-		return &u8(raw) + array_data_header_size
+		return &u8(raw) + array_data_header_size()
 	}
 }
 
diff --git a/vlib/v/gen/c/testdata/array_data_header_size_runtime.c.must_have b/vlib/v/gen/c/testdata/array_data_header_size_runtime.c.must_have
new file mode 100644
index 000000000..c2ebcae66
--- /dev/null
+++ b/vlib/v/gen/c/testdata/array_data_header_size_runtime.c.must_have
@@ -0,0 +1,4 @@
+VV_LOC int builtin__array_data_header_size(void) {
+return ((int)(sizeof(voidptr)));
+return ((u8*)(raw)) + builtin__array_data_header_size();
+return ((ArrayDataHeader*)(base_data - builtin__array_data_header_size()));
diff --git a/vlib/v/gen/c/testdata/array_data_header_size_runtime.vv b/vlib/v/gen/c/testdata/array_data_header_size_runtime.vv
new file mode 100644
index 000000000..b939bb553
--- /dev/null
+++ b/vlib/v/gen/c/testdata/array_data_header_size_runtime.vv
@@ -0,0 +1,3 @@
+fn main() {
+	_ = []string{len: 2}
+}
-- 
2.39.5