From fa904c495e94176fbeda9b9b8751b43a667321a8 Mon Sep 17 00:00:00 2001
From: kbkpbot <kbkpbot@sina.com>
Date: Mon, 14 Jul 2025 01:56:28 +0800
Subject: [PATCH] builtin,cgen,markused: add struct @[aligned] support for
 structs allocated on the heap too (#24886)

---
 vlib/builtin/builtin.c.v                   | 128 +++++++++++++++++++--
 vlib/builtin/builtin_d_gcboehm.c.v         |   2 +
 vlib/builtin/builtin_notd_gcboehm.c.v      |   2 +
 vlib/builtin/cfns.c.v                      |  11 ++
 vlib/builtin/prealloc.c.v                  |  62 +++++++---
 vlib/builtin/wasm_bare/libc_impl.c.v       |  11 +-
 vlib/v/ast/table.v                         |   1 +
 vlib/v/checker/struct.v                    |   4 +
 vlib/v/eval/expr.c.v                       |   4 +-
 vlib/v/gen/c/assign.v                      |  45 +++++++-
 vlib/v/gen/c/cheaders.v                    |   1 +
 vlib/v/gen/c/struct.v                      |  34 +++++-
 vlib/v/markused/markused.v                 |   3 +
 vlib/v/tests/structs/struct_aligned_test.v |  13 +++
 14 files changed, 285 insertions(+), 36 deletions(-)
 create mode 100644 vlib/v/tests/structs/struct_aligned_test.v

diff --git a/vlib/builtin/builtin.c.v b/vlib/builtin/builtin.c.v
index dff69c42bc..41e594cafd 100644
--- a/vlib/builtin/builtin.c.v
+++ b/vlib/builtin/builtin.c.v
@@ -453,7 +453,15 @@ pub fn malloc(n isize) &u8 {
 		// so theoretically it is safe
 		res = unsafe { __malloc(usize(n)) }
 	} $else {
-		res = unsafe { C.malloc(n) }
+		$if windows {
+			// Warning! On windows, we always use _aligned_malloc to allocate memory.
+			// This ensures that we can later free the memory with _aligned_free
+			// without needing to track whether the memory was originally allocated
+			// by malloc or _aligned_malloc.
+			res = unsafe { C._aligned_malloc(n, 1) }
+		} $else {
+			res = unsafe { C.malloc(n) }
+		}
 	}
 	if res == 0 {
 		_memory_panic(@FN, n)
@@ -492,7 +500,15 @@ pub fn malloc_noscan(n isize) &u8 {
 	} $else $if freestanding {
 		res = unsafe { __malloc(usize(n)) }
 	} $else {
-		res = unsafe { C.malloc(n) }
+		$if windows {
+			// Warning! On windows, we always use _aligned_malloc to allocate memory.
+			// This ensures that we can later free the memory with _aligned_free
+			// without needing to track whether the memory was originally allocated
+			// by malloc or _aligned_malloc.
+			res = unsafe { C._aligned_malloc(n, 1) }
+		} $else {
+			res = unsafe { C.malloc(n) }
+		}
 	}
 	if res == 0 {
 		_memory_panic(@FN, n)
@@ -538,7 +554,15 @@ pub fn malloc_uncollectable(n isize) &u8 {
 	} $else $if freestanding {
 		res = unsafe { __malloc(usize(n)) }
 	} $else {
-		res = unsafe { C.malloc(n) }
+		$if windows {
+			// Warning! On windows, we always use _aligned_malloc to allocate memory.
+			// This ensures that we can later free the memory with _aligned_free
+			// without needing to track whether the memory was originally allocated
+			// by malloc or _aligned_malloc.
+			res = unsafe { C._aligned_malloc(n, 1) }
+		} $else {
+			res = unsafe { C.malloc(n) }
+		}
 	}
 	if res == 0 {
 		_memory_panic(@FN, n)
@@ -570,7 +594,15 @@ pub fn v_realloc(b &u8, n isize) &u8 {
 	} $else $if gcboehm ? {
 		new_ptr = unsafe { C.GC_REALLOC(b, n) }
 	} $else {
-		new_ptr = unsafe { C.realloc(b, n) }
+		$if windows {
+			// Warning! On windows, we always use _aligned_realloc to reallocate memory.
+			// This ensures that we can later free the memory with _aligned_free
+			// without needing to track whether the memory was originally allocated
+			// by malloc or _aligned_malloc/_aligned_realloc.
+			new_ptr = unsafe { C._aligned_realloc(b, n, 1) }
+		} $else {
+			new_ptr = unsafe { C.realloc(b, n) }
+		}
 	}
 	if new_ptr == 0 {
 		_memory_panic(@FN, n)
@@ -616,7 +648,15 @@ pub fn realloc_data(old_data &u8, old_size int, new_size int) &u8 {
 	$if gcboehm ? {
 		nptr = unsafe { C.GC_REALLOC(old_data, new_size) }
 	} $else {
-		nptr = unsafe { C.realloc(old_data, new_size) }
+		$if windows {
+			// Warning! On windows, we always use _aligned_realloc to reallocate memory.
+			// This ensures that we can later free the memory with _aligned_free
+			// without needing to track whether the memory was originally allocated
+			// by malloc or _aligned_malloc/_aligned_realloc.
+			nptr = unsafe { C._aligned_realloc(old_data, new_size, 1) }
+		} $else {
+			nptr = unsafe { C.realloc(old_data, new_size) }
+		}
 	}
 	if nptr == 0 {
 		_memory_panic(@FN, isize(new_size))
@@ -642,7 +682,19 @@ pub fn vcalloc(n isize) &u8 {
 	} $else $if gcboehm ? {
 		return unsafe { &u8(C.GC_MALLOC(n)) }
 	} $else {
-		return unsafe { C.calloc(1, n) }
+		$if windows {
+			// Warning! On windows, we always use _aligned_malloc to allocate memory.
+			// This ensures that we can later free the memory with _aligned_free
+			// without needing to track whether the memory was originally allocated
+			// by malloc or _aligned_malloc/_aligned_realloc/_aligned_recalloc.
+			ptr := unsafe { C._aligned_malloc(n, 1) }
+			if ptr != &u8(unsafe { nil }) {
+				unsafe { C.memset(ptr, 0, n) }
+			}
+			return ptr
+		} $else {
+			return unsafe { C.calloc(1, n) }
+		}
 	}
 	return &u8(unsafe { nil }) // not reached, TODO: remove when V's checker is improved
 }
@@ -704,7 +756,12 @@ pub fn free(ptr voidptr) {
 			unsafe { C.GC_FREE(ptr) }
 		}
 	} $else {
-		C.free(ptr)
+		$if windows {
+			// Warning! On windows, we always use _aligned_free to free memory.
+			unsafe { C._aligned_free(ptr) }
+		} $else {
+			C.free(ptr)
+		}
 	}
 }
 
@@ -757,6 +814,63 @@ pub fn memdup_uncollectable(src voidptr, sz isize) voidptr {
 	}
 }
 
+// memdup_align dynamically allocates a memory block of `sz` bytes on the heap,
+// copies the contents from `src` into the allocated space, and returns a pointer
+// to the newly allocated memory. The returned pointer is aligned to the specified `align` boundary.
+//   - `align` must be a power of two and at least 1
+//   - `sz` must be non-negative
+//   - The memory regions should not overlap
+@[unsafe]
+pub fn memdup_align(src voidptr, sz isize, align isize) voidptr {
+	$if trace_memdup ? {
+		C.fprintf(C.stderr, c'memdup_align size: %10d align: %10d\n', sz, align)
+	}
+	if sz == 0 {
+		return vcalloc(1)
+	}
+	n := sz
+	$if trace_malloc ? {
+		total_m += n
+		C.fprintf(C.stderr, c'_v_memdup_align %6d total %10d\n', n, total_m)
+		// print_backtrace()
+	}
+	if n < 0 {
+		_memory_panic(@FN, n)
+	}
+	mut res := &u8(unsafe { nil })
+	$if prealloc {
+		res = prealloc_malloc_align(n, align)
+	} $else $if gcboehm ? {
+		unsafe {
+			res = C.GC_memalign(align, n)
+		}
+	} $else $if freestanding {
+		// todo: is this safe to call malloc there? We export __malloc as malloc and it uses dlmalloc behind the scenes
+		// so theoretically it is safe
+		panic('memdup_align is not implemented with -freestanding')
+		res = unsafe { __malloc(usize(n)) }
+	} $else {
+		$if windows {
+			// Warning! On windows, we always use _aligned_malloc to allocate memory.
+			// This ensures that we can later free the memory with _aligned_free
+			// without needing to track whether the memory was originally allocated
+			// by malloc or _aligned_malloc.
+			res = unsafe { C._aligned_malloc(n, align) }
+		} $else {
+			res = unsafe { C.aligned_alloc(align, n) }
+		}
+	}
+	if res == 0 {
+		_memory_panic(@FN, n)
+	}
+	$if debug_malloc ? {
+		// Fill in the memory with something != 0 i.e. `M`, so it is easier to spot
+		// when the calling code wrongly relies on it being zeroed.
+		unsafe { C.memset(res, 0x4D, n) }
+	}
+	return C.memcpy(res, src, sz)
+}
+
 // GCHeapUsage contains stats about the current heap usage of your program.
 pub struct GCHeapUsage {
 pub:
diff --git a/vlib/builtin/builtin_d_gcboehm.c.v b/vlib/builtin/builtin_d_gcboehm.c.v
index ecb5601d92..6b0de80479 100644
--- a/vlib/builtin/builtin_d_gcboehm.c.v
+++ b/vlib/builtin/builtin_d_gcboehm.c.v
@@ -140,6 +140,8 @@ fn C.GC_REALLOC(ptr voidptr, n usize) voidptr
 
 fn C.GC_FREE(ptr voidptr)
 
+fn C.GC_memalign(align isize, size isize) voidptr
+
 // explicitly perform garbage collection now! Garbage collections
 // are done automatically when needed, so this function is hardly needed
 fn C.GC_gcollect()
diff --git a/vlib/builtin/builtin_notd_gcboehm.c.v b/vlib/builtin/builtin_notd_gcboehm.c.v
index aec3ffbb16..76b9ad60b1 100644
--- a/vlib/builtin/builtin_notd_gcboehm.c.v
+++ b/vlib/builtin/builtin_notd_gcboehm.c.v
@@ -14,6 +14,8 @@ fn C.GC_REALLOC(ptr voidptr, n usize) voidptr
 
 fn C.GC_FREE(ptr voidptr)
 
+fn C.GC_memalign(align isize, size isize) voidptr
+
 fn C.GC_get_heap_usage_safe(pheap_size &usize, pfree_bytes &usize, punmapped_bytes &usize, pbytes_since_gc &usize,
 	ptotal_bytes &usize)
 
diff --git a/vlib/builtin/cfns.c.v b/vlib/builtin/cfns.c.v
index 17cf9d296b..0c327ec622 100644
--- a/vlib/builtin/cfns.c.v
+++ b/vlib/builtin/cfns.c.v
@@ -23,6 +23,17 @@ fn C.realloc(a &u8, b int) &u8
 
 fn C.free(ptr voidptr)
 
+fn C.aligned_alloc(align isize, size isize) voidptr
+
+// windows aligned memory functions
+fn C._aligned_malloc(size isize, align isize) voidptr
+fn C._aligned_free(voidptr)
+fn C._aligned_realloc(voidptr, size isize, align isize) voidptr
+fn C._aligned_offset_malloc(size isize, align isize, offset isize) voidptr
+fn C._aligned_offset_realloc(voidptr, size isize, align isize, offset isize) voidptr
+fn C._aligned_msize(voidptr, align isize, offset isize) isize
+fn C._aligned_recalloc(voidptr, num isize, size isize, align isize) voidptr
+
 @[noreturn; trusted]
 fn C.exit(code int)
 
diff --git a/vlib/builtin/prealloc.c.v b/vlib/builtin/prealloc.c.v
index 0ca16edd07..6cc79388a9 100644
--- a/vlib/builtin/prealloc.c.v
+++ b/vlib/builtin/prealloc.c.v
@@ -37,7 +37,7 @@ fn vmemory_abort_on_nil(p voidptr, bytes isize) {
 }
 
 @[unsafe]
-fn vmemory_block_new(prev &VMemoryBlock, at_least isize) &VMemoryBlock {
+fn vmemory_block_new(prev &VMemoryBlock, at_least isize, align isize) &VMemoryBlock {
 	vmem_block_size := sizeof(VMemoryBlock)
 	mut v := unsafe { &VMemoryBlock(C.calloc(1, vmem_block_size)) }
 	vmemory_abort_on_nil(v, vmem_block_size)
@@ -49,16 +49,35 @@ fn vmemory_block_new(prev &VMemoryBlock, at_least isize) &VMemoryBlock {
 	if unsafe { prev != 0 } {
 		prev.next = v
 	}
-	block_size := if at_least < isize(prealloc_block_size) {
+	base_block_size := if at_least < isize(prealloc_block_size) {
 		isize(prealloc_block_size)
 	} else {
 		at_least
 	}
-	$if prealloc_trace_malloc ? {
-		C.fprintf(C.stderr, c'vmemory_block_new id: %d, block_size: %lld, at_least: %lld\n',
-			v.id, block_size, at_least)
+	block_size := if align > 0 {
+		if base_block_size % align == 0 {
+			base_block_size
+		} else {
+			base_block_size + align - (base_block_size % align)
+		}
+	} else {
+		base_block_size
+	}
+	$if prealloc_trace_malloc ? {
+		C.fprintf(C.stderr, c'vmemory_block_new id: %d, block_size: %lld, at_least: %lld, align: %lld\n',
+			v.id, block_size, at_least, align)
+	}
+
+	fixed_align := if align <= 1 { 1 } else { align }
+	$if windows {
+		v.start = unsafe { C._aligned_malloc(block_size, fixed_align) }
+	} $else {
+		if fixed_align == 1 {
+			v.start = unsafe { C.malloc(block_size) }
+		} else {
+			v.start = unsafe { C.aligned_alloc(fixed_align, block_size) }
+		}
 	}
-	v.start = unsafe { C.malloc(block_size) }
 	vmemory_abort_on_nil(v.start, block_size)
 	$if prealloc_memset ? {
 		unsafe { C.memset(v.start, int($d('prealloc_memset_value', 0)), block_size) }
@@ -69,15 +88,15 @@ fn vmemory_block_new(prev &VMemoryBlock, at_least isize) &VMemoryBlock {
 }
 
 @[unsafe]
-fn vmemory_block_malloc(n isize) &u8 {
+fn vmemory_block_malloc(n isize, align isize) &u8 {
 	$if prealloc_trace_malloc ? {
-		C.fprintf(C.stderr, c'vmemory_block_malloc g_memory_block.id: %d, n: %lld\n',
-			g_memory_block.id, n)
+		C.fprintf(C.stderr, c'vmemory_block_malloc g_memory_block.id: %d, n: %lld align: %d\n',
+			g_memory_block.id, n, align)
 	}
 	unsafe {
 		remaining := i64(g_memory_block.stop) - i64(g_memory_block.current)
 		if _unlikely_(remaining < n) {
-			g_memory_block = vmemory_block_new(g_memory_block, n)
+			g_memory_block = vmemory_block_new(g_memory_block, n, align)
 		}
 		res := &u8(g_memory_block.current)
 		g_memory_block.current += n
@@ -96,7 +115,7 @@ fn prealloc_vinit() {
 		C.fprintf(C.stderr, c'prealloc_vinit started\n')
 	}
 	unsafe {
-		g_memory_block = vmemory_block_new(nil, isize(prealloc_block_size))
+		g_memory_block = vmemory_block_new(nil, isize(prealloc_block_size), 0)
 		at_exit(prealloc_vcleanup) or {}
 	}
 }
@@ -170,20 +189,28 @@ fn prealloc_vcleanup() {
 	}
 	unsafe {
 		for g_memory_block != 0 {
-			C.free(g_memory_block.start)
+			$if windows {
+				// Warning! On windows, we always use _aligned_free to free memory.
+				C._aligned_free(g_memory_block.start)
+			} $else {
+				C.free(g_memory_block.start)
+			}
+			tmp := g_memory_block
 			g_memory_block = g_memory_block.previous
+			// free the link node
+			C.free(tmp)
 		}
 	}
 }
 
 @[unsafe]
 fn prealloc_malloc(n isize) &u8 {
-	return unsafe { vmemory_block_malloc(n) }
+	return unsafe { vmemory_block_malloc(n, 0) }
 }
 
 @[unsafe]
 fn prealloc_realloc(old_data &u8, old_size isize, new_size isize) &u8 {
-	new_ptr := unsafe { vmemory_block_malloc(new_size) }
+	new_ptr := unsafe { vmemory_block_malloc(new_size, 0) }
 	min_size := if old_size < new_size { old_size } else { new_size }
 	unsafe { C.memcpy(new_ptr, old_data, min_size) }
 	return new_ptr
@@ -191,7 +218,12 @@ fn prealloc_realloc(old_data &u8, old_size isize, new_size isize) &u8 {
 
 @[unsafe]
 fn prealloc_calloc(n isize) &u8 {
-	new_ptr := unsafe { vmemory_block_malloc(n) }
+	new_ptr := unsafe { vmemory_block_malloc(n, 0) }
 	unsafe { C.memset(new_ptr, 0, n) }
 	return new_ptr
 }
+
+@[unsafe]
+fn prealloc_malloc_align(n isize, align isize) &u8 {
+	return unsafe { vmemory_block_malloc(n, align) }
+}
diff --git a/vlib/builtin/wasm_bare/libc_impl.c.v b/vlib/builtin/wasm_bare/libc_impl.c.v
index d91bb55d2c..7b89d185b6 100644
--- a/vlib/builtin/wasm_bare/libc_impl.c.v
+++ b/vlib/builtin/wasm_bare/libc_impl.c.v
@@ -5,8 +5,17 @@ module builtin
 @[unsafe]
 pub fn __malloc(size usize) voidptr {
 	unsafe {
-		return C.malloc(int(size))
+		$if windows {
+			// Warning! On windows, we always use _aligned_malloc to allocate memory.
+			// This ensures that we can later free the memory with _aligned_free
+			// without needing to track whether the memory was originally allocated
+			// by malloc or _aligned_malloc.
+			return C._aligned_malloc(size, 1)
+		} $else {
+			return C.malloc(int(size))
+		}
 	}
+	return unsafe { nil }
 }
 
 @[unsafe]
diff --git a/vlib/v/ast/table.v b/vlib/v/ast/table.v
index 8fd18525cb..dfd2486a35 100644
--- a/vlib/v/ast/table.v
+++ b/vlib/v/ast/table.v
@@ -46,6 +46,7 @@ pub mut:
 	debugger       bool            // debugger is used
 	comptime_calls map[string]bool // resolved name to call on comptime
 	comptime_for   bool            // uses $for
+	memory_align   bool            // @[aligned] for struct
 }
 
 @[unsafe]
diff --git a/vlib/v/checker/struct.v b/vlib/v/checker/struct.v
index 400f8ffaba..94136501f5 100644
--- a/vlib/v/checker/struct.v
+++ b/vlib/v/checker/struct.v
@@ -67,6 +67,10 @@ fn (mut c Checker) struct_decl(mut node ast.StructDecl) {
 			if node.language != .c && attr.name == 'typedef' {
 				c.error('`typedef` attribute can only be used with C structs', node.pos)
 			}
+			aligned := if attr.arg == '' { 0 } else { attr.arg.int() }
+			if aligned > 1 {
+				c.table.used_features.memory_align = true
+			}
 		}
 
 		// Evaluate the size of the unresolved fixed array
diff --git a/vlib/v/eval/expr.c.v b/vlib/v/eval/expr.c.v
index 4fd2698f88..0656528a0b 100644
--- a/vlib/v/eval/expr.c.v
+++ b/vlib/v/eval/expr.c.v
@@ -55,12 +55,12 @@ pub fn (mut e Eval) expr(expr ast.Expr, expecting ast.Type) Object {
 						}
 						'malloc' {
 							return Ptr{
-								val: unsafe { C.malloc(args[0].int_val()) }
+								val: unsafe { malloc(isize(args[0].int_val())) }
 							}
 						}
 						'calloc' {
 							return Ptr{
-								val: unsafe { C.calloc(args[0].int_val(), args[1].int_val()) }
+								val: unsafe { vcalloc(isize(args[0].int_val() * args[1].int_val())) }
 							}
 						}
 						'getcwd' {
diff --git a/vlib/v/gen/c/assign.v b/vlib/v/gen/c/assign.v
index f64208ccaf..5a0622dc2a 100644
--- a/vlib/v/gen/c/assign.v
+++ b/vlib/v/gen/c/assign.v
@@ -720,6 +720,13 @@ fn (mut g Gen) assign_stmt(node_ ast.AssignStmt) {
 			}
 			final_left_sym := g.table.final_sym(g.unwrap_generic(var_type))
 			final_right_sym := g.table.final_sym(unwrapped_val_type)
+			mut aligned := 0
+			if final_left_sym.info is ast.Struct {
+				if attr := final_left_sym.info.attrs.find_first('aligned') {
+					aligned = if attr.arg == '' { 0 } else { attr.arg.int() }
+				}
+			}
+
 			if final_left_sym.kind == .bool && final_right_sym.kind == .bool
 				&& node.op in [.boolean_or_assign, .boolean_and_assign] {
 				extracted_op := match node.op {
@@ -947,7 +954,11 @@ fn (mut g Gen) assign_stmt(node_ ast.AssignStmt) {
 						is_option_unwrapped := val is ast.Ident && val.or_expr.kind != .absent
 						is_option_auto_heap := is_auto_heap && is_option_unwrapped
 						if is_auto_heap {
-							g.write('HEAP(${styp}, (')
+							if aligned != 0 {
+								g.write('HEAP_align(${styp}, (')
+							} else {
+								g.write('HEAP(${styp}, (')
+							}
 						}
 						if val.is_auto_deref_var() && !is_option_unwrapped {
 							g.write('*')
@@ -978,7 +989,11 @@ fn (mut g Gen) assign_stmt(node_ ast.AssignStmt) {
 							g.expr(val)
 						}
 						if is_auto_heap && !is_option_auto_heap {
-							g.write('))')
+							if aligned != 0 {
+								g.write('), ${aligned})')
+							} else {
+								g.write('))')
+							}
 						}
 					}
 				} else {
@@ -1073,10 +1088,21 @@ fn (mut g Gen) gen_multi_return_assign(node &ast.AssignStmt, return_type ast.Typ
 			g.write('*')
 		}
 		noscan := if is_auto_heap { g.check_noscan(return_type) } else { '' }
+		mut aligned := 0
+		sym := g.table.final_sym(node.left_types[i])
+		if sym.info is ast.Struct {
+			if attr := sym.info.attrs.find_first('aligned') {
+				aligned = if attr.arg == '' { 0 } else { attr.arg.int() }
+			}
+		}
 		if node.left_types[i].has_flag(.option) {
 			base_typ := g.base_type(node.left_types[i])
 			tmp_var := if is_auto_heap {
-				'HEAP${noscan}(${styp}, ${mr_var_name}.arg${i})'
+				if aligned != 0 {
+					'HEAP_align(${styp}, ${mr_var_name}.arg${i}, ${aligned})'
+				} else {
+					'HEAP${noscan}(${styp}, ${mr_var_name}.arg${i})'
+				}
 			} else if is_option {
 				'(*((${g.base_type(return_type)}*)${mr_var_name}.data)).arg${i}'
 			} else {
@@ -1098,13 +1124,16 @@ fn (mut g Gen) gen_multi_return_assign(node &ast.AssignStmt, return_type ast.Typ
 			}
 		} else {
 			g.expr(lx)
-			sym := g.table.final_sym(node.left_types[i])
 			if sym.kind == .array_fixed {
 				g.writeln2(';', 'memcpy(&${g.expr_string(lx)}, &${mr_var_name}.arg${i}, sizeof(${styp}));')
 			} else {
 				if cur_indexexpr != -1 {
 					if is_auto_heap {
-						g.writeln('HEAP${noscan}(${styp}, ${mr_var_name}.arg${i}) });')
+						if aligned != 0 {
+							g.writeln('HEAP_align(${styp}, ${mr_var_name}.arg${i}, ${aligned}) });')
+						} else {
+							g.writeln('HEAP${noscan}(${styp}, ${mr_var_name}.arg${i}) });')
+						}
 					} else if is_option {
 						g.writeln('(*((${g.base_type(return_type)}*)${mr_var_name}.data)).arg${i} });')
 					} else {
@@ -1113,7 +1142,11 @@ fn (mut g Gen) gen_multi_return_assign(node &ast.AssignStmt, return_type ast.Typ
 					g.cur_indexexpr.delete(cur_indexexpr)
 				} else {
 					if is_auto_heap {
-						g.writeln(' = HEAP${noscan}(${styp}, ${mr_var_name}.arg${i});')
+						if aligned != 0 {
+							g.writeln(' = HEAP_align(${styp}, ${mr_var_name}.arg${i}, ${aligned});')
+						} else {
+							g.writeln(' = HEAP${noscan}(${styp}, ${mr_var_name}.arg${i});')
+						}
 					} else if is_option {
 						g.writeln(' = (*((${g.base_type(return_type)}*)${mr_var_name}.data)).arg${i};')
 					} else {
diff --git a/vlib/v/gen/c/cheaders.v b/vlib/v/gen/c/cheaders.v
index 5d286d6ad8..a835dce7cd 100644
--- a/vlib/v/gen/c/cheaders.v
+++ b/vlib/v/gen/c/cheaders.v
@@ -581,6 +581,7 @@ const c_helper_macros = '//============================== HELPER C MACROS ======
 // copy something to the heap
 #define HEAP(type, expr) ((type*)memdup((void*)&((type[]){expr}[0]), sizeof(type)))
 #define HEAP_noscan(type, expr) ((type*)memdup_noscan((void*)&((type[]){expr}[0]), sizeof(type)))
+#define HEAP_align(type, expr, align) ((type*)memdup_align((void*)&((type[]){expr}[0]), sizeof(type), align))
 
 #define _PUSH_MANY(arr, val, tmp, tmp_typ) {tmp_typ tmp = (val); array_push_many(arr, tmp.data, tmp.len);}
 #define _PUSH_MANY_noscan(arr, val, tmp, tmp_typ) {tmp_typ tmp = (val); array_push_many_noscan(arr, tmp.data, tmp.len);}
diff --git a/vlib/v/gen/c/struct.v b/vlib/v/gen/c/struct.v
index ec957429f0..b1841fd0ce 100644
--- a/vlib/v/gen/c/struct.v
+++ b/vlib/v/gen/c/struct.v
@@ -58,9 +58,13 @@ fn (mut g Gen) struct_init(node ast.StructInit) {
 	if is_amp {
 		g.go_back(1) // delete the `&` already generated in `prefix_expr()
 	}
+	mut aligned := 0
 	mut is_anon := false
 	mut is_array_fixed_struct_init := false // return T{} where T is fixed array
 	if mut sym.info is ast.Struct {
+		if attr := sym.info.attrs.find_first('aligned') {
+			aligned = if attr.arg == '' { 0 } else { attr.arg.int() }
+		}
 		is_anon = sym.info.is_anon
 	}
 	is_generic_default := sym.kind !in [.struct, .array_fixed] && node.typ.has_flag(.generic) // T{}
@@ -92,9 +96,17 @@ fn (mut g Gen) struct_init(node ast.StructInit) {
 	} else if is_amp || g.inside_cast_in_heap > 0 {
 		if node.typ.has_flag(.option) {
 			basetyp := g.base_type(node.typ)
-			g.write('(${basetyp}*)memdup(&(${basetyp}){')
+			if aligned != 0 {
+				g.write('(${basetyp}*)memdup_align(&(${basetyp}){')
+			} else {
+				g.write('(${basetyp}*)memdup(&(${basetyp}){')
+			}
 		} else {
-			g.write('(${styp}*)memdup(&(${styp}){')
+			if aligned != 0 {
+				g.write('(${styp}*)memdup_align(&(${styp}){')
+			} else {
+				g.write('(${styp}*)memdup(&(${styp}){')
+			}
 		}
 	} else if node.typ.is_ptr() {
 		basetyp := g.styp(node.typ.set_nr_muls(0))
@@ -389,13 +401,25 @@ fn (mut g Gen) struct_init(node ast.StructInit) {
 		g.write('}')
 	}
 	if g.is_shared && !g.inside_opt_data && !g.is_arraymap_set {
-		g.write('}, sizeof(${shared_styp}))')
+		if aligned != 0 {
+			g.write('}, sizeof(${shared_styp}), ${aligned})')
+		} else {
+			g.write('}, sizeof(${shared_styp}))')
+		}
 	} else if is_amp || g.inside_cast_in_heap > 0 {
 		if node.typ.has_flag(.option) {
 			basetyp := g.base_type(node.typ)
-			g.write(', sizeof(${basetyp}))')
+			if aligned != 0 {
+				g.write(', sizeof(${basetyp}), ${aligned})')
+			} else {
+				g.write(', sizeof(${basetyp}))')
+			}
 		} else {
-			g.write(', sizeof(${styp}))')
+			if aligned != 0 {
+				g.write(', sizeof(${styp}), ${aligned})')
+			} else {
+				g.write(', sizeof(${styp}))')
+			}
 		}
 	}
 }
diff --git a/vlib/v/markused/markused.v b/vlib/v/markused/markused.v
index aa9d145096..e6e5de9c0b 100644
--- a/vlib/v/markused/markused.v
+++ b/vlib/v/markused/markused.v
@@ -219,6 +219,9 @@ pub fn mark_used(mut table ast.Table, mut pref_ pref.Preferences, ast_files []&a
 		if table.used_features.type_name {
 			core_fns << charptr_idx_str + '.vstring_literal'
 		}
+		if table.used_features.memory_align {
+			core_fns << 'memdup_align'
+		}
 		if pref_.trace_calls || pref_.trace_fns.len > 0 {
 			include_panic_deps = true
 			core_fns << 'vgettid'
diff --git a/vlib/v/tests/structs/struct_aligned_test.v b/vlib/v/tests/structs/struct_aligned_test.v
new file mode 100644
index 0000000000..59ee4af93a
--- /dev/null
+++ b/vlib/v/tests/structs/struct_aligned_test.v
@@ -0,0 +1,13 @@
+@[aligned: 512]
+struct MyStruct {
+	a int
+}
+
+fn test_struct_aligned() {
+	x := u64(voidptr(&MyStruct{}))
+	assert x % 512 == 0
+
+	y := MyStruct{}
+	ptr := u64(voidptr(&y))
+	assert ptr % 512 == 0
+}