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Use alignment when allocating vm and stack memory #91

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Merged
rdunnington merged 2 commits into from
Jun 8, 2026
Merged

Use alignment when allocating vm and stack memory #91

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adf20dc
Use alignment when allocating vm and stack memory
rtfeldman Jun 7, 2026
6e112cd
Use alignment when freeing vm and stack memory
rtfeldman Jun 7, 2026
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5 changes: 3 additions & 2 deletions src/Stack.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -113,7 +113,8 @@ pub fn init(allocator: std.mem.Allocator) Stack {

pub fn deinit(stack: *Stack) void {
if (stack.mem.len > 0) {
stack.allocator.free(stack.mem);
const alignment = @max(@alignOf(StackVal), @alignOf(Label), @alignOf(CallFrame));
stack.allocator.rawFree(stack.mem, comptime std.mem.Alignment.fromByteUnits(alignment), @returnAddress());
}
}

Expand All @@ -127,7 +128,7 @@ pub fn allocMemory(stack: *Stack, opts: AllocOpts) !void {
const begin_labels = values_alloc_size;
const begin_frames = values_alloc_size + labels_alloc_size;

stack.mem = try stack.allocator.alloc(u8, total_alloc_size);
stack.mem = try stack.allocator.alignedAlloc(u8, comptime std.mem.Alignment.fromByteUnits(alignment), total_alloc_size);
stack.values.ptr = @as([*]StackVal, @alignCast(@ptrCast(stack.mem.ptr)));
stack.values.len = opts.max_values;
stack.labels.ptr = @as([*]Label, @alignCast(@ptrCast(stack.mem[begin_labels..].ptr)));
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7 changes: 5 additions & 2 deletions src/instance.zig
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Expand Up @@ -744,6 +744,7 @@ pub const VM = struct {

allocator: std.mem.Allocator,
mem: []u8, // VM and impl memory live here
mem_alignment: std.mem.Alignment, // alignment `mem` was allocated with, so it can be freed symmetrically

impl: *anyopaque,

Expand All @@ -753,7 +754,7 @@ pub const VM = struct {
const impl_alloc_size = std.mem.alignForward(usize, @sizeOf(T), alignment);
const total_alloc_size = vm_alloc_size + impl_alloc_size;

var mem = try allocator.alloc(u8, total_alloc_size);
var mem = try allocator.alignedAlloc(u8, comptime std.mem.Alignment.fromByteUnits(alignment), total_alloc_size);

var vm: *VM = @as(*VM, @ptrCast(@alignCast(mem.ptr)));
const impl: *T = @as(*T, @ptrCast(@alignCast(mem[vm_alloc_size..].ptr)));
Expand All @@ -769,6 +770,7 @@ pub const VM = struct {
vm.resolve_func_ref_fn = T.resolveFuncRef;
vm.allocator = allocator;
vm.mem = mem;
vm.mem_alignment = comptime std.mem.Alignment.fromByteUnits(alignment);
vm.impl = impl;

T.init(vm);
Expand All @@ -781,7 +783,8 @@ pub const VM = struct {

var allocator = vm.allocator;
const mem = vm.mem;
allocator.free(mem);
const alignment = vm.mem_alignment;
allocator.rawFree(mem, alignment, @returnAddress());
}

fn instantiate(vm: *VM, module: *ModuleInstance, opts: ModuleInstantiateOpts) InstantiateError!void {
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