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std.mem.zeroes: Zero out entire extern union, including padding #17286

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Merged
andrewrk merged 1 commit into from
Oct 1, 2023
Merged

std.mem.zeroes: Zero out entire extern union, including padding #17286

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19 changes: 12 additions & 7 deletions lib/std/mem.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -254,7 +254,7 @@ pub fn zeroes(comptime T: type) T {
var structure: T = undefined;
inline for (struct_info.fields) |field| {
if (!field.is_comptime) {
@field(structure, field.name) = zeroes(@TypeOf(@field(structure, field.name)));
@field(structure, field.name) = zeroes(field.type);
}
}
return structure;
Expand Down Expand Up @@ -292,12 +292,11 @@ pub fn zeroes(comptime T: type) T {
return @splat(zeroes(info.child));
},
.Union => |info| {
if (comptime meta.containerLayout(T) == .Extern) {
// The C language specification states that (global) unions
// should be zero initialized to the first named member.
return @unionInit(T, info.fields[0].name, zeroes(info.fields[0].type));
if (info.layout == .Extern) {
var item: T = undefined;
@memset(asBytes(&item), 0);
return item;
}

@compileError("Can't set a " ++ @typeName(T) ++ " to zero.");
},
.ErrorUnion,
Expand All @@ -318,10 +317,14 @@ pub fn zeroes(comptime T: type) T {
test "zeroes" {
const C_struct = extern struct {
x: u32,
y: u32,
y: u32 align(128),
};

var a = zeroes(C_struct);

// Extern structs should have padding zeroed out.
try testing.expectEqualSlices(u8, &[_]u8{0} ** @sizeOf(@TypeOf(a)), asBytes(&a));

a.y += 10;

try testing.expect(a.x == 0);
Expand Down Expand Up @@ -402,9 +405,11 @@ test "zeroes" {

var c = zeroes(C_union);
try testing.expectEqual(@as(u8, 0), c.a);
try testing.expectEqual(@as(u32, 0), c.b);

comptime var comptime_union = zeroes(C_union);
try testing.expectEqual(@as(u8, 0), comptime_union.a);
try testing.expectEqual(@as(u32, 0), comptime_union.b);

// Ensure zero sized struct with fields is initialized correctly.
_ = zeroes(struct { handle: void });
Expand Down