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stage2 LLVM: Use a packed aggregate for union payload init

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Without the packed qualifier, the type layout that we use to
initialize doesn't match the correct layout of the underlying
storage, causing corrupted data and past-the-end writes.
This commit is contained in:
Cody Tapscott 2022-10-10 23:57:48 -07:00 committed by Andrew Kelley
parent 8635c18e40
commit e6ebdcb82e
3 changed files with 32 additions and 2 deletions
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4
src/codegen/llvm.zig
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@ -8897,7 +8897,7 @@ pub const FuncGen = struct {
return union_llvm_ty.constInt(tag_int, .False);
}
assert(isByRef(union_ty));
// The llvm type of the alloca will the the named LLVM union type, which will not
// The llvm type of the alloca will be the named LLVM union type, and will not
// necessarily match the format that we need, depending on which tag is active. We
// must construct the correct unnamed struct type here and bitcast, in order to
// then set the fields appropriately.
@ -8922,7 +8922,7 @@ pub const FuncGen = struct {
const fields: [2]*llvm.Type = .{
field_llvm_ty, self.context.intType(8).arrayType(padding_len),
};
break :p self.context.structType(&fields, fields.len, .False);
break :p self.context.structType(&fields, fields.len, .True);
};
if (layout.tag_size == 0) {
const fields: [1]*llvm.Type = .{payload};

1
test/behavior.zig
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@ -100,6 +100,7 @@ test {
_ = @import("behavior/bugs/12928.zig");
_ = @import("behavior/bugs/12945.zig");
_ = @import("behavior/bugs/12984.zig");
_ = @import("behavior/bugs/13128.zig");
_ = @import("behavior/byteswap.zig");
_ = @import("behavior/byval_arg_var.zig");
_ = @import("behavior/call.zig");

29
test/behavior/bugs/13128.zig Normal file
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@ -0,0 +1,29 @@
const std = @import("std");
const builtin = @import("builtin");
const expect = std.testing.expect;
const U = union(enum) {
x: u128,
y: [17]u8,
};
fn foo(val: U) !void {
try expect(val.x == 1);
}
test "runtime union init, most-aligned field != largest" {
if (builtin.zig_backend == .stage2_c) return error.SkipZigTest; // TODO
if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO
if (builtin.zig_backend == .stage2_x86_64) return error.SkipZigTest; // TODO
if (builtin.zig_backend == .stage2_wasm) return error.SkipZigTest; // TODO
var x: u8 = 1;
try foo(.{ .x = x });
const val: U = @unionInit(U, "x", x);
try expect(val.x == 1);
const val2: U = .{ .x = x };
try expect(val2.x == 1);
}