[ICE] Incorrect memcpy for struct when alignment < size

[jyn514]

Expected behavior
RCC should memcpy the whole struct up to the nearest multiple of the alignment.

Actual Behavior
RCC only copies the size of the struct, without the padding bits.

Code

int main() {
	struct S { int *y, z; } s, ss;
	s = ss;
}
The application panicked (crashed).
Message:  `size` is smaller than `dest` and `src`'s alignment value.
Location: /home/joshua/.local/lib/cargo/registry/src/github.com-1ecc6299db9ec823/cranelift-frontend-0.58.0/src/frontend.rs:820

Backtrace

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ BACKTRACE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
                          (4 post panic frames hidden)                          
 4: cranelift_frontend::frontend::FunctionBuilder::emit_small_memmove::ha82eaace5e0d7fa5
    at /home/joshua/.local/lib/cargo/registry/src/github.com-1ecc6299db9ec823/cranelift-frontend-0.58.0/src/frontend.rs:820
 5: rcc::ir::expr::<impl rcc::ir::Compiler>::assignment::hba6a3763c064d501
    at src/ir/expr.rs:511
 6: rcc::ir::expr::<impl rcc::ir::Compiler>::compile_expr::hf2862280ec6077e1
    at src/ir/expr.rs:102
 7: rcc::ir::stmt::<impl rcc::ir::Compiler>::compile_stmt::h7e24c153b5470ada
    at src/ir/stmt.rs:37
 8: rcc::ir::stmt::<impl rcc::ir::Compiler>::compile_all::hf59a3cda5830301d
    at src/ir/stmt.rs:15
 9: rcc::ir::Compiler::compile_func::hff5573813724a524
    at src/ir/mod.rs:321
10: rcc::ir::compile::h9967cd2f3830dff1
    at src/ir/mod.rs:75
11: rcc::compile::h56c7e62b242f942d
    at src/lib.rs:179
12: rcc::real_main::h6aa73fa5e305122a
    at src/main.rs:109
13: rcc::main::hd71a6cc32e4b0a3f
    at src/main.rs:172

Thanks to @Byter09 for the fuzzing.

[jyn514]

Hmm ... maybe the issue here is that the size should be rounded up to the nearest multiple of the alignment?

[jyn514]

Instructions:

• In src/arch/mod.rs, get the alignment with self.align()
• If the size is an Ok variant, round it up to the nearest multiple of the alignment (e.g. using one of https://users.rust-lang.org/t/solved-rust-round-usize-to-nearest-multiple-of-8/25549).