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Error in stack frame diagram? #45

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pixelshot91 opened this issue Feb 18, 2024 · 2 comments · May be fixed by #48
Open

Error in stack frame diagram? #45

pixelshot91 opened this issue Feb 18, 2024 · 2 comments · May be fixed by #48

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@pixelshot91
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In https://highassurance.rs/chp4/assure_stack_1.html#the-stack, the stack diagram show that the stack frame for the square function still exist under all the recursive_count_down stack frames.
https://github.com/tnballo/high-assurance-rust/blob/main/src/chp4/stack_example.svg

But in my understanding, the stack frame of square should pop before the stack frames of recursive_count_down are added.

Indeed if I print the backtrace with:

        println!("Boom!");
        println!("{:#?}", backtrace::Backtrace::capture());
        return x;

I get:

Backtrace [
    { fn: "stack_test::recursive_count_down", file: "./src/main.rs", line: 8 },
    { fn: "stack_test::recursive_count_down", file: "./src/main.rs", line: 13 },
    { fn: "stack_test::recursive_count_down", file: "./src/main.rs", line: 13 },
    { fn: "stack_test::recursive_count_down", file: "./src/main.rs", line: 13 },
    { fn: "stack_test::recursive_count_down", file: "./src/main.rs", line: 13 },
    { fn: "stack_test::main", file: "./src/main.rs", line: 35 },
...

Did I miss something ?
@tnballo
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tnballo commented Feb 21, 2024

Nope, you're not missing anything - this is indeed an error in the diagrams!

let _ = recursive_count_down(square(x)); does evaluate square(x) first and pop the frame, before calling recursive_count_down.

I'll fix the diagrams and add a blurb on printing the stack trace as you've described (seems there's no built-in environment variable to get a backtrace on stack overflow automatically, although the aptly-named backtrace-on-stack-overflow crate can help debug this issue in larger programs.

@tnballo
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tnballo commented Feb 21, 2024

Also thank you for spotting this error 💯

@pixelshot91 pixelshot91 linked a pull request Feb 22, 2024 that will close this issue
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chp4: stack_example.svg: remove 'square' stack frame pixelshot91/high-assurance-rust
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@pixelshot91 @tnballo