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Soundness: try/catch is checked as if the catch block always runs

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#364 0 comentários 0 reações 0 responsáveis Ver no GitHub

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Avaliação

Dificuldade
4/5
Tempo estimado
3-5 dias
Facilidade para iniciantes
50/100
Tipo de issue
Bug
Clareza
Claramente especificada
Status de atividade
Ativa
Stack de tecnologia
java
Domínio
compilers

Direção de pesquisa

Locate where the verifier visits try/catch statements (search the visitor/checker for the try-statement case) and compare it with how if/else merges branch states at the join point — the issue says try/catch is currently sequenced instead of merged. Work out how both branches (normal exit from try, entry into catch at an arbitrary point) should be joined, and how the state after the join relates to the state on entry. Done means both reproducers in the issue report errors, the swapped-value case reports correctly, and existing verification tests still pass; add the reproducers as regression tests.

Escrita pelo modelo de indexação a partir do texto da issue.

Descrição

bug

Impact: a real bug passes verification (false negative).

Description

The verifier checks try and catch blocks one after the other, so after a try/catch a variable keeps whatever the catch block last assigned. The path where the try finishes normally is lost. An if/else instead merges both branches after the join, and try/catch should be merged the same way.

Also, an exception can be thrown at any point in the try. The catch block should therefore not assume the try ran to completion, or that it never ran at all.

Minimal reproducer

import liquidjava.specification.ExternalRefinementsFor;
import liquidjava.specification.StateRefinement;
import liquidjava.specification.StateSet;

@ExternalRefinementsFor("java.lang.Throwable")
@StateSet({"withThrowable", "noThrowable"})
interface ThrowableRefinements {
    @StateRefinement(to = "noThrowable(this)")
    void Throwable(String message);

    @StateRefinement(to = "withThrowable(this)")
    void Throwable(String message, Throwable cause);

    @StateRefinement(from = "noThrowable(this)", to = "withThrowable(this)")
    Throwable initCause(Throwable cause);
}

public class Repro {
    static void load() throws Exception { throw new Exception("x"); }

    static void m() {
        Throwable t = new Throwable("start");
        try {
            load();
            t = new Throwable("try", new RuntimeException()); // withThrowable
        } catch (Exception e) {
            t = new Throwable("catch");                       // noThrowable
        }
        t.initCause(new RuntimeException()); // not reported, but t is withThrowable if load() returns
    }
}

Expected: a State Refinement Error on t.initCause(...), because t may be withThrowable.

Actual: Correct! Passed Verification.

Same bug with value refinements

static void m() {
    int y = 0;
    try {
        load();
        y = -5;
    } catch (Exception e) {
        y = 7;
    }
    @Refinement("_ > 0")
    int z = y; // not reported, but y == -5 if load() returns
}

Actual: Correct! Passed Verification. If the values are swapped (5 in the try, -5 in the catch), the error is reported, but as z == -5 is not a subtype of z > 0: only the catch path is considered.

Found while reviewing #362 (catch parameters, #333).

Linguagem predominante
Java
Estrelas
67
Forks
36
Merge médio
2d 3h
PRs com merge (30d)
29

Preparar o ambiente

Primeiros passos

  1. Leia a issue inteira e depois o guia de contribuição do projeto.
  2. Comente na issue dizendo que vai assumir — evita que duas pessoas façam o mesmo trabalho.
  3. Faça um fork do repositório e trabalhe em uma branch.
  4. Abra um pull request que referencie o número da issue.

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