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Merged
merged 1 commit into from
May 13, 2021
Merged

Check for validity of pointers in assigns clause #6077

merged 1 commit into from
May 13, 2021

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ArenBabikian
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Consider the following example:

void bar(int *x, int *y) __CPROVER_assigns(*x, *y)
{
  *x = 3;
  if(y != NULL)
    *y = 5;
}

void foo(int *x) __CPROVER_assigns(*x)
{
  bar(x, NULL);
  *x = 3;
}

The potential problem in this case is that foo calls bar by passing a null pointer. Of course, considering the contents of bar, this will not be problematic. However, the assigns clause for bar is not aware of what is inside bar, so the assigns clause previously could not handle the null pointer.

This PR adds support for such cases, by checking for passed null pointers at the goto program level.

Note: currently, this PR only supports pointers, which is required for function contracts for the coreJSON project.

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feliperodri
feliperodri requested changes May 4, 2021
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I few minor comments.

@feliperodri feliperodri added aws Bugs or features of importance to AWS CBMC users Code Contracts Function and loop contracts labels May 6, 2021
@feliperodri feliperodri changed the title Supports passing NULL to a function that may assign to the corresponding parameter Avoid havoc of NULL assignable symbols May 6, 2021
@ArenBabikian ArenBabikian mentioned this pull request May 6, 2021
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@feliperodri feliperodri changed the title Avoid havoc of NULL assignable symbols Check for validity of pointers in assigns clause May 6, 2021
SaswatPadhi
SaswatPadhi suggested changes May 6, 2021
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@ArenBabikian ArenBabikian force-pushed the assign-to-null branch 2 times, most recently from 7e05751 to a9712e2 Compare May 10, 2021 16:37
@ArenBabikian ArenBabikian mentioned this pull request May 10, 2021
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feliperodri
feliperodri approved these changes May 10, 2021
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LGTM

SaswatPadhi
SaswatPadhi suggested changes May 10, 2021
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Mostly LGTM, but I left a few minor comments.

Also, please check why the builds are failing.

@ArenBabikian ArenBabikian mentioned this pull request May 11, 2021
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@feliperodri feliperodri requested a review from SaswatPadhi May 11, 2021 20:06
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codecov bot commented May 11, 2021 •
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Codecov Report

Merging #6077 (d5402d9) into develop (4c14789) will increase coverage by 0.59%.
The diff coverage is 100.00%.

Impacted file tree graph

@@             Coverage Diff             @@
##           develop    #6077      +/-   ##
===========================================
+ Coverage    74.52%   75.12%   +0.59%     
===========================================
  Files         1447     1447              
  Lines       157808   157825      +17     
===========================================
+ Hits        117610   118563     +953     
+ Misses       40198    39262     -936
Impacted Files Coverage Δ
src/goto-instrument/code_contracts.cpp 85.03% <100.00%> (+0.29%) ⬆️
src/ansi-c/expr2c.cpp 69.20% <0.00%> (+0.09%) ⬆️
src/solvers/smt2/smt2_conv.cpp 60.63% <0.00%> (+0.22%) ⬆️
src/solvers/lowering/byte_operators.cpp 92.16% <0.00%> (+0.36%) ⬆️
src/util/pointer_expr.h 77.71% <0.00%> (+0.36%) ⬆️
src/ansi-c/c_typecast.cpp 79.00% <0.00%> (+0.55%) ⬆️
src/goto-programs/goto_program.h 91.63% <0.00%> (+0.64%) ⬆️
src/goto-instrument/wmm/cycle_collection.cpp 88.04% <0.00%> (+3.26%) ⬆️
src/goto-instrument/rw_set.h 47.27% <0.00%> (+5.45%) ⬆️
src/goto-instrument/wmm/event_graph.h 71.29% <0.00%> (+6.48%) ⬆️
... and 12 more

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SaswatPadhi
SaswatPadhi reviewed May 11, 2021
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Almost there. A couple of previous comments that are unaddressed:

@ArenBabikian
Adds support for null pointers passed as function call parameter.
d5402d9 
This adds support for the cases where a null pointer is passed as
a parameter to a function that may assign to it. We add checks in
goto program to handle such instances as special cases of assigns
clause handling.
SaswatPadhi
SaswatPadhi approved these changes May 12, 2021
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LGTM. Thanks for all the changes! 😄

chrisr-diffblue
chrisr-diffblue approved these changes May 13, 2021
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LGTM

@SaswatPadhi SaswatPadhi merged commit 0b4a3e8 into diffblue:develop May 13, 2021
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@feliperodri feliperodri feliperodri approved these changes

@SaswatPadhi SaswatPadhi SaswatPadhi approved these changes

@chrisr-diffblue chrisr-diffblue chrisr-diffblue approved these changes

@martin-cs martin-cs Awaiting requested review from martin-cs martin-cs is a code owner

@peterschrammel peterschrammel Awaiting requested review from peterschrammel peterschrammel is a code owner

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