Rearchitect var args support (making it actually work) [blocks: #4329] by tautschnig · Pull Request #4238 · diffblue/cbmc

tautschnig · 2019-02-21T00:39:05Z

Previously all the logic to access values of variable argument lists was put
into our va_arg() implementation. This required guessing what the parameters
could have been, and did not take into account the initial value passed to
va_start.

Now va_start triggers constructing an array of pointers to parameters, the first
of which is the original argument to va_start. The va_list is then just a
pointer to the first element of the array. va_arg just increments the pointer.
goto_program conversion places a side_effect_exprt where va_start was, and
goto-symex populates the array with the actual values applicable for a
particular invocation of the function.

Each commit message has a non-empty body, explaining why the change was made.
n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
n/a My commit message includes data points confirming performance improvements (if claimed).
My PR is restricted to a single feature or bugfix.
n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

tautschnig · 2019-02-21T23:11:29Z

Apologies for dragging in some many reviewers, that's just because I had to add the commits from #2068 to make things also work with the approach that Visual Studio uses for var args. Just the last three commits in this PR are actually new.

allredj

✔️
Passed Diffblue compatibility checks (cbmc commit: ec8797e).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/102429546

allredj

⚠️
This PR failed Diffblue compatibility checks (cbmc commit: 93ba1d6).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/102970072
Status will be re-evaluated on next push.
Common spurious failures:

the cbmc commit has disappeared in the mean time (e.g. in a force-push)
the author is not in the list of contributors (e.g. first-time contributors).
the compatibility was already broken by an earlier merge.

allredj

⚠️
This PR failed Diffblue compatibility checks (cbmc commit: 7755806).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/102970915
Status will be re-evaluated on next push.
Common spurious failures:

the cbmc commit has disappeared in the mean time (e.g. in a force-push)
the author is not in the list of contributors (e.g. first-time contributors).
the compatibility was already broken by an earlier merge.

allredj

✔️
Passed Diffblue compatibility checks (cbmc commit: 00f323d).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/104075038

martin-cs

Very little touches my areas of responsibility but those bits ae fine.

allredj

✔️
Passed Diffblue compatibility checks (cbmc commit: 0c5f08c).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/105810019

allredj

⚠️
This PR failed Diffblue compatibility checks (cbmc commit: dfd298a).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/108813088
Status will be re-evaluated on next push.
Common spurious failures include: the cbmc commit has disappeared in the mean time (e.g. in a force-push); the author is not in the list of contributors (e.g. first-time contributors); compatibility was already broken by an earlier merge.

kroening · 2019-05-15T09:46:47Z

regression/cbmc/va_list3/windows-preprocessed.desc

+^SIGNAL=0$
+^VERIFICATION SUCCESSFUL$
+--
+^warning: ignoring


Can you add a comment, say in the .desc file, how windows-preprocessed.i was produced?

It was kind-of noted in the commit message, but I'll add a note in the .desc file as well!

kroening · 2019-05-15T09:47:48Z

src/ansi-c/expr2c.cpp

-      return convert_function(src, "gcc_builtin_va_arg_next");
+    else if(statement == ID_va_start)
+      return convert_function(src, CPROVER_PREFIX "va_start");
    else


Does dumping still work with that change? Meaning do we still get a C program that gcc compiles?

The changes (in this PR) to goto-instrument/goto_program2code.cpp take care of this.

kroening · 2019-05-15T09:54:23Z

src/solvers/flattening/bv_pointers.cpp

-      op_type.id() == ID_c_enum_tag || op_type.id() == ID_bv)
+      can_cast_type<bitvector_typet>(op_type) || op_type.id() == ID_c_enum ||
+      op_type.id() == ID_c_enum_tag)
    {


Note that ID_bool is not a bit vector type, i.e., this case is lost.

Ah, thanks, fixed!

kroening · 2019-05-15T09:56:19Z

src/goto-symex/symex_builtin_functions.cpp

+      fits_slot,
+      typecast_exprt::conditional_cast(parameter_expr, void_ptr_type),
+      typecast_exprt::conditional_cast(
+        address_of_exprt{parameter_expr}, void_ptr_type)};


I am a bit surprised that this distinction needs to be a formula -- sure this isn't known at compile time?

I believe that almost always the simplifier will be able to take care of this - but apart from that this used to construct an object that doesn't even exist at compile time, so I'm not really sure what you'd like me to do?

Even floating-point values are ok to just be re-interpreted as bit strings.

This will aid debugging as Visual Studio mostly just uses macros to implement the va_* functions.

We carry typedef names all the way now, there is no need for additional annotations to preserve the typedef name of va_list for dump-c.

Previously all the logic to access values of variable argument lists was put into our va_arg() implementation. This required guessing what the parameters could have been, and did not take into account the initial value passed to va_start. Now va_start triggers constructing an array of pointers to parameters, the first of which is the original argument to va_start. The va_list is then just a pointer to the first element of the array. va_arg just increments the pointer. goto_program conversion places a side_effect_exprt where va_start was, and goto-symex populates the array with the actual values applicable for a particular invocation of the function.

allredj

✔️
Passed Diffblue compatibility checks (cbmc commit: 18cbd69).
Build URL: https://travis-ci.com/diffblue/test-gen/builds/111914482

tautschnig added the bugfix label Feb 21, 2019

tautschnig requested review from chrisr-diffblue, danpoe, hannes-steffenhagen-diffblue, kroening, martin-cs, peterschrammel, pkesseli and smowton as code owners February 21, 2019 00:39

tautschnig changed the title ~~Rearchitect var args support (making it actually work)~~ Rearchitect var args support (making it actually work) [blocks: #4329] Feb 21, 2019

tautschnig added the blocker label Feb 21, 2019

tautschnig force-pushed the var-args branch from 40a5b94 to 278efde Compare February 21, 2019 01:17

tautschnig self-assigned this Feb 21, 2019

tautschnig force-pushed the var-args branch from 278efde to d1cbaad Compare February 21, 2019 22:27

tautschnig requested review from allredj and romainbrenguier as code owners February 21, 2019 22:27

tautschnig changed the title ~~Rearchitect var args support (making it actually work) [blocks: #4329]~~ Rearchitect var args support (making it actually work) [depends-on: #2068, blocks: #4329] Feb 21, 2019

tautschnig added the dependent - do not merge label Feb 21, 2019

smowton approved these changes Feb 22, 2019

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tautschnig force-pushed the var-args branch 2 times, most recently from 33cbaa7 to 6c85222 Compare February 22, 2019 20:05

tautschnig changed the title ~~Rearchitect var args support (making it actually work) [depends-on: #2068, blocks: #4329]~~ Rearchitect var args support (making it actually work) [blocks: #4329] Feb 26, 2019

tautschnig removed the dependent - do not merge label Feb 26, 2019

tautschnig force-pushed the var-args branch from 6c85222 to ec8797e Compare February 26, 2019 19:17

tautschnig assigned kroening, peterschrammel and chrisr-diffblue and unassigned tautschnig Feb 26, 2019

allredj reviewed Feb 27, 2019

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peterschrammel approved these changes Mar 3, 2019

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peterschrammel removed their assignment Mar 3, 2019

tautschnig force-pushed the var-args branch from ec8797e to 93ba1d6 Compare March 3, 2019 21:08

tautschnig removed the Needs rebase label Mar 3, 2019

tautschnig unassigned chrisr-diffblue Mar 3, 2019

tautschnig force-pushed the var-args branch from 93ba1d6 to 7755806 Compare March 3, 2019 21:26

allredj reviewed Mar 3, 2019

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tautschnig force-pushed the var-args branch 2 times, most recently from 617c92a to 00f323d Compare March 12, 2019 12:30

allredj reviewed Mar 12, 2019

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martin-cs approved these changes Mar 26, 2019

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tautschnig force-pushed the var-args branch from 00f323d to 0c5f08c Compare March 26, 2019 08:13

allredj reviewed Mar 26, 2019

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tautschnig force-pushed the var-args branch from 0c5f08c to dfd298a Compare April 18, 2019 07:24

allredj reviewed Apr 18, 2019

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tautschnig force-pushed the var-args branch from dfd298a to cdc6726 Compare April 30, 2019 23:44

kroening reviewed May 15, 2019

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tautschnig added 4 commits May 15, 2019 11:24

Typecast to pointer: support all bitvector types

163f629

Even floating-point values are ok to just be re-interpreted as bit strings.

Add Visual Studio 2017 preprocessed variant of va_list3 test

5358144

This will aid debugging as Visual Studio mostly just uses macros to implement the va_* functions.

Remove ID_gcc_builtin_va_list

f5a14db

We carry typedef names all the way now, there is no need for additional annotations to preserve the typedef name of va_list for dump-c.

tautschnig force-pushed the var-args branch from cdc6726 to 18cbd69 Compare May 15, 2019 11:24

allredj reviewed May 15, 2019

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kroening approved these changes May 15, 2019

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kroening merged commit bc76446 into diffblue:develop May 15, 2019

tautschnig deleted the var-args branch May 16, 2019 08:39

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