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De-duplicate and fix code of value-set backed function pointer removal #6985

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Jun 30, 2022
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De-duplicate and fix code of value-set backed function pointer removal #6985

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51 changes: 51 additions & 0 deletions regression/goto-instrument/value-set-fi-fp-removal7/main.c
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Original file line number Diff line number Diff line change
@@ -0,0 +1,51 @@
#include <assert.h>

struct PtrWrapperInner
{
int *value;
};

struct PtrWrapper
{
int *value;
struct PtrWrapperInner inner;
};

struct AltPtrWrapperInner
{
int *value;
};

struct AltPtrWrapper
{
unsigned int *value;
// A) Doesn't work
struct AltPtrWrapperInner inner;
// B) Works
// struct PtrWrapperInner inner;
};

void fn(struct PtrWrapper wrapper)
{
assert(*wrapper.value == 10);
assert(*wrapper.inner.value == 10);
}

int main()
{
int ret = 10;
int *ptr = &ret;

struct AltPtrWrapper alt;
alt.inner.value = ptr;
alt.value = ptr;

// Casting the structure itself works.
struct PtrWrapper wrapper = *(struct PtrWrapper *)&alt;
assert(*wrapper.value == 10);
assert(*wrapper.inner.value == 10);

// This only works if there is one level of casting.
int (*alias)(struct AltPtrWrapper) = (int (*)(struct AltPtrWrapper))fn;
alias(alt);
}
11 changes: 11 additions & 0 deletions regression/goto-instrument/value-set-fi-fp-removal7/test.desc
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@@ -0,0 +1,11 @@
CORE
main.c
--value-set-fi-fp-removal
^VERIFICATION SUCCESSFUL$
^EXIT=0$
^SIGNAL=0$
--
--
This test checks that the value-set-fi-based function pointer removal performs
suitable type conversion when argument and parameter types do not match. Source
file is a copy of cbmc/Function_Pointer19/main.c.
180 changes: 13 additions & 167 deletions src/goto-instrument/value_set_fi_fp_removal.cpp
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Expand Up @@ -8,176 +8,14 @@ Author: Daniel Kroening, [email protected]

#include "value_set_fi_fp_removal.h"

#include <goto-programs/goto_model.h>

#include <pointer-analysis/value_set_analysis_fi.h>

#include <util/c_types.h>
#include <util/fresh_symbol.h>
#include <util/message.h>
#include <util/namespace.h>
#include <util/pointer_expr.h>
#include <util/std_code.h>

#ifdef USE_STD_STRING
# include <util/dstring.h>
#endif

void fix_argument_types(
code_function_callt &function_call,
const namespacet &ns)
{
const code_typet &code_type =
to_code_type(ns.follow(function_call.function().type()));

const code_typet::parameterst &function_parameters = code_type.parameters();

code_function_callt::argumentst &call_arguments = function_call.arguments();

for(std::size_t i = 0; i < function_parameters.size(); i++)
{
// casting pointers might result in more arguments than function parameters
if(i < call_arguments.size())
{
call_arguments[i] = typecast_exprt::conditional_cast(
call_arguments[i], function_parameters[i].type());
}
}
}

void fix_return_type(
code_function_callt &function_call,
goto_programt &dest,
goto_modelt &goto_model)
{
// are we returning anything at all?
if(function_call.lhs().is_nil())
return;

const namespacet ns(goto_model.symbol_table);

const code_typet &code_type =
to_code_type(ns.follow(function_call.function().type()));

// type already ok?
if(function_call.lhs().type() == code_type.return_type())
return;

const symbolt &function_symbol =
ns.lookup(to_symbol_expr(function_call.function()).get_identifier());

symbolt &tmp_symbol = get_fresh_aux_symbol(
code_type.return_type(),
id2string(function_call.source_location().get_function()),
"tmp_return_val_" + id2string(function_symbol.base_name),
function_call.source_location(),
function_symbol.mode,
goto_model.symbol_table);

const symbol_exprt tmp_symbol_expr = tmp_symbol.symbol_expr();

exprt old_lhs = function_call.lhs();
function_call.lhs() = tmp_symbol_expr;

dest.add(goto_programt::make_assignment(
code_assignt(old_lhs, typecast_exprt(tmp_symbol_expr, old_lhs.type()))));
}

void remove_function_pointer(
goto_programt &goto_program,
goto_programt::targett target,
const std::set<symbol_exprt> &functions,
goto_modelt &goto_model)
{
const exprt &function = as_const(*target).call_function();
PRECONDITION(function.id() == ID_dereference);

// this better have the right type
code_typet call_type = to_code_type(function.type());

// refine the type in case the forward declaration was incomplete
if(call_type.has_ellipsis() && call_type.parameters().empty())
{
call_type.remove_ellipsis();
for(const auto &argument : as_const(*target).call_arguments())
call_type.parameters().push_back(code_typet::parametert(argument.type()));
}

const exprt &pointer = to_dereference_expr(function).pointer();

// the final target is a skip
goto_programt final_skip;
goto_programt::targett t_final = final_skip.add(goto_programt::make_skip());

// build the calls and gotos

goto_programt new_code_calls;
goto_programt new_code_gotos;

for(const auto &fun : functions)
{
// call function
goto_programt::targett t1 =
new_code_calls.add(goto_programt::make_function_call(
as_const(*target).call_lhs(),
fun,
as_const(*target).call_arguments(),
target->source_location()));

// the signature of the function might not match precisely
const namespacet ns(goto_model.symbol_table);
fix_argument_types(to_code_function_call(t1->code_nonconst()), ns);
fix_return_type(
to_code_function_call(t1->code_nonconst()), new_code_calls, goto_model);

// goto final
new_code_calls.add(goto_programt::make_goto(t_final, true_exprt()));

// goto to call
address_of_exprt address_of(fun, pointer_type(fun.type()));

new_code_gotos.add(goto_programt::make_goto(
t1,
equal_exprt(
pointer,
typecast_exprt::conditional_cast(address_of, pointer.type()))));
}

goto_programt::targett t =
new_code_gotos.add(goto_programt::make_assertion(false_exprt()));
t->source_location_nonconst().set_property_class("pointer dereference");
t->source_location_nonconst().set_comment("invalid function pointer");

goto_programt new_code;

// patch them all together
new_code.destructive_append(new_code_gotos);
new_code.destructive_append(new_code_calls);
new_code.destructive_append(final_skip);

// set locations
for(auto &instruction : new_code.instructions)
{
irep_idt property_class =
instruction.source_location().get_property_class();
irep_idt comment = instruction.source_location().get_comment();
instruction.source_location_nonconst() = target->source_location();
if(!property_class.empty())
instruction.source_location_nonconst().set_property_class(property_class);
if(!comment.empty())
instruction.source_location_nonconst().set_comment(comment);
}

goto_programt::targett next_target = target;
next_target++;

goto_program.destructive_insert(next_target, new_code);
#include <goto-programs/goto_model.h>
#include <goto-programs/remove_function_pointers.h>

// We preserve the original dereferencing to possibly catch
// further pointer-related errors.
*target = goto_programt::make_other(
code_expressiont(function), function.source_location());
}
#include <pointer-analysis/value_set_analysis_fi.h>

void value_set_fi_fp_removal(
goto_modelt &goto_model,
Expand Down Expand Up @@ -210,7 +48,7 @@ void value_set_fi_fp_removal(
const auto &pointer = to_dereference_expr(function).pointer();
auto addresses = value_sets.get_values(f.first, target, pointer);

std::set<symbol_exprt> functions;
std::unordered_set<symbol_exprt, irep_hash> functions;

for(const auto &address : addresses)
{
Expand All @@ -230,8 +68,16 @@ void value_set_fi_fp_removal(
<< " function: " << f.get_identifier() << messaget::eom;

if(functions.size() > 0)
{
remove_function_pointer(
f.second.body, target, functions, goto_model);
message_handler,
goto_model.symbol_table,
f.second.body,
f.first,
target,
functions,
true);
}
}
}
}
Expand Down