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document why sizeof(void) works #2279

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Merged
merged 1 commit into from
Jun 5, 2018
Merged

document why sizeof(void) works #2279

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30 changes: 17 additions & 13 deletions src/ansi-c/c_typecheck_expr.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -935,26 +935,30 @@ void c_typecheck_baset::typecheck_expr_sizeof(exprt &expr)
throw 0;
}

exprt new_expr;

if(type.id()==ID_c_bit_field)
{
err_location(expr);
error() << "sizeof cannot be applied to bit fields" << eom;
throw 0;
}

if(type.id()==ID_empty &&
expr.operands().size()==1 &&
expr.op0().id()==ID_dereference &&
expr.op0().op0().type()==pointer_type(void_type()))
type=char_type();

exprt new_expr=size_of_expr(type, *this);

if(new_expr.is_nil())
else if(type.id() == ID_empty)
{
err_location(expr);
error() << "type has no size: " << to_string(type) << eom;
throw 0;
// This is a gcc extension.
// https://gcc.gnu.org/onlinedocs/gcc-4.8.0/gcc/Pointer-Arith.html
new_expr = size_of_expr(char_type(), *this);
}
else
{
new_expr = size_of_expr(type, *this);

if(new_expr.is_nil())
{
err_location(expr);
error() << "type has no size: " << to_string(type) << eom;
throw 0;
}
}

new_expr.swap(expr);
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44 changes: 35 additions & 9 deletions src/solvers/flattening/bv_pointers.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -348,10 +348,18 @@ bvt bv_pointerst::convert_pointer_type(const exprt &expr)
CHECK_RETURN(bv.size()==bits);

typet pointer_sub_type=it->type().subtype();

if(pointer_sub_type.id()==ID_empty)
pointer_sub_type=char_type();
size=pointer_offset_size(pointer_sub_type, ns);
CHECK_RETURN(size>0);
{
// This is a gcc extension.
// https://gcc.gnu.org/onlinedocs/gcc-4.8.0/gcc/Pointer-Arith.html
size = 1;
}
else
{
size = pointer_offset_size(pointer_sub_type, ns);
CHECK_RETURN(size > 0);
}
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Yes, looks good, but this same change should be applied in the other two places in this file using char_type(). At that point it may be possible to get rid of #include <util/c_types.h>.

}
}

Expand Down Expand Up @@ -423,10 +431,19 @@ bvt bv_pointerst::convert_pointer_type(const exprt &expr)
bv=convert_bv(expr.op0());

typet pointer_sub_type=expr.op0().type().subtype();
mp_integer element_size;

if(pointer_sub_type.id()==ID_empty)
pointer_sub_type=char_type();
mp_integer element_size=pointer_offset_size(pointer_sub_type, ns);
DATA_INVARIANT(element_size>0, "object size expected to be positive");
{
// This is a gcc extension.
// https://gcc.gnu.org/onlinedocs/gcc-4.8.0/gcc/Pointer-Arith.html
element_size = 1;
}
else
{
element_size = pointer_offset_size(pointer_sub_type, ns);
DATA_INVARIANT(element_size > 0, "object size expected to be positive");
}

offset_arithmetic(bv, element_size, neg_op1);

Expand Down Expand Up @@ -488,10 +505,19 @@ bvt bv_pointerst::convert_bitvector(const exprt &expr)
bvt bv=bv_utils.sub(op0, op1);

typet pointer_sub_type=expr.op0().type().subtype();
mp_integer element_size;

if(pointer_sub_type.id()==ID_empty)
pointer_sub_type=char_type();
mp_integer element_size=pointer_offset_size(pointer_sub_type, ns);
DATA_INVARIANT(element_size>0, "object size expected to be positive");
{
// This is a gcc extension.
// https://gcc.gnu.org/onlinedocs/gcc-4.8.0/gcc/Pointer-Arith.html
element_size = 1;
}
else
{
element_size = pointer_offset_size(pointer_sub_type, ns);
DATA_INVARIANT(element_size > 0, "object size expected to be positive");
}

if(element_size!=1)
{
Expand Down