There is a subtle but important issue with the varargs code in yajl_config() and yajl_gen_config(). The problem is with this code:
int
yajl_config(yajl_handle h, yajl_option opt, ...)
{
int rv = 1;
va_list ap;
va_start(ap, opt);
The opt parameter is declared as the enum type yajl_option. But when you pass "opt" to va_start, it undergoes integer promotion, which results in undefined behavior. Clang is adding a warning for this, which is how this issue came to our attention.
You can see a bit of information about this here. The key part is:
// Undefined by C99 7.15.1.4p4 (va_start):
// "If the parameter parmN is declared with the register storage
// class, with a function or array type, or with a type that is
// not compatible with the type that results after application of
// the default argument promotions, the behavior is undefined."
Enum gets promoted to int, which is not compatible with int.
There are a couple possible solutions:
The easiest one would be to change the declared type of the parameter to int or unsigned int. That should be interface-compatible with existing clients.
Another option would be to rearrange the parameters so that the yajl_handle parameter would be passed to va_start() instead. Since that type doesn't undergo promotion, it doesn't trigger the undefined behavior. However this would be an API-incompatible change.
There is a subtle but important issue with the varargs code in
yajl_config()andyajl_gen_config(). The problem is with this code:The
optparameter is declared as the enum typeyajl_option. But when you pass "opt" to va_start, it undergoes integer promotion, which results in undefined behavior. Clang is adding a warning for this, which is how this issue came to our attention.You can see a bit of information about this here. The key part is:
Enum gets promoted to int, which is not compatible with int.
There are a couple possible solutions:
intorunsigned int. That should be interface-compatible with existing clients.yajl_handleparameter would be passed tova_start()instead. Since that type doesn't undergo promotion, it doesn't trigger the undefined behavior. However this would be an API-incompatible change.