https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68024
Bug ID: 68024
Summary: Diagnose variadic functions defined without prototypes
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: jsm28 at gcc dot gnu.org
Target Milestone: ---
As a quality-of-implementation-issue, we should diagnose code such as:
void f (int, ...);
void f (a) int a; {}
which defines a variadic function without using "...".
The types are compatible as defined by ISO C (see C11 6.7.6.3#15), so no
diagnostic is required. However, this case is explicitly undefined behavior
(C11 6.9.1#8: "If a function that accepts a variable number of arguments is
defined without a parameter type list that ends with the ellipsis notation, the
behavior is undefined."; likewise back to C90). So it is valid to reject it
(this is undefined behavior as a property of a program, not of a particular
execution of a program), and certainly seems a good idea at least to give a
diagnostic.
This showed up with such a (declaration, definition) pair in glibc only being
diagnosed after converting the definition from K&R style to prototype-style.
