---
** [bugs:#149] missing prototypes for GCC __atomic_* builtins**
**Status:** open
**Group:** Bug
**Created:** Mon Nov 10, 2014 06:43 PM UTC by Ben Liblit
**Last Updated:** Mon Nov 10, 2014 06:43 PM UTC
**Owner:** nobody
gcc-4.7 introduced a new suite of builtins for atomic operations. These
`__atomic_*` builtins are intended to replace the older `__sync_*` builtins,
although the latter are being retained for backward compatibility. CIL does
not have any inbuilt prototypes for these newer `__atomic_*` builtins. If any
code uses them, CIL generates generic (and wrong) prototypes for what it thinks
are calls to ordinary, undeclared functions. These explicit prototypes then
result in undefined symbol references in the compiled object files, which in
turn prevent the CIL-transformed program from linking. This is especially of
concern to me because the version of GNOME that will ship with Fedora 21 now
uses these `__atomic_*` builtins for various purposes. Thus, this CIL bug
prevents me from building instrumented versions of GNOME applications, which is
a fairly important thing for me to do.
The attached C source file demonstrates the problem, though without any GNOME
dependencies. This source file compiles just fine using `gcc test.c`.
However, when compiled using `cilly test.c`, we get a compile-time warning
about `conflicting types for built-in function '__atomic_load_4'`, and then a
link-time error about `undefined reference to '__atomic_load_4'`. Inspecting
intermediate files clearly shows that the cilly-compiled object file has an
undefined reference to `__atomic_load_4`, but the gcc-compiled object file does
not.
See
<https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html#g_t_005f_005fatomic-Builtins>
for details about the types of these builtin functions. Note that most are
overloaded to work with multiple types, similar to the overloading of
`__sync_*`. I hope that this will be a relatively easy fix by creating new CIL
builtin entries for `__atomic_*` similar to those CIL already has for
`__sync_*`.
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