On 3 December 2013 01:19, Nicolas Pitre <nicolas.pi...@linaro.org> wrote: > On Mon, 2 Dec 2013, Riku Voipio wrote: > >> Hi, >> >> According the debian bug report [1], it is not possible to use std::future >> on armv5 targetting toolchains. This is because libstdc++ will only enable >> std::future if ATOMIC_INT_LOCK_FREE > 1. There is no LDREX for armv5 and >> older, so this definition is set to ATOMIC_INT_LOCK_FREE when compiling for >> ARMv4t or ARMv5. >> >> My impression is that you should be able to use the kernel helpers for >> atomic operations in lockfree (?) manner, so the ATOMIC_INT_LOCK_FREE >> definition is probably incorrect on older arm archs then? > > You're absolutely right. > > Please see Documentation/arm/kernel_user_helpers.txt in the kernel > source tree for details. There is even an example implementation for > atomic_add() there. > > Also I remember gcc being added some native atomic operation support at > some point and they were implemented in terms of the kernel helpers when > the architecture level wasn't high enough to benefit from load/store > exclusive instructions. > > > Nicolas
Nicolas is right, GCC has now a set of bult-in functions which try to match the Cxx11 memory model. The description is in the manual here: http://gcc.gnu.org/onlinedocs/gcc-4.8.2/gcc/_005f_005fatomic-Builtins.html#_005f_005fatomic-Builtins Yvan -- To UNSUBSCRIBE, email to debian-gcc-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/cad57ucd_beazypx0vcppdjmm0ypqxcqojksi-ztyguxxpqh...@mail.gmail.com
