On Mon, 20 Dec 2010, Stephen Boyd wrote: > On 12/20/2010 01:49 PM, Arnaud Lacombe wrote: > > Hi, > > > > On Mon, Dec 20, 2010 at 3:08 PM, Stephen Boyd <sboyd@xxxxxxxxxxxxxx> wrote: > >> Without marking the asm __dcc_getstatus() volatile my compiler > >> decides [...] > > What compiler ? That might be a usefull information to know, > > espectially 5 years from now when tracing code history. There has been > > similar issue with gcc 4.5 recently. AFAIK, in the same idea, the > > final change has been to mark the asm volatile. > > Sure, we can replace "my compiler" with "my compiler (arm-eabi-gcc (GCC) > 4.4.0)". Compiler version doesn't matter -- this is a simple correctness issue. If an inline asm statement provides an output value then the compiler is free to cache that value in a register, unless the inline asm is marked so that the value may change from one invocation to another. Also, the compiler is free to eliminate the inline asm statement entirely as well if the output value provided by that inline asm is never used... unless if the inline asm is marked as having side effects. In both cases the volatile qualifier does indicate that the returned value may change (new status flag state) and that the asm code therein has side effects (e.g. pop a character off a FIFO). Sometimes the desired effect can be indicated by clever usage of parameter constraints, but in this case the volatile keyword is most appropriate. Nicolas -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
